Empty Vector Control Research Articles

Abstract 3971: Progesterone impacts regulatory T cell activity to promote immunosuppression in the mammary gland

Abstract Estrogen and progesterone signaling together drive hormone-receptor positive breast cancer growth and progression. However, there have been limited studies on the independent role that progesterone and its receptor, the progesterone receptor (PR), play in the development of breast cancer. Studies in the Hagan lab have shown that progesterone signaling promotes mammary tumor growth and changes the immune landscape of the mammary gland towards immunosuppression. Regulatory T-cells (Tregs) are immune cells known to promote immunosuppression in the tumor microenvironment. The data from our lab shows that among hormone receptor positive breast cancers, higher levels of PR expression correlates to higher levels of Tregs in the tumor microenvironment. To determine if progesterone signaling increases the number of Tregs in the tumor-bearing mammary gland, we used a syngeneic orthotopic murine tumor model, E0771 cells, engineered to express mouse PR or control empty vector. Mice were treated with progesterone or placebo for 7 days before implantation of the modified E0771 cells. The results of this study show that progesterone promoted tumor growth, and flow cytometry analysis at tumor endpoint showed that PR-positive tumors treated with progesterone harbored more Tregs than mice treated with placebo. Additionally, initial studies using flow cytometry and RNA-seq indicate increased Treg activity following progesterone treatment in PR+ tumor-bearing mice. As progesterone treatment promoted tumor growth and Treg recruitment in progesterone receptor-positive tumors, these data imply that progesterone treatment may promote the release of secreted factors impacting the immune cells in the mammary microenvironment. To determine if progesterone treatment results in cytokine or chemokine changes that may affect Treg recruitment, cytokine arrays and enzyme-linked immunosorbent assays (ELISAs) were performed using cell culture supernatant from murine mammary tumor cells expressing progesterone receptor (E0771-PR) treated with progesterone (0-72 hours). E0771-PR cells treated with progesterone showed higher levels of cytokines and chemokines that have been linked to Treg recruitment and differentiation, such as MCSF. Our findings demonstrate that progesterone signaling promotes an immune suppressed microenvironment in the mammary gland through an increase in Tregs. This evidence provides rationale to investigate the use of anti-progestins as a mechanism to overcome the immune-cold tumor microenvironment seen in progesterone receptor positive breast tumors. Citation Format: Eilidh I. Chowanec, Lauryn R. Werner, Christy R. Hagan. Progesterone impacts regulatory T cell activity to promote immunosuppression in the mammary gland [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3971.

Abstract 45: Driving AMPK signaling in CD4+ CART cells enhances metabolic capacity, memory formation, and anti-leukemia activity

Abstract Background: While Chimeric Antigen Receptor (CAR)T cell therapy has seen great success in pediatric and young adult acute lymphoblastic leukemia, up to 50% of patients will relapse following treatment. Increased memory formation and mitochondrial capacity, particularly in the CD4+ subset, have been linked to improved CART cell function and enhanced in vivo persistence, leading to long-term relapse-free survival. AMP-activated protein kinase (AMPK) is a cellular energy sensor responsible for promoting metabolic efficiency and T cell memory formation. We have previously demonstrated AMPK activity can be increased in human T cells via overexpression of the AMPKγ2 domain. We hypothesized that overexpression of AMPKγ2 in CART cells would enhance their metabolic capacity and improve their anti-leukemia function. Methods: Human CART cells bearing a CD19-CAR utilizing a 41BB costimulatory domain were generated from healthy human donors via lentiviral transduction and co-transduced with AMPKγ2 (AMPK) or an empty vector (EV) control. Flow sorting for the co-transduced populations yielded >95% CD4+ CART cells. CARTs were expanded in IL-2 for approximately 2 weeks, followed by overnight stimulation and subsequent metabolic analysis using the Seahorse Metabolic Analyzer. Memory status was assessed by CD62L and CCR7 co-expression. In vitro CART function was assessed using Zs-green+ NALM6 targets, with loss of green fluorescence over time measured on the Incucyte analyzer. Where indicated, tumor conditioned media was harvested from 72-hour NALM6 cultures. For in vivo experiments, immunodeficient NOD-scid IL2Rγnull (NSG) mice were injected with luciferase+ NALM6 targets, followed one week later by AMPK- or EV-CARTs. Leukemia burden, via IVIS imaging, and survival were followed over time. Results: CD4+ CARTs co-transduced with AMPKγ2 (AMPK-CARTs) increased oxygen consumption, maximal respiration, and spare respiratory capacity following overnight stimulation by ~20% compared to CARTs co-transduced with the EV (EV-CARTs) (p<0.05). Following expansion, CD62L+CCR7+ central memory cells were 4.5-fold more abundant in the AMPK-CART group (2.4-6.2-fold, p<0.01). In vitro, while AMPK-CARTs demonstrated similar cytotoxicity against NALM6 targets as EV-CARTs in standard media, they mediated faster killing of NALM6 targets when challenged in tumor conditioned media (p<0.001). In vivo, recipients of AMPK-CARTs showed a consistent decrease in tumor burden as measured by median radiance values, translating to a significant survival advantage (p<0.05). Conclusions: Increasing AMPK signaling in CD4+ CARTs via overexpression of AMPKγ2 improved metabolic profile, increased memory generation, and enhanced toxicity against leukemia targets both in vitro and in vivo. Together, these features make elevating AMPK signaling an attractive method to increase the efficacy of CART therapy. Citation Format: Erica Braverman, Herbert Schuler, Mengtao Qin, Craig Byersdorfer. Driving AMPK signaling in CD4+ CART cells enhances metabolic capacity, memory formation, and anti-leukemia activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 45.

Abstract 2875: Resistance to conventional chemo and radiotherapy associated with increased DNA repair and stem cell-like phenotype in head and neck squamous cell carcinoma expressing HPV E5

Abstract Human papillomavirus-associated head and neck squamous cell carcinoma (HPV+ HNSCC) is one of the fastest-rising cancers in the US. While HPV+ HNSCC patients exhibit better responses to chemoradiation compared to HPV- HNSCC patients, a subset of HPV+ patients do not respond as well and develop recurrent/refractory disease. In this study, we investigated the potential role of HPV E5 in promoting resistance to conventional chemo- and radiotherapy, and the underlying molecular mechanisms. HPV E5 is a small hydrophobic viral oncoprotein with multiple functions including regulation of tumor cell differentiation and apoptosis, modulation of H+ ATPase responsible for acidification of late endosomes, and immune modulation. To test the impact of HPV E5 on therapeutic resistance, we generated HNSCC cell lines and normal keratinocytes expressing HPV16 E5. Upon treatment with radiation (2Gy, 4Gy, 8Gy) and/or cisplatin, HNSCC cells and keratinocytes expressing HPV 16 E5 had increased cell viability, decreased apoptosis, and increased colony-forming capacity compared to empty vector (EV) control lines. Specifically, treatment with 4Gy radiation, 4µM cisplatin, or the combination led to a ~2-fold decrease in % of apoptotic cells in HPV16 E5-expressing HNSCC cells compared to EV and HPV16 E6/E7 HNSCC cells (p <0.05). Examination of DNA damage response and repair pathways indicated that while HPV16 E5 HNSCC cells initially had increased phosphorylation of H2AX 6 hours post treatment, at 24 hours post treatment H2AX phosphorylation in HPV16 E5 cells was significantly decreased compared to EV or HPV16 E6/E7 HNSCC cells. These findings indicate increased DNA repair capacity of HPV16 E5 HNSCC cells. To identify mechanisms underlying this phenotype, we performed RNA-seq and observed enhanced signaling pathways associated with epithelial development and increased expression of stem cell markers in HPV16 E5 HNSCC cells compared to EV control lines. Functionally, we observed a ~2.5-fold increase in sphere-forming capacity and increased expression of markers associated with stem cell phenotype in HPV16 E5 HNSCC cells compared to EV and HPV E6/E7 HNSCC cells. To determine whether these findings translated clinically, 18 HPV+ HNSCC patients from the GSE74927 dataset were grouped according to median expression level of HPV E5 (High vs Low). In support of our hypothesis, HPV E5-High patients exhibited enrichment of pathways associated with extrinsic apoptotic signaling, pluripotency of stem cells, and positive regulation of DNA repair. Taken together these results identify HPV E5 as a potential mediator of resistance to conventional radiation and chemotherapy in HNSCC and suggest that patient tumors expressing HPV E5 may have increased DNA repair capacity and cell survival after cytotoxic therapies. Citation Format: Souvick Roy, Sayuri Miyauchi, Riley Jones, Sangwoo Kim, Andrew B. Sharabi. Resistance to conventional chemo and radiotherapy associated with increased DNA repair and stem cell-like phenotype in head and neck squamous cell carcinoma expressing HPV E5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2875.

Abstract 5635: TPM4 overexpression promotes colon epithelial cell tumorigenesis in vitro and correlates with human colon tumor progression in vivo

Abstract Because colon cancer still exerts a heavy burden on human health, we are interested in identifying very early events in colon epithelial cell tumorigenesis in order to develop strategies to treat and possibly prevent colon carcinogenesis. We hypothesize that aberrant expression of genes involved in crypt-luminal colon epithelial cell migration, needed for proliferative, undifferentiated stem cells at the crypt bottom to mature into growth arrested, mature effector cells near the lumen, may disrupt normal differentiation and initiate events that can trigger the transition from a normal to premalignant state in colon epithelial cells. Forced upregulation of tropomyosin 4 (TPM4), an actin-binding protein that exerts many effects on contractility and migration, prevents certain aspects of Caco2 maturation induced by contact inhibition of growth, including increased expression of the digestive enzyme sucrose isomaltase and glutathione S-transferase alpha 1. Furthermore, TPM4.2-overexpressing cells exhibit numerous morphological abnormalities. Compared to untransfected Caco2 cells and empty-vector stable transfectant controls, TPM4.2-overexpressing Caco2 cell clones elaborate aberrant thin membrane protrusions and expanded membrane ruffles. Particularly striking are defective maintenance of dome structures at middle (day 14) and late (day 21) time points of induced differentiation in TPM4.2-overeexpressing clones. We further hypothesize that TPM4 is overexpressed in human colon tumors, particularly at early stages of tumorigenesis. In order to test this hypothesis, we examined TPM4 RNA expression in datasets obtained from human colon tissue at premalignant as well as tumorigenic stages. TPM4 trends toward overexpression in premalignant, relative to normal, human colon tissue (uninvolved mucosa from patients with familial adenomatous polyposis, or FAP) and is significantly overexpressed in adenocarcinoma tissue relative to normal controls. Interestingly, TPM4 overexpression may be more pronounced at earlier, rather than later, stages of adenocarcinoma. Our results suggest that aberrant TPM4 overexpression in colon epithelial cells can promote adoption of a tumorigenic state. Certain aspects of Caco2 cell maturation are disrupted by forced TPM4 overexpression during induced differentiation, and TPM4 overexpression correlates with early stages of colon tumorigenesis. Misregulation of TPM4 gene expression may therefore represent a critical molecular event that can block normal differentiation and induce early events in colon epithelial cell tumorigenesis. TPM4 expression level may therefore prove to be a useful biomarker that can, along with other diagnostics, help to determine tumorigenic progression in human colon tissue and to develop novel strategies to prevent colon cancer and treat it at early stages. Citation Format: Giulio Ferrero, Barbara Pardini, Alessio Naccarati, Michael Papetti. TPM4 overexpression promotes colon epithelial cell tumorigenesis in vitro and correlates with human colon tumor progression in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5635.

Abstract 5675: An intronic SINE-VNTR-Alu element insertion in CASP8 alters gene expression and confers resistance to induction of cell death in gastrointestinal cancer

Abstract Transposable elements are a major source of variation in the human genome. SINE-VNTR-Alus (SVAs), the hominid-specific and youngest active retrotransposon family, are highly polymorphic within the human germline and can contribute to disease risk and progression. In fact, polymorphic SVAs have previously been linked to several human diseases, including rare cases of hereditary cancer syndromes such as neurofibromatosis type I and Lynch syndrome. These examples illustrate that the mobility of SVAs in the genome can significantly impact gene function. Here, we sought to evaluate the potential of SVAs inserting into known tumor suppressors and oncogenes. To this end, we surveyed genomic data from Pan-Cancer Analysis of Whole Genomes (PCAWG) and identified 1956 unique germline SVA insertions in the introns of 1933 genes. Among these, we discovered a highly prevalent polymorphic SVA_E (subfamily) in an intronic region of CASP8. Given caspase-8’s canonical role in apoptosis, we hypothesized that this SVA may impact both caspase-8 expression as well as cell death in cancer. We first created a panel of colon and gastric cancer cell lines genotyped by PCR for the presence or absence of the CASP8-SVA (SVA+/+: RKO, NCI-N87, HT29, NCI-H747, OCUM-1; SVA-/-: HCT116, LoVo, SNU-407, 23132/87, KM12). RT-qPCR analysis showed significantly higher CASP8 expression in SVA+/+ cell lines, which was concordant with caspase-8 protein expression by immunoblot. Treatment of these cell lines with cytotoxic chemotherapy (FOLFOXIRI) in vitro demonstrated increased resistance to cell death in SVA+/+ cell lines. Direct induction of caspase-8-mediated apoptosis via TRAIL (TNF-related apoptosis-inducing ligand) revealed decreased TRAIL-mediated cell death in SVA+/+ cell lines; interestingly, caspase-8 enzymatic activity was also decreased in SVA+/+ cell lines upon TRAIL stimulation despite increased pro-caspase-8 expression. To further isolate the effects of the CASP8-SVA, we generated an isogenic cell line (RKO CASP8-SVA knockout) model via CRISPR-Cas9. Deletion of the CASP8-SVA redemonstrated decreased CASP8 expression at the mRNA and protein levels. Treatment with FOLFOXIRI in the CASP8-SVA KO cell line exhibited increased sensitivity compared to empty vector control. In summary, our findings indicate that an intronic SVA insertion in CASP8 increases gene and protein expression but decreases canonical caspase-8 activity, which was associated with increased resistance to FOLFIRINOX or TRAIL induced cell death. Additional interrogation of SVA-induced effects on transcriptional regulation (e.g., epigenetic effects) as well as non-canonical functions of caspase-8 (e.g., activation of NF-κB) is ongoing. To our knowledge this is the first report describing the mechanistic effects of a germline SVA insertion in the context of cancer and therapeutic resistance. Citation Format: Eric W. Lin, Joshua R. Kocher, Chong Chu, Peter J. Park, David T. Ting. An intronic SINE-VNTR-Alu element insertion in CASP8 alters gene expression and confers resistance to induction of cell death in gastrointestinal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5675.

Abstract 1998: ABCB1 promotes uveal melanoma cell resistance to FR900359 and identifies a tumor cell subpopulation with a distinct gene expression signature

Abstract Uveal melanoma (UM) is the leading form of intraocular cancer in adults and the second most common form of melanoma. Although rare, UM has a median survival rate of ~1 year after metastasis occurs. Metastatic UM is largely refractory to treatment and there are no effective pharmacological therapies, resulting in poor overall survival. In >90% UM cases, the oncogenic initiator proteins are constitutively active mutant GNAQ or GNA11 proteins (GNAQ/11). FR900359 (FR) is a natural compound that inhibits GNAQ/11 and has anti-proliferative effects on UM cells. To identify key oncogenic mechanisms downstream of mutant GNAQ/11, we performed a Sleeping Beauty (SB) transposon forward genetic screen to identify drivers of FR resistance. The SB screen identified ATP-binding cassette sub-family B member 1 (ABCB1) as one of the top genes upregulated by SB in FR-resistant UM cell populations. We determined that although ABCB1 does not provide immediate resistance to FR, the overexpression of ABCB1 leads to emergence of resistant colonies at a much higher rate than spontaneous resistance, validating ABCB1 as contributors to FR resistance. Unexpectedly, immunofluorescence revealed that a relatively small fraction of UM cells strongly expresses the transgenes after stable transfection. Immunoblotting confirmed that ABCB1 expression was initially modest in ABCB1-transfected populations but increased in the cells that developed resistance to FR. To examine the kinetics of FR resistance, population doubling versus time (PDVT) assays were performed in UM cells expressing ABCB1 or empty vector control treated with FR or vehicle. FR potently suppressed the proliferation of vector control cells. Drug-naïve ABCB1-transfected cells developed resistance to FR over time but accomplished fewer population doublings than vehicle-treated cells in the same time interval. Once transgenic populations emerged as resistant populations in FR, they grew similarly in drug or vehicle. Ongoing RNA-sequencing analysis from PDVT samples has identified distinct gene expression signatures associated with FR treatment and ABCB1 expression. These findings are expected to illuminate tumor cell heterogeneity amongst UM cell populations that may be related to drug resistance and metastasis. Citation Format: Sarina Dion Murray, Jesse D. Riordan, Eric R. Anderson, Michael D. Onken, Kendall J. Blumer, Adam J. Dupuy, Christopher S. Stipp. ABCB1 promotes uveal melanoma cell resistance to FR900359 and identifies a tumor cell subpopulation with a distinct gene expression signature [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1998.

ZNF862 induces cytostasis and apoptosis via the p21-RB1 and Bcl-xL-Caspase 3 signaling pathways in human gingival fibroblasts.

This study investigates the effects of ZNF862 on the proliferation and apoptosis of human gingival fibroblasts and their related mechanisms. As a major transcription factor family, zinc finger proteins (ZFPs) regulate cell differentiation, growth, and apoptosis through their conserved zinc finger motifs, which allow high flexibility and specificity in gene regulation. In our previous study, ZNF862 mutation was associated with hereditary gingival fibromatosis. Nevertheless, little is known about the biological function of ZNF862. Therefore, this study was aimed to reveal intracellular localization of ZNF862, the influence of ZNF862 on the growth and apoptosis of human gingival fibroblasts (HGFs) and its potential related mechanisms. Immunohistochemistry, immunofluorescence staining, and western blotting were performed to determine the intracellular localization of ZNF862 in HGFs. HGFs were divided into three groups: ZNF862 overexpression group, ZNF862 interference group, and the empty vector control group. Then, the effects of ZNF862 on cell proliferation, migration, cell cycle, and apoptosis were evaluated. qRT-PCR and western blotting were performed to further explore the mechanism related to the proliferation and apoptosis of HGFs. ZNF862 was found to be localized in the cytoplasm of HGFs. Invitro experiments revealed that ZNF862 overexpression inhibited HGFs proliferation and migration, induced cell cycle arrest at the G0/G1-phase and apoptosis. Whereas, ZNF862 knockdown promoted HGFs proliferation and migration, accelerated the transition from the G0/G1 phase into the S and G2/M phase and inhibited cell apoptosis. Mechanistically, the effects of ZNF862 on HGFs proliferation and apoptosis were noted to be dependent on inhibiting the cyclin-dependent kinase inhibitor 1A (p21)-retinoblastoma 1 (RB1) signaling pathway and enhancing the B-cell lymphoma-extra-large (Bcl-xL)-Caspase 3 signaling pathway. Our results for the first time reveal that ZNF862 is localized in the cytoplasm of HGFs. ZNF862 can inhibit the proliferation of HGFs by inhibiting the p21-RB1 signaling pathway, and it also promotes the apoptosis of HGFs by enhancing the Bcl-xL-Caspase 3 signaling pathway.

Zero-valent iron (nZVI) nanoparticles mediate SlERF1 expression to enhance cadmium stress tolerance in tomato

Cadmium (Cd) pollution threatens plant physiological and biochemical activities and crop production. Significant progress has been made in characterizing how nanoparticles affect Cd stress tolerance; however, the molecular mechanism of nZVI nanoparticles in Cd stress remains largely uncharacterized. Plants treated with nZVI and exposed to Cd had increased antioxidant capacity and reduced Cd accumulation in plant tissues. The nZVI treatment differentially affected the expression of genes involved in plant environmental responses, including those associated with the ERF transcription factor. SlEFR1 was upregulated by Cd stress in nZVI-treated plants when compared with the control and the predicted protein-protein interactions suggested SlERF1 interacts with proteins associated with plant hormone signaling pathway and related to stress. Yeast overexpressing SlEFR1 grew faster after Cd exposure and significantly had higher Cd stress tolerance when compared with empty vector controls. These results suggest that nZVI induces Cd stress tolerance by activating SlERF1 expression to improve plant growth and nutrient accumulation. Our study reveals the molecular mechanism of Cd stress tolerance for improved plant growth and will support new research on overcoming Cd stress and improving vegetable crop production.

Characterization of soybean chitinase genes induced by rhizobacteria involved in the defense against Fusarium oxysporum.

Rhizobacteria are capable of inducing defense responses via the expression of pathogenesis-related proteins (PR-proteins) such as chitinases, and many studies have validated the functions of plant chitinases in defense responses. Soybean (Glycine max) is an economically important crop worldwide, but the functional validation of soybean chitinase in defense responses remains limited. In this study, genome-wide characterization of soybean chitinases was conducted, and the defense contribution of three chitinases (GmChi01, GmChi02, or GmChi16) was validated in Arabidopsis transgenic lines against the soil-borne pathogen Fusarium oxysporum. Compared to the Arabidopsis Col-0 and empty vector controls, the transgenic lines with GmChi02 or GmChi16 exhibited fewer chlorosis symptoms and wilting. While GmChi02 and GmChi16 enhanced defense to F. oxysporum, GmChi02 was the only one significantly induced by Burkholderia ambifaria. The observation indicated that plant chitinases may be induced by different rhizobacteria for defense responses. The survey of 37 soybean chitinase gene expressions in response to six rhizobacteria observed diverse inducibility, where only 10 genes were significantly upregulated by at least one rhizobacterium and 9 genes did not respond to any of the rhizobacteria. Motif analysis on soybean promoters further identified not only consensus but also rhizobacterium-specific transcription factor-binding sites for the inducible chitinase genes. Collectively, these results confirmed the involvement of GmChi02 and GmChi16 in defense enhancement and highlighted the diverse inducibility of 37 soybean chitinases encountering F. oxysporum and six rhizobacteria.

Pharmaco-phosphoproteomic analysis of cancer-associated KIT mutations D816V and V560G.

The CD117 mast/stem cell growth factor receptor tyrosine kinase (KIT) is critical for haematopoiesis, melanogenesis and stem cell maintenance. KIT is commonly activated by mutation in cancers including acute myeloid leukaemia, melanoma and gastrointestinal stromal tumours (GISTs). The kinase and the juxtamembrane domains of KIT are mutation hotspots; with the kinase domain mutation D816V common in leukaemia and the juxtamembrane domain mutation V560G common in GISTs. Given the importance of mutant KIT signalling in cancer, we have conducted a proteomic and phosphoproteomic analysis of myeloid progenitor cells expressing D816V- and V560G-KIT mutants, using an FDCP1 isogenic cell line model. Proteomic analysis revealed increased abundance of proteases and growth signalling proteins in KIT-mutant cells compared to empty vector (EV) controls. Pathway analysis identified increased oxidative phosphorylation in D816V- and V560G-mutant KIT cells, which was targetable using the inhibitor IACS010759. Dysregulation of RNA metabolism and cytoskeleton/adhesion pathways was identified in both the proteome and phosphoproteome of KIT-mutant cells. Phosphoproteome analysis further revealed active kinases such as EGFR, ERK and PKC, which were targetable using pharmacological inhibitors. This study provides a pharmaco-phosphoproteomic profile of D816V- and V560G-mutant KIT cells, which reveals novel therapeutic strategies that may be applicable to a range of cancers.

Abstract B034: Characterization of MHC-I-mediated immune evasion in triple-negative breast cancer using human transcriptomic datasets and immunocompetent mouse models

Abstract In Triple-Negative Breast Cancer (TNBC) patients, adaptive immune system activity in the tumor microenvironment is associated with improved prognosis. However, tumors can evolve to evade immune detection, likely leading to worse patient outcomes. Multi-omic data of paired primary and metastatic breast tumors demonstrate that TNBC metastases frequently lose expression of genes involved in major histocompatibility complex class I (MHC-I) antigen presentation, a key pathway for adaptive immune activation (PMID: 36585450). Therefore, understanding and addressing MHC-I-mediated immune evasion may have profound clinical benefits for TNBC patients. We hypothesize that breast tumor MHC-I loss results in a unique immune-evasive phenotype, which we are characterizing using human clinical datasets and immunocompetent mouse models of breast cancer. First, using large transcriptomic datasets (i.e., SCAN-B and TCGA), we are characterizing molecular and clinical features of MHC-I-low human breast tumors using expression of the MHC-I gene human leukocyte antigen A (HLA-A) as a continuous variable. We found HLA-A expression varies significantly between PAM50 molecular and clinical subtypes of breast cancer and has differing impacts on patient survival based on clinical subtype. In TNBCs, low HLA-A expression is associated with worse outcomes, while in HR+/HER2- tumors, low HLA-A predicts improved outcomes. We also identified genes highly correlated with HLA-A regardless of molecular subtype. This list was functionally rich, related to antigen processing machinery, adaptive immune-mediated cytotoxicity, and T cell exhaustion features. To complement human genomic data, we are empirically testing the role of MHC-I in syngeneic mouse mammary tumor models by individually knocking out murine MHC-I genes–H2-K, H2-D, and B2m–through CRISPR/Cas9-mediated genome editing. We have generated and validated knockouts (KOs) of H2-K and B2m, as well as empty vector control clones from the “immune-hot” and immune checkpoint inhibitor (ICI) responsive mammary tumor cell lines KPB25L-UV and T11-APOBEC. RNA sequencing of KPB25L-UV H2-K and B2m KO versus wildtype cell lines in vitro identified lists of differentially expressed genes, many of which are related to proteolytic and peptide antigen processing. Next, these CRISPR-modified cell lines were injected into the mammary fat pad of syngeneic immunocompetent mice, and the resulting tumors were harvested for RNA sequencing. Differentially expressed genes in KPB25L-UV H2-K KO versus wildtype tumors were related to increased MHC Class II antigen presentation and dendritic cell activity. Preliminary data suggests that mice bearing KPB25L-UV H2-K KO tumors have shortened survival compared to H2-K wildtype tumors. Experiments are ongoing to further characterize the growth dynamics, metastatic potential, single-cell transcriptomic profiles, and ICI sensitivities of these KO tumors in vivo. Our long-term goal is to identify therapeutic means to overcome this common immune-evasive phenotype to improve TNBC patient outcomes. Citation Format: Constandina E O'Connell, Brooke M Felsheim, Aranzazu Fernandez-Martinez, Kevin R Mott, Charles M Perou. Characterization of MHC-I-mediated immune evasion in triple-negative breast cancer using human transcriptomic datasets and immunocompetent mouse models [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B034.

Abstract B019: Tumor-derived PTHrP molds an immunosuppressive microenvironment

Abstract Purpose[JP1] : Molecular phenotyping of PDAC [PJ2] has revealed an aggressive squamous/basal/quasi-mesenchymal[JP3] subtype, clinically presenting as highly metastatic and harboring genetic amplifications of KRAS. Our previous work indicated that a squamous identity gene, Parathyroid Hormone Like Hormone (PTHLH; encoding for the PTHrP protein), is frequently co-amplified with KRAS and skews PDAC towards a squamous identity. Further, PTHrP is secreted by tumor cells and promotes tumor growth and metastasis through autocrine signaling. However, pathological analysis of PTHrP-null tumors indicated that the tumor microenvironment (TME) was re-organized upon loss of PTHrP. Thus, we hypothesized that PTHrP is a tumor-derived factor that shapes the TME through its systemic secretion and mobilization of immunosuppressive myeloid cells. Methods: In vivo experiments used KrasG12D; p53R172H; Pdx1-Cre; YFP (KPCY) and KPCY-PthlhloxP/WT (KPCY-Pthlhhet) for spontaneous tumor formation in immune competent mice. Orthotopic implantation experiments used Pthlh overexpressing KPCY tumor cells (herein KPCY-PthlhOE) or empty vector control cells (KPCY-PthlhEV). Tumor immunophenotyping was done using flow cytometry. Cytokine expression was performed using qPCR and ELISA. Results: In vivo investigation of tumors from KPCY-Pthlhhet mice revealed less MDSC and greater CD8+ T cell infiltration than KPCY controls, demonstrating the necessity of PTHrP for immunosuppression[PJ4]. Orthotopic implantation of KPCY-PthlhOE cell lines reduced overall TME immune cell recruitment, while simultaneously increasing the proportion of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) infiltration. A concomitant decrease in the frequency of T cells in the KPCY-PthlhOE tumors was also observed, showing the sufficiency of PTHrP to organize an immunosuppressive TME[PJ5]. Additionally, a reduction of PD-1+ and CD44high CD8+ T cells revealed they were less activated. Interestingly, recombinant human PTHrP was sufficient to induce MDSC mobilization in vivo.[JP6] To interrogate the mechanism of MDSC trafficking into the TME, cytokine production by was analyzed in vitro. KPCY-PthlhOE exhibited a pronounced increase and decrease of Cxcl1 and Cxcl10 expression, respectively, relative to the KPCY-EV control. Conclusions: The work herein describes a new mechanism for the mobilization and infiltration of immune suppressive MDSC in the tumor microenvironment, initiated by PTHrP. The PTHrP-dependent immunosuppressive TME excludes and inhibits effector immune cells, such as CD8+ T cells. This phenomenon has been described in squamous-like PDAC but may also apply to other squamous adenocarcinomas. [PJ7] Further elucidation of the mechanism by which PTHrP is the genesis of the immune suppressive TME may spur the development of novel treatments for these more clinically severe cancer subtypes. Citation Format: Calvin P. Johnson, Boyang Ma, Jason Pitarresi. Tumor-derived PTHrP molds an immunosuppressive microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B019.

Virus induced gene silencing confirms oligogenic inheritance of brown stem rot resistance in soybean.

Brown Stem Rot (BSR), caused by the soil borne fungal pathogen Phialophora gregata, can reduce soybean yields by as much as 38%. Previous allelism studies identified three Resistant to brown stem Rot genes (Rbs1, Rbs2, and Rbs3), all mapping to large, overlapping regions on soybean chromosome 16. However, recent fine-mapping and genome wide association studies (GWAS) suggest Rbs1, Rbs2, and Rbs3 are alleles of a single Rbs locus. To address this conflict, we characterized the Rbs locus using the Williams82 reference genome (Wm82.a4.v1). We identified 120 Receptor-Like Proteins (RLPs), with hallmarks of disease resistance receptor-like proteins (RLPs), which formed five distinct clusters. We developed virus induced gene silencing (VIGS) constructs to target each of the clusters, hypothesizing that silencing the correct RLP cluster would result in a loss of resistance phenotype. The VIGS constructs were tested against P. gregata resistant genotypes L78-4094 (Rbs1), PI 437833 (Rbs2), or PI 437970 (Rbs3), infected with P. gregata or mock infected. No loss of resistance phenotype was observed. We then developed VIGS constructs targeting two RLP clusters with a single construct. Construct B1a/B2 silenced P. gregata resistance in L78-4094, confirming at least two genes confer Rbs1-mediated resistance to P. gregata. Failure of B1a/B2 to silence resistance in PI 437833 and PI 437970 suggests additional genes confer BSR resistance in these lines. To identify differentially expressed genes (DEGs) responding to silencing, we conducted RNA-seq of leaf, stem and root samples from B1a/B2 and empty vector control plants infected with P. gregata or mock infected. B1a/B2 silencing induced DEGs associated with cell wall biogenesis, lipid oxidation, the unfolded protein response and iron homeostasis and repressed numerous DEGs involved in defense and defense signaling. These findings will improve integration of Rbs resistance into elite germplasm and provide novel insights into fungal disease resistance.

Evaluation of supplemented protein-L-isoaspartate-O-methyltransferase (PIMT) gene of Carica papaya and Ricinus communis in stress survival of Escherichia coli BL21(DE3) cells

In growing plant population, effect of stress is a perturb issue affecting its physiological, biochemical, yield loss and developmental growth. Protein-L-isoaspartate-O-methyltransferase (PIMT) is a broadly distributed protein repair enzyme which actuate under stressful environment or aging. Stress can mediate damage converting protein bound aspartate (Asp) residues to isoaspartate (iso-Asp). This spontaneous and deleterious conversion occurs at an elevated state of stress and aging. Iso-Asp formation is associated with protein inactivation and compromised cellular survival. PIMT can convert iso-Asp back to Asp, thus repairing and contributing to cellular survival. The present work describes the isolation, cloning, sequencing and expression of PIMT genes of Carica papaya (Cp pimt) and Ricinus communis (Rc pimt) Using gene specific primers, both the pimts were amplified from their respective cDNAs and subsequently cloned in prokaryotic expression vector pProEXHTa. BL21(DE3) strain of E. coli cells were used as expression host. The expression kinetics of both the PIMTs were studied with various concentrations of IPTG and at different time points. Finally, the PIMT supplemented BL21(DE3) cells were evaluated against different stresses in comparison to their counterparts with the empty vector control.

Metabolic Pathway Engineering Improves Dendrobine Production in Dendrobium catenatum.

The sesquiterpene alkaloid dendrobine, widely recognized as the main active compound and a quality control standard of medicinal orchids in the Chinese Pharmacopoeia, demonstrates diverse biological functions. In this study, we engineered Dendrobium catenatum as a chassis plant for the production of dendrobine through the screening and pyramiding of key biosynthesis genes. Initially, previously predicted upstream key genes in the methyl-D-erythritol 4-phosphate (MEP) pathway for dendrobine synthesis, including 4-(Cytidine 5'-Diphospho)-2-C-Methyl-d-Erythritol Kinase (CMK), 1-Deoxy-d-Xylulose 5-Phosphate Reductoisomerase (DXR), 2-C-Methyl-d-Erythritol 4-Phosphate Cytidylyltransferase (MCT), and Strictosidine Synthase 1 (STR1), and a few downstream post-modification genes, including Cytochrome P450 94C1 (CYP94C1), Branched-Chain-Amino-Acid Aminotransferase 2 (BCAT2), and Methyltransferase-like Protein 23 (METTL23), were chosen due to their deduced roles in enhancing dendrobine production. The seven genes (SG) were then stacked and transiently expressed in the leaves of D. catenatum, resulting in a dendrobine yield that was two-fold higher compared to that of the empty vector control (EV). Further, RNA-seq analysis identified Copper Methylamine Oxidase (CMEAO) as a strong candidate with predicted functions in the post-modification processes of alkaloid biosynthesis. Overexpression of CMEAO increased dendrobine content by two-fold. Additionally, co-expression analysis of the differentially expressed genes (DEGs) by weighted gene co-expression network analysis (WGCNA) retrieved one regulatory transcription factor gene MYB61. Overexpression of MYB61 increased dendrobine levels by more than two-fold in D. catenatum. In short, this work provides an efficient strategy and prospective candidates for the genetic engineering of D. catenatum to produce dendrobine, thereby improving its medicinal value.

Genome-wide analysis of the SCAMPs gene family of soybean and functional identification of GmSCAMP5 in salt tolerance

The effect of salt damage on plants is mainly caused by the toxic effect of Na+. Studies showed that the secretory carrier membrane proteins were associated with the Na+ transport. However, the salt tolerance mechanism of secretory carrier protein (SCAMP) in soybean was yet to be defined. In this study, ten potential SCAMP genes distributed in seven soybean chromosomes were identified in the soybean genome. The phylogenetic tree of SCAMP domain sequences of several plants can divide SCAMPs into two groups. Most GmSCAMPs genes contained multiple Box4, MYB and MYC cis-elements indicated they may respond to abiotic stresses. We found that GmSCAMP1, GmSCAMP2 and GmSCAMP4 expressed in several tissues and GmSCAMP5 was significantly induced by salt stress. GmSCAMP5 showed the same expression patterns under NaCl treatment in salt-tolerant and salt-sensitive soybean varieties, but the induced time of GmSCAMP5 in salt-tolerant variety was earlier than that of salt-sensitive variety. To further study the effect of GmSCAMP5 on the salt tolerance of soybean plants, compared to GmSCAMP5-RNAi and EV-Control plants, GmSCAMP5-OE had less wilted leave and higher SPAD value. Compared to empty vector control, less trypan blue staining was observed in GmSCAMP5-OE leaves while more staining in GmSCAMP5-RNAi leaves. The Na+ of GmSCAMP5-RNAi plants leaves under NaCl stress were significantly higher than that in EV-Control plants, while significantly lower Na+ in GmSCAMP5-OE plants than in that EV-Control plants. The contents of leaves K+ of GmSCAMP5-RNAi, EV-Control, and GmSCAMP5-OE plants under NaCl stress were opposite to that of leaves Na+ content. Finally, salt stress-related genes NHX1, CLC1, TIP1, SOD1, and SOS1 in transformed hairy root changed significantly compared with the empty control. The research will provide novel information for study the molecular regulation mechanism of soybean salt tolerance.

KLF14 activates the JNK-signaling pathway to induce S-phase arrest in cervical cancer cells.

To explore the role of Krüppel-like factor 14 (KLF14) and its underlying mechanism(s) of action in cell-cycle regulation in cervical cancer. Lentiviral infection was used to construct KLF14, KLF14 zinc-finger structural mutations, and empty vector controls in SiHa and HeLa cervical cancer cells. The effect of KLF14 on cervical cancer cell cycle was detected by flow cytometry. The effect of KLF14 on the expression of cyclin-dependent kinase 2 (CDK2), cyclin A2 (CCNA2), and MAPK signalling pathway-related molecules was detected by fluorescence quantitative RT-PCR (qRT-PCR) and western blot. Cervical cancer cells were treated with JNK-pathway inhibitors/agonists before we assessed changes in the cell cycle and the expression of the CDK2, CCNA2, and p-JNK/JNK. Subcutaneous xenograft studies to explore the effects of KLF14 on cervical cancer cell proliferation in vivo, and western blotting was implemented to measure the expression of CCNA2, CDK2, and the activation levels of the MAPK-signaling pathway proteins in tumours. The proportion of cells in the S phase was increased in the KLF14-overexpressing group compared with the control group (P<0.001); CDK2, CCNA2, and p-JNK/JNK expression levels were elevated in the KLF14-overexpressing group relative to the control group (all P<0.05). When JNK-pathway activation was inhibited/promoted, the proportion of cells in the S phase was reduced/increased (P<0.05) and CDK2 and CCNA2 expression levels were reduced/decreased, respectively (all P<0.05). Vivo experiments revealed that KLF14 inhibited cervical cancer cell proliferation (P<0.01) and that p-JNK/JNK, CDK2, and CCNA2 expression levels were augmented in tumours in the overexpression group (P<0.01). KLF14 induced S-phase arrest in cervical cancer cells and inhibited the proliferation of cervical cancer cells in vivo; the induction of S-phase arrest was related to its zinc-finger structure. KLF14 also activated the JNK pathway to induce S-phase arrest and promote the expression of CDK2 and CCNA2. In summary, KLF14 activates the JNK-signaling pathway to induce S-phase arrest in cervical cancer cells.

Recombinant expression of Yersinia ruckeri outer membrane proteins in Escherichia coli extracellular vesicles

The secretion of extracellular vesicles (EVs) is a common process in Gram-negative bacteria and can be exploited for biotechnological applications. EVs pose a self-adjuvanting, non-replicative vaccine platform, where membrane and antigens are presented to the host immune system in a non-infectious fashion. The secreted quantity of EVs varies between Gram-negative bacterial species and is comparatively high in the model bacterium E. coli. The outer membrane proteins OmpA and OmpF of the fish pathogen Y. ruckeri have been proposed as vaccine candidates to prevent enteric redmouth disease in aquaculture. In this work, Y.ruckeri OmpA or OmpF were expressed in E. coli and recombinant EVs were isolated. To avoid competition between endogenous E. coli OmpA or OmpF, Y. ruckeri OmpA and OmpF were expressed in E. coli strains lacking ompA, ompF, and in a quadruple knockout strain where the four major outer membrane protein genes ompA, ompC, ompF and lamB were removed. Y.ruckeri OmpA and OmpF were successfully expressed in EVs derived from the E. coli mutants as verified by SDS-PAGE, heat modifiability and proteomic analysis using mass-spectrometry. Transmission electron microscopy revealed the presence of EVs in all E. coli strains, and increased EV concentrations were detected when expressing Y. ruckeri OmpA or OmpF in recombinant EVs compared to empty vector controls as verified by nanoparticle tracking analysis. These results show that E. coli can be utilized as a vector for production of EVs expressing outer membrane antigens from Y. ruckeri.

The Role of over-Expressed β Globin in Driving Relapsed B - Cell Acute Lymphoblastic Leukemia (B-ALL)

Background: The prognosis for patients with relapsed acute lymphoblastic leukemia (ALL) remains suboptimal despite intensification of chemotherapy, immunotherapy and stem cell transplant. We and others have identified genetic and epigenetic alterations enriched at relapse that drive drug resistance and relapse. In our recent work mapping the epigenetic landscape of B-ALL, we discovered novel super-enhancers (SEs), or regions with increased H3K27 acetylation, enriched at relapse in a majority of patients, implicating a role in clonal evolution. One of these SEs was upstream of the β globin locus and lead to aberrant expression of hemoglobin beta subunit ( HBB) mRNA. HBB upregulation at relapse was also found in a large meta-analysis of gene expression data from pediatric diagnosis/relapse pairs. Of note, b globin is normally found in erythrocytes that interacts with other subunits to form functional hemoglobin. We hypothesized that HBB upregulation in blasts plays a role in relapse and aimed to determine whether it leads to drug tolerance, an early recovery phenotype and/or increased clonal potential. Methods: B-lineage REH, RS4;11 and 697 ALL cell lines were transduced with lentiviral vectors overexpressing either wild-type (WT) HBB or an empty vector (EV) control. Real time PCR was performed to confirm RNA expression and Western Blot analysis was performed to detect protein expression. We generated additional cell lines with a mutation in the translation start codon and another leading to a premature stop codon to unequivocally interrupt protein expression. The generated cell lines were then plated and evaluated for differences in apoptosis via Annexin V assay and proliferation, in response to chemotherapeutic agents commonly used in the treatment of ALL. Clonogenic growth in vitro was also assessed using MethoCult TM media. To test the possibility that HBB acted in generating a persistor cell phenotype, cell lines were placed in mercaptopurine and prednisone for 10-14 days at two different concentrations and counted throughout drug exposure and for an additional 10-14 days following removal of drug. Results: We did not observe significant differences in chemosensitivity to various chemotherapies used in the treatment of B-ALL. However, we did observe less cells undergoing apoptosis in HBB expressing cells compared to control following prolonged treatment with 6-mercaptopurine, suggesting an increase in a small population of drug tolerant cells. However, this did not result in a difference in recovery time following removal of the drug. We also demonstrated that β globin overexpression led to increased clonal growth in methylcellulose compared to control (Fig. 1A, REH) and this observation was replicated in a second cell line (Fig. 1B, RS4;11). While we confirmed mRNA expression, we were not able to confirm protein expression by Western blot or by immunoprecipitation. We therefore hypothesized that b globin mRNA, rather than protein, mediates the observed increase in clonal growth. Interestingly, we observed the same phenotype of increased clonal growth (Fig. 1) in mutated cell lines, suggesting a catalytic role for β globin RNA in expanding a leukemia stem cell population. Conclusions: The increased clonal potential upon overexpression of HBB could be indicative of the ability to reconstitute a tumor from a small subpopulation following treatment. Additionally, our data suggests that protein is not required for increased clonal growth leading us to hypothesize that catalytic RNA is responsible. We are also currently analyzing RNAseq data from the cell lines and will compare differential gene expression between the empty vector and HBB expressing cells to discover downstream pathways impacted by HBB. We will be testing this hypothesis further by performing limiting dilution analysis in an immunocompromised mouse model (with David Teachey, Children's Hospital of Philadelphia).

Aberrant Expression of Spliced WNK2 Is an Early Event in MYD88 Mutated WM That Activates ERK1/2 and Supports Tumor Growth

Background: Waldenström's Macroglobulinemia (WM) patients carry MYD88 (MYD88 MUT) and CXCR4 (CXCR4 MUT) mutations in 95-97% and 30-40% of cases, respectively. The mechanisms of MYD88-driven lymphomagenesis remain to be clarified. Our previous transcriptome analysis highlighted WNK2 as a highly dysregulated gene in MYD88 MUT WM (Guerrera ML et al, Haematologica 2018). WNK2 is a serine/threonine protein kinase that negatively regulates ERK1/2 activation in a kinase-dependent manner; is a known tumor suppressor in certain solid cancers, where it is primarily silenced by promoter methylation. ERK1/2 is a pro-survival signal in WM; its activation is accompanied by the release of inflammatory cytokines and can mediate ibrutinib resistance. We previously demonstrated WNK2 transcriptional and protein upregulation in CXCR4 WT and silencing in CXCR4 MUT WM and identified several mechanisms of WNK2 transcriptional dysregulation including i) the preferential expression of short isoforms lacking the kinase domain; ii) the recurrence of an identical, aberrant, exon skipping event in all gene isoforms; and iii) aberrant methylation and chromatin accessibility in CXCR4 WT vs CXCR4 MUT WM. We therefore hypothesized that spliced WNK2 may contribute to MYD88 MUT WM oncogenesis. Methods: We investigated WNK2 regulation in 253 untreated WM patients by combined transcriptome and PacBio IsoSeq analysis in a subgroup of 12 WM and 3 healthy donors (HD). Lentiviral transduction was used to overexpress and functionally characterize WNK2 isoforms in MYD88 MUT BCWM1 and MWCL1 WM and control lymphoma cell lines. Results: We identified that tumors from patients with MYD88 MUTCXCR4 WT WM preferentially expressed the short Ensembl WNK2-207 transcript, whose annotation is incomplete. Via PacBio analysis, we identified 8 previously undocumented short isoforms of WNK2 mapping to the original WNK2-207 annotation, all of which lack the kinase domain and bear the same mRNA skipping of two exons near the 3' end. RNA-Seq analysis of 253 WM patents confirmed the IsoSeq predictions and showed that the novel PacBio isoform WNK2-PB4 was among the most expressed transcripts in WM. We next sought to functionally characterize WNK2-PB4 overexpression in MYD88 mutated lymphoma cells. We successfully cloned WNK2-PB4 from patient CD19+ BM cells and obtained an artificial construct of WNK2-PB4 that included the 2 skipped exons, WNK2-SKEX, through the Genewiz gene synthesis service. Stable cell lines overexpressing either WNK2-PB4 or WNK2-SKEX or the empty vector were successfully generated by lentiviral transduction. Overexpression of WNK2-PB4 showed increased phosphorylation of ERK1/2 and SRC family members in the BCWM1 and MWCL1 cells; in contrast, no activation of those targets was seen in MYD88 MUT DLBCL TMD8 and MYD88 WT Burkitt Ramos cell lines ( Figure 1). Increased activation of ERK1/2 was also observed in WM cell lines overexpressing WNK2-SKEX. Study of the downstream signaling of ERK1/2 by WB revealed increased phosphorylation of p90RSK in BCWM1 WNK2-PB4 cells. BCWM1 and MWCL1 overexpressing WNK2-PB4 showed greater proliferation compared to the empty vector control by CellTrace Violet, while no differences in apoptosis were noticed. By co-immunoprecipitation, we observed WNK2 complexed with HCK. Upon treatment with the highly potent dual HCK/BTK inhibitor KIN-8194, we observed dose-dependent decreases in phosphorylation levels of HCK, BTK, and ERK and total levels of WNK2 in WNK2-PB4 overexpressing BCWM.1 and MWCL-1 cells versus vector control transduced cells. Transcriptome analysis of WM samples based on a novel subtype and early/late evolutionary staging classification for WM (Hunter et al, ASH 2022) revealed that WNK2 was aberrantly upregulated from an early stage of WM and was either silenced or further upregulated with disease progression in the B-cell like or Plasma cell like WM subgroups, respectively. Conclusions: Taken together, our findings show a high selection pressure to aberrantly regulate WNK2 expression at an early stage of MYD88 MUT WM with different evolution in CXCR4 WT vs CXCR4 MUT WM, thus suggesting a role for aberrantly spliced WNK2 in the oncogenesis of MYD88 MUT WM. Overexpression of the aberrantly spliced WNK2-PB4 isoform in stable WM cell lines provided a proliferation advantage and led to ERK1/2 activation, which may be induced by the WNK2/HCK interaction.