Wild-type STAT3 Research Articles

Extracellular Vesicles based STAT3 delivery as innovative therapeutic approach to restore STAT3 signaling deficiency

Extracellular Vesicles (EVs) have been proposed as a promising tool for drug delivery because of their natural ability to cross biological barriers, protect their cargo, and target specific cells. Moreover, EVs are not recognized by the immune system as foreign, reducing the risk of an immune response and enhancing biocompatibility. Herein, we proposed an alternative therapeutic strategy to restore STAT3 signaling exploiting STAT3 loaded EVs. This approach could be useful in the treatment of Autosomal Dominant Hyper-IgE Syndrome (AD-HIES), a rare primary immunodeficiency and multisystem disorder due to the presence of mutations in STAT3 gene. These mutations alter the signal transduction of STAT3, thereby impeding Th17 CD4+ cell differentiation that leads to the failure of immune response. We set up a simple and versatile method in which EVs were loaded with fully functional STAT3 protein. Moreover, our method allows to follow the uptake of STAT3 loaded vesicles inside cells due to the presence of EGFP in the EGFP-STAT3 fusion protein construct. Taken together, the data presented in this study could provide the scientific background for the development of new therapeutic strategy aimed to restore STAT3 signaling in STAT3 misfunction associated diseases like AD-HIES. In the future, the administration of fully functional wild type STAT3 to CD4+ T cells of AD-HIES patients might compensate its loss of function and would be beneficial for these patients, lowering the risk of infections, the use of medications, and hospitalizations.

Targeting C21orf58 is a Novel Treatment Strategy of Hepatocellular Carcinoma by Disrupting the Formation of JAK2/C21orf58/STAT3 Complex.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Functionally uncharacterized genes are an attractive repository to explore candidate oncogenes. It is demonstrated that C21orf58 displays an oncogenic role in promoting cell growth, tumorigenesis and sorafenib resistance of HCC cells by abnormal activation of STAT3 signaling. Mechanistically, a novel manner to regulate STAT3 signaling that adaptor C21orf58 forms a ternary complex is reveal with N-terminal domain of STAT3 and SH2 domain of JAK2, by which C21orf58 overactivates wild-type STAT3 by facilitating its phosphorylation mediated by JAK2, and hyper-activates of constitutively mutated STAT3 due to preferred binding with C21orf58 and JAK2. Moreover, it is validated that inhibition of C21orf58 with drug alminoprofen, selected by virtual screening, could effectively repress the viability and tumorigenesis of HCC cells. Therefore, it is identified that C21orf58 functions as an oncogenic adaptor, reveal a novel regulatory mechanism of JAK2/STAT3 signaling, explain the cause of abnormal activity of activated mutants of STAT3, and explore the attractive therapeutic potential by targeting C21orf58 in HCC.

The acetylation of STAT3 at K685 attenuates NPM-ALK-induced tumorigenesis

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), a fusion protein generated by a chromosomal translocation, is a causative gene product of anaplastic large cell lymphoma (ALCL). It induces cell proliferation and tumorigenesis by activating the transcription factor, signal transducer and activator of transcription factor 3 (STAT3). We herein demonstrated that STAT3 underwent acetylation at K685 in a manner that was dependent on the kinase activity of NPM-ALK. To investigate the role of STAT3 acetylation in NPM-ALK-induced oncogenesis, we generated Ba/F3 cells expressing NPM-ALK in which STAT3 was silenced by shRNA, named STAT3-KD cells, and then reconstituted wild-type STAT3 or the STAT3 K685R mutant into these cells. The phosphorylation level of the K685R mutant at Y705 and S727 was significantly higher than that of wild-type STAT3 in STAT3-KD cells. The expression of STAT3 target genes, such as IL-6, Pim1, Pim2, and Socs3, was more strongly induced by the reconstitution of the K685R mutant than wild-type STAT3. In addition, the proliferative ability of STAT3-KD cells reconstituted with the K685R mutant was slightly higher than that of STAT3-KD cells reconstituted with wild-type STAT3. In comparisons with the inoculation of STAT3-KD cells reconstituted with wild-type STAT3, the inoculation of STAT3-KD cells reconstituted with the K685R mutant significantly enhanced tumorigenesis and hepatosplenomegaly in nude mice. Collectively, these results revealed for the first time that the acetylation of STAT3 at K685 attenuated NPM-ALK-induced oncogenesis.

IL-6/gp130/STAT3 signaling contributed to the activation of the PERK arm of the unfolded protein response in response to chronic β-adrenergic stimulation

Prolonged activation of the PERK branch of the unfolded protein response (UPR) promotes cardiomyocytes apoptosis in response to chronic β-adrenergic stimulation. STAT3 plays a critical role in β-adrenergic functions in the heart. However, whether STAT3 contributed to β-adrenoceptor-mediated PERK activation and how β-adrenergic signaling activates STAT3 remains unclear. This study aimed to investigate whether STAT3-Y705 phosphorylation contributed to the PERK arm activation in cardiomyocytes and if IL-6/gp130 signaling was involved in the chronic β-AR-stimulation-induced STAT3 and PERK arm activation. We found that the PERK phosphorylation was positively associated with STAT3 activation. Wild-type STAT3 plasmids transfection activated the PERK/eIF2α/ATF4/CHOP pathway in cardiomyocytes while dominant negative Y705F STAT3 plasmids caused no obvious effect on PERK signaling. Stimulation with isoproterenol produced a significant increase in the level of IL-6 in the cardiomyocyte's supernatants, while IL-6 silence inhibited PERK phosphorylation but failed to attenuate STAT3 activation in response to isoproterenol stimulation. Gp130 silence attenuated isoproterenol-induced STAT3 activation and PERK phosphorylation. Inhibiting IL-6/gp130 pathway by bazedoxifene and inhibiting STAT3 by stattic both reversed isoproterenol-induced STAT3-Y705 phosphorylation, ROS production, PERK activation, IRE1α activation, and cardiomyocytes apoptosis in vitro. Bazedoxifene (5 mg/kg/day by oral gavage once a day) exhibited similar effect as carvedilol (10 mg/kg/day by oral gavage once a day) on attenuating chronic isoproterenol (30 mg/kg by abdominal injection once a day, 7 days) induced cardiac systolic dysfunction, cardiac hypertrophy and fibrosis in C57BL/6 mice. Meanwhile, bazedoxifene attenuates isoproterenol-induced STAT3-Y705 phosphorylation, PERK/eIF2α/ATF4/CHOP activation, IRE1α activation, and cardiomyocytes apoptosis to a similar extend as carvedilol in the cardiac tissue of mice. Our results showed that chronic β-adrenoceptor-mediated stimulation activated the STAT3 and PERK arm of the UPR at least partially via IL-6/gp130 pathway. Bazedoxifene has great potential to be used as an alternative to conventional β-blockers to attenuate β-adrenoceptor-mediated maladaptive UPR.

PRDM1 Deletion and STAT3 Mutations Cooperatively Promote CD8+ T-Cell and NK-Cell Growth in Vitro

PRDM1 loss and STAT3 activating mutations commonly co-occur in several non-Hodgkin lymphomas, including ALK negative Anaplastic Large Cell Lymphoma (ALCL) and NK-cell lymphoma (NKCL). PRDM1 is a tumor suppressor gene in NKCL, and also plays important roles in the homeostasis and differentiation of CD8+ T-cells. STAT3 encodes a critical transcription factor involved in specific cytokine-mediated JAK/STAT pathway activation in lymphocytes, controlling proliferation, apoptosis, and other cellular functions. However, it remains unclear whether these two abnormalities cooperate during lymphomagenesis. Here, we introduced PRDM1 deletion and STAT3 mutants into primary human T- or NK-cells isolated from PBMCs of healthy donors and performed functional studies on the genetically modified cells. When either of the two common STAT3 mutants, STAT3Y640F or STAT3D661Y, was transduced into T- or NK-cells, the transduced cells showed short term growth advantage but could not persist, indicating that STAT3 activating mutations may provide stimulatory signals to T- and NK-cells initially, but inhibitory pathways could be activated that prevent long-term sustainable growth. When we knocked out PRDM1 first and then transduced the cells with the STAT3 mutants, the double modified T- or NK-cells showed sustained competitive growth advantage during in vitro culture. The effects were specific to STAT3 mutants as transduction of wild-type (WT) STAT3 or the STAT5BN642H mutant did not improve cell growth. These findings suggest that PRDM1 loss and STAT3 mutations synergistically promote growth in primary T- and NK-cells. We further showed that PRDM1-null, STAT3Y640F-transduced NK-cells displayed better survival and growth compared to PRDM1-deleted or WT cells with feeder cell stimulation. More importantly, the double mutant NK-cells were more independent of feeder cell stimulation, and they were able to expand when supplemented with a single cytokine (IL-15 or IL-2). This feature may be relevant to lymphoma development in vivo where stimulatory cytokines may be limiting. In addition, these double mutant NK-cells had reduced expression of exhaustion markers Tim-3 and Tigit. Similarly, genetically modified CD8+ T cells with PRDM1 knockout and STAT3-mutant were found to express much lower levels of PD-1, Tim-3, and Tigit, an important feature that may promote their growth in vivo where ligands of these co-inhibitory molecules may be expressed in the microenvironment. These double mutant CD8+ T cells exhibited greater stem memory (Tscm) phenotype, marked by CD45RA+, CD62L+, and CCR7+, suggesting the switch to a memory rather than an effector program. Taken together, our in vitro experiments using primary human cells have provided evidences for the functional cooperation between PRDM1 loss and STAT3 activating mutation in promoting CD8+ T- and NK-cell growth. Some features shown by the double mutant cells may facilitate their survival and growth more significantly in vivo. We are currently investigating the adoptive transfer of modified mouse or human cells into littermates or NSG-Tg(huIL15) mice respectively to observe the in vivo development and evolution of the transferred cells. The detailed mechanistic interactions between these two genetic abnormalities in lymphoma development will be further investigated.

SS-4 is a highly selective small molecule inhibitor of STAT3 tyrosine phosphorylation that potently inhibits GBM tumorigenesis in vitro and in vivo

Glioblastoma (GBM) is a highly aggressive cancer with a dismal prognosis. Constitutively active STAT3 has a causal role in GBM progression and is associated with poor patient survival. We rationally designed a novel small molecule, SS-4, by computational modeling to specifically interact with STAT3. SS-4 strongly and selectively inhibited STAT3 tyrosine (Y)-705 phosphorylation in MT330 and LN229 GBM cells and inhibited their proliferation and induced apoptosis with an IC50 of ∼100 nM. The antiproliferative and apoptotic actions of SS-4 were Y-705 phosphorylation dependent, as evidenced by its lack of effects on STAT3 knockout (STAT3KO) cells or STAT3KO cells that overexpressed a phospho-Y705 deficient (STAT3Y705F) mutant, and the recovery of effects when wild-type STAT3 or a phospho-serine (S)727 deficient mutant was expressed in STAT3KO cells. SS-4 increased the expression of STAT3 repressed genes, while decreasing the expression of STAT3 promoted genes. Importantly, SS-4 markedly reduced the growth of GBM intracranial tumor xenografts. These data together identify SS-4 as a potent STAT3 inhibitor that selectively blocks Y705-phosphorylation, induces apoptosis, and inhibits growth of human GBM models in vitro and in vivo.

Selective Targeting of Splicing Factor Mutant Hematopoietic Stem and Progenitor Cells Via STAT3 Inhibition

Myelodysplastic syndrome (MDS) is a bone marrow failure disorder driven by dysfunction of hematopoietic stem and progenitor cells (HSPCs). Patient sequencing studies over the last decade have revealed that mutations in splicing machinery predominate in MDS, thus selective targeting of these cells is therapeutically attractive. STAT3 inhibition has been explored previously as a means to eradicate HSPCs in MDS. While efficacy was demonstrated in a subset of samples, the underlying mechanism for this selectivity remains unknown. We examined RNAseq of MDS CD34+ HSPCs with splicing factor mutations versus wildtype, finding alternative splicing and differential expression of STAT3 pathway components. Functionally, we explored if STAT3 signaling represents a novel vulnerability in SF3B1 mutant HSPCs using a multi-model approach of in vivo zebrafish and mouse systems, and in vitro assays of CRISPR-engineered human leukemia K562 cells and primary MDS samples. Utilizing the small molecule STAT3 inhibitor STATTIC, we found that human cells carrying MDS-associated SF3B1 point mutations had heightened sensitivity to STAT3 inhibition compared to wildtype controls. To evaluate the activity of STAT3 inhibition in vivo, we utilized an Mx1-cre conditional knock-in mouse model of mutant SF3B1 (Sf3b1+/K700E). We demonstrated that in vivo STATTIC treatment selectively depleted Sf3b1 mutant cells over wildtype in vivo. RNAseq of sf3b1 homozygous mutantzebrafish cells revealed conserved dysregulation of STAT3 pathway splicing and target expression. Diminishing Stat3 (via morpholino knockdown, stable mutants, or STATTIC treatment) decreased HSPCs in sf3b1 heterozygotes but not wildtype embryos, demonstrating synthetic lethality between Sf3b1 and Stat3. Our data indicate that SF3B1 heterozygosity, regardless of the type of mutation, confers a heightened sensitivity to STAT3 inhibition in zebrafish, mouse, and human HSPCs. Critically, our data indicate that SF3B1-mutant cells can be selectively killed in vivo while sparing wildtype cells. We sought to rescue HSPCs in sf3b1 homozygous mutant zebrafish, however overexpression of ligands Osm and Il6 or wildtype Stat3 was insufficient. Instead, overexpression of constitutively-active Stat3 partially restored HSPCs, indicating that functional Stat3 signaling downstream of Sf3b1 is critical for HSPC formation. To investigate the specificity of the synthetic lethality for SF3B1, we assessed the STAT3 synthetic lethal interaction with other mutated splicing factors in MDS. Similar to SF3B1, we demonstrated STAT3 synthetic lethality with U2AF1 and SRSF2 heterozygosity in zebrafish and human cells. RNA-sequencing analysis of STATTIC-treated K562 cells revealed an exacerbation of splicing alterations upon STAT3 inhibition that was more pronounced in SF3B1+/K666N cells compared to wildtype. Even more strikingly, we demonstrated that constitutive activation of STAT3 could partially reverse defective splicing in zebrafish sf3b1 homozygous mutant cells. Mechanistically, these data strongly support coordinated splicing dysfunction as the underlying cause for STAT3-SF3B1 synthetic lethality. Together, we demonstrated a conserved and selective synthetic lethal interaction between STAT3 function and splicing factor defects that represents a novel liability for mutant HSPCs with important implications for MDS treatment. DisclosuresShastri: Guidepoint: Consultancy; Kymera Therapeutics: Research Funding; Onclive: Honoraria; GLC: Consultancy. Verma: Curis: Research Funding; BMS: Research Funding; Stelexis: Consultancy, Current equity holder in publicly-traded company; Eli Lilly: Research Funding; Medpacto: Research Funding; Incyte: Research Funding; GSK: Research Funding; Novartis: Consultancy; Acceleron: Consultancy; Celgene: Consultancy; Stelexis: Current equity holder in publicly-traded company; Throws Exception: Current equity holder in publicly-traded company.

Therapeutic Efficacy of Mcl-1 Antagonism in Large Granular Lymphocyte Leukemia

Introduction: Large granular lymphocyte (LGL) leukemia is a spectrum of rare clonal lymphoproliferative disorders, all of which involve expansion of large granular lymphocytes. Immunosuppressive regimens using methotrexate or cyclophosphamide are utilized as front-line treatments in LGL leukemia but are not curative nor are they effective in all patients. The aggressive LGL variants have no effective treatment and are refractory to conventional chemotherapy. The lack of effective and targeted therapies results from an incomplete picture of survival mechanisms that contribute to the pathogenesis of leukemic LGLs.We have previously reported that STAT3 is constitutively active in LGL leukemia cells and up to 40% of patients harbor activating mutations in STAT3 within the leukemic clone. We have also reported that the pro-survival Bcl-2-family protein Mcl-1 is upregulated in LGL leukemia patients. Additionally, we have identified MCL1 as a transcriptional target of STAT3 in leukemic LGLs. Recently, novel small molecule inhibitors of Mcl-1 have been identified including marinopyrrole A (maritoclax) and its derivative KS18. These inhibitors effectively induced apoptosis in Mcl-1-dependent cells and suppressed the growth of Mcl-1-dependent hematologic cancer xenografts in nude mice without apparent toxicity. Thus, this study further investigates the role of Mcl-1 in LGL leukemia and the potential therapeutic application of the Mcl-1 antagonists maritoclax and KS18.Results: Knockdown of Mcl-1 in human-derived LGL leukemia cell lines (TL1 and NKL) resulted in decreased cell viability by MTS assay and increased apoptosis by flow cytometry in Mcl-1 siRNA versus scramble siRNA-transfected cells (NKL and TL-1 cells: p < 0.001). Treatment with maritoclax or KS18 decreased cell proliferation and increased apoptosis in NKL, TL1 and RNK16 (rat-derived LGL leukemia cell line) cells (Maritoclax, EC50: 2.45, 1.43 and 1.23 μM respectively) (KS18, EC50: 1.30, 0.60 and 0.31 μM respectively). Ex vivo treatment with maritoclax and KS18 induced selective apoptosis in PBMCs from LGL leukemia patients (NK-LGL, n = 6; T-LGL, n = 12) but not normal donor PBMCs (n = 4) (Maritoclax and KS18, p < 0.0001). Importantly, there was no significant difference in treatment efficacy in patient cells with wild-type STAT3 (n = 9) versus mutant STAT3 (Y640F, n = 5; D661Y, n = 3). We then proceeded to mechanistic studies of Mcl-1 antagonism. Both maritoclax and KS18 induced selective and dose-dependent Mcl-1 degradation by western blot in NKL, TL1, RNK16 and PBMCs from LGL leukemia patients. We further delineated that this effect was proteasome dependent as it is reversible by pre-treatment with MG132, a proteasome inhibitor.Preclinical in vivo studies were then conducted in Fisher F344 rats that were transplanted with primary leukemic LGL cells and monitored for signs of leukemia through serial CBC and body weight measurements. Leukemic rats developed progressive anemia, thrombocytopenia and leukocytosis and significant weight loss. Rats were treated with vehicle or KS18 (2.5 or 5.0 mg/kg i.p. daily) upon detection of leukemic features. In non-leukemic KS18-treated rats, there were no observed toxicities and there was no difference in survival or weight gain versus vehicle-treated non-leukemic rats. However, leukemic KS18-treated rats exhibited findings consistent with tumor lysis syndrome, including sudden death associated with severely increased serum LDH and increased apoptosis in heart and spleen tissues. At necropsy, leuk/KS18 rats exhibited significantly decreased infiltration and elevated apoptosis of leukemic cells in heart and spleen tissues. Conversely, in leuk/veh rats, spleen tissue lacked normal histologic structure with red pulp replaced almost completely by leukemia cells. Ex vivo KS18 treatment also decreased the viability of PBMC and spleen cells from leukemic animals (p < 0.0001). These data indicate that Mcl-1 is a promising therapeutic target as evidenced by potent therapeutic efficacy of KS18 in LGL cell lines and primary patient material and in an aggressive rat model of LGL leukemia. Further studies are required in order to optimize drug dose, timing and concentrations of KS18 in order to prevent potential tumor lysis syndrome and optimize therapeutic benefit. DisclosuresGru:Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Transcriptional Profiling of STAT1 Gain-of-Function Reveals Common and Mutation-Specific Fingerprints.

STAT1 gain-of-function (GOF) is a primary immunodeficiency typically characterized by chronic mucocutaneous candidiasis (CMC), recurrent respiratory infections, and autoimmunity. Less commonly, also immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX)-like syndromes with CMC, and combined immunodeficiency without CMC have been described. Recently, our group and others have shown that different mutation-specific mechanisms underlie STAT1 GOF in vitro, including faster nuclear accumulation (R274W), and reduced mobility (R321, N574I) to near immobility in the nucleus (T419R) upon IFNγ stimulation. In this work, we evaluated the transcriptomic fingerprint of the aforementioned STAT1 GOF mutants (R274W, R321S, T419R, and N574I) relative to STAT1 wild-type upon IFNγ stimulation in an otherwise isogenic cell model. The majority of genes up-regulated in wild-type STAT1 cells were significantly more up-regulated in cells expressing GOF mutants, except for T419R. In addition to the common interferon regulated genes (IRG), STAT1 GOF mutants up-regulated an additional set of genes, that were in part shared with other GOF mutants or mutation-specific. Overall, R274W and R321S transcriptomes clustered with STAT1 WT, while T419R and N574I had a more distinct fingerprint. We observed reduced frequency of canonical IFNγ activation site (GAS) sequences in promoters of genes up-regulated by all the STAT1 GOF mutants, suggesting loss of DNA binding specificity for the canonical GAS consensus. Interestingly, the T419R mutation, expected to directly increase the affinity for DNA, showed the most pronounced effects on the transcriptome. T419R STAT1 dysregulated more non-IRG than the other GOF mutants and fewer GAS or degenerate GAS promotor sequences could be found in the promoter regions of these genes. In conclusion, our work confirms hyperactivation of common sets of IFNγ-induced genes in STAT1 GOF with additional dysregulation of mutation-specific genes, in line with the earlier observed mutation-specific mechanisms. Binding to more degenerate GAS sequences is proposed as a mechanism toward transcriptional dysregulation in R274W, R321S, and N574I. For T419R, an increased interaction with the DNA is suggested to result in a broader and less GAS-specific response. Our work indicates that multiple routes leading to STAT1 GOF are associated with common and private transcriptomic fingerprints, which may contribute to the phenotypic variation observed in vivo.

IRF-1 expressed in the inner cell mass of the porcine early blastocyst enhances the pluripotency of induced pluripotent stem cells

BackgroundDespite years of research, porcine-induced pluripotent stem cells (piPSCs) with germline chimeric capacity have not been established. Furthermore, the key transcription factors (TFs) defining the naïve state in piPSCs also remain elusive, even though TFs in the inner cell mass (ICM) are believed to be key molecular determinants of naïve pluripotency. In this study, interferon regulatory factor 1 (IRF-1) was screened to express higher in ICM than trophectoderm (TE). But the impact of IRF-1 on maintenance of pluripotency in piPSCs was not determined.MethodsTranscriptome profiles of the early ICM were analyzed to determine highly interconnected TFs. Cells carrying these TFs’ reporter were used to as donor cells for somatic cell nuclear transfer to detect expression patterns in blastocysts. Next, IRF1-Flag was overexpressed in DOX-hLIF-2i piPSCs and AP staining, qRT-PCR, and RNA-seq were conducted to examine the effect of IRF-1 on pluripotency. Then, the expression of IRF-1 in DOX-hLIF-2i piPSCs was labeled by GFP and qRT-PCR was conducted to determine the difference between GFP-positive and GFP-negative cells. Next, ChIP-Seq was conducted to identify genes target by IRF-1. Treatment with IL7 in wild-type piPSCs and STAT3 phosphorylation inhibitor in IRF-1 overexpressing piPSCs was conducted to confirm the roles of JAK-STAT3 signaling pathway in IRF-1’s regulation of pluripotency. Moreover, during reprogramming, IRF-1 was overexpressed and knocked down to determine the change of reprogramming efficiency.ResultsIRF-1 was screened to be expressed higher in porcine ICM than TE of d6~7 SCNT blastocysts. First, overexpression of IRF-1 in the piPSCs was observed to promote the morphology, AP staining, and expression profiles of pluripotency genes as would be expected when cells approach the naïve state. Genes, KEGG pathways, and GO terms related to the process of differentiation were also downregulated. Next, in the wild-type piPSCs, high-level fluorescence activated by the IRF-1 promoter was associated with higher expression of naïve related genes in piPSCs. Analysis by ChIP-Seq indicated that genes related to the JAK-STAT pathway, and expression of IL7 and STAT3 were activated by IRF-1. The inhibitor of STAT3 phosphorylation was observed could revert the expression of primed genes in IRF-1 overexpressing cells, but the addition of IL7 in culture medium had no apparent change in the cell morphology, AP staining results, or expression of pluripotency related genes. In addition, knockdown of IRF-1 during reprogramming appeared to reduce reprogramming efficiency, whereas overexpression exerted the converse effect.ConclusionThe IRF-1 expressed in the ICM of pigs’ early blastocyst enhances the pluripotency of piPSCs, in part through promoting the JAK-STAT pathway.

Analysis of Genomic Landscape of Large Granular Lymphocyte Leukemia Reveals Etiologic Insights

Introduction: Large Granular Lymphocyte (LGL) leukemia is a rare lymphoproliferative disorder characterized by clonal expansion of either CD3+ cytotoxic T cells expressing T cell receptor (TCR) alpha beta or CD3- natural killer (NK) cells. A less frequent CD3+ T cell subtype expresses TCR gamma delta (GD). Here, we present the molecular landscape of known LGL types (T, NK, GD) from analysis of the largest patient cohort assembled to date. An integrative analysis of genomic datasets from all LGL subtypes is necessary to more precisely define the shared and unique etiology of this rare disorder. Methods: We collected paired saliva and PBMC samples and related clinical information from 116 LGL leukemia patients after informed consent. The assembled cohort consisted of 93 T-LGL, 11 NK-LGL, and 12 GD T-LGL patients. Genomic analyses were performed on the leukemic (PBMC) and germline (saliva) samples after whole exome sequencing (WES) and transcriptome sequencing (RNAseq, PBMC only). Results: Somatic mutations were detected in the previously described potential drivers STAT3 (n=56), TNFAIP3 (n=9), and PIK3R1 (n=4). We also identified somatic mutations in CDH8 (n=3) and CCL22 (n=4), which we postulate as putative drivers based on mutational clustering. CDH8 was mutated in all three LGL subtypes, but CCL22 somatic mutations were only observed in NK-LGL patients. We observed that STAT3 and CCL22 together account for 64% (7/11) of NK-LGL cases. STAT3 is the most recurrently mutated gene in LGL leukemia, yet concurrent molecular and clinical features are incompletely defined. Interestingly, patients with STAT3 mutations have a higher mutational burden (P=0.0006) compared to those with wild-type (WT) STAT3. This effect is independent of the age of the patient, which correlates with the mutational burden (R=0.26, P=0.0039) and agrees with the finding that the dominant mutational signatures in this cohort exhibit clock-like properties. We also observed that patients with STAT3 mutations are enriched (P=0.0273) for additional mutations in chromatin modifier enzymes such as KMT2D, TET2, DNMT3A, and SETD1B (Figure 1). We found that ~10% of the samples exhibit broad somatic copy-number aberrations, and a patient with somatic mutations in STAT3 and KMT2D displayed high-level microsatellite instability. STAT3 mutations were also significantly associated with increased expression of genes involved in apoptosis, complement activation, and interferon cytokine signaling compared to STAT3 WT (FDR &amp;lt; 0.05). Early-onset LGL patients with age 51 years or less (n=28), as defined by the bottom quartile of the cohort, displayed no differential enrichment of the somatic driver genes. Interestingly, the age of the patient was significantly associated with absolute neutrophil counts (ANC) (P = 0.0068), with younger patients exhibiting lower neutrophil counts, even after adjusting for the presence of STAT3 mutation, as it is associated with lower ANC. As neutropenia is a hallmark feature of LGL leukemia and often a trigger for initiating therapy, the association of young age with lower neutrophil counts and lower somatic mutational burden suggests other mechanisms may be involved. Focusing on the germline variants, we found that 17 of the patients (14.6%) had at least one pathogenic or likely pathogenic germline variant with known oncogenic association as annotated using CharGer. 5 patients had pathogenic mutations in known tumor suppressors including FANCC (n=1), BRCA1 (n=1), PALB2 (n=1), MUTYH (n=1), and SDHA (n=1), while 1 patient had pathogenic mutations in ALK, a known oncogene. Conclusions: We report on the genomic analyses done on whole exome and RNA-seq data from the largest cohort assembled for LGL leukemia to date. We show that the presence of STAT3 mutation is significantly associated with an increase in mutation burden and additional somatic mutations in chromatin modifiers, hinting at potential pathogenic mechanisms within STAT3 mutated patients. By combining LGL subtypes in our analysis, we were able to identify CDH8 as a putative driver that is present in T, NK, and GD subtypes. Additionally, we report CCL22 mutations specific to NK-LGL leukemia, however did not detect any subtype specific mutations in GD T-LGL. We found that about 15% of the patients carry at least one pathogenic germline variant with known oncogenic associations. These findings highlight emerging etiologic insights into this rare disorder. Disclosures Feith: Kymera Therapeutics: Membership on an entity's Board of Directors or advisory committees. Loughran:Keystone Nano: Membership on an entity's Board of Directors or advisory committees; Bioniz Therapeutics: Membership on an entity's Board of Directors or advisory committees; Kymera Therapeutics: Membership on an entity's Board of Directors or advisory committees; Dren Bio: Membership on an entity's Board of Directors or advisory committees.

Cytotoxicity of apigenin toward multiple myeloma cell lines and suppression of iNOS and COX-2 expression in STAT1-transfected HEK293 cells

BackgroundApigenin is one of the most abundant dietary flavonoids that possesses multiple bio-functions. PurposeThis study was designed to determine the influence of apigenin on gene expressions, cancer cells, as well as STAT1/COX-2/iNOS pathway mediated inflammation and tumorigenesis in HEK293-STAT1 cells. Furthermore, the cytotoxic activity toward multiple myeloma (MM) cell lines was investigated. MethodsBioinformatic analyses were used to predict the sensitivity and resistance of tumor cells toward apigenin and to determine cellular pathways influenced by this compound. The cytotoxic and ferroptotic activity of apigenin was examined by the resazurin reduction assay. Additionally, we evaluated apoptosis, and cell cycle distribution, induction of reactive oxygen species (ROS) and loss of integrity of mitochondrial membrane (MMP) by using the flow cytometry analysis. DAPI staining was used to detect characteristic apoptotic features. Furthermore, we verified its anti-inflammatory and additional mechanism of cell death by western blotting. ResultsCOMPARE and hierarchical cluster analyses exhibited that 29 of 55 tumor cell lines were sensitive against apigenin (p < 0.001). The Ingenuity Pathway Analysis data showed that important bio-functions affected by apigenin were: gene expression, cancer, hematological system development and function, inflammatory response, and cell cycle. The STAT1 transcription factor was chosen as target protein on the basis of gene promoter binding motif analyses. Apigenin blocked cell proliferation of wild-type HEK293 and STAT1 reporter cells (HEK293-STAT1), promoted STAT1 suppression and subsequent COX-2 and iNOS inhibition. Apigenin also exhibited synergistic activity in combination with doxorubicin toward HEK293-STAT1 cells. Apigenin exerted excellent growth-inhibitory activity against MM cells in a concentration-dependent manner with the greatest activity toward NCI-H929 (IC50 value: 10.73 ± 3.21 μM). Apigenin induced apoptosis, cell cycle arrest, ferroptosis and autophagy in NCI-H929 cells. ConclusionApigenin may be a suitable candidate for MM treatment. The inhibition of the STAT1/COX-2/iNOS signaling pathway by apigenin is an important mechanism not only in the suppression of inflammation but also in induction of apoptosis.

Autosomal dominant hyper IgE syndrome from a single centre in Chongqing, China (2009-2018).

Autosomal dominant hyper IgE syndrome (AD-HIES) caused by STAT3 gene mutation is a rare primary immunodeficiency disease. To better understand the disease, we described the clinical characteristics of 20 AD-HIES patients in Chongqing, China and explored the effect of mutations in different domains of STAT3 gene on the function of STAT3 protein by Western blot and confocal microscopy. The mean age at onset was 0.12years. The mean age at diagnosis was 5.31years. The most common presentation was eczema, pneumonia, skin abscesses and chronic mucocutaneous candidiasis. Seven patients suffered from BCG complications. R382W/Q were identified in 12 patients, V637M mutation in three patients. Three patients have died. The phosphorylated STAT3 was expressed more in wild-type(WT) and R382W mutant STAT3 in the cytoplasm of COS7 cells with epidermal growth factor(EGF) stimulation, less in the V637M mutation and T620S mutation. Dynamic observation showed that STAT3 cytoplasmic accumulation and nuclear translocation occurred rapidly after EGF stimulation in WT-STAT3-GFP, the time of accumulation and nuclear translocation was later and the expression was less in R382W-STAT3-GFP compared with WT-STAT3-GFP, followed by V637M and T620S mutation. These results suggested that our patients had earlier onset, diagnostic age and higher rate of BCG complications. However, our patients had higher incidence of mortality though the earlier diagnostic age. We did not find a significant genotype/phenotype correlation, but Src homology 2 domain mutations (V637M and T620S) had a greater effect on STAT3 phosphorylation and nuclear translocation than DNA-binding domain mutation (R382W) in vitro.

Identification of novel regulators of STAT3 activity.

STAT3 mediates signalling downstream of cytokine and growth factor receptors where it acts as a transcription factor for its target genes, including oncogenes and cell survival regulating genes. STAT3 has been found to be persistently activated in many types of cancers, primarily through its tyrosine phosphorylation (Y705). Here, we show that constitutive STAT3 activation protects cells from cytotoxic drug responses of several drug classes. To find novel and potentially targetable STAT3 regulators we performed a kinase and phosphatase siRNA screen with cells expressing either a hyperactive STAT3 mutant or IL6-induced wild type STAT3. The screen identified cell division cycle 7-related protein kinase (CDC7), casein kinase 2, alpha 1 (CSNK2), discoidin domain-containing receptor 2 (DDR2), cyclin-dependent kinase 8 (CDK8), phosphatidylinositol 4-kinase 2-alpha (PI4KII), C-terminal Src kinase (CSK) and receptor-type tyrosine-protein phosphatase H (PTPRH) as potential STAT3 regulators. Using small molecule inhibitors targeting these proteins, we confirmed dose and time dependent inhibition of STAT3-mediated transcription, suggesting that inhibition of these kinases may provide strategies for dampening STAT3 activity in cancers.

Rotenone-induced reactive oxygen species signal the recruitment of STAT3 to mitochondria.

STAT3, a transcription factor involved in various physiological and pathological processes, is also present in mitochondria. Mitochondrial STAT3 regulates complex I activity and reactive oxygen species (ROS) production, yet the mechanisms governing its translocation to mitochondria remain poorly understood. In this study, we show that rotenone-induced ROS triggers the Ser727 phosphorylation of STAT3 and its increased mitochondrial localisation. Furthermore, we show that STAT3-depleted cells display increased ROS levels during rotenone treatment. Targeted expression in mitochondria of wild-type STAT3 - but not S727A mutant - lowers ROS levels, indicating the importance of Ser727 phosphorylation, both in rotenone-induced mitochondrial targeting and quenching of ROS levels. Together, our results demonstrate a novel STAT3-mediated feedback mechanism to maintain redox homeostasis during stress.

A deep intronic splice mutation of STAT3 underlies hyper IgE syndrome by negative dominance

Heterozygous in-frame mutations in coding regions of human STAT3 underlie the only known autosomal dominant form of hyper IgE syndrome (AD HIES). About 5% of familial cases remain unexplained. The mutant proteins are loss-of-function and dominant-negative when tested following overproduction in recipient cells. However, the production of mutant proteins has not been detected and quantified in the cells of heterozygous patients. We report a deep intronic heterozygous STAT3 mutation, c.1282-89C>T, in 7 relatives with AD HIES. This mutation creates a new exon in the STAT3 complementary DNA, which, when overexpressed, generates a mutant STAT3 protein (D427ins17) that is loss-of-function and dominant-negative in terms of tyrosine phosphorylation, DNA binding, and transcriptional activity. In immortalized B cells from these patients, the D427ins17 protein was 2 kDa larger and 4-fold less abundant than wild-type STAT3, on mass spectrometry. The patients' primary B and T lymphocytes responded poorly to STAT3-dependent cytokines. These findings are reminiscent of the impaired responses of leukocytes from other patients with AD HIES due to typical STAT3 coding mutations, providing further evidence for the dominance of the mutant intronic allele. These findings highlight the importance of sequencing STAT3 introns in patients with HIES without candidate variants in coding regions and essential splice sites. They also show that AD HIES-causing STAT3 mutant alleles can be dominant-negative even if the encoded protein is produced in significantly smaller amounts than wild-type STAT3.

Abstract 3343: Identifying kinases and phosphatases that regulate STAT3 activity

Abstract The STAT3 transcription factor is hyperactivated in many cancers where it induces cancer progression by driving drug resistance, metastasis and pro-cancer inflammation. We therefore sought new strategies to target the activation of STAT3. Many kinases and signalling pathways can cause STAT3 activation, and it is not well understood how this is regulated in cancer cells. In some rare solid and hematological cancers, such as NK-/T-cell large granular lymphocytic leukemia and inflammatory hepatocellular adenomas, STAT3 has also been found to be mutated, resulting in a constitutively active STAT3 protein. In testing mock transfected vs. STAT3(Y640F)-transfected cells, as a means to introduce activated STAT3 in already transformed cells, in a screen against 525 anticancer agents, we identified that activated STAT3 protects the cells from cytotoxic effects of several classes of anticancer compounds. Therefore, we performed RNAi screens to identify kinases and phosphatases that regulate STAT3 activity and therefore may act as drug-sensitizing targets. Using STAT3 transcription-driven luciferase reporter cell lines expressing active wild type (WT) or mutant (Y640F) STAT3, we identified several candidate genes (CDC7, CDK8, CSK, CSNK2A1, PI4KII, PTPRH, DDR2) whose downregulation led to differential STAT3 transcriptional activity. Strikingly, none of the hits caused highly selective effect on either mutant or wild-type STAT3 expressing cells, suggesting that the phosphoregulation of hyperactive mutant and IL6 induced wild-type STAT3 are mechanistically similar. Using small molecule inhibitors targeting CDK8, CSNK2A1, DDR2 and CDC7, we confirmed that STAT3 transcriptional activity was inhibited in a dose and time dependent fashion without severely affecting cell viability. Small molecules targeting of CSNK2A1, DDR2 and CDC7 kinase activity caused a slow inhibition of STAT3 transcriptional activity where the strongest effects were only seen after 72 h. CDK8 kinase inhibition, on the other hand, reduced STAT3 activity effectively already after 4 h. This suggests that CDK8 regulates STAT3 activity more directly than CSNK2A1, DDR2 and CDC7. Inhibition of CDK8 and CSNK2A1 resulted in decrease of STAT3 phosphorylation in the STAT3(Y640F)-transfected cells, and knockdown of CSNK2A1 inhibited the nuclear localization of STAT3. In conclusion, we have found that hyperactive STAT3(Y640F) can protect cancer cells from several drug classes, mimicking the case when hyperactivated wild type STAT3 is acting as malignancy promoting protein in cancers. In a functional genetics screen, we found six kinases and a phosphatase that regulate transcriptional activity of STAT3. Using small molecule inhibitors, we could confirm that targeting the hit kinases regulate STAT3 transcriptional activity. Together, our data suggest that there are multiple kinases that may be targeted to counteract STAT3 mediated drug resistance in cancers. Citation Format: Elina Parri, Heikki Kuusanmäki, Arjan van Adrichem, Meri Kaustio, Laura Turunen, Krister Wennerberg. Identifying kinases and phosphatases that regulate STAT3 activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3343.

Abstract 5489: Characterization of mitochondrial STAT3 (mitostat3) function and the mitoStat3 interactome as a therapeutic strategy for multiple myeloma

Abstract The oncogenic transcription factor STAT3 is an appealing therapeutic target in cancer including multiple myeloma (MM) where its inhibition has the potential to downregulate aberrant signaling from various upstream molecules. STAT3 has been studied extensively as a transcription factor however, much less is known about its non-classical functions in the mitochondria and in turn, the role of mitochondrial STAT3 (mitoStat3) in cancer biology. Data suggests that mitoStat3 is critical for mediating Ras-induced oncogenic transformation. As activating mutations of the MAPK pathway are reported in over 50% of myeloma patients, we sought to characterize the function of mitoStat3 in MM. We first confirmed the presence of STAT3 in the mitochondria of myeloma cell lines, AMO1 and XG6 by Western blot analysis. We next used CRISPR/CAS9 to knockdown STAT3 in XG6 and AMO1 cells, which resulted in inhibition of cell proliferation (XG6 and AMO1), apoptosis (XG6) and reduced oxygen consumption rate as measured by extracellular flux analysis (Seahorse assay). To better define the role of mitoStat3 and to identify indirect strategies to interfere with STAT3 activity, we employed a proximity-dependent Biotin Identification (BioID) method to discover mitoStat3 interacting proteins. BioID is a unique method to screen for physiologically relevant protein interactions that occur in living cells. First, wild-type STAT3 was fused to a mitochondrial localization Signal (MLS-Stat3), cloned into pcDNA5 FRT/TO [MCS]-BirAR118G-FLAG plasmid and transfected into HEK293 TRE-x Flp-In cells. BioID identified 225 high confidence mitoStat3-interacting partners in MLS-Stat3 transfected cells. The most abundant proteins in the mitoStat3 interactome included those with roles in mitochondrial translation and mitochondrial electron transport. Futhermore, mitoStat3 was found to interact with the translocase of inner membrane protein Tim44, which together with Tim23 complex facilitates translocation of proteins into the mitochondrial matrix. Genetic knockdown of Tim23 in XG6 cells resulted in decreased mitoStat3 suggesting that this complex may be involved in the import of STAT3 into the mitochondria. Additional mitoStat3 interacting proteins identified by BioID are currently being validated and will be presented. Taken together, results support the further exploration of the role of mitoStat3 in myeloma cells. Further, identification of mitoStat3 interacting proteins including Tim44 and others may inform alternative strategies to therapeutically target oncogenic STAT3. Citation Format: Serges P. Tsofack, Aaron Botham, Zhihua Li, Ellen Nong Wei, Danielle Croucher, Ioulia Jitkova, Neil MacLean, Aaron D. Schimmer, Brian Raught, Suzanne Trudel. Characterization of mitochondrial STAT3 (mitostat3) function and the mitoStat3 interactome as a therapeutic strategy for multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5489.

The critical role that STAT3 plays in glioma-initiating cells: STAT3 addiction in glioma.

Glioma-Initiating Cells (GICs) are thought to be responsible for tumor initiation, progression and recurrence in glioblastoma (GBM). In previous studies, we reported the constitutive phosphorylation of the STAT3 transcription factor in GICs derived from GBM patient-derived xenografts, and that STAT3 played a critical role in GBM tumorigenesis. In this study, we show that CRISPR/Cas9-mediated deletion of STAT3 in an established GBM cell line markedly inhibited tumorigenesis by intracranial injection but had little effect on cell proliferation in vitro. Tumorigenesis was rescued by the enforced expression of wild-type STAT3 in cells lacking STAT3. In contrast, GICs were highly addicted to STAT3 and upon STAT3 deletion GICs were non-viable. Moreover, we found that STAT3 was constitutively activated in GICs by phosphorylation on both tyrosine (Y705) and serine (S727) residues. Therefore, to study STAT3 function in GICs we established an inducible system to knockdown STAT3 expression (iSTAT3-KD). Using this approach, we demonstrated that Y705-STAT3 phosphorylation was critical and indispensable for GIC-induced tumor formation. Both phosphorylation sites in STAT3 promoted GIC proliferation in vitro. We further showed that S727-STAT3 phosphorylation was Y705-dependent. Targeted microarray and RNA sequencing revealed that STAT3 activated cell-cycle regulator genes, and downregulated genes involved in the interferon response, the hypoxia response, the TGFβ pathway, and remodeling of the extracellular matrix. Since STAT3 is an important oncogenic driver of GBM, the identification of these STAT3 regulated pathways in GICs will inform the development of better targeted therapies against STAT3 in GBM and other cancers.

Alantolactone suppresses APOC3 expression and alters lipid homeostasis in L02 liver cells

A high level of APOC3 expression is an independent risk factor for some lipid metabolism-related diseases, such as cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD) and atherosclerosis (AS). This suggests that down-regulating APOC3 expression is a potential way of regulating lipid levels. In this study, we used luciferase reporter screening to identify a natural compound, alantolactone (ALA), that can inhibit the promoter activity of APOC3. ALA decreased APOC3 expression at both mRNA and protein levels. Then we pretreated L02 liver cells with oxLDL to investigate the function of ALA in lipid homeostasis. Intriguingly, ALA attenuated oxLDL-induced foam cell formation by reducing total cholesterol (TC) and triglyceride (TG) contents. Furthermore, these results could be reversed by overexpressing APOC3 protein. ALA inhibited tyrosine phosphorylation (Tyr705pho) of STAT3 to down-regulate APOC3 expression. Intriguingly, overexpression of a wild-type STAT3 or a constitutively active form of STAT3 (STAT3-C) up-regulated APOC3 expression and partly reversed the effect of ALA in oxLDL-induced L02 cells. Overexpression of wild-type STAT3 also increased TC but not TG contents in L02 cells. However, overexpression of STAT3-C significantly increased TC and TG contents, and the effect of ALA was partly attenuated by STAT3-C, although this was not statistically significant. These results suggest that ALA attenuates lipid accumulation through down-regulation of APOC3 expression, at least in part by inhibiting STAT3 signaling.