Hippo Tumor Suppressor Pathway Research Articles

Identification of resistance mechanisms to small-molecule inhibition of TEAD-regulated transcription

The Hippo tumor suppressor pathway controls transcription by regulating nuclear abundance of YAP and TAZ, which activate transcription with the TEAD1-TEAD4 DNA-binding proteins. Recently, several small-molecule inhibitors of YAP and TEADs have been reported, with some entering clinical trials for different cancers with Hippo pathway deregulation, most notably, mesothelioma. Using genome-wide CRISPR/Cas9 screens we reveal that mutations in genes from the Hippo, MAPK, and JAK-STAT signaling pathways all modulate the response of mesothelioma cell lines to TEAD palmitoylation inhibitors. By exploring gene expression programs of mutant cells, we find that MAPK pathway hyperactivation confers resistance to TEAD inhibition by reinstating expression of a subset of YAP/TAZ target genes. Consistent with this, combined inhibition of TEAD and the MAPK kinase MEK, synergistically blocks proliferation of multiple mesothelioma and lung cancer cell lines and more potently reduces the growth of patient-derived lung cancer xenografts in vivo. Collectively, we reveal mechanisms by which cells can overcome small-molecule inhibition of TEAD palmitoylation and potential strategies to enhance the anti-tumor activity of emerging Hippo pathway targeted therapies.

Vascular mimicry as a facilitator of melanoma brain metastasis.

Melanoma has the highest propensity among solid tumors to metastasize to the brain.Melanoma brainmetastases (MBM) are a leading cause of deathinmelanoma and affect 40-60% of patients with late-stagedisease.Therefore, uncovering the molecular mechanisms behind MBM is necessary to enhance therapeutic interventions.Vascular mimicry (VM) is a form of neovascularization linked to invasion, increased risk of metastasis, and poor prognosisin many tumor types, but its significance in MBM remains poorly understood.We found that VM density is elevated in MBM comparedto pairedextracranialspecimensand is associated with tumor volume andCNSedema. In addition, our studies indicate a relevant role of YAP and TAZ, two transcriptional co-factors scarcely studied in melanoma, in tumor cell-vasculogenesis and in brain metastasis. We recently demonstrated activation of the Hippo tumor suppressor pathway and increased degradation of its downstream targets YAP and TAZ in a metastasis impaired cell line model.In the current study we establish the utility of anti-YAP/TAZ therapy in mouse models of metastatic melanoma whereby treatment effectively inhibitsVM andprolongs survival of mice with MBM. The data presented herein suggest that VM may be an important and targetable mechanism in melanoma and that VM inhibition might be useful for treating MBM, an area of high unmet clinical need, thus having important implications for future treatment regimens for these patients.

Abstract 1092: RUNX2 inhibition alters PAX3::FOXO1 driven fusion-positive rhabdomyosarcoma cell state and growth

Abstract Investigation: Fusion-positive rhabdomyosarcoma (FP-RMS) is an aggressive pediatric cancer of skeletal muscle lineage. While the incidence of RMS is ~4.5 patients per million individuals aged <20 years, 5-year survival for high-risk children is <30%, and <8% when metastatic. The PAX3::FOXO1 (P3F) fusion gene, resulting from t(2:13), is the most prominent fusion oncogene that drives FP-RMS. P3F is a fusion transcription factor and supports FP-RMS by keeping it in a persistent myoblastic state. We found P3F functions in part by suppressing MST kinase activity in the Hippo tumor suppressor pathway, a developmental pathway involved in cell fate and organ size. To investigate how this may rewire gene expression to support FP-RMS, we performed ATAC-seq analysis of a myoblast-based model of FP-RMS in which MST was further inhibited and found the RUNX2 gene locus was more accessible. Since RUNX2 is a pioneer transcription factor known to interact with the “WW” domains of Hippo pathway members to support mesenchymal cell fate, we hypothesize that RUNX2 maintains these relationships to support FP-RMS cell state and survival. Methods & Results: Inquiry of in silico databases and previously published literature unveiled that sarcomas including RMS have a high dependency on RUNX2 and that P3F directly binds a RUNX2 enhancer. Interrogation of a proximity labeling proteomics study from our collaborators in the Counter lab found that RUNX2 was part of the protein interactome of 7/7 FP-RMS fusions including P3F. Additionally, Co-IP experiments confirmed that there is a direct protein-protein relationship between RUNX2, P3F, and TAZ. Next, we performed in vitro genetic loss of function (LOF) of RUNX2 using RNAi, which showed that suppression of RUNX2 caused cell death, growth inhibition, increased TAZ expression, and induction of both myogenic and osteogenic markers. We also performed complementary pharmacologic LOF using two available small molecules, AI-14-91 (Bushweller lab) in vitro, and CADD522 (commercially available) in vitro and in vivo. We found that these partially phenocopied the genetic LOF and that CADD522 reduces tumor volume and growth. Conclusions: RUNX2 is a vulnerability in RMS based on in silico, in vitro, and in vivo investigation, and may act to prevent osteogenic and myogenic differentiation via protein-protein relationships in the Hippo pathway. The next step will be assessing mechanistic relationships between the Hippo pathway and RUNX2, as well as the genome wide changes upon RUNX2 LOF by performing ChIP-seq, RNA-seq, and scRNA-seq experiments. Citation Format: Elizabeth A. Mendes, Audrey L. Chambers, Samantha J. Weitzel, Michael Deel, Aanandi Munshi, Christopher M. Counter, Seth Zimmerman, John Bushweller, Corinne M. Linardic. RUNX2 inhibition alters PAX3::FOXO1 driven fusion-positive rhabdomyosarcoma cell state and growth [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 1092.

Abstract 6589: Discovery of potent and selective pan-TEAD autopalmitoylation inhibitors for the treatment of Hippo-pathway altered cancers

Abstract TEAD1-4 are DNA bound transcription factors regulated by the Hippo tumor suppressor pathway that bind the coactivators YAP/TAZ to activate oncogenic gene expression programs involved in cell survival, proliferation, and drug resistance. TEAD-dependent transcription is activated in many tumor types through a variety of mechanisms including LOF Hippo pathway mutations (e.g. NF2, LATS) and YAP/TAZ amplification, and also as an adaptive resistance mechanism, for example in response to EGFR TKI and KRAS inhibition. Here, we report the initial characterization of a novel pan-TEAD inhibitor, AZ4331, which was identified following a structure-guided drug design campaign. AZ4331 disrupts the post-translational palmitoylation of TEAD proteins through covalent binding to a conserved cysteine residue resulting in inhibition of TEAD-dependent transcriptional output. AZ4331 inhibited the proliferation of NF2m NCI-H226 cells (GI50: 92 nM) while having no effect on Hippo-wild type NCI-H2452 (GI50: undetermined). Cell-based metabolic labeling studies demonstrated the ability of AZ4331 to inhibit palmitoylation of all four TEAD paralogs and led to disruption of the YAP/TEAD complex assessed by immunoprecipitation resulting in reduced TEAD transcriptional output as assessed by qPCR. Furthermore, in vivo profiling showed AZ4331 achieved sufficient exposures (plasma free Cmax: 2.7 µM) and robust target engagement as measured through reduction of multiple canonical TEAD target genes (CTGF [IC50: 0.127 µM], ANKRD1, AMOTL2 and CYR61) in Hippo-altered mesothelioma xenograft tumors. This target engagement in turn drove inhibition of tumor proliferation in xenograft models representing common Hippo-alterations. AZ4331 treatment of NF2m NCI-H226 and LATS1/2 loss MSTO-211H mesothelioma xenografts drove 50% and 93% regression of tumors, respectively. While treatment of head and neck squamous cell carcinoma FAT1m FaDu and YAP1amp Detroit562 xenografts lead to 58% tumor growth inhibition and 35% tumor regression, respectively. These findings identify AZ4331 as a potent inhibitor of the TEAD transcription factor family and further validate the inhibition of TEAD in Hippo-altered cancers as a potential therapeutic strategy. Citation Format: Jacob A. Gordon, Jolanta Dubauskaite, Michelle DuPont, Nin Guan, Geoff Holdgate, Scott Mlynarski, Neil Umbreit, Danielle Sanchez, Abhishek Srivastava, Janek Suski, Nancy Su, Ryan Richards, Sabina Cosulich, Corinne Reimer, James Brownell. Discovery of potent and selective pan-TEAD autopalmitoylation inhibitors for the treatment of Hippo-pathway altered cancers [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 6589.

Circular RNA hsa_circ_0051246 acts as a microRNA-375 sponge to promote the progression of gastric cancer stem cells via YAP1.

Gastric cancer (GC) stem cells play an important role in GC progression. Circular RNAs (circRNAs) act as microRNA (miRNA) sponges and inhibit the biological function of miRNAs in GC cytoplasm. MiRNAs also participate in GC progress. circ_0051246 was shown to be associated with miR-375 after analyzing GC microarray data GSE78091 and GSE83521. The oncoprotein Yes-associated protein 1 (YAP1) is targeted by miR-375 and can be inactivated via the Hippo tumor suppressor pathway. Due to insufficient research on circ_0051246, this study aimed to investigate its relationship with miR-375 and YAP1 in cancer stem cells (CSCs). SGC-7901 CSCs were used to establish knockdown/overexpression models of circ_0051246, miR-375, and YAP1. Malignant phenotypes of CSCs were assessed using Cell Counting Kit 8, colony/sphere formation, 5-Ethynyl-2'-deoxyuridine assay, flow cytometry, Transwell, and wound healing assays. To detect the interactions between circ_0051246, miR-375, and YAP1 in CSCs, a dual-luciferase reporter assay and fluorescence in situ hybridization were performed. In addition, 24 BALB/c nude mice were used to establish orthotopic xenograft tumor models. Four groups of mice were injected with CSCs (1 × 106 cells/100 µL) with circ_0051246 knockdown, miR-375 overexpression, or their respective control cells, and tumor progression and gene expression were observed by hematoxylin-eosin staining, immunohistochemistry. Western blot and quantitative real-time PCR were utilized to examine protein and gene expression, respectively. Circ_0051246 silencing reduced viability, promoted apoptosis, and inhibited proliferation, migration and invasion of CSCs. The functional effects of miR-375 mimics were comparable to those of circ_0051246 knockdown; however, the opposite was observed after miR-375 inhibitors treatment of CSCs. Furthermore, circ_0051246-overexpression antagonized the miR-375 mimics' effects on CSCs. Additionally, YAP1 overexpression promoted CSC features, such as self-renewal, migration, and invasion, inhibited apoptosis and E-cadherin levels, and upregulated the expression of N-cadherin, vimentin, YAP1, neurogenic locus notch homolog protein 1, and jagged canonical notch ligand 1. Conversely, YAP1-silenced produced the opposite effect. Moreover, miR-375 treatment antagonized the malignant effects of YAP1 overexpression in CSCs. Importantly, circ_0051246 knockdown and miR-375 activation suppressed CSC tumorigenicity in vivo. This study highlights the promotion of circ_0051246-miR-375-YAP1 axis activation in GC progression and provides a scientific basis for research on the molecular mechanism of CSCs.

Factor inhibiting HIF (FIH) promotes lung cancer progression.

Factor inhibiting HIF (FIH) is an asparagine hydroxylase that acts on hypoxia inducible factors (HIFs) to control cellular adaptation to hypoxia. FIH is expressed in several tumor types, but its impact in tumor progression remains largely unexplored. We observed that FIH was expressed on human lung cancer tissue. Deletion of FIH in mouse and human lung cancer cells resulted in an increased glycolytic metabolism, consistent with increased HIF activity. FIH-deficient lung cancer cells exhibited decreased proliferation. Analysis of RNA-seq data confirmed changes in the cell cycle and survival, and revealed molecular pathways that were dysregulated in the absence of FIH including the upregulation of angiomotin (Amot), a key component of the Hippo tumor suppressor pathway. We show that FIH-deficient tumors were characterized by higher immune infiltration of NK and T cells compared to FIH competent tumor cells. In vivo studies demonstrated that FIH deletion resulted in reduced tumor growth and metastatic capacity. Moreover, high FIH expression correlated with poor overall survival in non-small cell lung cancer (NSCLC). Together, our data unravel FIH as a therapeutic target for the treatment of lung cancer.

Inhibition of the interaction between Hippo/YAP and Akt signaling with ursolic acid and 3'3-diindolylmethane suppresses esophageal cancer tumorigenesis.

Hippo/YAP signaling hinders cancer progression. Inactivation of this pathway contributes to the development of esophageal cancer by activation of Akt. However, the possible interaction between Akt and Hippo/YAP pathways in esophageal cancer progression is unclear. In this study, we found that ursolic acid (UA) plus 3'3-diindolylmethane (DIM) efficiently suppressed the oncogenic Akt/Gsk-3β signaling pathway while activating the Hippo tumor suppressor pathway in esophageal cancer cells. Moreover, the addition of the Akt inhibitor LY294002 and the PI3K inhibitor 3-methyladenine enhanced the inhibitory effects of UA plus DIM on Akt pathway activation and further stimulated the Hippo pathway, including the suppression of YAP nuclear translocation in esophageal cancer cells. Silencing YAP under UA plus DIM conditions significantly increased the activation of the tumor suppressor PTEN in esophageal cancer cells, while decreasing p-Akt activation, indicating that the Akt signaling pathway could be down-regulated in esophageal cancer cells by targeting PTEN. Furthermore, in a xenograft nude mice model, UA plus DIM treatment effectively diminished esophageal tumors by inactivating the Akt pathway and stimulating the Hippo signaling pathway. Thus, our study highlights a feedback loop between the PI3K/Akt and Hippo signaling pathways in esophageal cancer cells, implying that a low dose of UA plus DIM could serve as a promising chemotherapeutic combination strategy in the treatment of esophageal cancer.

Abstract B022: Clinical outcomes in NF2-mutated RCC treated with contemporary immunotherapy regimens

Abstract Background: Neurofibromin-2 (NF2) encodes the cell scaffolding protein merlin, which is involved in the Hippo tumor suppressor pathway. Somatic loss of function NF2 alterations in renal cell carcinoma (RCC) are associated with poor prognosis and can also molecularly define a subset of unclassified renal cell carcinomas without a standard of care treatment. While immuno-oncology (IO) combination regimens such as ipilimumab/nivolumab (IO/IO) or PD-1 inhibitor with a VEGFR-targeted therapy (IO/VEGFR) are the standard of care for clear cell RCC, efficacy of IO-based regimens for NF2 mutated RCC remains unknown. We report the first comparison of clinical responses to IO/IO, IO/VEGFR, or other systemic therapies for NF2-mutated RCC. Methods: NF2-mutated RCC patients receiving systemic therapy at Memorial Sloan Kettering Cancer Center were retrospectively identified by screening of our targeted exome sequencing (MSK-IMPACT) database. Groups are defined by 1st line systemic therapy regimens: IO/IO, IO/VEGFR, and other (VEGFR-targeted monotherapy, IO monotherapy, everolimus/bevacizumab, and chemotherapy). PFS-2 is defined as time from start of 1st line to progression on next therapy, or death. ORR, PFS, and PFS-2 were measured by an independent RECIST radiologist (CD). PFS, PFS-2, and OS are estimated using the Kaplan-Meier method. Results: Histologic subtypes in the overall cohort were unclassified (N=25), clear cell (N=7), and papillary (N=3). ORR of IO containing regimens in any line of treatment (N=29) was 57% (95% CI 37, 75). In the 1st line setting, 8 patients received IO/IO, 12 received IO/VEGFR, and 15 received other regimens with an ORR of 38% (95% CI 9, 76), 75% (95% CI 43, 95), and 23% (95% CI 5, 54), respectively. Thirty-three patients were included for PFS and PFS-2 analysis and 34 for OS with a median duration of follow-up of 40 months. Median PFS is 11 months (95% CI 4, 19; 26 events), median PFS-2 is 14 months (95% CI 9, 25; 25 events) and median OS is 27 months (95% CI 13, 65; 21 events). PFS, PFS2, and OS did not differ by 1st line treatment group. Among patients who received any IO exposure in the 1st line versus patients who received non-IO-based therapy, there was no significant difference in median PFS (12 (95% CI 5, 22) vs 5 (95% CI 2,21) months, p=0.39), PFS2 (17 (95% CI 9, 28) vs 13 (95% CI 3, 25) months, p=0.49), or OS (27 (95% CI 13, 73) vs 26 (95% CI 4, NE), p=0.90). OS did not differ by tumor histologic subtype; however, sample size limits power to detect differences. Conclusion: In comparison to clear cell RCC, prognosis for patients with NF2-mutated RCC remains poor. IO-based therapy has activity in treating NF2-mutated RCC; patients may derive benefit even if first exposure to IO occurs ≥2nd treatment line. There was no significant difference in PFS, PFS2, or OS based on 1st line regimen for patients with NF2-mutated RCC. Further investigation of inhibitors specifically targeting downstream effectors of the Hippo pathway are warranted. Citation Format: Kelly N. Fitzgerald, Cihan Duzgol, Andrea Knezevic, Rachel Jacobi, Ritesh R. Kotecha, David H. Aggen, Maria I. Carlo, Neil J. Shah, Martin H. Voss, Darren R. Feldman, Robert J. Motzer, Chung-Han Lee. Clinical outcomes in NF2-mutated RCC treated with contemporary immunotherapy regimens [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr B022.

The Hippo Pathway Effectors YAP/TAZ-TEAD Oncoproteins as Emerging Therapeutic Targets in the Tumor Microenvironment

Various cancer cell-associated intrinsic and extrinsic inputs act on YAP/TAZ proteins to mediate the hyperactivation of the TEAD transcription factor-based transcriptome. This YAP/TAZ-TEAD activity can override the growth-limiting Hippo tumor-suppressor pathway that maintains normal tissue homeostasis. Herein, we provide an integrated summary of the contrasting roles of YAP/TAZ during normal tissue homeostasis versus tumor initiation and progression. In addition to upstream factors that regulate YAP/TAZ in the TME, critical insights on the emerging functions of YAP/TAZ in immune suppression and abnormal vasculature development during tumorigenesis are illustrated. Lastly, we discuss the current methods that intervene with the YAP/TAZ-TEAD oncogenic signaling pathway and the emerging applications of combination therapies, gut microbiota, and epigenetic plasticity that could potentiate the efficacy of chemo/immunotherapy as improved cancer therapeutic strategies.

TRIMming away colon cancer: TRIM21-mediated ubiquitination as an activator of the Hippo tumor suppressor pathway

In this issue of Cell Chemical Biology, Liu etal.1 identify TRIM21-mediated ubiquitination of the Hippo pathway kinase MST2, promoting its dimerization and activation. The antidepressant Vilazodone was found to bind to TRIM21, enhancing its activity toward MST2, increasing Hippo activation, and reducing colorectal cancer metastasis.

ATXN3 promotes prostate cancer progression by stabilizing YAP

BackgroundProstate cancer (PC) is the most common neoplasm and is the second leading cause of cancer-related deaths in men worldwide. The Hippo tumor suppressor pathway is highly conserved in mammals and plays an important role in carcinogenesis. YAP is one of major key effectors of the Hippo pathway. However, the mechanism supporting abnormal YAP expression in PC remains to be characterized.MethodsWestern blot was used to measure the protein expression of ATXN3 and YAP, while the YAP target genes were measured by real-time PCR. CCK8 assay was used to detect cell viability; transwell invasion assay was used to measure the invasion ability of PC. The xeno-graft tumor model was used for in vivo study. Protein stability assay was used to detect YAP protein degradation. Immuno-precipitation assay was used to detect the interaction domain between YAP and ATXN3. The ubiquitin-based Immuno-precipitation assays were used to detect the specific ubiquitination manner happened on YAP.ResultsIn the present study, we identified ATXN3, a DUB enzyme in the ubiquitin-specific proteases family, as a bona fide deubiquitylase of YAP in PC. ATXN3 was shown to interact with, deubiquitylate, and stabilize YAP in a deubiquitylation activity-dependent manner. Depletion of ATXN3 decreased the YAP protein level and the expression of YAP/TEAD target genes in PC, including CTGF, ANKRD1 and CYR61. Further mechanistic study revealed that the Josephin domain of ATXN3 interacted with the WW domain of YAP. ATXN3 stabilized YAP protein via inhibiting K48-specific poly-ubiquitination process on YAP protein. In addition, ATXN3 depletion significantly decreased PC cell proliferation, invasion and stem-like properties. The effects induced by ATXN3 depletion could be rescued by further YAP overexpression.ConclusionsIn general, our findings establish a previously undocumented catalytic role for ATXN3 as a deubiquitinating enzyme of YAP and provides a possible target for the therapy of PC.3-qkCcBYWdJCeJpbLXw1_hVideo

Low MST1/2 and negative LATS1/2 expressions are associated with poor prognosis of colorectal cancers

Mammalian STe20-like protein kinase 1/2 (MST1/2) and large tumor suppressor homolog 1/2 (LATS1/2) are the core components of the tumor-suppressive Hippo pathway. Dysregulation of this pathway is associated with the progression and metastasis of various cancers. However, MST1/2 and LATS1/2 expressions have not been systematically evaluated in colorectal cancers. We evaluated the clinicopathologic correlation and prognostic significance of MST1/2 and LATS1/2 immunohistochemical expressions in 327 colorectal cancer patients. Low MST1/2 expression, identified in 235 (71.9 %) cases, was significantly associated with poor differentiation (P = 0.018) and large size (P < 0.001) of the tumor. Negative LATS1/2 expression, identified in 226 (69.1 %) cases, was significantly correlated with low MST1/2 expression (P = 0.044). Low MST1/2 and negative LATS1/2 expressions were significantly associated with poor overall survivals (P = 0.015 and P = 0.038, respectively). Furthermore, the combined MST1/2lowLATS1/2negative expression group showed significantly worse overall survival than other groups (P = 0.003), and considered as an independent poor prognostic factor for colorectal cancer patients (hazard ratio = 1.720; 95 % confidence interval, 1.143–2.588; P = 0.009). Low MST1/2 and negative LATS1/2 expressions may serve as prognostic indicators in patients with colorectal cancer.

Targeting the Divergent Roles of STK3 Inhibits Breast Cancer Cell Growth and Opposes Doxorubicin-Induced Cardiotoxicity In Vitro

Breast cancer (BCa) is the most prevalent type of cancer in women. Several therapies used in the treatment of breast cancer are associated with clinically important rates of cardiovascular toxicity during or after treatment exposure, including anthracyclines. There is a need for new BCa therapeutics and treatments that mitigate chemotherapy-induced cardiotoxicity in BCa. In this study, we examine the effects of Serine/Threonine Kinase 3 (STK3) inhibition in the context of BCa therapy and cardioprotection from doxorubicin. STK3 (also known as MST2) is a key member of the Hippo Tumor-Suppressor Pathway, which regulates cell growth and proliferation by inhibiting YAP/TAZ co-transcription factors. Canonically, STK3 should restrict BCa growth; however, we observed that STK3 is amplified in BCa and associated with worse patient outcomes, suggesting a noncanonical pro-tumorigenic role. We found BCa cell lines have varying dependence on STK3. SUM52PE cells had the highest expression and dependence on STK3 in genetic and pharmacological assays. MCF-7 and MDA-MB-231 were less sensitive to STK3 targeting in standard proliferation assays, but were STK3 dependent in colony formation and matrigel invasion assays. In contrast, STK3 inhibition mitigated the toxic effects of doxorubicin in H9C2 rat cardiomyocytes by increasing YAP expression. Importantly, STK3 inhibition in BCa cells did not interfere with the therapeutic effects of doxorubicin. Our studies highlight STK3 is a potential molecular target for BCa with dual therapeutic effects: suppression of BCa growth and progression, and chemoprotection in cardiomyocytes.

Abstract B009: TEAD inhibition overcomes YAP1/TAZ-driven resistance to RAS inhibitors in KRASG12C-mutant cancers

Abstract Activated mutants of KRAS comprise the major oncogenic drivers in lung (LAC), colorectal (CRC), and pancreatic ductal (PDAC) adenocarcinoma. Recent success in covalently targeting one KRAS mutant (KRASG12C) led to FDA approval of the first anti-KRAS therapy (G12Ci). However, both primary and treatment-induced acquired resistance to G12Ci have been observed. While analyses of relapsed patients have identified reactivation of the key KRAS effector signaling network as a driver of resistance, the mechanisms in ~50% of patients are not known. To identify potential resistance mechanisms, we applied a CRISPR-Cas9 loss-of-function screen targeting the druggable genome. In addition to genes discovered recently in relapsed patients (e.g., PTEN, NF1), we also identified loss of multiple components of the Hippo tumor suppressor pathway as drivers of G12Ci resistance (NF2, LATS1/2, TAOK1/2 and STK3/4). We therefore determined if activation of the functionally related transcriptional co-activators, YAP1 and TAZ, normally inhibited by Hippo signaling, can drive resistance to G12Ci. We first determined that ectopic expression of constitutively activated YAP1/TAZ was sufficient to impair the anti-proliferative and pro-apoptotic effects of G12Ci treatment in KRASG12C-mutant LAC, CRC, and PDAC cell lines. Conversely, genetic suppression of YAP1/TAZ enhanced G12Ci sensitivity. YAP1/TAZ requires association with TEAD and other transcription factors to regulate transcription. We determined that YAP1/TAZ mutants deficient in TEAD binding failed to drive resistance to G12Ci treatment. Further supporting a role for TEAD, both overexpression of a TEAD dominant negative mutant and treatment with pan-TEAD pharmacological inhibitors phenocopied the effects of YAP1/TAZ genetic suppression and sensitized KRASG12C mutant cancer cells to G12Ci. Finally, transcriptional analyses support a model where YAP1/TAZ-TEAD overcomes KRASG12C addiction by restoring a subset of KRAS-dependent gene transcription. In summary, our observations support YAP1/TAZ-TEAD signaling as a novel driver of resistance to KRAS inhibition and support the use of TEAD inhibitors to enhance the anti-tumor efficacy of KRAS-targeted therapies. Citation Format: Alexander C. Edwards, Clint A. Stalnecker, Alexis J. Morales, Khalilah E. Taylor, Jill Hallin, Peter Olson, Tracy T. Tang, Lars Engstrom, Leonard Post, James G. Christensen, Adrienne D. Cox, Channing J. Der. TEAD inhibition overcomes YAP1/TAZ-driven resistance to RAS inhibitors in KRASG12C-mutant cancers [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr B009.

Deletion of Cd44 Inhibits Metastasis Formation of Liver Cancer in Nf2-Mutant Mice.

Primary liver cancer is the third leading cause of cancer-related death worldwide. An increasing body of evidence suggests that the Hippo tumor suppressor pathway plays a critical role in restricting cell proliferation and determining cell fate during physiological and pathological processes in the liver. Merlin (Moesin-Ezrin-Radixin-like protein) encoded by the NF2 (neurofibromatosis type 2) gene is an upstream regulator of the Hippo signaling pathway. Targeting of Merlin to the plasma membrane seems to be crucial for its major tumor-suppressive functions; this is facilitated by interactions with membrane-associated proteins, including CD44 (cluster of differentiation 44). Mutations within the CD44-binding domain of Merlin have been reported in many human cancers. This study evaluated the relative contribution of CD44- and Merlin-dependent processes to the development and progression of liver tumors. To this end, mice with a liver-specific deletion of the Nf2 gene were crossed with Cd44-knockout mice and subjected to extensive histological, biochemical and molecular analyses. In addition, cells were isolated from mutant livers and analyzed by in vitro assays. Deletion of Nf2 in the liver led to substantial liver enlargement and generation of hepatocellular carcinomas (HCCs), intrahepatic cholangiocarcinomas (iCCAs), as well as mixed hepatocellular cholangiocarcinomas. Whilst deletion of Cd44 had no influence on liver size or primary liver tumor development, it significantly inhibited metastasis formation in Nf2-mutant mice. CD44 upregulates expression of integrin β2 and promotes transendothelial migration of liver cancer cells, which may facilitate metastatic spreading. Overall, our results suggest that CD44 may be a promising target for intervening with metastatic spreading of liver cancer.

Abstract 2629: Single and combined inhibition of PAK and Hippo pathway in NF2-deficient schwannoma

Abstract Neurofibromatosis 2 (NF2) Syndrome is a rare, but devastating genetic condition that leads to non-cancerous tumors of the nervous system. NF2 patients are likely to develop Schwannomas on the eighth cranial nerve that lead to progressive deafness and spinal cord compression as well as meningiomas and peripheral nerve tumors. Effective treatment for these patients is lacking, with risky surgery being the most reliable approach and pharmacotherapies having inadequate results. The hallmark mutation of this condition is inactivation of NF2, which codes for the protein Merlin. Merlin plays several roles in the cell, two of the most consequential being inhibition of PAK1 and activation of the Hippo tumor suppressor pathway. However, drugs targeting these pathways have not yet been investigated in NF2-deficient Schwannoma. In this study, we explored the use of YAP-TEAD inhibitors as well as the combination of Hippo family and Group I PAK inhibition in NF2-deficient Schwannoma cells. We used several Schwannoma cells lines of human, mouse, and rat origin as well as a human Schwann cell line with NF2 knocked out via CRISPR compared to its wild-type control line. We investigated the role of YAP, the main effector of the Hippo pathway, and PAK1/2 in NF2 Schwannoma cells via genetic and pharmacologic inhibition. We also combined YAP-TEAD inhibitors with several PAK family inhibitors to induce a synergistic reduction in cell viability and proliferation as well as an increase in apoptosis. We found that genetic inhibition of both YAP and Group I PAK proteins led to partial reduction in Schwannoma growth. Using several YAP-TEAD binding inhibitors (TED-347, NSC682769, IK-930), Group I PAK inhibitors (FRAX-1036, G555) and PAK1-specific inhibitor (NVS-1-PAK1) we found that YAP-TEAD binding inhibition combined with Group I PAK inhibition has the greatest reduction on Schwannoma cell viability, proliferation, and increase in cell death. Taken together, our findings indicate that both the Hippo pathway and PAK proteins may be viable targets for Schwannoma therapies. Furthermore, combining the two may lead to a synergistic effect and further prevent growth of NF2-deficient Schwannomas. Citation Format: Dorothy Benton, Jonathan Chernoff. Single and combined inhibition of PAK and Hippo pathway in NF2-deficient schwannoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2629.

Abstract 4501: Novel EHE PDX model used for drug sensitivity

Abstract EHE is a low-to-intermediate grade angiocentric non-vasogenic tumor that exhibits a wide survival range dependent upon tumor size, stage, and location. Most tumors originate in the lung (37%), soft tissue (20%), or liver (16%), and those with multifocal peritoneal or pleural spread have a 5-year survival rate of ~22%. Solitary lesions are often resected for curative intent. However, treatment options for those with metastatic disease at diagnosis remain less well-defined. Generally, the chemo-resistant slow-growing soft-tissue EHEs can often be observed off therapy for years or decades. In contrast, pleural or peritoneal tumors required rapid intervention with systemic cytotoxic chemotherapies. Given the lack of effective treatments, there remains a significant unmet need. Unique among all cancer types, more than 90% of EHEs harbor in-frame chromosomal translocations with WWTR1 (TAZ) or YAP1 in the N-terminal domain. Given that YAP and TAZ are two paralogs, which share numerous epigenetic functions as YAP/TEAD or TAZ/TEAD transcriptional coactivators downstream of the Hippo tumor-suppressor pathway, the oncogenic effect of the resulting EHE-associated TAZ-CAMTA1 (TC) or YAP1-TFE (YT) fusion proteins must, with all certainty, continue to depend on the truncated YAP/TAZ proteins. Since no EHE cell lines exist, one cannot predict if the TC FP behaves similarly in human sarcomas that expose different tissue-specific TEAD binding sites. Trametinib (a MEK inhibitor) was chosen for initial evaluation. We determined the preclinical efficacy of trametinib in the only available EHE patient-derived tumor explant (PDX) in existence, which genetic testing confirmed harbored a TAZ-CAMTA1 translocation. We propagated EHE PDX tumors in mice, then treated with vehicle or trametinib for more than 80 days. Tumor volumes were measured 2-3 times a week, and tumors were collected for further histology and proteomic analysis. Trametinib demonstrated potent antineoplastic activity, consistent with the limited activity observed in recent clinical studies. A separate 10-day study was conducted to measure early pharmacodynamic studies of a potent, oral, selective small molecule palmitoylation inhibitor of TEAD provided by Ikena Oncology. Edge-Seq RNA sequencing and western blots were performed to validate the TEAD-dependent gene and protein expression. EdgeSeq analysis demonstrated significant down-regulation of multiple TEAD dependent genes, indicating on-target inhibition of TEAD in this model. Western blot protein analysis of YAP, TAZ, TEAD1, TC FP, CTGF, and CYR61, collected for pharmacodynamic analysis, demonstrated reduced CYR61, indicative of possible TEAD inhibitor activity; CTGF protein levels were unchanged. The use of one EHE PDX was a limitation, as this model may not fully recapitulate human tumor biology. Future research, using additional EHE PDX models, will be required in gauge the effect of different inhibitors. Citation Format: Sandhya Krishnan, Robert Porter, Danh Truong, Salah-Eddine Lamhamedi-Cherradi, Krzysztof Grela, Rafal Zielinski, Sharon Landers, Vinod Ravi, Joseph A. Ludwig. Novel EHE PDX model used for drug sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4501.

Blimp-1/PRDM1 and Hr3/RORβ specify the blue-sensitive photoreceptor subtype in Drosophila by repressing the hippo pathway.

During terminal differentiation of the mammalian retina, transcription factors control binary cell fate decisions that generate functionally distinct subtypes of photoreceptor neurons. For instance, Otx2 and RORβ activate the expression of the transcriptional repressor Blimp-1/PRDM1 that represses bipolar interneuron fate and promotes rod photoreceptor fate. Moreover, Otx2 and Crx promote expression of the nuclear receptor Nrl that promotes rod photoreceptor fate and represses cone photoreceptor fate. Mutations in these four transcription factors cause severe eye diseases such as retinitis pigmentosa. Here, we show that a post-mitotic binary fate decision in Drosophila color photoreceptor subtype specification requires ecdysone signaling and involves orthologs of these transcription factors: Drosophila Blimp-1/PRDM1 and Hr3/RORβ promote blue-sensitive (Rh5) photoreceptor fate and repress green-sensitive (Rh6) photoreceptor fate through the transcriptional repression of warts/LATS, the nexus of the phylogenetically conserved Hippo tumor suppressor pathway. Moreover, we identify a novel interaction between Blimp-1 and warts, whereby Blimp-1 represses a warts intronic enhancer in blue-sensitive photoreceptors and thereby gives rise to specific expression of warts in green-sensitive photoreceptors. Together, these results reveal that conserved transcriptional regulators play key roles in terminal cell fate decisions in both the Drosophila and the mammalian retina, and the mechanistic insights further deepen our understanding of how Hippo pathway signaling is repurposed to control photoreceptor fates for Drosophila color vision.

The molecular basis of the dichotomous functionality of MAP4K4 in proliferation and cell motility control in cancer.

The finely tuned integration of intra- and extracellular cues by components of the mitogen-activated protein kinase (MAPK) signaling pathways controls the mutually exclusive phenotypic manifestations of uncontrolled growth and tumor cell dissemination. The Ser/Thr kinase MAP4K4 is an upstream integrator of extracellular cues involved in both proliferation and cell motility control. Initially identified as an activator of the c-Jun N-terminal kinase (JNK), the discovery of diverse functions and additional effectors of MAP4K4 beyond JNK signaling has considerably broadened our understanding of this complex kinase. The implication of MAP4K4 in the regulation of cytoskeleton dynamics and cell motility provided essential insights into its role as a pro-metastatic kinase in cancer. However, the more recently revealed role of MAP4K4 as an activator of the Hippo tumor suppressor pathway has complicated the understanding of MAP4K4 as an oncogenic driver kinase. To develop a better understanding of the diverse functions of MAP4K4 and their potential significance in oncogenesis and tumor progression, we have collected and assessed the current evidence of MAP4K4 implication in molecular mechanisms that control proliferation and promote cell motility. A better understanding of these mechanisms is particularly relevant in the brain, where MAP4K4 is highly expressed and under pathological conditions either drives neuronal cell death in neurodegenerative diseases or cell dissemination in malignant tumors. We review established effectors and present novel interactors of MAP4K4, which offer mechanistic insights into MAP4K4 function and may inspire novel intervention strategies. We discuss possible implications of novel interactors in tumor growth and dissemination and evaluate potential therapeutic strategies to selectively repress pro-oncogenic functions of MAP4K4.

Transmembrane protein KIRREL1 regulates Hippo signaling via a feedback loop and represents a therapeutic target in YAP/TAZ-active cancers.

The Hippo tumor-suppressor pathway is frequently dysregulated in human cancers and represents a therapeutic target. However, strategies targeting the mammalian Hippo pathway are limited because of the lack of a well-established cell-surface regulator. Here, we show that transmembrane protein KIRREL1, by interacting with both SAV1 and LATS1/2, promotes LATS1/2 activation by MST1/2 (Hippo kinases), and LATS1/2 activation, in turn, inhibits activity of YAP/TAZ oncoproteins. Conversely, YAP/TAZ directly induce the expression of KIRREL1 in a TEAD1-4-dependent manner. Indeed, KIRREL1 expression positively correlates with canonical YAP/TAZ target gene expression in clinical tumor specimens and predicts poor prognosis. Moreover, transgenic expression of KIRREL1 effectively blocks tumorigenesis in a mouse intrahepatic cholangiocarcinoma model, indicating a tumor-suppressor role of KIRREL1. Hence, KIRREL1 constitutes a negative feedback mechanism regulating the Hippo pathway and serves as a cell-surface marker and potential drug target in cancers with YAP/TAZ dependency.