Addressing the Hippo in the Room: Investigating the Mechanism of YAP/TAZ as a Treatment Target in Clear Cell Renal Cell Carcinoma

Abstract

Ph.D.Clear Cell Renal Cell Carcinoma (ccRCC) is the most common subtype of kidney neoplasms characterized by a near universal inactivation of the von Hippel-Lindau (VHL) tumor suppressor protein. Targeted therapies that inhibit the unfettered transcriptional signaling of Hypoxia-inducible Factor 2ɑ (HIF2ɑ) transcription factor and its downstream pro-angiogenic effectors, consequential to VHL loss, has undoubtedly improved patient survival. Despite these improvements, a substantial fraction of patients with advanced ccRCC experience upfront or acquired resistance to presently available treatment options, warranting the investigation into adjunct therapies capable of improving efficacy and response duration to existing treatments. Assessing tumor copy number alteration, methylation, and expression data from large ccRCC patient cohorts, we demonstrate that dysregulation of the Hippo tumor suppressor pathway occurs commonly in ccRCC, correlates with increased YAP/TAZ target gene expression, and is associated with worse overall survival in treatment naïve patients. In addition, we showed that high YAP/TAZ gene signature is associated with poor treatment response to therapies that target HIF2ɑ-VEGF signaling. In vivo efficacy studies with a first-in-class TEAD palmitoylation inhibitor or YAP/TAZ-targeted shRNAs showed both forms of YAP/TAZ silencing substantially delays the development of acquired resistance to a clinical HIF2ɑ inhibitor in a ccRCC xenograft model sensitive to HIF2ɑ inhibition. Moreover, the TEAD inhibitor also exhibited profound single agent anti-tumor efficacy in a patient-derived ccRCC xenograft model of upfront resistance to HIF2ɑ-targeted treatments. By combining ATAC-seq, BRB-seq and Cut&Tag analysis, we assessed the chromatin binding and gene regulation of YAP and HIF2ɑ, and unveiled that these two proteins are co-recruited to AP-1 sites through interactions with the AP-1 transcription factors. YAP/TAZ, HIF2ɑ and JUN are dependent on each other to maintain their expression, and function cooperatively to promote the expression of highly expressed transcription factors and other important oncogenes. Our findings not only revealed the therapeutic potentials of adjunct YAP/TAZ-based therapies in the treatment of advanced ccRCC, but also revealed novel mechanistic insights into the dynamic interactions among YAP, HIF2ɑ and AP-1 proteins that could be further exploited to improve treatment for ccRCC