Abstract B18: YAP1 and TAZ Mediate BET Inhibitor-Dependent Immune Regulation in NSCLC

Bromodomain and extra-terminal domain proteins inhibitors (BETi) are promising immunomodulatory agents, able to regulate gene expression in tumor microenvironment (TME), influencing immune cell differentiation and activation. However, immune-related molecular mechanisms underlying BETi activity need to be clarified. We demonstrated that BET protein BRD4 is an important regulator of YAP1/TAZ oncogene expression in several cancer cell lines, including non-small cell lung cancer (NSCLC) cells. YAP1 and TAZ are paralogue genes involved in tumor cell proliferation, migration, and survival. BETi affect YAP1/TAZ expression and impair their transcriptional program. As previously reported, YAP1 and TAZ oncogenes are also involved in tumor immune escape, through the impairment of lymphocyte activation and enhanced PD-L1 expression. We investigated whether BETi-dependent immune regulation depends on YAP1/TAZ activity in NSCLC patients. To this end, we isolated NSCLC patient-derived tissue-originated spheroids (CTOS) and tumor-infiltrating lymphocytes (TILs) and treated both populations with BETi (JQ1 or OTX-015). BETi treatment significantly increased the activation of TILs, which was also associated with decreased expression of the immune checkpoint receptors PD-1, LAG-3, TIM-3, BTLA, and CD160. Notably, BETi treatment also downregulated the expression of corresponding immune checkpoint ligands (PD-L1, LGALS9, and TNFRSF14). Intriguingly, patients displaying higher expression of immune checkpoint molecules exhibited also higher expression of YAP1 and TAZ, suggesting that these transcription factors may be involved in this regulatory network. Accordingly, YAP1 and TAZ were significantly downregulated after BETi treatment in both CTOS and TILs. To confirm specific YAP/TAZ activity in immune regulation, the knockout (KO) of YAP1 or TAZ was achieved through CRISPR/Cas9 approach in NSCLC cell lines. Of interest, YAP1 and TAZ display distinct regulatory effects, suggesting a not overlapping function. The KO of YAP1, but not of TAZ, was sufficient to downregulate PD-L1 expression. Conversely, KO of TAZ alone efficiently downregulated LGALS9, which was not affected by YAP1 KO. TNFRSF14 was significantly reduced in both TAZ and YAP1 KO. These preliminary data suggest that BETi exert a YAP/TAZ-dependent immunomodulatory activity, acting on both tumor cells and TME immune landscape. In this context, BETi may reactivate immune response against tumor cells, acting on both immune checkpoint inhibitor expression and TIL-specific activation. These findings further support the use of BETi as immunomodulatory agents in NSCLC patients. Citation Format: Francesca Reggiani, Giulia Gobbi, Filippo Lococo, Massimiliano Paci, Eleonora Zznetti, Simonetta Piana, Alessia Ciarrocchi, Valentina Sancisi. YAP1 and TAZ mediate BET inhibitor-dependent immune regulation in NSCLC [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B18.