Abstract B21: YAP1-mediated circadian oscillation in sarcoma

Soft-tissue sarcomas present a unique challenge to researchers due to their heterogeneity. However, one common mechanism associated with more than 25% of diagnosed sarcomas is deregulation of the Hippo pathway, a critical signaling cascade that responds to cell contact inhibition, among other factors, and negatively regulates cell proliferation. In quiescent cells the pathway remains “on,” which maintains activation of the kinase cascade that phosphorylates and degrades YAP1. However, inactivation of the pathway stabilizes YAP1, allowing it to translocate to the nucleus and activate transcription of pro-proliferative gene targets. Microarray analysis of tumor tissue from the LSLKrasG12D/+;Trp53fl/fl (KP) mouse model of undifferentiated pleomorphic sarcoma (UPS) revealed that YAP1 deletion (KPY) reduces sarcoma cell proliferation and increases expression of circadian rhythm genes. Notably, deletion of YAP1 in KP tumors resulted in a 2.5-fold increase in expression of PER1. Although PER1 has primarily been characterized as a negative regulator of the circadian clock, upregulation of PER1 is known to modulate the G2/M cell cycle checkpoint at both the protein and mRNA levels. Our findings represent a novel link between the circadian clock and Hippo pathway. Our studies also indicate that Hippo signaling is epigenetically regulated in sarcomas. Thus we employed the epigenetic modulating drugs JQ1, a BET inhibitor, and SAHA, an HDAC inhibitor, to regain control of this pathway. Treatment with these inhibitors significantly reduced YAP1 expression, decreased sarcoma growth in vivo and in vitro, and surprisingly increased muscle cell differentiation markers, including the master muscle regulator MyoD. Under JQ1 and SAHA drug treatment, as well as YAP1 shRNA knockdown conditions, we demonstrated that PER1 is significantly increased at both the protein and transcriptional levels in KP tumor derived cells. Together, these results suggest that YAP1 represses PER1 expression in sarcoma, and that epigenetic therapies can cause reexpression of PER1. Another key cellular response to SAHA/JQ1 exposure in sarcoma cells is alteration in NF-κB signaling. NF-κB, a critical signaling cascade for muscle cell progenitor proliferation, oscillates temporally in sarcoma cells treated with SAHA and JQ1. We hypothesize that this oscillation may be disrupted when PER1 is suppressed due to high YAP1 levels in sarcoma leading to uncontrolled proliferation. NF-κB activation enhances proliferation and suppresses differentiation in normal muscle progenitor cells and myoblasts by preventing MyoD upregulation. Importantly, it has been reported that MyoD is a clock-controlled gene. Given this relationship between MyoD and PER1, it is possible that PER1 functions to regulate MyoD through NF-κB in sarcoma and thus alters the balance between cell proliferation and differentiation. Citation Format: Gloria Marino, Shaun Egolf, Shuai Ye, Koreana Pak, Jenn Shah, Adrian Rivera-Reyes, Susan Chor, T. S. Karin Eisinger-Mathason. YAP1-mediated circadian oscillation in sarcoma [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr B21.