Abstract 348: Homeobox A4 Suppresses Vascular Smooth Muscle Cell Phenotypic Switching as a Novel Regulator of YAP/TEAD Transcriptional Activity

Abstract

The Hippo signaling pathway is involved in the pathophysiology of various cardiovascular diseases. Yes-associated protein (YAP) and transcriptional enhancer activator domain (TEAD) transcriptional factors, the main transcriptional complex of the Hippo pathway, were recently identified as modulators of phenotypic switching of vascular smooth muscle cells (VSMCs). However, the intrinsic regulator of YAP/TEAD-mediated gene expressions in VSMCs remains to be elucidated, then we sought to investigate a novel regulator of YAP/TEAD transactivation involved in vascular diseases. We first investigated novel YAP/TEAD regulators using lentiviral shRNA library in HEK 293T-based TEAD-responsive reporter cell line and detected Homeobox A4 (HOXA4) as a potent repressor of YAP/TEAD transcriptional activity. HOXA4 attenuated YAP/TEAD-mediated gene expression independently of YAP phosphorylation, and co-immunoprecipitation assays revealed that HOXA4 interacts with TEADs but not YAP. Mechanistically, HOXA4 attenuated YAP/TEAD-mediated transcription by competing with YAP for TEAD binding. We also clarified that the expression of HOXA4 is relatively abundant in the vasculature, especially in VSMCs. In vitro experiments in human VSMCs showed HOXA4 maintains the differentiation state of VSMCs via inhibition of YAP/TEAD-induced phenotypic switching characterized by cell morphology, cell proliferation, and gene expression patterns. We generated Hoxa4-decifient mice and confirmed the downregulation of smooth muscle-specific contractile genes and the exacerbation of vascular remodeling after carotid artery ligation in vivo. Our results demonstrate HOXA4 is a novel repressor of VSMC phenotypic switching by inhibiting YAP/TEAD-mediated transcription. These findings give us a better understanding of the vascular pathophysiology and a novel therapeutic approach for vascular remodeling.