Abstract 13987: RBX1-CRLs Are Essential for Perinatal Heart Development by Regulating Hippo-YAP Signaling

Abstract

Defects in cardiac development can lead to congenital heart diseases (CHD) or predispose the heart to cardiomyopathies in adult life. The molecular mechanisms that regulate this process remain elusive. Cullin-RING E3 ligases (CRLs) are multi-subunit complexes that are critical to maintain protein homeostasis by targeting a variety of protein substrates for proteasomal degradation. In the CRLs, RBX1 serves as the catalytic subunit that promotes the transfer of ubiquitin to the target protein. Previous animal studies uncovered a crucial role for RBX1 in development. However, its importance in the developing heart has not been explored. Here, we report for the first time the indispensable role of RBX1 in perinatal cardiac development. We created mice with cardiac-specific deletion of RBX1 driven by αMHC Cre . Compared with littermate control mice, RBX1-deficient mouse embryos exhibited no gross morphological abnormalities at E12.5 and E14.5, displayed peripheral edema at E16.5 indicative of heart failure, and eventually died around E18.5. Histological analysis revealed myocardial hypoplasia and a substantially thinner compact layer in E16.5 mutant hearts. This event was preceded by a remarkable decrease in cardiomyocyte proliferation and diminished nuclear localization of YAP, a powerful regulator of cardiomyocyte proliferation, at E14.5. In cultured cardiomyocytes, depletion of RBX1 inhibited proliferation and induced profound transcriptomic changes like the upregulation of cardiomyopathy-related genes. Mechanistically, RBX1 deficiency destabilized multiple CRLs and resulted in the accumulation of Hippo kinases and adaptor proteins such as SAV1, LATS1/2, and MOB1 leading to the inactivation of YAP by phosphorylation. We further demonstrated that RBX1 degrades the Hippo adaptors SAV1 and MOB1. Collectively, we propose that the fine-tuned, RBX1-mediated removal of Hippo components serves as a critical checkpoint to activate YAP signaling ensuring cardiac ventricular chamber development and morphogenesis.