3146HECTD3 attenuates cardiac hypertrophy acting as an E3 ligase of SUMO2

Background: Small ubiquitin-like modifiers (SUMO) are essential for numerous cellular processes including cell growth, proliferation, apoptosis, as well as protein trafficking. We recently reported SUMO2 as an inducer of cardiomyocyte hypertrophy via activation of calcineurin-NFAT signaling in vitro and in vivo. Purpose: Utilizing a Yeast-two hybrid screen, HECTD3, an E3 ubiquitin ligase, was found to interact with SUMO2 via its “APC10” domain, a necessary domain for ubiquitination of HECTD3 substrates. We therefore hypothesized that SUMO2 is one of the bona fide cardiac substrates of HECTD3. Methods and results: Adenovirus-mediated expression of HECTD3 in neonatal rat ventricular cardiomyocytes (NRVCMs) resulted in degradation of endogenous as well as overexpressed SUMO2. Proteasome inhibitor MG132 treatment inhibited HECTD3-mediated SUMO2 degradation, further substantiating the involvement of ubiquitin-proteasome system. HECTD3 impeded SUMO2-dependent prohypertrophic effects and activation of calcineurin-signaling in NRVCMs. Importantly, these in vitro findings were recapitulated in mice, where, AAV9-mediated overexpression of HECTD3 not only reduced cardiac SUMO2 levels, but significantly attenuated pathological hypertrophy induced by transverse aortic constriction or Angiotensin-II. Moreover, inverse correlation of SUMO2 and HECTD3 expression was observed in human patients suffering from hypertrophic cardiomyopathy (HCM). Mechanistically, we found that HECTD3 disrupts recently proposed SUMO2-calcineurin interaction, inhibiting nuclear localization of Calcineurin and thereby suppressing downstream signaling and consequent hypertrophy.