TRIM24 Promotes While TRIM32 Inhibits Cardiomyocyte Hypertrophy via Regulation of Dysbindin Protein Levels [Signal Transduction]

We have previously shown that Dysbindin is a potent inducer of cardiomyocyte hypertrophy via activation of Rho-dependent SRF signaling. We now performed a Yeast-two hybrid screen using Dysbindin as bait against a cardiac cDNA library to identify the cardiac Dysbindin interactome. Amongst several putative binding proteins, we identified Tripartite motif-containing protein 24 (TRIM24) and confirmed this interaction by co-immunoprecipitation and co-immunostaining. Another TRIM family protein, TRIM32 has earlier been reported as an E3 ubiquitin ligase for Dysbindin in skeletal muscle. Consistently, we found that TRIM32 degraded Dysbindin in neonatal rat ventricular cardiomyocytes (NRVCMs) as well. Surprisingly however, TRIM24 did not promote Dysbindin decay but rather protected Dysbindin against degradation by TRIM32. Correspondingly, TRIM32 attenuated the activation of SRF-signaling and hypertrophy due to Dysbindin, whereas, TRIM24 promoted these effects in NRVCMs. The present study also implies that TRIM32 is a key regulator of cell viability and apoptosis in cardiomyocytes via simultaneous activation of p53 and Caspase-3/-7, and inhibition of XIAP (X-linked inhibitor of apoptosis). In conclusion, we here provide a novel mechanism of post-translational regulation of Dysbindin and hypertrophy via TRIM24 and TRIM32, and importance of TRIM32 in cardiomyocyte apoptosis in vitro.

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