Abstract 195: TIP30 Interferes With Protein Synthesis And Inhibits Cardiac Hypertrophy

Abstract

Background: Pathological cardiac hypertrophy is a crucial risk factor for the development of heart failure. It is characterized by a massive increase of contractile and structural proteins within cardiomyocytes, mainly as a result of enhanced protein synthesis. The regulatory mechanisms of increased RNA translation during hypertrophy, however, remain largely unknown. Here, we examined the cardiac function of TIP30, which has previously emerged as a tumor suppressor gene with reduced expression in malignant tumours. Results: We identified myocardial TIP30 mRNA as dramatically downregulated (>80%) in a mouse model of dilative cardiomyopathy (MLP knock-out mice) as well as in human failing hearts. A protein pull-down screen with a GST-TIP30 fusion protein and proteomic candidate identification revealed the eukaryotic translation elongation factor 1A1 (eEF1A1) as binding partner of TIP30, which was independently verified by GST-pulldown and co-immunoprecipitation (IP). Interestingly, this interaction between TIP30 and eEF1A1 was not detectable during pro-hypertrophic (phenylephrine, PE) stimulation in neonatal rat cardiac myocytes (NRCM). Adenoviral (Ad-) TIP30 overexpression in NRCM during PE stimulation led to a reduced hypertrophic response compared to Ad-control infected cells (cell size in % of control: Ad-TIP30 135 ± 4 vs. Ad-control 200 ± 3 p<0.05). At the same time, a dramatic decrease in protein:DNA ratio was observed. siRNA downregulation of eEF1A1 ablated the anti-hypertrophic effects of TIP30. Measurement of translational activity by determination of the polysome/monosome ratio revealed a blunted translation rate after TIP30 overexpression. In line with our in vitro data, myocardial overexpression of TIP30 by an adeno-associated virus (AAV9-TIP30) significantly reduced cardiac hypertrophy during two weeks of Angiotensin (Ang)/PE infusion in vivo. In turn, Ang/PE infusion as well as aortic constriction (TAC) led to an increased hypertrophic response in TIP30 knock-out versus wild-type mice. Conclusion: TIP30 inhibits hypertrophy and translational activity most likely through inhibition of eEF1A1 in cardiomyocytes. TIP30 is downregulated in human failing hearts and could thereby contribute to aggravated hypertrophy.