Myocardin is well known to play a key role in the development of cardiomyocyte
hypertrophy. But the exact molecular mechanism regulating
myocardin stability and transactivity to affect cardiomyocyte
hypertrophy has not been studied clearly. We now report that NF-κB (p65) can inhibit
myocardin-induced cardiomyocyte
hypertrophy. Then we explore the molecular mechanism of this response. First, we show that p65 can functionally repress
myocardin transcriptional activity and also reduce the
protein expression of
myocardin. Second, the function of
myocardin can be regulated by epigenetic modifications.
Myocardin sumoylation is known to transactivate cardiac genes, but whether p65 can inhibit SUMO modification of
myocardin is still not clear. Our data show that p65 weakens
myocardin transcriptional activity through attenuating SUMO modification of
myocardin by SUMO1/PIAS1, thereby impairing
myocardin-mediated cardiomyocyte
hypertrophy. Furthermore, the expression of
myocardin can be regulated by several
microRNAs, which play important roles in the development and function of the heart and muscle. We next investigated potential role of miR-1 in cardiac hypotrophy. Our results show that p65 can upregulate the level of miR-1 and miR-1 can decrease
protein expression of
myocardin in cardiac myocytes. Notably, miR-1 expression is also controlled by
myocardin, leading to a feedback loop. These data thus provide important and novel insights into the function that p65 inhibits
myocardin-mediated cardiomyocyte
hypertrophy by downregulating the expression and SUMO modification of
myocardin and enhancing the expression of miR-1.