RE1-silencing transcription factor (REST) and REST-interacting LIM domain protein (RILP) affect P19CL6 differentiation

During cardiac development, the heart produces the atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). These peptides are found in high levels in cardiomyocytes and, like a number of other embryonic genes, are up-regulated in both failing and hypertrophied ventricles. At the transcriptional level, BNP and ANP genes are regulated through RE1 regulatory element, which binds RE1-silencing transcription factor (REST). REST/NRSF-interacting LIM domain protein (RILP) is required for the nuclear targeting and function of REST. In this study, the role of RILP and REST in cardiomyocyte development using a model system was studied by analyzing the expression of RILP and REST as well as several cardiac-specific genes during P19CL6 cell differentiation. Effects of RILP overexpression and transcriptional regulation of RILP in differentiating P19CL6 cells were also studied. RILP expression is transiently reduced during P19CL6 cell differentiation; however, REST expression remains unchanged. This transient reduction in RILP expression correlates with de-repression of sarcomeric myosin heavy chain, a marker for cardiomyocyte differentiation. Reporter gene analysis shows that RILP gene is down-regulated through 5'-regulatory elements before cardiac-specific gene expression. These results suggest that RILP expression and function control REST action more so than does REST expression and is an important regulatory role in cardiomyocyte differentiation.