All-trans retinoic acid regulates c-jun expression via ERK5 in cardiac myoblasts.

Retinoic acid (RA) is an active metabolite of vitamin A and plays an important role in biological processes including cell proliferation. MAPKs play a pivotal role in regulating many critical cellular processes in the heart. The aim of the study was to determine whether all-trans RA (atRA) affects the proliferation of H9c2 rat ventricular cells and whether ERK family is involved in this process. H9c2 myocardial cells were cultured and subjected to MTT and (3)H-thymidine incorporation assays for proliferation detection. Luciferase reporter gene and Western blot assays were used to detect the transcription and protein expression of c-jun. In addition, the activities of ERK5 and ERK1 were determined by Western blot assay. The subcellular distribution of ERK5 and ERK1 was analyzed by confocal microscopy. It was shown that atRA (0.05 microM) facilitated the proliferation of H9c2 myocardial cells and increased the transcription and protein expression of c-jun. Inhibition of ERK5 significantly decreased atRA-induced pJluc expression (P<.01). The activity of ERK5 but not ERK1 was induced by atRA. Furthermore, atRA promoted the nuclear translocation of ERK5 but not ERK1. These results suggest that ERK5 pathway may be involved in the process that atRA regulates proliferation in the developing heart.