cAMP-activated Nr4a1 expression requires ERK activity and is modulated by MAPK phosphatase-1 in MA-10 Leydig cells

Abstract

In Leydig cells, LH and cAMP promote ERK1/2 activation and MAPK phosphatase-1 (MKP-1) induction. MKP-1 up-regulation, which involves post-translational modifications such as ERK1/2-mediated phosphorylation, reduces ERK1/2 phosphorylation as well as Steroidogenic Acute Regulatory (StAR) protein expression and steroidogenesis. As LH- and cAMP-promoted StAR transcription requires the induction of Nur77, product of Nr4a1 gene, we analyzed the roles of ERK1/2 and MKP-1 in 8Br–cAMP-mediated Nr4a1 expression in MA-10 Leydig cells. Pharmacological blockade of ERK1/2 activation partially reduced the 8Br–cAMP-mediated increase in both Nr4a1 messenger levels and promoter activity. MKP-1 knock-down increased 8Br–cAMP-induced promoter activity, while its over-expression produced the opposite effect. It is concluded that Nr4a1 induction is dependent on ERK1/2 and that MKP-1 negatively regulates this induction. Experiments based on the over-expression of MKP-1 mutated forms revealed that MKP-1 half life is determined by post-translational modifications in ERK-consensus sites, a regulation that modulates the effect of MKP-1 on Nr4a1 expression.