Regulation of Leydig cell steroidogenesis by extracellular signal-regulated kinase 1/2: role of protein kinase A and protein kinase C signaling

• DOI: 10.1677/joe-06-0201
• Publication Date: 2007-03-30T21:03:25Z
• Authors: Pulak R Manna; Youngah Jo; Douglas M Stocco
• Keywords: Male; 0303 health sciences; DAX-1 Orphan Nuclear Receptor; Blotting, Western; Leydig Cells; Isoquinolines; Phosphoproteins; Chorionic Gonadotropin; Cyclic AMP-Dependent Protein Kinases; DNA-Binding Proteins; Enzyme Activation; Mice; 03 medical and health sciences; Bucladesine; Cell Line, Tumor; Nitriles; Butadienes; Animals; Phosphorylation; Extracellular Signal-Regulated MAP Kinases; Progesterone; Protein Kinase C

The steroidogenic acute regulatory (StAR) protein plays a central role in the regulation of steroid biosynthesis. While steroidogenesis is influenced by many processes, their modes of actions, in a few cases, remain obscure. In this study, we explored the mechanism of action of one such signaling pathway, the extracellular signal-regulated kinase 1/2 (ERK1/2), in regulating StAR expression and steroidogenesis in conjunction with the protein kinase A (PKA) and protein kinase C (PKC) pathways. Using MA-10 mouse Leydig tumor cells, we demonstrate that the activation of PKC and PKA signaling, by phorbol-12-myristate-13-acetate (PMA) and dibutyryl cAMP (dbcAMP)/human chorionic gonadotropin (hCG) respectively, was able to phosphorylate ERK1/2, an event markedly decreased by an upstream kinase inhibitor, U0126. Treatment with PMA enhanced StAR protein expression (associated with a slight increase in progesterone synthesis) but not its phosphorylation (P-StAR), which, in contrast, coordinately increased in response to dbcAMP/hCG. Inhibition of ERK1/2 activity by U0126 decreased PMA-treated StAR expression but increased dbcAMP/hCG-mediated StAR and P-StAR; however, progesterone levels were attenuated. U0126 was found to affect StAR expression and steroidogenesis both at the transcriptional and translational levels. Further studies demonstrated that the effect of U0126 on PMA- and dbcAMP/hCG-mediated StAR expression and steroid synthesis was tightly correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (DAX-1) and scavenger receptor class B type 1 (SR-B1). In fact, both DAX-1 and SR-B1 appear to play important roles in hormone-regulated steroidogenesis. These findings clearly demonstrate that the ERK1/2 signaling cascade involved in regulating StAR expression and steroid synthesis is mediated by multiple factors and pathways and is stimulus specific in mouse Leydig cells.