LH/chorionic gonadotropin signaling pathway involves protein tyrosine phosphatase activity downstream of protein kinase A activation: evidence of an obligatory step in steroid production by Leydig cells

Our recent reports indicate that protein tyrosine phosphorylation is an obl igatory component of the mechanism of action of ACTH in its stimulatory act ion of corticosteroid production in adrenal zona fasciculata (ZF). The role of protein tyrosine phosphatase (PTP) activity, in the regulation of stero idogenesis by LH/chorionic gonadotropin (CG) was tested using cell-permeabl e PTP inhibitors. Thus. PTP inhibition blocks LH- and 8-bromo-cAMP-stimulat ed testosterone production by Leydig cells without affecting 22(R)OH-choles terol-supported steroidogenesis, similar results to those obtained in the a drenal ZF/ACTH system, leading us to propose that PTP action is all obligat ory and common step in the cascade triggered by both hormones. Then, we con tinued the study testing whether LH modulates PTP activity in MA-10 cells, a Leydig cell line. In this regard, we observed by an in-gel PTP assay two PTPs of 110 and 50 kDa that are activated by hormone and 8-bromo-cAMP activ ation of the cells. Moreover, there is a transient increase by the second m essenger in total PTP activity that correlates with the higher activity dis played by the 110 and 50 kDa proteins in the in-gel assay. In accordance wi th these results, analysis of tyrosine phosphorylated proteins showed the L H-induced dephosphorylation of proteins of 120. 68 and 50 kDa. The results of this study indicate that PTPs play an important role in the regulation o f Leydig cell functions and that there exists a cross talk between serine/t hreonine phosphorylation and tyrosine dephosphorylation mediated by hormone -activated cAMP-dependent protein kinase and PTPs. These results are the fi rst evidence of PTP having a role in LH/CG-stimulated steroidogenesis.