REGULATION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE ACTIVITY BY CA2-DEPENDENTAND PROTEIN-KINASE C-DEPENDENT PATHWAYS IN SERTOLI CELLS()

gamma-Glutamyl transpeptidase (gamma-GTP) activity in Sertoli cells ca n be stimulated by FSH. This cAMP-dependent metabolic event can be enh anced when Sertoli cells are cocultured with germ cells, suggesting th at different signal transduction pathways may be involved in the regul ation of gamma-GTP activity. In this study we examined the participati on of Ca2+- and protein kinase C (pkC)-dependent signal transduction p athways in the regulation of basal and FSH-stimulated gamma-GTP activi ty. Under basal conditions, the increase in extracellular Ca2+ concent ration or the addition of the Ca2+ ionophore 4Br-A23187 produced a dec rease in gamma-GTP activity. Conversely, blockage of voltage-dependent Ca2+ channels with verapamil or nifedipine or inhibition of Ca2+-calm odulin dependent processes with trifluoperazine resulted in an increas e in gamma-GTP activity. To study the role of a pkC-dependent pathway the effects of low doses of staurosporine were evaluated. Under these experimental conditions an increase in gamma-GTP activity was observed . It was then investigated whether these signal transduction pathways could interact with the FSH-stimulated cAMP-dependent pathway to regul ate gamma-GTP activity. Increase in extracellular Ca2+ concentration, the addition of 4Br-A23187 or the blockage of voltage-dependent Ca2+ c hannels did not modify FSH-stimulated gamma-GTP activity. However, sta urosporine produced an additional increase in FSH-stimulated gamma-GTP activity and this effect was also observed when cells were stimulated with dbcAMP. In summary, our data are consistent with an inhibitory r ole of Ca2+-calmodulin- and pkC-dependent pathways in the regulation o f basal gamma-GTP activity. Similar to what has been shown for other S ertoli cell parameters, a pkC-dependent pathway can interact with the FSH-stimulated cAMP-dependent pathway. The precise steps involved in t his interaction are still unknown.