Germ cell stimulation of Sertoli cell protein phosphorylation

Cultures of Sertoli cells were treated with freshly isolated, intact germ cells to determine if germ cells were capable of influencing Sertoli cell function. By using two-dimensional polyacrylamide gel electrophoresis and autoradiography, germ cells were found to increase several-fold the incorporation of [32P]orthophosphate into two phosphoproteins (which we term germ cell-dependent phosphoproteins 1 and 2 or GC1 and GC2) of Sertoli cells. Increased phosphorylation of GC1 and GC2 was rapid, germ cell dose dependent, and calcium dependent. The increased phosphorylation of GC1 appears to involve calmodulin-dependent protein kinase, while phosphorylation of GC2 appears to involve the activation of calcium/phospholipid-dependent protein kinase (protein kinase C). Medium conditioned by germ cells was capable of eliciting the same response in Sertoli cells. Germ cells had no effect on the phosphorylation of proteins in Chinese hamster ovarian cells, but did result in increased phosphorylation of a protein in TR-ST cells, which migrated similarly to GC1 of Sertoli cells. Neither Chinese hamster ovarian nor TR-ST cells had any effect on Sertoli cell protein phosphorylation. These results indicate that germ cells may be directly involved in the local regulation of Sertoli cell function within the seminiferous epithelium. The results further suggest that the mechanism of germ cell-Sertoli cell interaction involves the mobilization of intracellular calcium, activation of Ca2+/calmodulin-dependent protein kinase, and protein kinase C. We infer from these results that germ cell-Sertoli cell interaction may operate via hydrolysis of Sertoli cell membrane phophatidylinositols.