Somatostatin inhibits stem cell factor messenger RNA expression by Sertoli cells and stem cell factor-induced DNA synthesis in isolated seminiferous tubules

Abstract

Immature porcine Sertoli cells have been reported to be targets for the regulatory peptide somatostatin (SRIF), which inhibits the basal and FSH-induced proliferation of Sertoli cells through a decrease of cAMP production. In the present study, we show that SRIF inhibits both basal and FSH-stimulated expression of the stem cell factor (SCF), a Sertoli cell-specific gene. The SRIF-mediated inhibition of forskolin-triggered, but not of 8-bromoadenosine-cAMP-triggered, SCF mRNA expression demonstrates the involvement of adenylyl cyclase in underlying peptide actions. Moreover, these effects require functional coupling of specific plasma membrane receptors to adenylyl cyclase via inhibitory G proteins, because pertussis toxin prevents SRIF-mediated inhibition of SCF mRNA expression. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assays suggest the involvement of sst2 receptors in SRIF actions on Sertoli cells. The biological relevance of these data is supported by an SRIF-mediated decrease in SCF-induced incorporation of [3H] thymidine in isolated seminiferous tubules. In situ hybridization and confocal microscopy show that, in seminiferous tubules only, spermatogonia display both c-kit and sst2 receptors. Taken together, these results suggest that SCF-stimulated DNA synthesis can be inhibited by SRIF in spermatogonia, but not in Sertoli and peritubular cells. Combined RT-PCR and immunohistochemical approaches point toward spermatogonia and Leydig cells as the source of testicular SRIF. These data argue in favor of paracrine/autocrine SRIF actions in testis.