Specific testicular cellular localization and hormonal regulation of the PKIα and PKIβ isoforms of the inhibitor protein of the cAMP-dependent protein kinase

Abstract

We have previously demonstrated that there exist two distinct genes for the thermostable inhibitor protein of the cAMP-dependent protein kinase, PKIα and PKIβ (Van Patten, S. M., Howard, P., Walsh, D. A., and Maurer. R. A. (1992) Mol. Endocrinol 6, 2114-2122). We have also shown that in the testis, at least eight forms of PKIβ exist, differing as a result of at least post-translational modification and alternate translational initiation (Kumar, P., Van Patten, S. M., and Walsh, D. A. (1997) J. Biol. Chem. 272, 20011-20020). We now report that in the testis, there is a unique cellular distribution of protein kinase inhibitor forms, with PKIβ being essentially (if not exclusively) a germ cell protein and PKIα being expressed primarily in Sertoli cells. Furthermore, there is a progressive change in the forms of PKIβ that are present within germ cells with development that is initiated in testis tubules and continues as the germ cells migrate through the epididymis. These conclusions are derived from studies with isolated cell populations and with the at/at germ cell-deficient mouse line, by in situ hybridization, and by following the developmental expression of these proteins in both testis and epididymis. We have also shown that follicle- stimulating hormone (FSH) can increase the expression of both PKIα and PKIβ. The FSH-regulated expression of PKIα in the Sertoli cell likely occurs via the normal route of second messenger signal transduction. In contrast, the FSH-dependent PKIβ expression must arise by some form of Sertoli cell-germ cell intercommunication.