Stage-Specific Nuclear Expression of NF-kB in Mammalian Testis

The Rel/nuclear factor (NF)-kB family of transcription factors are important intracellular conveyors of extracellular signals in a number of systems. However, little is known of their roles in the specialized, hormonally regulated environment of the mammalian testis. In this study NF-kB p50 and p65 proteins were found to be constitutively present and active in the nucleus of Sertoli cells cultured from rat testis. In vivo, NF-kB proteins are present in the nucleus of Sertoli cells during all 14 (I–XIV) cyclical stages of spermatogenesis; however, nuclear NF-kB expression was elevated in stage XIV and remained high in stages I–VII. In contrast, NF-kB p50 and p65 subunits are transiently expressed in the nuclei of germ cells with peak levels found in pachytene spermatocytes during stages VII–XI and lower levels in stage I-VII spermatids. Tumor necrosis factor-a, which is produced by round spermatids in the testis, increased nuclear NF-kB binding activity when added to Sertoli cells. Stimulation of Sertoli cells with activators of the cAMP-protein kinase A (PKA) signaling pathway such as forskolin or FSH also increased NF-kB DNA binding activity. Consistent with the cellular localization studies, NF-kB was found to be activated as high basal levels of NF-kB-stimulated reporter gene expression were detected in transient transfection studies of Sertoli cells. Addition of tumor necrosis factor-a to Sertoli cells further stimulated kB enhancer-mediated transcription. These findings suggest that NF-kB proteins are stage specifically localized to Sertoli cell and spermatocyte nuclei and may play a role in the regulation of stage-specific gene expression during the process of spermatogenesis. (Molecular Endocrinology 12: 1696–1707, 1998)