Stage-specific nuclear expression of NF-κB in mammalian testis

The Rel/nuclear factor (NF)-kappa B 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-kappa B 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-kappa B proteins are present in the nucleus of Sertoli cells during all 14 (I-XIV) cyclical stages of spermatogenesis; however, nuclear NF-kappa B expression was elevated in stage XIV and remained high in stages I-VII. In contrast, NF-kappa B 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-alpha, which is produced by round spermatids in the testis, increased nuclear NF-kappa B 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-kappa B DNA binding activity. Consistent with the cellular localization studies, NF-kappa B was found to be activated as high basal levels of NF-kappa B-stimulated reporter gene expression were detected in transient transfection studies of Sertoli cells. Addition of tumor necrosis factor-alpha to Sertoli cells further stimulated kappa B enhancer-mediated transcription. These findings suggest that NF-kappa B 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.