Involvement of inhibitory nuclear factor-kappaB (NFkappaB)-independent NFkappaB activation in the gonadotropic regulation of X-linked inhibitor of apoptosis expression during ovarian follicular development in vitro.

Increased X-linked inhibitor of apoptosis (XIAP) expression and suppressed follicular apoptosis are important determinants in the regulation of follicular development by FSH. The objective of the present study was to examine the role and regulation of nuclear factor-kappaB (NFkappaB) in the gonadotropic control of granulosa cell XIAP expression and follicular growth in vitro. FSH (100 ng/ml) increased rat granulosa cell XIAP mRNA abundance and protein content. The gonadotropin also induced granulosa cell p65 subunit-containing NFkappaB translocation from cytoplasm to nucleus and increased NFkappaB-DNA binding activity. Supershift EMSA indicated the FSH-activated NFkappaB contained p65 and p50 subunits. Unlike TNFalpha, FSH failed to elicit a significant change in granulosa cell phospho- and total-inhibitory NFkappaB (IkappaB) IkappaB contents in vitro and dominant-negative IkappaB expression was ineffective in blocking the increase in NFkappaB-DNA-binding activity and XIAP protein content induced by the gonadotropin. In contrast, SN50 (a cell permeable inhibitory peptide of NFkappaB translocation, 50-200 ng/ml) suppressed FSH-stimulated NFkappaB-DNA binding, XIAP expression, and follicular growth. FSH also increased granulosa cell phospho-Akt contents, a response sensitive to the PI-3K inhibitor LY294002 (10 microM). In conclusion, the present studies demonstrate that the FSH-induced XIAP expression is mediated through the NFkappaB pathway through activation of phosphatidylinositol 3-kinase rather than the classical IkappaB kinase.