As the follicles matured toward the preovulatory stage, increased prohibitin expression was observed in the theca-interstitial cells, which also had increased P450scc enzyme activity. These findings are in agreement with those of previous studies concerning the expression of this steroidogenic factor during follicular development in the rat ovary.
Our results raise the interesting possibility that induction of prohibitin expression may initiate events involved in differentiated action of gonadotropin in the ovary. Additionally, these results may also reflect increased metabolic activity within the mitochondria. In this context, Coates et al. have reported that prohibitin is highly expressed in cells showing a particular reliance on mitochondrial metabolism, including those in prostate and melanoma tumors. In support of this result, we observed a strong immunostaining pattern for prohibitin, primarily in the cytoplasmic or perinuclear region of epithelial cells in papillary serous ovarian carcinoma and endometrioid adenocarcinoma (unpublished results). Whether prohibitin plays a directed role in granulosa cell differentiation or mitochondrial metabolism awaits further investigation.