Whether this regulatory mechanism exists in the antiapoptotic action for prohibitin in the ovary remains to be determined. We observed translocation of prohibitin from the cytoplasm to the nucleus in granulosa cells of atretic follicles, although the significance of this observation is not immediately apparent. The mechanism by which prohi-bitin interacts with established cell death pathways to regulate apoptosis is also not known.
Treatment of immature rats with eCG stimulated follicular maturation and increased prohibitin expression. One-and two-dimensional Western blot analyses have shown not only significant increases in prohibitin protein levels but an elevation in the more acidic isoform of the protein in gonadotropin-stimulated granulosa cells. On the basis of the electrophoretic studies, the prohibitin protein clearly is differentially processed on gonadotropin stimulation. These results are consistent with posttranslational modification by phosphorylation of prohibitin, as previously reported by Thompson et al.. The physiological role of these isoforms is unknown, and whether their presence and differential response to gonadotropic stimulation accounts for the multifunctional nature of this protein remains to be determined.