Ad4-binding protein (Ad4BP) has been demonstrated recently as a
transcription factor that serves as a general regulator of all steroidogenic P450 genes. We examined the expression of Ad4BP in 32 normal cycling human ovaries and 22 human ovarian
sex cord stromal tumors by immunoblotting and immunohistochemistry. Immunoblotting of normal cycling human ovaries revealed a single band of 53 kilodaltons, corresponding to the mol wt of Ad4BP. We also correlated Ad4BP expression with the immunolocalization of the steroidogenic
enzymes (side-chain cleavage
cytochrome P450,
cytochrome P450 17 alpha-
hydroxylase, and
cytochrome P450 aromatase). Ad4BP immunoreactivity, which was present only in the nuclei, was observed sporadically in the granulosa cells and adjacent stromal cells in the preantral follicles. In the dominant
antral follicles, Ad4BP was detected in both granulosa and theca interna cells. However, in the nondominant
antral follicles, Ad4BP was observed only in theca interna cells. In the corpus luteum, Ad4BP was present in both luteinized granulosa and thecal cells. Ad4BP was also expressed in some atretic follicles and degenerating corpora lutea. The spatial and temporal localization of Ad4BP in the normal cycling human ovary generally correlated well with that of steroidogenic
enzymes. However, expression of the steroidogenic
enzymes followed that of Ad4BP during the developing stages of the preantral follicle and vice versa during the process of follicular atresia. In ovarian
sex cord stromal tumors, Ad4BP expression was observed in
tumor cells that were positive for steroidogenic
enzymes, but not in nonsteroidogenic
tumor cells. These results, especially the in situ colocalization of Ad4BP and the steroidogenic
enzymes, suggest that Ad4BP has the potential to control steroidogenic P450 expression in both normal and pathological human ovaries.