Association of Ad4BP/SF-1 transcription factor with steroidogenic activity in oncogene-transformed granulosa cells

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Adrenal binding protein 4 (Ad4BP) known also as steroidogenic factor 1 (SF-1) is a cell specific transcription factor regulating all steroidogenic P450 genes and is present exclusively in steroidogenic tissues. In this study, we examined whether Ad4BP expression is affected by oncogene-induced cell transformation. Using a gel shift assay we report here that nuclear extracts of steroidogenic granulosa cell lines, transformed by SV40 DNA and the Ha-ras oncogene show specific binding activity towards an Ad4 recognition sequence oligonucleotide. In contrast, nuclear extracts obtained from granulosa cells transformed with SV40 alone, which lost their steroidogenic activity, did not exhibit any binding to the Ad4 oligonucleotide. Using a specific antibody to Ad4BP, it was demonstrated that only the steroidogenic cell lines, i.e. transfected with SV40+Ha-ras, expressed significant amount of the protein. No binding activity to the Ad4 oligonucleotide was evident in fibroblasts transformed with the same oncogenes (SV40+Ha-ras). Steroidogenic activity in SV40+Ha-ras transformed granulosa cells was markedly elevated following forskolin or follice stimulating factor (FSH) and further augmented by incubation of the cells with dexamethasone. However, no change in Ad4BP expression and binding activity was observed following such stimulations. It is suggested that Ha-ras expression in SV40 transformed granulosa cells can play an important role in restoring Ad4BP expression and activity, which are required for their steroidogenic function. Thus, expression of Ad4BP is essential for steroidogenesis both in primary and in oncogene transformed granulosa cells.