Functional difference between Ad4BP and ELP, and their distributions in steroidogenic tissues

Ad4BP, a zinc finger DNA-binding protein, was identified as a transcription factor regulating steroidogenic P-450 genes in a cAMP-dependent manner. Immunochemical and immunohistochemical studies with steroidogenic tissues, adrenal, ovary, and testis, were performed using the antiserum to Ad4BP. Ad4BP was expressed to the same extent in the three zones of the adrenal cortex. Immunohistochemical examination of ovarian follicle and corpus luteum showed the expression of Ad4BP. The granulosa and thecal cells, the two distinct types of the steroidogenic cells in the follicle, gave Ad4BP signals, which were stronger than in the latter cells than in the former. Immunoblot analyses of mature and regressed corpora lutea indicated a parallel expression of Ad4BP and side-chain cleavage P-450, and both proteins significantly decreased in the regressed tissues. Leydig cells surrounding seminiferous tubules gave clear immunostaining signals for Ad4BP. ELP, a mammalian counterpart of Drosophila FTZ-F1 detected in EC cells, and are isoforms transcribed from the same gene. The Ad4BP and ELP forms recognize same nucleotide sequences. Reverse transcriptase-polymerase chain reaction with specific primers for ELP revealed that steroidogenic tissues contained ELP as well as Ad4BP. The effects of the two proteins on the transcription of the CYP11B gene were compared using the expression vectors of Ad4BP and ELP. ELP did not activate transcription and showed a weak inhibitor effect on the Ad4BP-dependent transactivation of the CYP11B gene promoter when transfected simultaneously. A gel shift analysis using in vitro synthesized Ad4BP and ELP revealed that the binding activity of ELP is significantly weaker than that of Ad4BP.