The NGFI-B family of transcription factors regulates expression of 3β-hydroxysteroid dehydrogenase type 2 in the human ovary

The nerve growth factor-induced clone B (NGFI-B) family of transcription factors are orphan members of the steroid hormone receptor superfamily. The NGFI-B expression was recently shown in the rat ovarian tissue and appears to be regulated by gonadotrophins. The purpose of our study was to investigate the role of the three members of this family [NGFI-B, Nur-related factor 1 (NURR1) and neuron derived orphan receptor 1 (NOR-1)] in the transcription of genes that encode key steroidogenic enzymes and examine expression in the human ovary. Real-time RT-PCR was used to quantify mRNA expression levels of the NGFI-B family members in human ovarian follicles, corpora lutea and in human granulosa cells after FSH, phorbol ester (TPA) and forskolin treatment. NGFI-B was expressed at higher levels than both NURR1 and NOR-1 in both ovarian follicles and corpora lutea. In human granulosa tumour (HGT) cells, the NGFI-B expression increased after TPA, and to a lesser extent, after forskolin treatment. Treatment of primary cultures of human granulosa cells with forskolin and FSH rapidly increased the NGFI-B mRNA levels followed by an increase in 3β-hydroxysteroid dehydrogenase type 2 (HSD3B2). Transcription of HSD3B2 was studied by transfecting NGFI-B and steroidogenic factor 1 (SF1) expression vectors with reporter constructs prepared with human steroidogenic acute regulatory protein, cholesterol side-chain cleavage, and HSD3B2 genes. NGFI-B increased the transcription of HSD3B2 in HGT cells which is significantly more than SF1. Mutation or deletion of the NGFI-B response element in the HSD3B2 promoter significantly reduced the NGFI-B-mediated transcription of HSD3B2. Therefore, our data suggest that the NGFI-B may play a significant role in up-regulation of HSD3B2 that leads to the increase in progesterone production that is seen in granulosa cells at ovulation.