Transcriptional regulation of human Oct4 by steroidogenic factor-1

Abstract

Oct4 encodes a transcription factor that is involved in the maintenance of self-renewal in stem cells. Recently, the molecular mechanisms that regulate Oct4 expression have come under investigation. In this study, we demonstrate that the orphan nuclear receptor steroidogenic factor-1 (SF-1) behaves as a transcriptional activator of human Oct4 (hOct4) through direct interaction with a SF-1 binding element in the hOct4 proximal promoter. We found that Oct4 and SF-1 were co-expressed in undifferentiated human embryonal carcinoma NCCIT cells and downregulated during retinoic acid-mediated differentiation. We examined the functional role played by SF-1 in regulation of hOct4 transcription using a luciferase reporter assay and Western blot analysis. Overexpression of SF-1 increased up to about threefold hOct4 promoter activity and endogenous hOct4 protein expression. Sequence analysis of the hOct4 promoter revealed that the transcriptional activity was closely linked to Conserved Regions 1 (CR1) and 2 (CR2), which contain three putative SF-1-binding sites (1st, 2nd, and 3rd SF-1). Binding assays and mutagenesis of binding sites indicated that the 1st and 2nd SF-1 elements (in CR1 and CR2, respectively) might be important cis-regulatory elements in hOct4 promoter activity. However, differences in response to SF-1 overexpression between wild-type and mutant hOct4 promoters revealed that the 1st SF-1 element is the key binding site for SF-1-mediated transcriptional activation. Thus, our data indicate that SF-1 plays a crucial role in the regulation of hOct4 transcription through direct binding to the 1st SF-1 in CR1 of the hOct4 proximal promoter.