AB46. Screening and identification for the target genes of androgen receptor in mouse Sertoli cells

Abstract: Androgen and androgen receptor (AR) play important roles in spermatogenesis, yet detailed androgen/AR signals in Sertoli cells remain unclear. To identify AR target genes in Sertoli cells, we analyzed the gene expression profiles of testis between mice lacking AR in Sertoli cells (S-AR) and their littermate wild-type (WT) mice. Digital gene expression analysis identified 2,276 genes downregulated and 2,865 genes upregulated in the S-AR mice testis compared to WT ones. To further nail down the difference within Sertoli cells, we first constructed Sertoli cell line TM4 with stably transfected AR (named as TM4/AR) and found androgens failed to transactivate AR in Sertoli TM4 and TM4/AR cells. Interestingly, additional transient transfection of AR-cDNA resulted in significant androgen responsiveness with TM4/AR cells showing ten times more androgen sensitivity than TM4 cells. In the condition where maximal androgen response was demonstrated, we then analyzed gene expression and found the expression levels of 2313 genes were changed more than twofold by transient transfection of AR-cDNA in the presence of testosterone. Among these genes, 603 androgen-/AR-regulated genes, including 164 up-regulated and 439 down-regulated, were found in both S-AR mice testis and TM4/AR cells.

Ubiquitin-conjugating enzyme E2B (Ube2b) is one of the regulated genes from the digital gene expression analysis. The expression of UBE2B was decreased in the testes of the S-AR mice analyzed by quantitative RT-PCR (qRT-PCR) and immunofluorescence. The up-regulation of Ube2b gene by testosterone was further demonstrated by Western blot and qRT-PCR in TM4 cells. Moreover, luciferase assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay validated that the ligand-bound AR activated Ube2b transcription via directly binding to the androgen-responsive element of the Ube2b promoter. In vitro analyses showed that testosterone increased UBE2B expression and activated H2A ubiquitylation, while downregulation of UBE2B blocked the testosterone-induced H2A ubiquitylation. The ubiquitylation of H2A was markedly decreased in the testes of S-AR mice by immunohistochemistry. Digital gene expression analysis showed that 113 genes were significantly down-regulated and 71 were up-regulated by UBE2B in TM4 cells. These results suggest that Ube2b, as a direct AR transcriptional target in Sertoli cells, mediates the function of AR in spermatogenesis by promoting H2A ubiquitylation.

Our previous digital gene expression analysis data also showed that heat shock transcription factors 1 (HSF1) was regulated by androgen in mouse Sertoli cells. We found that the expression of Hsf1 was increased in the testes of S-AR mice compared with wild-type mice by quantitative real-time PCR and the expression of HSF1 in the S-ARSertoli cells was significantly increased as examined by immunofluorescence analysis. Besides, in vitro study showed that testosterone repressed the expression of Hsf1 in TM4 cells. Moreover, luciferase assay, electrophoretic mobility shift assay and chromatin immunoprecipitation assay showed that testosterone repressed Hsf1 expression by facilitating the binding of androgen receptor to Hsf1 promoter. Our experiment also demonstrated that testosterone downregulated the expression of heat shock protein HSP105 and HSP60 by inhibiting the transcription of Hsf1. Taken together, these results reveal that HSF1 is a novel target of androgen receptor in mouse Sertoli Cells, and testosterone and its receptor regulate the process of spermatogenesis partially by inhibiting HSF1 expression.

Keywords: Androgen receptor; UBE2B; heat shock transcription factors 1 (HSF1)