The transcription factors NR5A1 and JUNB cooperate to activate the Axl promoter in mouse Sertoli cell lines

The Axl gene is a receptor tyrosine kinase essential for male fertility. With other Tyro3 family members, it regulates cell apoptosis and preserves the organization of seminiferous tubules. However, the regulation of the expression of Axl in testicular Sertoli cells is not entirely understood. The transcription factors NR5A1 and JUNB are involved in several male fertility mechanisms such as sex development and steroidogenesis. We hypothesize that Axl promoter activity is regulated by cooperation between JUNB and NR5A1 in Sertoli cells.

Following transfections of TM4 Sertoli cells with DsiRNA interference against Axl, our results show that cell morphology may be regulated by AXL. Using transfections of expression plasmids and reporter plasmids containing the Axl promoter, we report that Axl expression is highly activated by cooperation between NR5A1 and JUNB in TM4 and 15P-1 Sertoli cells. Chromatin immunoprecipitation and luciferase reporter assays with 5′ promoter deletions demonstrate that JUNB and NR5A1 are being recruited to DNA regulatory elements in the proximal region of the Axl promoter. The fourth intronic region of Axl also participates in the recruitment of JUNB.

Thus, Axl expression is regulated by a cooperation between the transcription factors JUNB and NR5A1 and influences the morphology of TM4 Sertoli cells.