The AP-1 transcription factors differentially regulate Cx43 expression in a ERK1/2-dependent manner in MA-10 Leydig cells

Leydig cells, found between the seminiferous tubules of the testis, are the main androgen-producing cells in males. These cells communicate with each other via communicating junctions composed mainly of connexin43 (Cx43, GJA1), to synchronize their regulation of steroidogenesis activity. In our previous studies, we demonstrated that the transcription factors JUN and FOS cooperate to activate the Cx43 promoter in MA-10 Leydig cells. However, which AP-1 members more strongly activate Cx43 expression, and the signaling pathways involved, remain to be confirmed. Thus, promoter analyses by co-transfections of promoter/reporter plasmid constructs were completed in MA-10 and TM3 Leydig cells. In addition, the importance of potential MAPK-dependent pathways in regulating Cx43 expression was assessed. Our results show that the AP-1 members JUND and FOS is one of the most effective combinations for activating shorter Cx43 promoter regions in MA-10 Leydig cells. Moreover, overexpression of MAP2K1 (MEK1) enhances the cooperation between these transcription factors to regulate Cx43 expression. Thus, increased expression of Cx43 in Leydig cells depends on the activation of the ERK1/ERK2 signaling pathway and the formation of a heterodimer between AP-1 transcription factors.