Nectin-2 expression in testicular cells is controlled via the functional cooperation between transcription factors of the Sp1, CREB, and AP-1 families

Abstract

Nectin-2, a major protein component of the adherens junctions (AJs), is found between Sertoli cells and germ cells in the seminiferous epithelium. Recent studies have shown that the expression of nectin-2 gene in testis is crucial to maintain normal spermatogenesis since male knockout mice lacking nectin-2 gene are sterile and possess morphologically abnormal spermatozoa. However, the molecular mechanisms governing its basal transcription remain poorly understood. By the use of Sertoli and germ cell-lines (TM4 and GC-2spd(ts) cells, respectively) in transient transfection studies, we showed that the minimal mouse nectin-2 promoter was located between nucleotides -316 and -211 (relative to the translation start site). Two putative Sp1 motifs and one each of the CRE, AP1, and AP2 motifs were identified within this region. Mutational studies showed that these two Sp1 motifs cooperated synergistically with the CRE motif, but not the AP1 and AP2 motifs, to regulate nectin-2 gene transcription in both TM4 and GC-2spd(ts) cells. By EMSAs, we found that an AP-1 consensus sequence was able to inhibit DNA-protein complex formation with the CRE motif, suggesting an interaction between the AP-1 transcription factor (c-Jun) and CREB within the CRE motif. Overexpressions of CREB and c-Jun, but not c-Fos, also significantly increased the promoter activity, which suggests that CREB and c-Jun are the crucial transcription factors involved in regulating nectin-2 gene transcription. Chromatin immunoprecipitation assay has shown that, in vivo, CREB, c-Jun, and Sp1 family proteins are bound to the mouse nectin-2 promoter. Analysis of the staged tubules has confirmed that the cyclic expressions of CREB and nectin-2 coincide with the event of adherens junction restructuring between Sertoli cells and germ cells. The cross-talk between CREB, c-Jun, and Sp1 family protein is believed to be a major transcription machinery to drive nectin-2 expression in Sertoli cells.