Regulation of JAM-B expression via an interplay of transcription factors of Elk-1, Sp, and E2F families in testicular cells

Abstract

In the mammalian testis, junctional adhesion molecule-B (JAM-B), a transmembrane protein, is found in adhering junctions between Sertoli and germ cells. Its expression is tightly regulated to allow the migration of developing germ cells from the basal to the adluminal compartment of the seminiferous epithelium. In this study, we elucidate how the basal transcription of JAM-B is modulated by interacting with various transcription factors. Site-directed mutagenesis performed in GATA-1, Elk-1, AP-2, proximal Sp1 (pSp1) and E2F motifs have significantly reduced the promoter activity of JAM-B in the mouse Sertoli cell line, MSC-1 cells. Electrophoretic mobility shift assay (EMSA) has showed that Elk-1, Sp1 and Sp3 proteins are bound onto Elk-1, pSp1+E2F motifs, whereas E2F1, E2F2 and E2F3 form a DNA-protein complex with Elk-1 motif. Overexpression of Elk-1, Sp1 and Sp3 could significantly increase the promoter activity; while overexpression of E2F1 and E2F2 exert an opposite effect. Cotransfection studies have shown that Sp3 protein abolishes the negative regulatory effect of E2F1 and E2F2 on the JAM-B promoter in a dosedependent manner. In addition, the basal transcription of JAM-B mediated by Elk-1 requires the activation of p38 MAP kinase. Addition of p38 inhibitor, SB202190, downregulates Elk-1 mediated transactivation. In summary, an interplay of Elk-1, Sp and E2F families provides a precise mechanism to regulate the expression of JAM-B gene in the mouse testicular cells.