Combined effects of Elk-1/NRSF and TGIF/E2F regulate junctional adhesion molecule-B gene expression in mouse testicular cells.

Abstract

Introduction: Junctional adhesion molecule-B (JAM-B) is a transmembrane protein found at the adherens junctions between Sertoli and germ cells in mammalian testes. Its expression is tightly regulated to allow the migration of developing germ cells along the seminiferous epithelium and release of spermatids from the epithelium at spermiation. We have studied how basal transcription of JAM-B is modulated by the interactions of various transcription factors on the promoter sequences. Methods and Results: Mutagenic analyses performed in TGIF, Elk- 1, REST/NRSF, proximal Sp1 (pSp1) and E2F motifs significantly reduced the promoter activity of JAM-B in the mouse Sertoli cell line, MSC-1 cells. Electrophoretic mobility shift assay (EMSA) showed that Elk-1, Sp1 and Sp3 proteins were bound onto Elk-1, pSp1+E2F and TGIF motifs, whereas E2F3 form a DNA-protein complex with Elk-1 and NRSF motifs respectively. Furthermore, Smad3 and Smad4 proteins were recruited to the formation of a DNA-protein complex with TGIF motif. Over-expression of Elk-1, NRSF and Sp proteins could significantly increase the promoter activity; while over-expression of E2F3 and Smad exerted opposite effects. Co-transfection studies showed that E2F3 dose-dependently suppressed Elk-1 and Sp3- mediated gene transactivation. An increasing amount of Sp3, but not Elk-1, was shown to abolish E2F3-mediated gene repression. In vivo binding of Elk-1, NRSF, E2F, Smad and Sp proteins were confirmed by chromatin immunoprecipitation. Conclusions: An interplay of transcription factors on the Elk-1/ NRSF and TGIF/E2F motifs of the promoter exerts adverse effects and provides a combined mechanism to regulate JAM-B expression in the mouse testicular cells. Acknowledgements: This work was supported by Hong Kong Research Council grants (HKU7609/06M to WYL and HKU7599/ 06M to WML) and HKU/CRCG Seed Funding for Basic Research.