title: Transforming growth factor-β3 regulates cell junction restructuring via MAPK-mediated mRNA destabilization and Smad-dependent protein degradation of junctional adhesion molecule B (JAM-B).
abstract: Junctional adhesion molecule-B (JAM-B) is found between Sertoli cells at the blood-testis barrier (BTB) as well as between Sertoli and germ cells at the apical ectoplasmic specializations (ES) in the testis. The expression of JAM-B is tightly regulated to modulate the passage of spermatocytes across the BTB as well as the release of mature spermatozoa from the seminiferous epithelium. Transforming growth factor beta (TGF-β) family is implicated in the regulation of testicular cell junction dynamics during spermatogenesis. This study aims to investigate the effects of TGF-β3 on the expression of JAM-B as well as the underlying mechanisms on how TGF-β3 regulates JAM-B expression to facilitate the disassembly of the BTB and apical ES. Our results revealed that TGF-β3 suppresses JAM-B at post-transcriptional and post-translational levels. Inhibitor, siRNA knockdown and co-immunoprecipitation have shown that TGF-β3 induces JAM-B protein degradation via ubiquitin-proteasome pathway. Immunofluorescence staining further confirmed that blockage of ubiquitin-proteasome pathway could abrogate TGF-β3-induced loss of JAM-B at the cell-cell interface. siRNA knockdown and immunofluorescence staining also demonstrated that activation of Smad signaling is required for TGF-β3-induced JAM-B protein degradation. In addition, TGF-β3 reduces JAM-B mRNA levels, at least in part, via post-transcriptional regulation. mRNA stability assay has confirmed that TGF-β3 promotes the degradation of JAM-B transcript and TGF-β3-mediated mRNA destabilization requires the activation of ERK1/2 and p54 JNK signal cascades. Taken together, TGF-β3 significantly downregulates JAM-B expression via post-transcriptional and post-translational modulation and results in the disruption of BTB and apical ES.
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Zhang
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong, China. Electronic address: wylui@hku.hk.
authors.forename: Wing-Yee
authors.initials: WY
authors.lastname: Lui
mesh_terms: D001814:Blood-Testis Barrier; D004705:Endocytosis / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007365:Intercellular Junctions / Q000235:genetics* / Q000378:metabolism; D062765:Junctional Adhesion Molecule B / Q000096:biosynthesis / Q000235:genetics*; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D020871:RNA Stability / Q000235:genetics; D012708:Sertoli Cells / Q000378:metabolism; D013090:Spermatocytes / Q000254:growth & development / Q000378:metabolism; D013091:Spermatogenesis / Q000235:genetics*; D013737:Testis / Q000254:growth & development / Q000378:metabolism; D053782:Transforming Growth Factor beta3 / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D062765:Junctional Adhesion Molecule B; D053782:Transforming Growth Factor beta3; D020929:Mitogen-Activated Protein Kinase Kinases
keywords: Cell junction; Cytokine; JAM-B; Spermatogenesis; TGF-beta