Adhering junction dynamics in the testis are regulated by an interplay of β 1-integrin and focal adhesion complex-associated proteins
Siu,Michelle K.Y.; Mruk,Dolores D.; Lee,William M.; Cheng,Chuen-yan
Endocrinology 144(5): 2141-2163
Publication date: 2003
During spermatogenesis, the movement of developing germ cellsacross the seminiferous epithelium associates with extensiverestructuring of cell-cell actin-based adherens junctions (AJs),such as ectoplasmic specialization (ES, a testis-specific AJjunction), between Sertoli and germ cells. Although this eventof germ cell movement is essential to the completion of spermatogenesis,the mechanism(s) that regulates AJ restructuring is largelyunknown. Using Sertoli-germ cells cocultured in vitro to studythe regulation of AJ assembly, it was shown that this eventassociated with a transient induction of ß1-integrin,vinculin, p-FAK-Tyr, and phosphatidylinositol 3-kinase (PI3K)but not the nonphosphorylated form of focal adhesion kinase(FAK), paxillin, and p130 Cas. Furthermore, p-FAK-Tyr wasshown to coimmunoprecipitate with ß1-integrin, vinculin,and c-Src both in vitro and in vivo using Sertoli-germ cellcocultures and seminiferous tubules, respectively. These resultsseemingly suggest that the testis is using constituent proteinsof the focal adhesion complex (FAC) found in other epitheliabetween cell and extracellular matrix to regulate AJ dynamics.To further confirm that p-FAK, a putative FAC protein in otherepithelia, is indeed present at the site of ES, immunohistochemistryand immunofluorescent microscopy were used. The p-FAK-Tyrand p-FAK-Tyr were found to localize almost exclusively atthe site of apical ES with weak staining at the basal ES inthe seminiferous epithelium in a stage-specific manner, beinghighest at stages VI-VIII. In contrast, FAK was largelyrestricted to the basal compartment but with weak staining atthe apical compartment. When rats were treated with 1-(2,4-dichlorobenzyl)-indazole-3-carbohydrazide(AF-2364) to perturb Sertoli-germ cell AJs, an induction ofß1-integrin, vinculin, p-FAK-Tyr, PI3K, and p130Cas but not the nonphosphorylated form of FAK and paxillin wasalso detected in the testis, coinciding with the time spermatidsbegan to deplete from the epithelium, indicating their involvementin AJ disassembly. Thereafter, the levels of vinculin, p-FAK-Tyr,PI3K, and p130 Cas in the testis plunged, coinciding with thedeclining events of AJ disruption when virtually all spermatidswere depleted from the epithelium. Taken collectively, theseresults suggest a bifunctional role of p-FAK, being involvedin the events of Sertoli-germ cell AJ assembly and disassembly.In summary, the events of AJ dynamics in the testis, in particularat the site of ES, are regulated, at least in part, by proteinsthat are found in the FAC in other epithelia, such as ß1-integrin,vinculin, and FAK utilizing the integrin/pFAK/PI3K/p130 Cassignaling pathway.