Sertoli-germ cell anchoring junction dynamics in the testis are regulated by an interplay of lipid and protein kinases.
When Sertoli and germ cells were co-cultured in vitro in serum-free chemically defined medium, functional anchoring junctions such as cell-cell intermediate filament-based desmosome-like junctions and cell-cell actin-based adherens junctions (e.g. ectoplasmic specialization (ES)) were formed within 1-2 days. This event was marked by the induction of several protein kinases such as phosphatidylinositol 3-kinase (PI3K), phosphorylated protein kinase B (PKB; also known as Akt), p21-activated kinase-2 (PAK-2), and their downstream effector (ERK) as well as an increase in PKB intrinsic activity. PI3K, phospho (p)-PKB, and PAK were co-localized to the site of apical ES in the seminiferous epithelium of the rat testis in immunohistochemistry studies. Furthermore, PI3K also co-localized with p-PKB to the same site in the epithelium as determined by fluorescence microscopy, consistent with their localization at the ES. These kinases were shown to associate with ES-associated proteins such as beta1-integrin, phosphorylated focal adhesion kinase, and c-Src by co-immunoprecipitation, suggesting that the integrin.laminin protein complex at the apical ES likely utilizes these protein kinases as regulatory proteins to modulate Sertoli-germ cell adherens junction dynamics via the ERK signaling pathway. To validate this hypothesis further, an in vivo model using AF-2364 (1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide) to perturb Sertoli-germ cell anchoring junction function, inducing germ cell loss from the epithelium in adult rats, was used in conjunction with specific inhibitors. Interestingly, the event of germ cell loss induced by AF-2364 in vivo was also associated with induction of PI3K, p-PKB, PAK-2, and p-ERK as well as a surge in intrinsic PKB activity. Perhaps the most important of all, pretreatment of rats with wortmannin (a PI3K inhibitor) or anti-beta1-integrin antibody via intratesticular injection indeed delayed AF-2364-induced spermatid loss from the epithelium. In summary, these results illustrate that Sertoli-germ cell anchoring junction dynamics in the testis are regulated, at least in part, via the beta1-integrin/PI3K/PKB/ERK signaling pathway.
Siu
Michelle K Y
MK
Center for Biomedical Research, Population Council, New York, New York 10021, USA.
Wong
Ching-Hang
CH
Lee
Will M
WM
Cheng
C Yan
CY
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002450:Cell Communication; D018929:Cell Culture Techniques; D002614:Chelating Agents / Q000494:pharmacology; D018920:Coculture Techniques; D003470:Culture Media / Q000494:pharmacology; D016895:Culture Media, Serum-Free / Q000378:metabolism / Q000494:pharmacology; D003599:Cytoskeleton / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005854:Germ Cells / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D019012:Integrin beta1 / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008297:Male; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D012708:Sertoli Cells / Q000166:cytology*; D015398:Signal Transduction; D013091:Spermatogenesis; D013737:Testis / Q000378:metabolism*; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry; D000077191:Wortmannin
D000730:Androstadienes; D002614:Chelating Agents; D003470:Culture Media; D016895:Culture Media, Serum-Free; D004492:Edetic Acid; D004533:Egtazic Acid; D048049:Extracellular Signal-Regulated MAP Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019012:Integrin beta1; D008055:Lipids; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014443:Tyrosine; D000077191:Wortmannin; C496052:Ptk2 protein, rat; C494920:Akt1 protein, rat