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Spermatogenesis is a dynamic process that is regulated by adhesive interactions between germ and Sertoli cells. Germ cells express the Junctional Adhesion Molecule-C (JAM-C, encoded by Jam3), which localizes to germ/Sertoli cell contacts. JAM-C is involved in germ cell polarity and acrosome formation. Using a proteomic approach, we demonstrated that JAM-C interacted with the Golgi reassembly stacking protein of 55 kDa (GRASP55, encoded by Gorasp2) in developing germ cells. Generation and study of Gorasp2-/- mice revealed that knock-out mice suffered from spermatogenesis defects. Acrosome formation and polarized localization of JAM-C in spermatids were altered in Gorasp2-/- mice. In addition, Golgi morphology of spermatocytes was disturbed in Gorasp2-/- mice. Crystal structures of GRASP55 in complex with JAM-C or JAM-B revealed that GRASP55 interacted via PDZ-mediated interactions with JAMs and induced a conformational change in GRASP55 with respect of its free conformation. An in silico pharmacophore approach identified a chemical compound called Graspin that inhibited PDZ-mediated interactions of GRASP55 with JAMs. Treatment of mice with Graspin hampered the polarized localization of JAM-C in spermatids, induced the premature release of spermatids and affected the Golgi morphology of meiotic spermatocytes., Author summary Spermatogenesis defects are a common cause of male sterility. Spermatogenesis occurs in the seminiferous tubules of the testes and involves adhesive interactions between developing germ cells and Sertoli cells. Knock-out mouse models identified several adhesion molecules that are critically involved in spermatogenesis. We previously demonstrated that the Junctional Adhesion Molecule-C (JAM-C) plays a crucial role in establishing spermatids polarity. The latter involves rearrangements of the Golgi apparatus in spermatids which contribute to acrosome formation. The present study demonstrated that the C-terminal cytosolic region of JAM-C interacted with the Golgi reassembly stacking protein of 55 kDa (GRASP55) encoded by Gorasp2 and that spermatogenesis was impaired in Gorasp2-deficient mice. We developed an inhibitor of GRASP55 interaction with JAM-C and demonstrated that treatment of wild-type mice with the inhibitory compound induced germ cell loss. Therefore, the male infertility-associated pathway identified in this study is important not only from a genetic point of view, but also as a potential target for male contraception.

International audience; no abstract

International audience; Background information. Previous studies have reported that cross-talk between integrins may be an important regulator of integrin-ligand binding and subsequent signalling events that control a variety of cell functions in many tissues. We previously demonstrated that alpha v beta 5/beta 6 integrin represses alpha 2 beta 1-dependent cell migration. The alpha v subunits undergo an endoproteolytic cleavage by protein convertases, whose role in tumoral invasion has remained controversial. Results. Inhibition of convertases by the convertase inhibitor alpha 1-PDX (alpha 1-antitrypsin Portland variant), leading to the cell-surface expression of an uncleaved form of the av integrin, stimulated cell migration toward type I collagen. Under convertase inhibition, alpha 2 beta 1 engagement led to enhanced phosphorylation of both FAK (focal adhesion kinase) and MAPK (mitogen-activated protein kinase). This outside-in signalling stimulation was associated with increased levels of activated integrin located in larger than usual focal-adhesion structures and a cell migration that was independent of the PI3K (phosphoinositide 3-kinase)/Akt (also called protein kinase B) pathway. Conclusions. The increase in cell migration observed upon convertases inhibition appears to be due to the up-regulation of beta 1 integrins and to their location in larger focal-adhesion structures. The endoproteolytic cleavage of av subunits is necessary for alpha v beta 5/beta 6 integrin to control alpha 2 beta 1 function and could thus play an essential role in colon cancer cell migration.