DnaJC5 and Hsc70 are present and necessary for acrosomal exocytosis in human sperm

BERBERIAN MV; FLORES MONTERO K; RUETE MC

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Calcium-triggered exocytosis, which releases neurotransmitters and hormones into the extracellular medium, is a key cellular event mediated by the fusion of large and dense secretory granules with the plasma membrane. The sperm acrosome reaction (AR) is a unique, regulated exocytosis with special characteristics that plays a central role in the fertilization process. The human sperm possesses a single, large, flat granule that is released during AR. Acrosomal exocytosis involves the opening of a large number of fusion pores, merging the outer acrosomal and plasma membranes. In this process, the monomeric SNARE proteins are assembled into trans complexes, causing the irreversible docking of these membranes (acrosome and plasmatic). The fusion-competent conformation of the SNARE proteins and the SNARE-complex assembly are maintained by molecular chaperones. Molecular chaperones DnaJC5 and Hsc70 have been reported to facilitate the correct folding of polypeptides and to regulate the assembly of protein complexes involved in neurons and neuroendocrine cells exocytosis. However, the role of these chaperones in sperm remains unknown. Our goal is to determine the presence, localization and the role of these molecular chaperones in the assembly of trans-SNARE complexes in acrosomal exocytosis. By western blot, immunofluorescence and electronic microscopy, we show that both DnaJC5 and Hsc70 proteins are present in human sperm. Besides, we demonstrate that DnaJC5 is predominantly membrane bound, whereas Hsc70 is cytosolic. Moreover, by functional assays, using anti-DnaJC5 or anti-Hsc70 antibodies, we show that they are functionally active in secretion since they inhibited AR in a concentration-dependent manner. These results therefore assist in our understanding of the role of DnaJC5 and Hsc70 in acrosomal exocytosis.