DNAJC5 Y HSC70 ARE PRESENT AND NECESSARY FOR ACROSOMAL EXOCYTOSIS IN HUMAN SPERM

FLORES MONTERO, KARINA JOHANA; BERBERIÁN, MARIA VICTORIA; RUETE, CELESTE

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2018

Calcium-triggered exocytosis, which releases neurotransmittersand hormones into the extracellular medium, is a key cellular eventmediated by the fusion of large and dense secretory granules withthe plasma membrane.The sperm acrosome reaction (AR) is a unique, regulated exocytosiswith special characteristics that plays a central role in the fertilizationprocess. The human sperm possesses a single, large, flatgranule that is released during AR. Acrosomal exocytosis involvesthe opening of a large number of fusion pores, merging the outeracrosomal and plasma membranes. In this process, the monomericSNARE proteins are assembled into trans complexes, causing theirreversible docking of these membranes (acrosome and plasmatic).The fusion-competent conformation of the SNARE proteins andthe SNARE-complex assembly are maintained by molecular chaperones.Molecular chaperones DnaJC5 and Hsc70 have been reportedto facilitate the correct folding of polypeptides and to regulate theassembly of protein complexes involved in neurons and neuroendocrinecells exocytosis. However, the role of these chaperones insperm remains unknown. Our goal is to determine the presence,localization and the role of these molecular chaperones in the assemblyof trans-SNARE complexes in acrosomal exocytosis.By western blot, immunofluorescence and electronic microscopy,we show that both DnaJC5 and Hsc70 proteins are present in humansperm. Besides, we demonstrate that DnaJC5 is predominantlymembrane bound, whereas Hsc70 is cytosolic. Moreover, by functionalassays, using anti-DnaJC5 or anti-Hsc70 antibodies, we showthat they are functionally active in secretion since they inhibited ARin a concentration-dependent manner. These results therefore assistin our understanding of the role of DnaJC5 and Hsc70 in acrosomalexocytosis.