Immunodetection of Glucose-regulated protein 78 (GRP78) in human sperm and evaluation of its participation in gamete interaction

MARÍN-BRIGGILER C; GONZÁLEZ-ECHEVERRÍA F; CORRIGALL V; PANAYI G; HELLMAN U; VAZQUEZ-LEVIN M

Buenos Aires, Argentina

Congreso; VIII Jornadas Multidisciplinarias de la Sociedad Argentina de Biologia; 2006

Sociedad Argentina de Biologia

 Glucose-regulated protein 78 (GRP78; BiP) is an endoplasmic reticulum chaperone, also found on the surface of eukaryotic cells. Recently, GRP78 was identified on the luminal surface of bovine oviduct epithelial cells, and found to bind to bull sperm (Boilard et al, 2004). The aim of this study was to immunodetect endogenous GRP78 in human sperm, and to assess recombinant protein (recGRP78) association to live cells, and its effect upon sperm-zona pellucida (ZP) interaction. Western immunoblot analysis with monoclonal and policlonal antibodies revealed a 78 kDa sperm protein, confirmed to be GRP78 by MALDI-TOF analysis. Immunocytochemical studies showed GRP78 localization in the sperm cytoplasmic droplet and flagellum (n=5). Sperm incubation with 100 mg/ml recGRP78 resulted in its association to the acrosomal cap, a sperm region involved in gamete interaction. In the presence of 100 and 10 mg/ml recGRP78, a significant increase in the number of sperm bound to homologous ZP was observed (100 mg/ml recGRP78=41±8* vs medium=25±6 bound sperm/hemizona; 10 mg/ml recGRP78=28±5* vs medium=15±1; mean±SEM; *p<0.05; n=7). No increment in sperm-ZP binding was observed using 1 or 0.1 mg/ml of recGRP78 or rec-b-galactosidase (100 mg/ml) as control (n=7). In conclusion, GRP78 is present in the human sperm flagellum, can associate to the acrosomal region and increase in vitro sperm-ZP binding levels, suggesting its participation in gamete interaction.