Glucose-regulated protein 78 (Grp78/BiP) is secreted by human oviduct epithelial cells and the recombinant protein modulates sperm-zona pellucida binding.

Objective: To determine the secretion of Grp78 by human oviduct epithelial cells, its association to spermatozoa, and its involvement in gamete interaction.
Design: Prospective study.
Setting: Basic research laboratory.
Subject(s): Semen samples obtained from normozoospermic volunteers. Tubal tissue provided by patients undergoing hysterectomies. Oocytes collected from women undergoing IVF-ET.
Intervention(s): Analysis of Grp78 expression and secretion by oviductal tissue. Gamete incubation with recombinant Grp78 (rec-Grp78).
Main Outcome Measure(s): Assessment of protein expression and secretion by immunohistochemistry and Western immunoblotting, respectively. Evaluation of rec-Grp78 binding to human spermatozoa by immunocytochemistry, and analysis of its effect upon gamete interaction using the hemizona assay.
Result(s): Grp78 was found in the surface of oviduct epithelial cells. Soluble Grp78 was detected in oviductal fluids from women in the periovulatory period and in oviductal tissue conditioned medium. Rec-Grp78 was able to bind to the sperm acrosomal cap, and its presence during gamete interaction led to a decrease in the number of spermatozoa bound to the zona pellucida (ZP). When calcium ions from the incubation medium were replaced by strontium, rec-Grp78 enhanced sperm-ZP interaction.
Conclusion(s): Grp78 is expressed and secreted by oviduct epithelial cells. The protein would bind to the gametes and may modulate their interaction in a calcium-dependent manner.
(Copyright 2010 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)