Progesterone action on the human sperm surface is potentiated by an egg-associated acrosin activator

The progesterone-induced Ca2+ influx and acrosomal exocytosis in human sperm are recently described examples of non-genomic steroid action on the cell surface. These progesterone effects are known to be inhibited by synthetic protease inhibitors. In this study we tested a hypothesis that a physiological activator of the sperm protease acrosin modulates the sperm response to progesterone. It was found that the activator augments the amplitude of the progesterone-induced Ca2+ transient and accelerates the progesterone-induced acrosomal exocytosis. These observations suggest a physiological significance of the modulation of nongenomic steroid effects by protease regulators.