REGULATION OF PROTEIN-TYROSINE PHOSPHORYLATION AND HUMAN SPERM CAPACITATION BY REACTIVE OXYGEN DERIVATIVES

Spermatozoa undergoing capacitation, a necessary prerequisite event to successful fertilization that can be induced in vitro by reactive oxy gen species (ROS), generate superoxide anion (O-2(.-)). Because, in ne utrophils, the generation of O-2(.-) is associated with tyrosine phosp horylation of several proteins, the aim of the present study was to in vestigate the association between protein-tyrosine phosphorylation and ROS-induced human sperm capacitation. Human spermatozoa express two m ajor phosphotyrosine-containing proteins of 105 and 81 kDa, the phosph otyrosine content of which is increased when spermatozoa are incubated under capacitating conditions. Superoxide dismutase and catalase abol ish both sperm capacitation and tyrosine phosphorylation of p105 and p 81, suggesting the involvement of O-2(.-) and hydrogen peroxide in the se two processes. Inhibitors of NADPH oxidase, the enzyme responsible for the neutrophil's respiratory burst, decrease both p105 and p81 tyr osine phosphorylation and sperm capacitation while hydrogen peroxide s timulates these two processes. Tyrosine phosphorylation of p105 and p8 1 occurs through a herbimycin A-sensitive tyrosine kinase, and sperm i ncubation with phosphotyrosine-protein phosphatase inhibitors results in an increase in phosphotyrosine content of these two proteins. Indir ect immunocytochemical studies reveal phosphotyrosine-containing prote ins mostly in the principal piece of the flagellum, in agreement with the localization of p105 and p81 in the human sperm fibrous sheath. Al though tyrosine phosphorylation of p105 and p81 and sperm capacitation are related in a time-dependent fashion, some discrepancies are obser ved in the regulation of these two processes according to the redox st atus of the spermatozoa. Copyright (C) 1997 Elsevier Science Inc.