P. Leclerc et al., REGULATION OF PROTEIN-TYROSINE PHOSPHORYLATION AND HUMAN SPERM CAPACITATION BY REACTIVE OXYGEN DERIVATIVES, Free radical biology & medicine, 22(4), 1997, pp. 643-656
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.