Requirement of protein tyrosine kinase and phosphatase activities for human sperm exocytosis

TOMES, C.N; ROGGERO, C.M; DE BLAS, G; SALING, P.M; MAYORGA, L.S

DEVELOPMENTAL BIOLOGY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 2004 vol. 265 p. 399 - 415

0012-1606

The acrosome is a membrane-limited granule that overlies the nucleus of the mature spermatozoon. In response to physiological orpharmacological stimuli, sperm undergo calcium-dependent exocytosis termed the acrosome reaction, which is an absolute prerequisite forfertilization. Protein tyrosine phosphorylation and dephosphorylation are mechanisms by which multiple cellular events are regulated. Herewe report that calcium induces tyrosine phosphorylation in streptolysin O (SLO)-permeabilized human sperm. As expected, pretreatmentwith tyrphostin A47?a tyrosine kinase inhibitor?abolishes the calcium effect. Interestingly, the calcium-induced increase in tyrosinephosphorylation has a functional correlate in sperm exocytosis. Masking of phosphotyrosyl groups with a specific antibody or inhibition oftyrosine kinases with genistein, tyrphostin A47, and tyrphostin A51 prevent the acrosome reaction. By reversibly sequestering intraacrosomalcalcium with a photo-inhibitable chelator, we show a requirement for protein tyrosine phosphorylation late in the exocytoticpathway, after the efflux of intra-acrosomal calcium. Both mouse and human sperm contain highly active tyrosine phosphatases. Importantly,this activity declines when sperm are incubated under capacitating conditions. Inhibition of tyrosine phosphatases with pervanadate, bis(N,Ndimethylhydroxoamido)hydroxovanadate, ethyl-3,4-dephostatin, and phenylarsine oxide prevents the acrosome reaction. Our results showthat both tyrosine kinases and phosphatases play a central role in sperm exocytosis.