Molecular Human Reproduction, Vol. 9, No. 3, 125-131,
March 2003
© 2003 European Society of Human Reproduction and Embryology
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Role of protein tyrosine phosphorylation in the thapsigargin-induced intracellular Ca2+ store depletion during human sperm acrosome reaction
Submitted on August 15, 2002; resubmitted on November 1, 2002. accepted on November 26, 2002
1 Département d’Obstétrique/Gynécologie and Centre de recherche en Biologie de la Reproduction, Université Laval, and Centre de recherche du CHUQ, Québec, G1L 3L5 and 2 Centre de recherche du CHUL, Québec, Canada G1V 4G2
3 To whom correspondence should be addressed at: Endocrinologie de la Reproduction, Pav. St-François d’Assise, 10 de L’Espinay, Québec, PQ, Canada, G1L 3L5. e-mail: pierre.leclerc{at}crsfa.ulaval.ca
During human sperm capacitation, an increase in phosphotyrosine content of specific proteins results partially from an increase in the intracellular free Ca2+ concentrations. In the present study, the inter-regulation between protein phosphotyrosine content and the intracellular Ca2+ concentration during the thapsigargin treatment of capacitated human sperm was investigated. The involvement of a tyrosine kinase pathway in the thapsigargin-induced acrosome reaction was also investigated. In response to thapsigargin, two sperm subpopulations, called LR (low responsive) and HR (high responsive), according to their increase in intracellular Ca2+, were observed. In addition to their high increase in intracellular Ca2+, sperm from the HR population expressed a higher protein phosphotyrosine content, and a higher proportion (P < 0.05) of them underwent the acrosome reaction in response to thapsigargin, as compared with LR sperm. Although the tyrosine kinase inhibitor PP2 abolished the thapsigargin-induced increase in protein phosphotyrosine content, it did not affect the intracellular Ca 2+ concentration or the percentage of acrosome-reacted sperm. The inability of an src-related tyrosine kinase inhibitor to block the thapsigargin-mediated Ca2+ increase and acrosomal exocytosis suggests that, during the acrosome reaction, the signalling pathway mediated by src-related tyrosine kinases is involved upstream of the capacitative Ca2+ entry.
Key words: acrosome/calcium store/Ca 2+-ATPase/capacitation/phosphotyrosine
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