title: Pentoxifylline induced signalling events during capacitation of hamster spermatozoa: significance of protein tyrosine phosphorylation.
abstract: To fertilize the oocyte, mammalian spermatozoa must undergo capacitation and acrosome reaction. These events are believed to be associated with various biochemical changes primarily mediated by cAMP, Ca2+ and protein kinases. But the precise signaling mechanisms governing sperm function are not clear. To study this, we used pentoxifylline (PF), a sperm motility stimulant and a cAMP-phosphodiesterase inhibitor, during capacitation and acrosome reaction of hamster spermatozoa. PF induced an early onset of sperm capacitation and its action involved modulation of sperm cell signaling molecules viz, cAMP, [Ca2+]i and protein kinases. The PF-induced capacitation was associated with an early and increased total protein phosphorylation coupled with changes in the levels of reactive oxygen species. Protein kinase (PK)-A inhibitor (H-89) completely inhibited phosphorylation of a 29 kDa protein while PK-C inhibitor (staurosporine) did not inhibit phosphorylation. Interestingly, PF induced protein tyrosine phosphorylation of a set of proteins (Mr 45-80 K) and a greater proportion of PF-treated spermatozoa exhibited protein tyrosine phosphorylation, compared to untreated controls (82 + 9% vs 34 +/- 10%; p < 0.001); tyrosine-phosphorylated proteins were localized specifically to the mid-piece of the sperm. The profile of protein tyrosine phosphorylation was inhibitable by higher concentrations (> 0.5 mM) of tyrosine kinase inhibitor, tyrphostin A47. However, at lower (0.1-0.25 mM) concentrations, the compound interestingly induced early sperm capacitation and protein tyrosine phosphorylation, like PF. These results show that protein tyrosine phosphorylation in the mid-piece segment (mitochondrial sheath) appears to be an early and essential event during PF-induced capacitation and a regulated level of tyrosine phosphorylation of sperm proteins is critical for capacitation of hamster spermatozoa.
authors.affiliation: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India. polani@mrdg.iisc.ernet.in
authors.forename: P B
authors.initials: PB
authors.lastname: Seshagiri
authors.forename: M
authors.initials: M
authors.lastname: Thomas
authors.forename: A
authors.initials: A
authors.lastname: Sreekumar
authors.forename: P
authors.initials: P
authors.lastname: Ray
authors.forename: D
authors.initials: D
authors.lastname: Mariappa
mesh_terms: D020101:Acrosome Reaction / Q000187:drug effects*; D000818:Animals; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008647:Mesocricetus; D010431:Pentoxifylline / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013075:Sperm Capacitation / Q000187:drug effects*; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D047428:Protein Kinase Inhibitors; D017382:Reactive Oxygen Species; D020032:Tyrphostins; D000242:Cyclic AMP; D011494:Protein Kinases; D019311:Staurosporine; D010431:Pentoxifylline