Regulation of Protein Tyrosine Phosphorylation in Human Sperm by a Calcium/Calmodulin-Dependent Mechanism: Identification of A Kinase Anchor Proteins as Major Substrates for Tyrosine Phosphorylation

Abstract

Signal transduction pathways regulate various aspects of mammalian sperm function. When human sperm were incubated in a medium supporting capacitation, proteins became tyrosine-phosphorylated in a time-dependent manner. This phosphorylation was inhibited by genistein, a protein tyrosine kinase inhibitor. Phosphorylation was also reduced when sperm were incubated either in the presence of increasing concentrations of extracellular Ca2+ or in a medium containing the Ca2+ ionophore A23187. This Ca2+-induced dephosphorylation was calmodulin-dependent, suggesting that calcineurin was involved. In this regard, the calcineurin inhibitor deltamethrin inhibited the Ca2+ ionophore-induced dephosphorylation. A limited number of Mr 80,000-105,000 polypeptides were the most prominent phosphotyrosine-containing proteins present in human sperm. Unlike mouse sperm, which contains a tyrosine-phosphorylated isoform of hexokinase, a phosphotyrosine-containing hexokinase in human sperm was not detected. Most of the tyrosine-phosphorylated proteins were Triton X-100-insoluble and were localized to the principal piece of the flagellum, the region where the cytoskeletal fibrous sheath is found. Prominent phosphotyrosine-containing proteins of Mr 82,000 and 97,000 were identified as the human homologues of mouse sperm AKAP82, the major fibrous sheath protein, and pro-AKAP82, its precursor polypeptide, respectively. These proteins are A Kinase Anchor Proteins, polypeptides that sequester protein kinase A to subcellular locations. Taken together, these results suggest that protein tyrosine phosphorylation may be part of a signal transduction cascade(s) regulating events pertaining to capacitation and/or motility in mammalian sperm and that an interrelationship between tyrosine kinase and cAMP signaling pathways exists in these cells.

Performance of some Table Grape Cultivars Grafting on Different Rootstocks in El-Nubaria Region

“…Kraphuna had the largest leaf surface area per vine when it was grafted on chasselasx Barlandien rootstock. In addition Carrera et al (1996) reported that rootstocks 110R, SO4 and 140 Ruggeri had the most productive scions. Also, Ezzahouani and Larry (1997) found that the scion cultivar Italla was most vigorous on rootstocks 101-14 and Rupestris dulot.…”

Teasing out the role of aromatase in the healthy and diseased testis

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Moving to the beat: a review of mammalian sperm motility regulation

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