Serine/threonine phosphorylation associated with hamster sperm hyperactivation

Abstract

Mammalian sperm activation and hyperactivation is regulated by protein phosphorylation. Although tyrosine phosphorylation is considered very important, several studies have investigated whether serine and threonine phosphorylation are also associated with sperm activation and hyperactivation, and that was also the aim of the present study. Protein phosphorylation of hamster spermatozoa was detected by Western blotting using antiphospho-amino acid monoclonal antibodies after tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amino acid sequences were analyzed using a peptide sequencer. Four proteins were phosphorylated at serine residues during hyperactivation via activation and their approximate molecular weights were 90, 38, 32 and 10 kDa, respectively. Five proteins were phosphorylated or dephosphorylated at threonine residues and their approximate molecular weights were 90, 70, 65, 35 and 10 kDa, respectively. The 10-kDa protein corresponded to a previously reported 10-kDa tyrosine phosphoprotein. N-terminal sequences of the 10-kDa protein were similar to carcinustatin, which is a neuropeptide. During hyperactivation, four serine phosphorylation and five threonine phospho- or dephosphorylations occurred, which suggested that the 10-kDa protein was phosphorylated at tyrosine residues when spermatozoa were activated and then dual-phosphorylated at the serine and threonine residues during hyperactivation. (Reprod Med Biol 2004;: 223-230).

Regulation of hyperactivation by PPP2 in hamster spermatozoa

“…Therefore, it seems that tyrosine phosphorylation is generally regulated by serine/threonine phosphorylation. On the other hand, serine/threonine phosphorylation of a 10 kDa protein occurred during hyperactivation after it was phosphorylated at the tyrosine residues (Fujinoki et al 2004). Moreover, tyrosine phosphorylation of the 10 kDa protein occurred in a cAMP-dependent manner when hamster spermatozoa were activated (Fujinoki et al 2001b).…”

“…But reaction of PPP3 was very weak. Moreover, PPP1CA, PPP2, and PPP3 were mainly detected from the urea extracts, which include sperm proteins without the fibrous sheath and nucleus (Fujinoki et al 2004). On the other hand, PPP1CC was detected from both the urea extracts and the urea-thiourea extracts, which include fibrous sheath proteins (Fujinoki et al 2004).…”

“…Moreover, it is suggested that protein serine/threonine phosphorylation is also associated with the regulation of hyperactivation (Naz 1999, Jha & Shivaji 2002b, Fujinoki et al 2004. On the other hand, it has been suggested that protein dephosphorylation is also associated with the regulation of hyperactivation (Fujinoki et al 2006).…”

“…Because cAMP-dependent protein kinase is generally a serine/threonine kinase, it has been proposed that spermatozoa have a cAMP-dependent tyrosine kinase or a tyrosine kinase regulated by cAMPdependent protein kinase. Recently, several studies have suggested that serine/threonine phosphorylation is associated with the regulation of hyperactivation (Naz 1999, Jha & Shivaji 2002b, Fujinoki et al 2004. Serine/threonine phosphorylation occurred before tyrosine phosphorylation occurred (Fujinoki et al 2006).…”

Serotonin-enhanced hyperactivation of hamster sperm

“…HCO K 3 stimulates AC, thereby increasing cAMP levels (Okamura et al 1985). cAMP activates protein kinase A (PKA), leading to protein serine/threonine phosphorylation and to sperm flagellar movement , Visconti et al 1999, Fujinoki et al 2003, 2004a, 2004b, 2006. In many cases, protein tyrosine phosphorylation also occurs in a cAMP-dependent manner (Visconti et al 1995, 1999, Fujinoki et al 2001b.…”