Tyrosine Phosphorylation, Thiol Status, and Protein Tyrosine Phosphatase in Rat Epididymal Spermatozoa

Abstract

Sperm thiol oxidation and the ability to undergo protein tyrosine phosphorylation are associated with the acquisition of sperm motility and fertilizing ability during passage of spermatozoa through the epididymis. Phosphotyrosine levels in various cells are controlled by tyrosine kinase versus phosphatase, with the latter known to be inhibited by oxidation. In the present paper we examine whether changes in thiol status during sperm maturation affect rat sperm protein phosphotyrosine levels and protein phosphotyrosine phosphatase (PTP) activity. Tyrosine phosphorylation, as demonstrated by immunoblotting (IB), was significantly increased in several sperm tail proteins during maturation in the epididymis. Sperm thiol oxidation with diamide enhanced tail protein phosphorylation; reduction of disulfides with dithiothreitol diminished phosphorylation. In the sperm head, a moderate increase in tyrosine phosphorylation was accompanied by altered localization of phosphotyrosine proteins during maturation. Blocking of thiols and PTP activity with N-ethylmaleimide led to increased tyrosine phosphorylation of protamine in caput sperm heads. Several PTP bands were identified by IB. In the caput spermatozoa, a prominent level of the 50 kDa band was present, whereas in the cauda spermatozoa a very low level of the 50 kDa band was found. PTP activity, measured by using p-nitrophenyl phosphate as a substrate, was significantly higher in the caput spermatozoa (high thiol content) than in the cauda spermatozoa (low thiol content). Our results show that PTP activity is correlated with sperm thiol status and suggest that tyrosine phosphorylation of sperm proteins during sperm maturation is promoted by thiol oxidation and diminished PTP.

Protein tyrosine phosphatase non-receptor type 14 is a novel sperm-motility biomarker

“…Their finding supported the idea that capacitation might modulate tyrosine phosphorylation through inhibition of some PTPs [49]. Similarly, Seligman et al suggested that diminished PTP activity promoted tyrosine phosphorylation of sperm proteins during rat sperm maturation [50]. In contrast, a recent study showed that PTPN11 activity played a positive role in the regulation of mammalian sperm motility [33].…”

Role of Posttranslational Protein Modifications in Epididymal Sperm Maturation and Extracellular Quality Control

“…Finally, sperm sulfhydryl oxidation has been shown to facilitate protein tyrosine phosphorylation. Spermatozoa exposed to diamide to form disulfi des exhibited enhanced tail protein phosphorylation while the reduction of disulfi des by treatment with DTT decreased phosphorylation [ 103 ]. Further studies also showed a correlation of protein phosphotyrosine phosphatase activity with sperm thiol status [ 103 ].…”

The roles of the epididymis and prostasomes in the attainment of fertilizing capacity by stallion sperm

“…The changes are regulated by intracellular mediators such as cyclic AMP, calcium and pH, derived from the epididymal environment. Sperm structures like the outer dense fibres of the flagellum are stabilised by disulphide linkages which result from phosphorylation events triggered by the oxidation of thiol (Seligman et al, 2004). Protein phosphorylation is the net result of the actions of protein kinases and phosphatases, and immotile sperm in the caput epididymis have significantly greater protein phosphatase activity than motile sperm in the cauda epididymis.…”