Participation of calpain in protein-tyrosine phosphorylation and dephosphorylation in human blood platelets.
The possible role of calpains in protein-tyrosine phosphorylation in platelets was examined by the use of the cell-permeant calpain inhibitor calpeptin. In platelets stimulated by 1 U/mL thrombin, protein-tyrosine phosphorylation was maximal after 2 minutes and was followed by protein-tyrosine dephosphorylation. Calpeptin (30 mumol/L) or vanadate (2 mmol/L) enhanced protein-tyrosine phosphorylation and delayed protein-tyrosine dephosphorylation. The effects of these two compounds were not additive. We also observed proteolysis of pp60src and autoproteolysis of mu-calpain. Cleavage of the former was significantly slower than that of the latter and slower than protein-tyrosine dephosphorylation. The activity of protein-tyrosine phosphatase in the platelet lysate was transiently increased to 190% by addition of Ca2+. Ca(2+)-dependent activation of protein-tyrosine phosphatase was not observed in the presence of leupeptin. Those observations suggest that platelet calpains may be involved in modulation of protein-tyrosine phosphorylation through activation of protein-tyrosine phosphatase rather than through the inactivation of pp60src, a mechanism that was previously suggested.
Ariyoshi
H
H
Department of Surgery, Beth Israel Hospital, Harvard Medical School, Boston, Mass 02215, USA.
Oda
A
A
Salzman
E W
EW
D001792:Blood Platelets / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D004151:Dipeptides / Q000494:pharmacology; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
D004151:Dipeptides; C071482:calpeptin; D014638:Vanadates; D017027:Protein Tyrosine Phosphatases; D002154:Calpain