Anisomycin does not activate p38(MAPK) in human platelets

Human platelets are known to contain three forms of mitogen-activated prote in kinases; erk1, erk2, and p38(MAPK). However the role(s) of mitogen-activ ated protein kinase cascades in platelet function remains to be determined. Evidence has been presented that suggests that these kinases are involved in the cytoskeleton and in the activation of phospholipase A(2); however, o ther functions seem likely. The object of the present study was to examine the role of the p38(MAPK) in platelet function using anisomycin, a reported activator of p38(MAPK), and SB203580, an inhibitor of p38(MAPK). Thrombin and collagen caused the phosphorylation of p38(MAPK) and this was inhibited by SB203580. Anisomycin did not cause the aggregation of either intact or saponin-permeabilised platelets. In addition anisomycin failed to produce s ynergistic aggregation responses with submaximal concentrations of collagen , thrombin, the thromboxane mimetic U46619, or the calcium ionophore A23187 . There was no detectable phosphorylation of p38(MAPK) in either intact pla telets or platelet lysates incubated with anisomycin. Anisomycin also faile d to modulate p38(MAPK) phosphorylation in response to submaximal concentra tions of collagen, thrombin, U46619, or A23187. In contrast anisomycin did cause p38(MAPK) phosphorylation in rabbit lung and C3 fibroblasts and in ra bbit lung fibroblast lysates. These data demonstrate that anisomycin has no detectable effect on either platelet function or p38(MAPK) phosphorylation and, therefore, that anisomycin has proven to be an ineffective tool to de fine the role that p38(MAPK) plays in platelet function. (C) 1999 Elsevier Science Ltd. All rights reserved.