Role for p38 Mitogen-activated Protein Kinase in Platelet Aggregation Caused by Collagen or a Thromboxane Analogue

doi:10.1074/jbc.271.12.6586

Role for p38 Mitogen-activated Protein Kinase in Platelet Aggregation Caused by Collagen or a Thromboxane Analogue (*)

From the (1)Cytokine Laboratory, Department of Development and Signalling, The Babraham Institute, Babraham, Cambridge CB2 4AT, United Kingdom, the
(2)Department of Cellular Biochemistry, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, the
(3)Strangeways Research Laboratory, Wort's Causeway, Cambridge CB1 4RN, United Kingdom, and the
(4)Department of Biochemistry, University of Cambridge CB2 1QW, United Kingdom

Abstract

p38 mitogen-activated protein kinase (MAPK) was identified in platelets on the basis of (a) its reactivity with antibodies to C-terminal and N-terminal peptides, and (b) its ability to activate MAPK-activated protein kinase-2, which phosphorylates the small heat shock protein, hsp27. p38 MAPK was activated in platelets by collagen fibers, a collagen-related cross-linked peptide, thrombin, or the thromboxane analogue U46619. A highly specific inhibitor of p38 MAPK, a pyridinyl imidazole known as SB203580, inhibited the platelet enzyme in vitro (IC 0.5 μM). At similar concentrations it also inhibited agonist-stimulated phosphorylation of hsp27 in platelets, and platelet aggregation and secretion induced by minimal aggregatory concentrations of collagen or U46619, but not thrombin. Inhibition of aggregation was overcome by increasing agonist dose. SB203580 might act by inhibiting thromboxane generation, but this was only inhibited by 10-20% at low agonist concentrations.

p38 MAPK provides a crucial signal, which is necessary for aggregation caused by minimal concentrations of collagen fibers or U46619. Thrombin or high doses of these agonists generate signals that bypass the enzyme, or render the enzyme no longer rate-limiting.

Footnotes

↵^§ Member of the external scientific staff of the Medical Research Council.
↵* This work was supported by the Medical Research Council of the United Kingdom and the Arthritis and Rheumatism Council. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations and trivial names used are:

MAPK

mitogen-activated protein kinase

hsp

heat shock protein

IL1

interleukin 1

JNK

Jun N-terminal kinase

MAPKAPK-2

mitogen-activated protein kinase-activated protein kinase-2

PMA

phorbol 12-myristate 13-acetate

SB203580

4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5(4-pyridyl) imidazole

SKF86002

6-(4-fluorophenyl)-2,3-dihydro-5-(4-pyridinyl)imidazo[2,1-b]thiazole

SKF105809

(2-4-methylsulfonylphenyl)-3- (4-pyridyl)-6,7-dihydro-[5H]-dpyrrolo[1,2-a]imidazole.
- Received December 28, 1995.
- Revision received January 22, 1996.