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 Blood, 15 December 2007, Vol. 110, No. 13, pp. 4243-4252.
Prepublished online as a Blood First Edition Paper on September 7, 2007; DOI 10.1182/blood-2006-10-050633.

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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY

Insulin-like growth factor-1 potentiates platelet activation via the IRS/PI3K{alpha} pathway

Ingeborg Hers1

1 Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, United Kingdom

As insulin-like growth factor-1 (IGF-1) is present in the {alpha} granules of platelets and its receptor is expressed on the platelet surface, it may contribute to the amplification of platelet responses and pathogenesis of cardiovascular disease. The functional and signaling pathways that are involved in IGF-1 modulation of platelet function, however, are presently unknown. Here, I report that IGF-1 stimulation of platelets results in dose-dependent phosphorylation of the IGF receptor in the range of 1 to 100 nM. Phosphorylation of the IGF receptor is rapid and sustained, with maximal phosphorylation reached within 1 minute. Furthermore, IGF-1 stimulates tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and IRS-2 and their association with the p85 subunit of phosphoinositide-3 kinase (PI3K). IGF-1–stimulated tyrosine phosphorylation of IRS-1 and IRS-2 and subsequent p85 binding is transient and precedes phosphorylation of protein kinase B (PKB) on Ser473. PAR-1–mediated platelet aggregation is potentiated by IGF-1 and this potentiation, together with PKB phosphorylation, is abolished by the PI3K{alpha} inhibitors PI-103 and PIK-75. Importantly, the IGF receptor inhibitor NVP-AEW541 and the neutralization antibody {alpha}IR3 inhibit SFLLRN-stimulated aggregation, implicating IGF-1 in autocrine regulation of platelet function. These results demonstrate that IGF-1 activates the IGF receptor/IRS/PI3K/PKB pathway, and that PI3K{alpha} is essential for the potentiatory effect of IGF-1 on platelet responses.


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