Dual regulation of Glycogen Synthase Kinase 3 (GSK3)alpha/beta by Protein Kinase C (PKC)alpha and Akt promotes Thrombin-mediated Integrin alpha(IIb)beta(3) activation and granule secretion in platelets

Samantha F. Moore, Marion T. J. van den Bosch, Roger W. Hunter, Kei Sakamoto, Alastair W. Poole, Ingeborg Hers

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    Glycogen synthase kinase-3 is a Ser/Thr kinase, tonically active in resting cells but inhibited by phosphorylation of an N-terminal Ser residue (Ser(21) in GSK3 alpha and Ser(9) in GSK3 beta) in response to varied external stimuli. Recent work suggests that GSK3 functions as a negative regulator of platelet function, but how GSK3 is regulated in platelets has not been examined in detail. Here, we show that early thrombin-mediated GSK3 phosphorylation (0-30 s) was blocked by PKC inhibitors and largely absent in platelets from PKC alpha knock-out mice. In contrast, late (2-5 min) GSK3 phosphorylation was dependent on the PI3K/Akt pathway. Similarly, early thrombin-mediated inhibition of GSK3 activity was blocked in PKC alpha knock-out platelets, whereas the Akt inhibitor MK2206 reduced late thrombin-mediated GSK3 inhibition and largely prevented GSK3 inhibition in PKC alpha knock-out platelets. More importantly, GSK3 phosphorylation contributes to platelet function as knock-in mice where GSK3 alpha Ser(21) and GSK3 beta Ser(9) were mutated to Ala showed a significant reduction in PAR4-mediated platelet aggregation, fibrinogen binding, and P-selectin expression, whereas the GSK3 inhibitor CHIR99021 enhanced these responses. Together, these results demonstrate that PKC alpha and Akt modulate platelet function by phosphorylating and inhibiting GSK3 alpha/beta, thereby relieving the negative effect of GSK3 alpha/beta on thrombin-mediated platelet activation.

    Original languageEnglish
    Pages (from-to)3918-3928
    Number of pages11
    JournalJournal of Biological Chemistry
    Issue number6
    Publication statusPublished - 2013


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