title: Dual regulation of glycogen synthase kinase 3 (GSK3)α/β by protein kinase C (PKC)α and Akt promotes thrombin-mediated integrin αIIbβ3 activation and granule secretion in platelets.
abstract: 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 GSK3α and Ser(9) in GSK3β) 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 PKCα 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 PKCα knock-out platelets, whereas the Akt inhibitor MK2206 reduced late thrombin-mediated GSK3 inhibition and largely prevented GSK3 inhibition in PKCα knock-out platelets. More importantly, GSK3 phosphorylation contributes to platelet function as knock-in mice where GSK3α Ser(21) and GSK3β 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 PKCα and Akt modulate platelet function by phosphorylating and inhibiting GSK3α/β, thereby relieving the negative effect of GSK3α/β on thrombin-mediated platelet activation.
authors.affiliation: School of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Samantha F
authors.initials: SF
authors.lastname: Moore
authors.forename: Marion T J
authors.initials: MT
authors.lastname: van den Bosch
authors.forename: Roger W
authors.initials: RW
authors.lastname: Hunter
authors.forename: Kei
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Alastair W
authors.initials: AW
authors.lastname: Poole
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Hers
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006575:Heterocyclic Compounds, 3-Ring / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D019007:P-Selectin / Q000096:biosynthesis; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: C473711:Chir 99021; D006575:Heterocyclic Compounds, 3-Ring; C548887:MK 2206; D019007:P-Selectin; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011725:Pyridines; D011743:Pyrimidines; D005340:Fibrinogen; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; C496630:Prkca protein, mouse; D051571:Protein Kinase C-alpha; D038362:Glycogen Synthase Kinase 3; D013917:Thrombin