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J. Biol. Chem., Vol. 277, Issue 15, 12874-12878, April 12, 2002
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From the School of Animal & Microbial Sciences, University of
Reading, Whiteknights, Reading RG6 6AJ, United Kingdom
Phosphoinositide 3-kinase (PI3K) is
a critical component of the signaling pathways that control the
activation of platelets. Here we have examined the regulation of
protein kinase B (PKB), a downstream effector of PI3K, by the platelet
collagen receptor glycoprotein (GP) VI and thrombin receptors.
Stimulation of platelets with collagen or convulxin (a
selective GPVI agonist) resulted in PI3K-dependent, and
aggregation independent, Ser473 and
Thr308 phosphorylation of PKB
Protein Kinase B Is Regulated in Platelets by the Collagen
Receptor Glycoprotein VI*
, which results in PKB
activation. This was accompanied by translocation of PKB to cell
membranes. The phosphoinositide-dependent kinase PDK1 is
known to phosphorylate PKB on Thr308, although the
identity of the kinase responsible for Ser473
phosphorylation is less clear. One candidate that has been implicated as being responsible for Ser473 phosphorylation, either
directly or indirectly, is the integrin-linked kinase (ILK). In this
study we have examined the interactions of PKB, PDK1, and ILK in
resting and stimulated platelets. We demonstrate that in platelets PKB
is physically associated with PDK1 and ILK. Furthermore, the
association of PDK1 and ILK increases upon platelet stimulation. It
would therefore appear that formation of a tertiary complex between
PDK1, ILK, and PKB may be necessary for phosphorylation of PKB. These
observations indicate that PKB participates in cell signaling
downstream of the platelet collagen receptor GPVI. The role of PKB in
collagen- and thrombin-stimulated platelets remains to be determined.
*
This work was supported by funding from the Medical Research
Council.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: Tel.: 44-118-987-5123 (ext. 7082); Fax: 44-118-931-0180; E-mail:
j.m.gibbins@reading.ac.uk.
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