A G(i) -independent mechanism mediating Akt phosphorylation in platelets.
BACKGROUND
The serine-threonine kinase Akt plays an important role in regulating platelet activation. Stimulation of platelets with various agonists results in Akt activation as indicated by Akt phosphorylation. However, the mechanisms of Akt phosphorylation in platelets are not completely understood.


OBJECTIVE
We used P2Y₁ knockout mice to address the role of P2Y₁₂ in Akt phosphorylation in response to thrombin receptors in platelets.


RESULTS
Thrombin or the PAR4 thrombin receptor peptide AYPGKF at high concentrations stimulated substantial phosphorylation of Akt residues Thr³⁰⁸ and Ser⁴⁷³ in P2Y₁₂-deficient platelets. AYPGKF-induced Akt phosphorylation is enhanced by expression of recombinant human PAR4 cDNA in Chinese hamster ovary (CHO) cells. P2Y₁₂ -independent Akt phosphorylation was not inhibited by integrin inhibitor peptide RGDS or integrin β₃ deficiency. Akt phosphorylation induced by thrombin or AYPGKF in P2Y₁₂-deficient platelets was inhibited by the calcium chelator dimethyl-BAPTA, the Src family kinase inhibitor PP2, and PI3K inhibitors, respectively.


CONCLUSIONS
Our results reveal a novel P2Y₁₂-independent signaling pathway mediating Akt phosphorylation in response to thrombin receptors.
Xiang
B
B
Division of Cardiovascular Medicine, The Gill Heart Institute, University of Kentucky, Lexington, KY, USA.
Zhang
G
G
Liu
J
J
Morris
A J
AJ
Smyth
S S
SS
Gartner
T K
TK
Li
Z
Z
D000818:Animals; D001792:Blood Platelets / Q000166:cytology* / Q000378:metabolism; D016466:CHO Cells; D002614:Chelating Agents / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D018076:DNA, Complementary / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D058925:Receptors, Purinergic P2Y12 / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry; D012694:Serine / Q000737:chemistry; D013917:Thrombin / Q000737:chemistry
D002614:Chelating Agents; D018076:DNA, Complementary; C548576:P2RY12 protein, human; C548577:P2ry12 protein, mouse; D010455:Peptides; D058925:Receptors, Purinergic P2Y12; D011994:Recombinant Proteins; D012694:Serine; D051057:Proto-Oncogene Proteins c-akt; D013917:Thrombin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go