Integrin ?IIb-mediated PI3K/Akt activation in platelets.

ABSTRACT: Integrin ?IIb?3 mediated bidirectional signaling plays a critical role in thrombosis and haemostasis. Signaling mediated by the ?3 subunit has been extensively studied, but ?IIb mediated signaling has not been characterized. Previously, we reported that platelet granule secretion and TxA2 production induced by ?IIb mediated outside-in signaling is negatively regulated by the ?3 cytoplasmic domain residues R(724)KEFAKFEEER(734). In this study, we identified part of the signaling pathway utilized by ?IIb mediated outside-in signaling. Platelets from humans and gene deficient mice, and genetically modified CHO cells as well as a variety of kinase inhibitors were used for this work. We found that aggregation of TxA2 production and granule secretion by ?3?724 human platelets initiated by ?IIb mediated outside-in signaling was inhibited by the Src family kinase inhibitor PP2 and the PI3K inhibitor wortmannin, respectively, but not by the MAPK inhibitor U0126. Also, PP2 and wortmannin, and the palmitoylated ?3 peptide R(724)KEFAKFEEER(734), each inhibited the phosphorylation of Akt residue Ser473 and prevented TxA2 production and storage granule secretion. Similarly, Akt phosphorylation in mouse platelets stimulated by the PAR4 agonist peptide AYPGKF was ?IIb?3-dependent, and blocked by PP2, wortmannin and the palmitoylated peptide p-RKEFAKFEEER. Akt was also phosphorylated in response to mAb D3 plus Fg treatment of CHO cells in suspension expressing ?IIb?3-?724 or ?IIb?3E(724)AERKFERKFE(734), but not in cells expressing wild type ?IIb?3. In summary, SFK(s) and PI3K/Akt signaling is utilized by ?IIb-mediated outside-in signaling to activate platelets even in the absence of all but 8 membrane proximal residues of the ?3 cytoplasmic domain. Our results provide new insight into the signaling pathway used by ?IIb-mediated outside-in signaling in platelets.

SUBMITTER: Niu H 

PROVIDER: S-EPMC3474815 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature