Protein kinase C regulates agonist‐mediated platelet activation downstream of 12‐lipoxygenase in human platelets

Abstract

Platelet activation plays an essential role in forming a clot following vascular injury and uncontrolled platelet activation results in vessel occlusion and stroke. Metabolism of arachidonic acid by 12-lipoxygenase (12-hLO) plays an important role in regulating the degree of platelet reactivity. Since PKC regulates platelet aggregation, secretion, and integrin activation, and our preliminary data supports a crucial role for 12-hLO in these processes, we hypothesized that a link exists between 12-hLO and PKC in regulation of agonist-mediated platelet reactivity. Aggregation, granule secretion, and αIIbβ3 activation were measured in the presence or absence of 12-hLO, PKC, or both. Dense granule secretion was completely eliminated in the absence of 12-hLO or PKC. Addition of PMA in the absence of 12-hLO rescued dense granule secretion. The EC50 for platelet aggregation, which was significantly shifted to the right in the absence of 12-hLO or PKC, was shifted leftward when PMA was added in the absence of 12-hLO. Similar shifts were observed in the level of integrin activation with PMA rescuing observed defects resulting from an absence of 12-hLO activity. Our data supports a crucial role for PKC activation downstream of 12-hLO activity. Elucidating how 12-hLO is regulating PKC and to what extent, will allow us to delineate the therapeutic potential of this pathway. This work was supported by NIH grant HL089457.