Functional Divergence of Platelet Protein Kinase C (PKC) Isoforms in Thrombus Formation on Collagen

• Published in: The Journal of biological chemistry 2010-07, Vol.285 (30), p.23410-23419
• Main Authors: Gilio, Karen, Harper, Matthew T., Cosemans, Judith M.E.M., Konopatskaya, Olga, Munnix, Imke C.A., Prinzen, Lenneke, Leitges, Michael, Liu, Qinghang, Molkentin, Jeffery D., Heemskerk, Johan W.M., Poole, Alastair W.
• Format: Article
• Language: English
• Subjects: Animals; Anticoagulants - pharmacology; Blood Platelets - drug effects; Blood Platelets - enzymology; Blood Platelets - metabolism; Blood Platelets - physiology; Calcium Imaging; Calcium Signaling - drug effects; Collagen - pharmacology; Gene Knockout; Humans; Isoenzymes - antagonists & inhibitors; Isoenzymes - deficiency; Isoenzymes - metabolism; Mice; Mouse; Platelet; Platelet Activation - drug effects; Platelet Membrane Glycoproteins - pharmacology; Protein Kinase C (PKC); Protein Kinase C - antagonists & inhibitors; Protein Kinase C - deficiency; Protein Kinase C - metabolism; Signal Transduction; Thrombosis; Thrombosis - blood; Thrombosis - chemically induced; Thrombosis - enzymology; Thrombosis - physiopathology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.136176

Arterial thrombosis, a major cause of myocardial infarction and stroke, is initiated by activation of blood platelets by subendothelial collagen. The protein kinase C (PKC) family centrally regulates platelet activation, and it is becoming clear that the individual PKC isoforms play distinct roles, some of which oppose each other. Here, for the first time, we address all four of the major platelet-expressed PKC isoforms, determining their comparative roles in regulating platelet adhesion to collagen and their subsequent activation under physiological flow conditions. Using mouse gene knock-out and pharmacological approaches in human platelets, we show that collagen-dependent α-granule secretion and thrombus formation are mediated by the conventional PKC isoforms, PKCα and PKCβ, whereas the novel isoform, PKCθ, negatively regulates these events. PKCδ also negatively regulates thrombus formation but not α-granule secretion. In addition, we demonstrate for the first time that individual PKC isoforms differentially regulate platelet calcium signaling and exposure of phosphatidylserine under flow. Although platelet deficient in PKCα or PKCβ showed reduced calcium signaling and phosphatidylserine exposure, these responses were enhanced in the absence of PKCθ. In summary therefore, this direct comparison between individual subtypes of PKC, by standardized methodology under flow conditions, reveals that the four major PKCs expressed in platelets play distinct non-redundant roles, where conventional PKCs promote and novel PKCs inhibit thrombus formation on collagen.