Functional divergence of platelet protein kinase C (PKC) isoforms in thrombus formation on collagen.
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 alpha-granule secretion and thrombus formation are mediated by the conventional PKC isoforms, PKCalpha and PKCbeta, whereas the novel isoform, PKC, negatively regulates these events. PKCdelta also negatively regulates thrombus formation but not alpha-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 PKCalpha or PKCbeta showed reduced calcium signaling and phosphatidylserine exposure, these responses were enhanced in the absence of PKC. 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.
Gilio
Karen
K
Department of Physiology and Pharmacology, School of Medical Sciences, Bristol University, Bristol BS8 1TD, United Kingdom.
Harper
Matthew T
MT
Cosemans
Judith M E M
JM
Konopatskaya
Olga
O
Munnix
Imke C A
IC
Prinzen
Lenneke
L
Leitges
Michael
M
Liu
Qinghang
Q
Molkentin
Jeffery D
JD
Heemskerk
Johan W M
JW
Poole
Alastair W
AW
D000818:Animals; D000925:Anticoagulants / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D003094:Collagen / Q000494:pharmacology*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000378:metabolism; D051379:Mice; D015539:Platelet Activation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000378:metabolism*; D013927:Thrombosis / Q000097:blood* / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology
D000925:Anticoagulants; D007527:Isoenzymes; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D003094:Collagen; D011493:Protein Kinase C