Pears Catherine J, Thornber Kelly, Auger Jocelyn M, Hughes Craig E, Grygielska Beata, Protty Majd B, Pearce Andrew C, Watson Steve P
Department of Biochemistry, University of Oxford, Oxford, United Kingdom.
PLoS One. 2008;3(11):e3793. doi: 10.1371/journal.pone.0003793. Epub 2008 Nov 24.
Increasing evidence suggests that individual isoforms of protein kinase C (PKC) play distinct roles in regulating platelet activation.
METHODOLOGY/PRINCIPAL FINDINGS: In this study, we focus on the role of two novel PKC isoforms, PKCdelta and PKCepsilon, in both mouse and human platelets. PKCdelta is robustly expressed in human platelets and undergoes transient tyrosine phosphorylation upon stimulation by thrombin or the collagen receptor, GPVI, which becomes sustained in the presence of the pan-PKC inhibitor, Ro 31-8220. In mouse platelets, however, PKCdelta undergoes sustained tyrosine phosphorylation upon activation. In contrast the related isoform, PKCepsilon, is expressed at high levels in mouse but not human platelets. There is a marked inhibition in aggregation and dense granule secretion to low concentrations of GPVI agonists in mouse platelets lacking PKCepsilon in contrast to a minor inhibition in response to G protein-coupled receptor agonists. This reduction is mediated by inhibition of tyrosine phosphorylation of the FcRgamma-chain and downstream proteins, an effect also observed in wild-type mouse platelets in the presence of a PKC inhibitor.
These results demonstrate a reciprocal relationship in levels of the novel PKC isoforms delta and epsilon in human and mouse platelets and a selective role for PKCepsilon in signalling through GPVI.
越来越多的证据表明，蛋白激酶C（PKC）的各个亚型在调节血小板活化中发挥着不同的作用。
方法/主要发现：在本研究中，我们聚焦于两种新型PKC亚型PKCδ和PKCε在小鼠和人类血小板中的作用。PKCδ在人类血小板中大量表达，在凝血酶或胶原受体GPVI刺激下会发生短暂的酪氨酸磷酸化，在泛PKC抑制剂Ro 31-8220存在时这种磷酸化会持续。然而，在小鼠血小板中，PKCδ在活化时会发生持续的酪氨酸磷酸化。相比之下，相关亚型PKCε在小鼠血小板中高表达，而在人类血小板中不表达。与对G蛋白偶联受体激动剂的轻微抑制相比，缺乏PKCε的小鼠血小板对低浓度GPVI激动剂的聚集和致密颗粒分泌有明显抑制。这种减少是由FcRγ链和下游蛋白酪氨酸磷酸化的抑制介导的，在存在PKC抑制剂的野生型小鼠血小板中也观察到了这种效应。
这些结果表明，新型PKC亚型δ和ε在人类和小鼠血小板中的水平存在相互关系，并且PKCε在通过GPVI的信号传导中具有选择性作用。
