AI Article Synopsis

  • PKC-delta is crucial for thrombin-induced NF-kappaB activation and ICAM-1 expression in endothelial cells, but its exact mechanisms are not fully understood.
  • The study reveals that protein-tyrosine kinase Syk is activated by PKC-delta and mediates thrombin signaling, as seen by its time-dependent phosphorylation when endothelial cells are stimulated with thrombin.
  • Inhibition of PKC-delta or Syk prevents the activation of NF-kappaB and ICAM-1 expression, indicating a novel signaling pathway where Syk acts downstream of PKC-delta, enhancing NF-kappaB transcriptional activity through tyrosine phosphorylation of RelA/p65.

Article Abstract

Protein kinase C-delta (PKC-delta) plays a pivotal role in mediating thrombin-induced NF-kappaB activation and ICAM-1 expression in endothelial cells. However, the downstream mechanisms mediating its function are unclear. In this study, we show that PKC-delta-mediated activation of protein-tyrosine kinase Syk plays an important role in thrombin signaling of NF-kappaB activation and intercellular adhesion molecule-1 (ICAM-1) expression in endothelial cells. Stimulation of human vascular endothelial cells with thrombin resulted in a time-dependent phosphorylation of Syk on tyrosine 525 and 526, an indication of Syk activation. Inhibition of PKC-delta by pharmacological and genetic approaches prevented Syk activation by thrombin. These results place Syk downstream of PKC-delta in transmitting thrombin-activated signaling in endothelial cells. Consistent with this, thrombin-induced NF-kappaB activity and ICAM-1 expression were prevented by the expression of a kinase-defective mutant or RNA interference knockdown of Syk. Similarly, inhibiting Syk also impaired NF-kappaB activity and ICAM-1 expression induced by a constitutively active mutant of PKC-delta. Analysis of the NF-kappaB pathway showed that Syk contributes to thrombin-induced NF-kappaB activation by controlling its transactivation potential and that this response is associated with tyrosine phosphorylation of RelA/p65. Thus, these data unveil a novel pathway in which Syk signals downstream of PKC-delta to mediate thrombin induced ICAM-1 expression in endothelial cells by increasing transcriptional capacity of NF-kappaB via a mechanism that relies on tyrosine phosphorylation of RelA/p65.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2386948PMC
http://dx.doi.org/10.1074/jbc.M802094200DOI Listing

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