Human cytomegalovirus increases HUVEC sensitivity to thrombin and modulates expression of thrombin receptors

Human cytomegalovirus (HCMV) establishes a life-long persistent infection. HCMV infection could be associated with chronic inflammatory diseases, such as cardiovascular disease and atherosclerosis. Here we observed that in HCMV (AD-169) pre-exposed human umbilical vein endothelial cells (HUVEC), thrombin-induced expression of IL-1alpha and M-CSF is markedly enhanced compared to the un-exposed cells. Study of the expression of thrombin receptor genes in HUVEC showed that HCMV triggered a time- and concentration-dependent expression of the thrombin receptors PAR1, PAR3 and PAR4 at the mRNA level. Induction of PAR1 and PAR3 mRNA expression is due to transcriptional activation of their promoters as shown by gene reporter assay. Furthermore, the virus induced expression of PAR1 and PAR3 but not PAR4 proteins, as analyzed by Western immunoblotting. However, flow cytometric analysis revealed that only PAR3, expressed at very low level in control HUVEC, is induced at the surface during the exposure to the virus. Our data suggest that although exposure to HCMV induces a minor increase of cell-surface receptors expression, it does make endothelial cells more responsive to additional thrombin stimulation.