Background: Human cytomegalovirus (HCMV) infection enhances the expression of the CXC chemokine, CXCL8, and the CC chemokines, CCL2 and CCL5. HCMV infection is presumed to contribute to atherosclerosis, and elevated levels of CCL2 are observed in atherosclerotic plaques, where macrophages expressing a specific receptor for CCL2, CCR2, abundantly infiltrate. Hence, HCMV and CCL2 may cooperatively contribute to several diseases including atherosclerosis. We previously revealed that tricin (4’,5,7-trihydroxy-3’,5’-dimethoxyflavone) exhibits anti-HCMV activity in a human embryonic lung fibroblast cells (HEL). Hence, in the present study, we examined the effects of tricin on HCMV infection with a focus on its effects on CCL2 expression.
Methods: HCMV Towne strain was propagated in HEL cells. Infectious virus production was titrated by using a plaque assay. The tricin compound used was synthetic, while siRNAs targeting CCL2 was commercially obtained. Western blot analysis and reverse transcription quantitative real-time PCR analysis examined protein and gene expression, respectively.
Results: HCMV infection induced CCL2 and CCR2 expression at the mRNA and the protein levels in HEL cells. CCL2 siRNA treatment reduced HCMV virion production. We further observed that CCL2 siRNA reduced the expression of HCMV IE and UL54 genes in a dose-dependent manner. Thus, HCMV infection can activate the CCL2-CCR2 interactions to further enhance HCMV infection and/or replication. Moreover, tricin reduced HCMV-induced CCL2 mRNA and protein expression together with inhibiting HCMV replication. Thus, tricin exerts its anti-HCMV activities at least partly by inhibiting the expression of CCL2, which can support HCMV infection and/or replication.
Conclusions: These results suggest that the CCL2/CCR2 interactions are associated with HCMV replication and that tricin is an anti-inflammatory compound with a potential anti-HCMV activity.