MMP9 and cytomegalovirus infection: The concept that other factors (in this case, HCMV infection) might amplify the fibrogenic phenotype of HK-2 cells undergoing TGF-β1 induced EMT has been validated by others, who have shown that epidermal growth factor enhances the migratory phenotype of HK-2 cells and synergistically increases MMP-9 production after TGF-β1 induced EMT [49].