VLDL activation of plasminogen activator inhibitor-1 (PAI-1) expression: involvement of the VLDL receptor

The potential role of the very low density lipoprotein (VLDL) receptor in m ediating VLDL-induced plasminogen activator inhibitor-1 (PAI-1) expression was studied iu vitro. Cultured endothelial cells incubated with VLDL showed an increased secretion of PAI-1, This response to VLDL could be completely prevented by the receptor-associated protein (RAP) and partially blocked b y rabbit polyclonal anti-VLDL receptor IgG, Furthermore, Chinese hamster ov ary (CHO) control cells and cells overexpressing the VLDL receptor were tra nsiently transfected with a PAI-1 promoter-reporter construct and incubated with VLDL, The PAI-1 promoter activity in response to VLDL was significant ly higher in the VLDL receptor overexpressing cells compared to the control cells. Addition of RAP completely blocked the VLDL-activated PAI-1 transcr iption. Electromobility shift assay was performed to investigate whether th e enhanced PAI-1 promoter activity seen in the VLDL receptor overexpressing cells in response to VLDL involved induction of the previously described V LDL-inducible factor(s) binding to the -675 to -653 region of the PAI-1 pro moter. We found that the binding of the VLDL-inducible factor in VLDL recep tor overexpressing cells was markedly enhanced by addition of VLDL as compa red to control cells where no increased binding could be seen in response t o VLDL. In summary, these results indicate that the VLDL receptor is a stro ng candidate for mediating VLDL effects on PAI-I synthesis and secretion in cells expressing this receptor.