LDL INDUCES TRANSCRIPTION FACTOR ACTIVATOR PROTEIN-1 IN HUMAN ENDOTHELIAL-CELLS

Low density lipoprotein (LDL) has been shown to perturb endothelial ce lls, with manifestations ranging from alterations in free radicals and arachidonate metabolism to stress fiber formation and monocyte recrui tment. Some of these changes are regulated by LDL at the transcription al level. Using mobility shift assays with consensus sequences for var ious transcription factors, we have detected an increase in activator protein 1 (AP-1), but not nuclear factor-kappa B (NF-kappa B), binding in human umbilical vein endothelial cells exposed to LDL. Following t ransfection, AP-1-driven chloramphenicol acetyltransferase and AP-1-dr iven-luciferase are upregulated by LDL. In contrast, there is no effec t on NF-kappa B-driven chloramphenicol acetyltransferase. AP-1 increas es in a biphasic fashion, with the first peak occurring 6 hours after and the second 48 hours after exposure to LDL. This AP-1 binding incre ase involves c-Jun, but not c-Fos, as shown by gel supershift, Norther n hybridization, and Western blotting analyses. c-Jun mRNA levels are elevated by 9 hours after and remain so until at least 24 hours after exposure to LDL. c-Jun protein levels increase at 12 hours and continu e to rise for 24 hours after exposure to LDL. Moreover, this LDL-incre ased AP-1 binding is suppressed by several protein kinase (PK) inhibit ors: the PKC inhibitor calphostin C, the cAMP-dependent PEI inhibitor H89, and the tyrosine PK inhibitors genistein and lavendustin A. This study demonstrates that (1) LDL is an endothelial agonist distinct fro m other cell stimulators, such as cytokines, endotoxin, and phorbol 12 -myristate 13-acetate, because LDL arrears to activate human umbilical vein endothelial cells predominantly through the transcription factor AP-1 and not NF-kappa B; and (2) LDL increases AP-1 via mechanisms in volving multiple kinase activities and c-Jun transcription.