Biphasic Regulation of Transcription Factor Nuclear Factor-κB Activity in Human Endothelial Cells by Lysophosphatidylcholine Through Protein Kinase C–Mediated Pathway

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Abstract
—Lysophosphatidylcholine (lysoPC), which is generated in oxidized LDL (Ox-LDL) and abundantly exists in atherosclerotic arterial walls, has been shown to alter various endothelial functions and induces several endothelial genes expressed in atherosclerotic arterial walls. Nuclear factor-kappa B (NF-κB), a pleiotropic transcription factor, plays an important role in regulation of expression of various genes implicated in atherosclerosis. We have previously reported that lysoPC transferred from Ox-LDL to endothelial surface membrane activates endothelial protein kinase C (PKC), leading to modulated endothelial functions. This study was aimed at determining whether lysoPC could modulate activity of transcription factors in cultured human umbilical vein endothelial cells (HUVECs) by using electrophoretic mobility shift assay. LysoPC was found to increase DNA-binding activity of NF-κB in HUVECs within 15 minutes, which peaked at 1 to 2 hours and subsequently declined to the baseline level at 6 hours. Lower concentrations (5 to 15 μmol/L) of lysoPC markedly increased NF-κB activity, but higher concentration (50 μmol/L) of lysoPC inhibited the activity. Phorbol 12-myristate 13-acetate, a potent activator of PKC, also augmented NF-κB activity in HUVECs, mimicking the effects of lysoPC; furthermore, calphostin C and chelerythrine chloride, specific PKC inhibitors, and α-tocopherol, a clinically potent PKC inhibitor, suppressed the lysoPC-induced NF-κB activation. These results indicate that lysoPC regulates NF-κB activity in a biphasic manner dependent on its concentrations and incubation time in human endothelial cells and the endothelial PKC activation may in part be involved in the lysoPC-induced NF-κB activation. Thus, the time course and the positive and negative biphasic regulatory actions of lysoPC on NF-κB activity in endothelial cells might exhibit a unique effect of lysoPC in arterial walls on the different stages of atherosclerosis.