Apolipoprotein CIII-Induced THP-1 Cell Adhesion to Endothelial Cells Involves Pertussis Toxin-Sensitive G Protein- and Protein Kinase Cα-Mediated Nuclear Factor-κB Activation

Abstract

Objective-Plasma apolipoprotein CIII (apoCIII) independently predicts risk for coronary heart disease (CHD). We recently reported that apoCIII directly enhances adhesion of human monocytes to endothelial cells (ECs), and identified the activation of PKC␣ as a necessary upstream event of enhanced monocyte adhesion. This study tested the hypothesis that apoCIII activates PKC␣ in human monocytic THP-1 cells, leading to NF-B activation. Methods and Results-Among inhibitors specific to PKC activators, phosphatidylcholine-specific phospholipase C (PC-PLC) inhibitor D609 limited apoCIII-induced PKC␣ activation and THP-1 cell adhesion. ApoCIII increased PC-PLC activity in THP-1 cells, resulting in PKC␣ activation. Pertussis toxin (PTX) inhibited apoCIII-induced PC-PLC activation and subsequent PKC␣ activation, implicating PTX-sensitive G protein pathway. ApoCIII further activated nuclear factor-B (NF-B) through PKC␣ in THP-1 cells and augmented ␤1-integrin expression. The NF-B inhibitor peptide SN50 partially inhibited apoCIII-induced ␤1-integrin expression and THP-1 cell adhesion. ApoCIII-rich VLDL had similar effects to apoCIII alone. Conclusions-PTX-sensitive G protein pathway participates critically in PKC␣ stimulation in THP-1 cells exposed to apoCIII, activating NF-B, and increasing ␤1-integrin. This action causes monocytic cells to adhere to endothelial cells. Key Words: apolipoproteins Ⅲ atherosclerosis Ⅲ adhesion molecules Ⅲ leukocytes Ⅲ signal transduction P revious clinical studies recognized apoCIII as an independent risk factor for coronary heart disease (CHD), 1-3 especially as a component of apoB lipoproteins. 1,4 Excessive apoCIII delays lipolysis of apoB lipoproteins 5 and inhibits their uptake by normal high-affinity receptors on hepatocytes, 6 causing hypertriglyceridemia. However, the direct effect of apoCIII on vascular cells or leukocytes remained untested. We recently reported that apoCIII alone or apoCIII-rich VLDL or LDL augment THP-1 cell adhesion to vascular ECs under static or flow conditions. 7 Protein kinase C (PKC) ␣ participated critically in this process. Ca 2ϩ , phospholipids, and diacylglycerol (DAG) activate PKC␣, one of the conventional PKC isoforms. 8,9 The literature currently provides little information regarding possible direct effects of apoCIII on these molecules, and the mechanism for PKC␣ activation by apoCIII remains undetermined. PKC participates importantly in several mechanisms in atherogenesis including monocyte-endothelial interaction. 8,10 However, the downstream pathway of PKC in apoCIII-treated THP-1 cells remains incompletely understood, although activation of RhoA partially contributes to the effect of apoCIII. 7 The present study demonstrates that pertussis toxin (PTX)-sensitive G protein and phosphatidylcholine-specific phospholipase C (PC-PLC) mediate apoCIII-induced PKC␣ activation, and that apoCIII-induced PKC␣ activation induces activation of nuclear factor-B (NF-B), a key regulator for inflammation in atherogenesis. Indeed, such activation leads to increased...

Apolipoprotein CIII Links Hyperlipidemia With Vascular Endothelial Cell Dysfunction

“…25,28 These results indicate a central role of PKC␤II in impaired insulin signaling induced by apoCIII. Although the mechanism(s) by which apoCIII activates PKCs in endothelial cells or monocytes remain to be fully elucidated, we recently reported that apoCIII activates PKCs through a pertussis toxin-sensitive G protein and phospholipase C in THP-1 cells, 29 suggesting that a distinct pathway or receptor may be involved in this process. Further studies are needed to elucidate the specific apoCIII signaling pathways.…”

ApoE derived from adipose tissue does not suppress atherosclerosis or correct hyperlipidemia in apoE knockout mice

“…An additional function of apoCIII relevant to our results has been reported. It has been shown that apoCIII, whether free or associated with VLDL, infl uences monocyte adhesion to the endothelium of the vessel wall ( 39,40 ), which could infl uence atherogenesis.…”

Rapid turnover of apolipoprotein C-III-containing triglyceride-rich lipoproteins contributing to the formation of LDL subfractions

“…The strong correlation between apoC-III and risk of coronary heart disease among population studies (1-3) may be attributable to apoC-III's direct involvement in atherogenesis. We recently reported that apoC-III alone or as a component of VLDL and LDL stimulates the adhesion of monocytes to vascular endothelial cells (29)(30)(31). ApoC-III activates b1-integrin in human monocytic cells and vascular cell adhesion molecule-1 and intercellular cell adhesion molecule-1 in endothelial cells.…”

“…First, the apoB concentration of TRLs that have apoC-III is an exceptionally strong risk factor for cardiovascular disease, eclipsing the effect of plasma triglyceride (3). Second, we recently demonstrated that apoC-III by itself and as a component of TRL and LDL is directly involved in atherogenesis by activating adhesion molecules in monocytes and endothelial cells and by activating proinflammatory nuclear factor-kB (29)(30)(31). For these reasons, we aim for better understanding of the mechanisms that produce or sustain high concentrations of apoB lipoproteins with apoC-III.…”