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...

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The reaction of cytidine with hydrazine to give N4-aminocytidine was greatly promoted by addition of a less-than-stoichiometric amount of bisulfite, and the product was isolated in a good yield. N4-Aminocytidine was strongly mutagenic to bacteria (Salmonella typhimurium TA100 and TA1535, and E. coli WP2 uvrA) and to phage (phi X174 am3). The activity did not require the presence of mammalian microsomal fraction in the system. The mutagenic potency of N4-aminocytidine in these systems was two orders of magnitude greater than that of N4-amino-2'-deoxycytidine, and more than two orders of magnitude greater than that of N4-hydroxycytidine. The greater activity of the riboside than the deoxyriboside was ascribed to the lack of deoxycytidine kinase in these cells. This compound may be useful as a powerful mutagen to induce a transition mutation in microorganisms.