Thesis (Ph.D.)--Chulalongkorn University, 2004

Arsenic exposure is associated with an increased risk of atherosclerosis and vascular diseases. While endothelial cells have long been considered to be the primary targets of arsenic toxicity, the underlying molecular mechanism remain largely unknown. This study was conducted to examine the signaling pathway triggered by sodium arsenite and its implication(s) on endothelial phenotype change. Human umbilical vein endothelial cell (HUVEC) was used as a model system for this study. We found that sodium arsenite produced time- and dose-dependent on viability of HUVECs. This effect correlated with an induction of p21[superscript Waf1/Cip1], a regulatory protein of cell cycle and apoptosis. Sodium arsenite-stimulated ErbB1 and ErbB2 receptor transactivation manifested as receptor tyrosine phosphorylation appeared to be a proximal signaling event leading to p21[superscript Waf1/Cip1] induction. Since both pharmacological receptor kinase inhibitors (AG1478 and AG825) as well as knockdown of the receptors by SiRNA blocked arsenite-induced the p21[superscript Waf1/Cip1] upregulation. The activation of these receptors culminated in a specific activation of the JNK pathway. Although arsenite increased both JNK and p38 MAPK phosphorylation, the activation of these two stress kinases was distinct, with only JNK as a downstream target of the ErbB1 receptor. Moreover, inhibition of JNK with SP600125 or dominant-negative MKK7 inhibited only p21[superscript Waf1/Cip1] induction, whereas the p38 MAPK inhibitor SB203580 or dominant-negative MKK4 inhibited both p21[superscript Waf1/Cip1] and p53 induction. Functionally, inhibition of p21[superscript Waf1/Cip1] induction prevented endothelial death due to arsenite treatment. Insofar as endothelial dysfunction promotes vascular diseases, these data provide a mechanism of sodium arsenite-mediated the diseases and p21[superscript Waf1/Cip1] may represent an attractive target to ameliorate endothelial dysfunction in vascular diseases.