P120 catenin (p120ctn) is an adherens junction protein recognized to regulate barrier function, but emerging evidence indicates that p120ctn may also exert control on other cellular functions such as transcriptional suppression of genes. We investigated the hypothesis that loss of p120ctn in human endothelial cells activates transcription of pro-inflammatory adhesion molecules. For study, siRNA targeted to p120ctn was transfected into brain microvascular (HBMECs) or pulmonary artery endothelial cells (HPAECs) for 24-120h, which depleted 50-80% of endogenous p120ctn. This loss of p120ctn resulted in increased promoter reporter activity of transcription factors, NFκB, AP-1, and Kaiso, as well as of target genes, MMP-1 and ICAM-1. Real-time RT-PCR analysis indicated that the mRNA for ICAM-1, VCAM-1, and E- and P-selectins were all upregulated during the period of 24-120h of p120ctn depletion, although the time-course and extent of the expression profiles differed. The upregulated mRNA of adhesion molecules corresponded with increased PMN adhesion to the EC surface and elevated ICAM-1 protein expression. We further explored the role of ERK1/2 as a potential signaling mechanism responsible for regulation of transcriptional activities by p120ctn. Results indicated that loss of p120ctn increased phosphorylated ERK1/2, and a MEK1 inhibitor (PD98059) prevented NFκB nuclear translocation. This implicates ERK1/2 in signaling the NFκB activation induced by p120ctn loss. The findings provide strong evidence that deficiency in p120ctn expression in endothelial cells is a potent stimulus for transcriptional upregulation of multiple adhesion molecules. We conclude that p120ctn functions to suppress transcription, which is an important and novel regulation in vascular endothelium.
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