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J. Biol. Chem., Vol. 283, Issue 3, 1282-1292, January 18, 2008

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Homocysteine Induces Monocyte Chemoattractant Protein-1 Expression in Hepatocytes Mediated via Activator Protein-1 Activation^*

From the Departments of Animal Science and Physiology, University of Manitoba, Canadian Centre for Agri-Food Research in Health and Medicine, St. Boniface Hospital Research Centre, Winnipeg R2H 2A6, Canada

Hyperhomocysteinemia is characterized by abnormally high concentrations of homocysteine (Hcy) in the plasma. It is a metabolic disorder associated with dysfunction of several organs such as atherosclerosis, altered lipid metabolism, and liver injury. In this study we investigated the effect of Hcy on transcriptional regulation of monocyte chemoattractant protein-1 (MCP-1), a potent chemokine, expression in hepatocytes. Hyperhomocysteinemia was induced in rats by a high-methionine diet for 4 weeks. MCP-1 mRNA and protein levels were significantly elevated in the liver tissue homogenate and in hepatocytes of hyperhomocysteinemic rats. The role of transcription factors in MCP-1 expression was examined by electrophoretic mobility shift assay. Activation of activator protein (AP)-1 but not nuclear factor B was detected in the liver tissue of those rats. Incubation of rat hepatocytes with Hcy (50–200 µM) caused a significant increase in AP-1 activation followed by an increase in intracellular MCP-1 mRNA expression and an elevation of MCP-1 protein secreted into the culture medium. Hcy markedly increased the DNA binding activity of human recombinant AP-1 (c-Fos and c-Jun proteins). The presence of a sulfhydryl group in Hcy was essential for Hcy-induced AP-1 activation. When hepatocytes were transfected with decoy AP-1 oligodeoxynucleotide to inhibit AP-1 activation, Hcy-induced MCP-1 mRNA expression was abolished. Further analysis revealed that increased hepatic MCP-1 expression was positively correlated with the serum MCP-1 level. These results suggest that Hcy-induced MCP-1 expression in the liver is mediated via AP-1 activation, which may contribute to chronic inflammation associated with hyperhomocysteinemia.

Received for publication, September 20, 2007 , and in revised form, November 8, 2007.

^* This work was supported by an Operating grant from the Natural Sciences and Engineering Research Council of Canada, an Operating grant from the Heart and Stroke Foundation of Manitoba, an Operating grant from the Canadian Institutes of Health Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Laboratory of Integrative Biology, St. Boniface Hospital Research Centre, 351 Tache Ave., Winnipeg, Manitoba R2H 2A6, Canada. Tel.: 204-235-3951; Fax: 204-235-1151; E-mail: karmino{at}sbrc.ca.

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