Regulation of cell–matrix contacts and β-catenin signaling in VSMC by integrin-linked kinase: implications for intimal thickening
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Vascular smooth muscle cell (VSMC) proliferation and migration is responsible for intimal thickening that occurs in restenosis and atherosclerosis. Integrin-linked kinase (ILK) is a serine/threonine protein kinase implicated in signaling pathways involved in cell proliferation and migration. We studied the involvement of ILK in intimal thickening. ILK expression was significantly increased in two models of intimal thickening: balloon-injured rat carotid arteries and human saphenous vein organ cultures. Over-expression of a dominant negative ILK (DN-ILK) significantly reduced intimal thickening by approximately 50% in human saphenous vein organ cultures, demonstrating an important role in intimal thickening. ILK protein and activity was reduced on laminin and up-regulated on fibronectin, indicating ILK protein expression is modulated by extracellular matrix composition. Inhibition of ILK by siRNA knockdown and DN-ILK significantly decreased VSMC proliferation and migration while wild type ILK significantly increased proliferation and migration on laminin, confirming an essential role of ILK in both processes. Localization of paxillin and vinculin and protein levels of FAK and phospho-FAK indicated that inhibition of ILK reduced focal adhesion formation. Additionally, inhibition of ILK significantly attenuated the presence of the cell–cell complex proteins N-cadherin and β-catenin, and β-catenin signaling. We therefore suggest ILK modulates VSMC proliferation and migration at least in part by acting as a molecular scaffold in focal adhesions as well as modulating the stability of cell–cell contact proteins and β-catenin signaling. In summary, ILK plays an important role in intimal thickening by modulating VSMC proliferation and migration via regulation of cell–matrix and cell–cell contacts and β-catenin signaling.
Key wordssmooth muscle intimal thickening cell signaling focal adhesions cadherins
We gratefully acknowledge the gift of wild-type and DN-ILK cDNA from Professor Shoukat Dedhar (Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada) and rat carotid arteries from Dr. Christopher L. Jackson (Bristol Heart Institute). We thank Dr. Jason Johnson and Jill Tarlton for their excellent technical assistance and the British Heart Foundation for funding this research.
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