Inflammation and tumor progression: a lesson from TNF-alpha-dependent FAK signaling in cholangiocarcinoma

Abstract

Focal Adhesion Kinase (FAK) is implicated in a wide array of cellular processes and also involved in the production of matrix metalloproteinases (MMPs) which degrade extracellular matrix (ECM). We have shown that FAK plays a critical role in MMP-9 production and subsequent invasion of the cholangiocarcinoma activated by an inflammatory cytokine, TNF-alpha. By nature, cholangiocarcinoma is frequently associated with hepatolithiasis that causes recurrent inflammation. As degradation of the ECM is a prerequisite step for the invasion and metastasis of cancer cells, we used an assay of gelatin-degrading MMPs by Zymography to clarify the characteristic feature of the matrix degrading systems of the cancer cells. Immunoprecipitation and western blot analysis together with site specific phosphorylated FAK antibodies showed aberrant FAK activity in inflammation-mediated tumor cells. Confocal immunofluorescence staining could confirm not only localization but also phosphotyrosine contents of phosphorylated FAK by TNF-alpha stimulation. Destruction or penetration of the basement membrane is thought to be an essential step in successful metastasis by tumor cells, we used a matrix of basement membrane which was reconstituted on to a filter in the Boyden Chamber and assayed the ability of cancer cells to penetrate through matrigel-coated filter. We demonstrated the effectiveness of FAK siRNA treatment to prevent tumor invasion. Our observations suggested the importance of FAK as a therapeutic target for malignant neoplasm.