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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:562.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

FXR Promotes Endothelial Cell Motility Through Coordinated Regulation of FAK and MMP-9

Amitava Das; Usman Yaqoob; Dolly Mehta; Vijay H. Shah

From the Gastroenterology Research Unit and Fiterman Center for Digestive Diseases (A.D., U.Y., V.H.S.), the Department of Internal Medicine (A.D., V.H.S.), Physiology and Cancer Cell Biology Program (V.H.S.), Mayo Clinic, Rochester, Minn; and the Department of Pharmacology (D.M.), University of Illinois, Chicago.

Correspondence to Amitava Das, PhD, Mayo Clinic, 200 First St SW, Rochester, MN 55905. E-mail das.amitava{at}mayo.edu

Objective— Farnesoid X Receptor (FXR) mediates important signaling functions of bile acids in diverse cell types including those residing in the vascular wall. Indeed, recent work has identified FXR as a potential regulator of vascular structure and function in part through transcriptional activation of MMP-9. However, the signal transduction pathways linking bile acids to changes in actin cytoskeleton that are responsible for bile acid-induced vascular cell migration remain unexplored.

Methods and Results— The FXR agonist and prototypical bile acid, chenodeoxycholic acid (CDCA), significantly increased endothelial cell (EC) motility, as analyzed by time lapse video microscopy, and tube formation, an in vitro correlate for angiogenesis. Increased cell motility was associated with prominent increases in focal adhesion (FA) plaques and was inhibited by FXR or MMP-9 siRNA, indicating a FXR-MMP-9-dependency of this signaling pathway. Mechanistically, incubation of cells with CDCA was associated with phosphorylation of a key FA protein, Focal Adhesion Kinase (FAK) at Y397 but not at Y576/577, or Y925. Studies using a site-specific phosphorylation mutant (phosphodeficient) of FAK revealed that FAK phosphorylation at tyrosine residue –397 was required for CDCA induced activation of the downstream FA assembly protein, paxillin. Lastly, siRNA-based silencing of FAK as well as phosphodeficient FAK mutant inhibited CDCA induced upregulation of MMP-9, cell motility, and vascular tube formation.

Conclusion— Thus, this study demonstrates a pivotal role for FAK in the process of FXR-induced and MMP-9-dependent EC motility and vascular tube formation.

The signaling pathways linking bile acid receptor FXR and its transcriptional target MMP-9 to changes in actin cytoskeleton, responsible for EC migration remains unexplored. Here, using a variety of complementary cell biological and biochemical approaches, we demonstrate a key role for tyrosine phosphorylation of FAK at Y397 in the process of FXR-induced MMP-9-dependent endothelial cell motility and in vitro vascular tube formation.

Key Words: bile acids • FXR • MMP-9 • FAK • angiogenesis