FXR promotes endothelial cell motility through coordinated regulation of FAK and MMP-9.
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.


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.


CONCLUSIONS
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.
Das
Amitava
A
Department of Internal Medicine, Mayo Clinic, Rochester, MN 55905, USA. das.amitava@mayo.edu
Yaqoob
Usman
U
Mehta
Dolly
D
Shah
Vijay H
VH
D045744:Cell Line, Tumor; D002465:Cell Movement; D002478:Cells, Cultured; D002635:Chenodeoxycholic Acid / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D042783:Endothelial Cells / Q000201:enzymology*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D020780:Matrix Metalloproteinase 9 / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D018919:Neovascularization, Physiologic; D051419:Paxillin / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D014443:Tyrosine; D000099150:Receptor, Farnesoid X-Activated
D002635:Chenodeoxycholic Acid; D004268:DNA-Binding Proteins; D051417:Focal Adhesion Kinase 1; D020780:Matrix Metalloproteinase 9; D051419:Paxillin; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D014443:Tyrosine; D000099150:Receptor, Farnesoid X-Activated; C496061:PXN protein, human; C496050:PTK2 protein, human