Submitted on February 18, 2008
Accepted on August 16, 2008
Lipid rafts mediate internalization of 
1 integrin in migrating intestinal epithelial cells
Elena V. Vassilieva1, Kirsten Gerner-Smidt1, Andrei I Ivanov2, and Asma Nusrat3*
1 Pathology and Lab. Medicine, Emory University, Atlanta, Georgia, United States
2 Medicine, The University of Rochester School of Medicine and Dentistry, Rochester, New York, United States
3 Pathology and Lab. Medicine, Emory University, Atlanta, Georgia, United States; Atlanta, Georgia, United States
* To whom correspondence should be addressed. E-mail: anusrat{at}emory.edu.
Intestinal mucosal inflammation is associated with epithelial wounds that rapidly reseal by migration of intestinal epithelial cells (IECs). Cell migration involves cycles of cell-matrix adhesion/de-adhesion that is mediated by dynamic turnover (assembly and disassembly) of integrin-based focal adhesions. Integrin endocytosis appears to be critical for de-adhesion of motile cells. However, mechanisms of integrin internalization during remodeling of focal adhesions of migrating IECs are not understood. This study was designed to define endocytic pathway that mediates internalization of beta1 integrin in migrating model IECs. We observed that in SK-CO15 and T84 colonic epithelial cells, beta1 integrin is internalized in a dynamin dependent manner. Pharmacological inhibition of clathrin-mediated endocytosis or macropinocytosis and siRNA-mediated knock-down of clathrin did not prevent beta1 integrin internalization. However, beta1 integrin internalization was inhibited following cholesterol extraction and after overexpression of lipid raft protein, caveolin-1. Furthermore, internalized beta1 integrin co-localized with a lipid rafts marker cholera toxin and siRNA mediated knock-down of caveolin-1 and flotillin-1/2 increased beta1 integrin endocytosis. Our data suggest that in migrating IEC beta1 integrin is internalized via a dynamin-dependent lipid-raft-mediated pathway. Such endocytosis is likely to be important for disassembly of integrin-based cell-matrix adhesions and therefore in regulating IEC migration and wound closure.
