Date of Graduation
Doctor of Philosophy (PhD)
The regulation of integrin-mediated adhesion is of vital importance to adaptive and innate immunity. Integrins are versatile proteins and mediate T cell migration and trafficking by binding to ECM or other cells, as well as initiating intracellular signaling cascades promoting survival or activation. The mitogen activated-protein kinase (MAPK) pathway is known to be downstream from integrins and regulate survival, differentiation, and motility. However, secondary roles for canonical MAPK pathway members are being discovered. We show chemical inhibition of RAF by Sorafenib or shRNA-mediated knockdown of B-Raf reduces T cell resistance to shear stress to α4β1 integrin ligands vascular cell adhesion molecule-1 (VCAM-1) and fibronectin (FN), while inhibition of MEK/ERK by U0126 had no effect. Microscopy showed that RAF inhibition leads to significant inhibition of T cell spreading on VCAM-1. The association of α4β1 integrin with the actin cytoskeleton was shown to be dependent on B-Raf activity or expression, while α4β1 integrin affinity for soluble VCAM-1 was not. These effects were shown to be specific for α4β1 integrin, and not other integrins such as α5β1 or LFA-1, or a variety of membrane proteins. We demonstrate a novel role for B-Raf in the selective regulation of α4β1 integrin-mediated adhesion.
T cell, adhesion, MAPK, B-RAF, VCAM, fibronectin