Polyamine dependent activation of Dbl Restores Migration via Rho‐GTPases

Abstract

Extracellular matrix (ECM) activated Rho GTPases, Src, and focal adhesion kinase in intestinal epithelial cells (IEC-6). Rac1, RhoA, and Cdc42 are required for optimal epithelial cell migration. Although, polyamine-depletion inhibited activities of Rho GTPases, Rac1 activation was sufficient for migration in the absence of polyamines due to its ability to activate RhoA and Cdc42 as well as its own effects on the process of cell migration indicating that polyamines are involved in a process upstream of Rac1. In this study, we examined the role of polyamines in the regulation of the guanine nucleotide exchange factor, Dbl, for Rho GTPases. Polyamine depletion decreased the level as well as the activation of Dbl protein. Dbl SiRNA altered cytoskeletal structure, decreased Rac1 activity and migration. Cells expressing constitutively active Dbl (CA-Dbl) increased migration, Rac1 activity, and proliferation. CA-Dbl restored migration in polyamine-depleted cells by activating RhoA, Rac1, and Cdc42. CA-Dbl caused extensive reorganization of the F-actin cortex into stress fibers. Dbl localized in the perinuclear region in polyamine-depleted cells, while it localized with the stress fibers in control cells. CA-Dbl localized with stress fibers in both the control and polyamine-depleted cells. These results suggest that polyamines regulate the activation of Dbl, a membrane proximal process upstream of Rac1. Supported by NIDDK grant DK-052784.