The Rho-specific Guanine Nucleotide Exchange Factor Dbs Regulates Breast Cancer Cell Migration

Zhuoming Liu,Homer C Adams,Ian P Whitehead

doi:10.1074/jbc.m901853200

Zhuoming Liu, Homer C Adams + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m901853200

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Abstract

Dbs is a Rho-specific guanine nucleotide exchange factor (RhoGEF) that regulates neurotrophin-3-induced cell migration in Schwann cells. Here we report that Dbs regulates cell motility in tumor-derived, human breast epithelial cells through activation of Cdc42 and Rac1. Cdc42 and Rac1 are activated in T47D cells that stably express onco- or proto-Dbs, and activation is dependent upon growth of the cells on collagen I. Transient suppression of expression of Cdc42 or Rac1 by small interfering RNAs attenuates Dbs-enhanced motility. Both onco- and proto-Dbs-enhanced motility correlates with an increase in tyrosine phosphorylation of focal adhesion kinase on Tyr-397 and p130(Cas) on Tyr-410 and an increase in the abundance of the Crk.p130(Cas) complex. Suppression of expression of Cdc42 or its effector, Ack1, reduces tyrosine phosphorylation of focal adhesion kinase and p130(Cas) and disrupts the Crk.p130(Cas) complex. We further determined that suppression of expression of Cdc42, Ack1, p130(Cas), or Crk reduces Rac1 activation and cell motility in Dbs-expressing cells to a level comparable with that in vector cells. Therefore, a cascade of activation of Cdc42 and Rac1 by Dbs through the Cdc42 effector Ack1 and the Crk.p130(Cas) complex is established. Suppression of the expression of endogenous Dbs reduces cell motility in both T47D cells and MDA-MB-231 cells, which correlates with the down-regulation of Cdc42 activity. This suggests that Dbs activates Cdc42 in these two human breast cancer cell lines and that the normal function of Dbs may be required to support cell movement.

Highlights

Rho GTPases are a subfamily of the Ras superfamily of small signaling molecules that are widely expressed in mammalian cells [1]
When expressed in murine fibroblasts, the transforming and catalytic activity of Dbs is subject to autoinhibition that is mediated by the NH2terminal Sec14 domain [15]
The endogenous function of Dbs is not known, recent studies suggest that Dbs and the Rac-specific exchange factor Tiam1 regulate neurotrophinstimulated cell migration in Schwann cells through activation of Cdc42 and Rac1, respectively [16, 17]

Summary

Introduction

Rho GTPases are a subfamily of the Ras superfamily of small signaling molecules that are widely expressed in mammalian cells [1]. When plated on poly-L-lysine, no differences were observed in RhoAGTP, Cdc42-GTP, or Rac1-GTP levels in the cell lines that stably express onco-Dbs, proto-Dbs, or vector (Fig. 2, A and B).

Results

Conclusion