Rabs and cancer cell motility.

The Rab family of small GTPases functions in regulating vesicular transport in all eukaryotes. In the past few years, several important reports have linked some members of the Rab family to intriguing mechanistic aspects of cancer cell migration and invasiveness. Rab5 and Rab21 associate with alpha-integrin subunits and modulate their endosomal traffic and subcellular localization. Expression of the latter enhances adhesion and migration of certain cancer cell types. Rab25 has been functionally linked to tumor progression and the invasiveness of some epithelial cancers. Rab25 promotes invasive migration of cells in three-dimensional microenvironments by associating with alpha5beta1 integrin, and directing its recycling to dynamic ruffling protrusions at the migrating cell front. Acting directly, or through its effector, the Rab-coupling protein, Rab25 could potentially engage both integrin and epidermal growth factor receptor and enhance their oncogenic recycling and signaling. Tumor invasiveness may also be modulated by Rab8-mediated exocytic traffic of MT1-matrix metalloproteinase, with the latter's activity likely influenced by interaction with the mammalian suppressor of Sec4 (Mss4), a Rab8 guanine nucleotide exchange factor, and integrin. We discuss highlights in the recent literature that point towards a role for Rab-mediated membrane traffic in cancer cell migration and invasion. (c) 2009 Wiley-Liss, Inc.