1. ¹Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, UK
2. ²Cancer and Polio Research Fund Laboratories, School of Biological Sciences, University of Liverpool, Liverpool, UK

Correspondence: Dr MK El-Tanani, Centre for Cancer Research and Cell Biology, Queen's University of Belfast, 97 Lisburn Road, Belfast BT9 7LB, UK. E-mail: m.el-tanani@qub.ac.uk

Received 2 August 2007; Revised 11 July 2008; Accepted 30 July 2008; Published online 15 September 2008.

Abstract

Osteopontin (OPN) is a phosphorylated glycoprotein that binds to v-containing integrins and is important in malignant transformation and cancer. Previously, we have utilized suppressive subtractive hybridization between mRNAs isolated from the Rama 37 (R37) rat mammary cell line and a subclone rendered invasive and metastatic by stable transfection with an expression vector for OPN to identify RAN GTPase (RAN) as the most overexpressed gene, in addition to that of OPN. Here we show that transfection of noninvasive R37 cells with an expression vector for RAN resulted in increased anchorage-independent growth, cell attachment and invasion through Matrigel in vitro, and metastasis in syngeneic rats. This induction of a malignant phenotype was induced independently of the expression of OPN, and was reversed by specifically reducing the expression of RAN using small-interfering RNAs. By using a combination of mutant protein and inhibitors, it was found that RAN signal transduction occurred through the c-Met receptor and PI3 kinase. This study therefore identifies RAN as a novel effector of OPN-mediated malignant transformation and some of its downstream signaling events in a mammary epithelial model of cancer invasion/metastasis.