1. ¹The Beatson Institute for Cancer Research, Cancer Research UK Beatson Laboratories, Glasgow, UK
2. ²ARIAD Pharmaceuticals, Cambridge, MA, USA

Correspondence: Dr MC Frame, The Beatson Institute for Cancer Research, Cancer Research UK Beatson Laboratories, Glasgow G61 1BD, UK. E-mail: m.frame@beatson.gla.ac.uk

³Current address: Advanced Science and Technology Laboratory, AstraZeneca R&D, Charnwood, Loughborough LE11 5RH, UK

Received 12 December 2005; Revised 24 February 2006; Accepted 2 March 2006; Published online 1 May 2006.

Abstract

Cancer cells can invade three-dimensional matrices by distinct mechanisms, recently defined by their dependence on extracellular proteases, including matrix metalloproteinases. Upon treatment with protease inhibitors, some tumour cells undergo a 'mesenchymal to amoeboid' transition that allows invasion in the absence of pericellular proteolysis and matrix degradation. We show here that in HT1080 cells, this transition is associated with weakened integrin-dependent adhesion, consistently reduced cell surface expression of the 21 integrin collagen receptor and impaired signalling downstream, as judged by reduced autophosphorylation of focal adhesion kinase (FAK). On examining cancer cells that use defined invasion strategies, we show that distinct from mesenchymal invasion, amoeboid invasion is independent of intracellular calpain 2 proteolytic activity that is usually needed for turnover of integrin-linked adhesions during two-dimensional planar migration. Moreover, an inhibitor of Rho/ROCK signalling, which specifically impairs amoeboid-like invasion, restores cell surface expression of 21 integrin, downstream FAK autophosphorylation and calpain 2 sensitivity – features of mesenchymal invasion. These findings link weakened integrin function to a lack of requirement for calpain 2-mediated integrin adhesion turnover during amoeboid invasion. In keeping with the need for integrin adhesion turnover, mesenchymal invasion is uniquely sensitive to Src inhibitors. Thus, the need for a major pathway that controls integrin adhesion turnover defines and distinguishes cancer cell invasion strategies.