Integrin {alphavbeta}6 sets the stage for colorectal cancer metastasis

The beta6 subunit of the alphavbeta6 integrin heterodimer has long been an enigma in cancer biology though recent research has provided many new insights into its biology. Collectively, these findings include discovery of the transcriptional, translational and cell biological mechanisms by which beta6 acts, the identification of the cellular influences beta6 exerts upon the cell proteome, the characterisation of multiple beta6-centric pro-metastatic signalling systems and the search for pharmacological therapies (industry and academia) targeted against beta6. Once expressional restriction is overcome in early colorectal cancer (CRC), epithelial cell surface restricted alphavbeta6 can physically interact with, and activate, known oncoproteins, and has the potential to enable the cross-talk through non-canonical signal transduction pathways, resulting in the adoption of an invasive/metastatic phenotype. This recent research has identified numerous interconnections and potential feedback loops, highlighting the fact that the expression of the beta6 subunit may initiate a cascade of downstream effects on the CRC cell rather than acting through a single mechanism. We here review these recent studies and postulate that the existence of a cell surface uPAR/alphavbeta6/TGFbeta metastasome interactome in/on a proportion of colorectal cancer cells, where beta6 expression sequesters and activates multiple systems at the invasive front of tumour lesions, promoting cancer metastasis and hence explaining why beta6 has been correlated with reduced patient survival in CRC.