Extracellular Hsp90 and TGFβ regulate adhesion, migration and anchorage independent growth in a paired colon cancer cell line model

Background: Tumour metastasis remains the major cause of death in cancer patients and, to date, the mechanism and signalling pathways governing this process are not completely understood. The TGF-beta pathway is the most commonly mutated pathway in cancer, however its role in cancer progression is controversial as it can function as both a promoter and a suppressor of metastasis. Although previous studies have suggested a role for the molecular chaperone Hsp90 in regulating the TGF-beta pathway, the level at which this occurs as well as the consequences in terms of colon cancer metastasis are unknown. Methods: The paired SW480 and SW620 colon cancer cell lines, derived from a primary tumour and its lymph node metastasis, respectively, were used as an in vitro model to study key cellular processes required for metastasis. The status of the TGF-beta pathway was examined in these cells using ELISA, flow cytometry, western blot analysis and confocal microscopy. Furthermore, the effect of addition or inhibition of the TGF-beta pathway and Hsp90 on adhesion, migration and anchorage-independent growth, was determined in the cell lines. Results: When comparing the canonical TGF-beta 1 pathway in the genetically paired cell lines our data suggests that this pathway may be constitutively active in the SW620 metastasis-derived cell line and not the SW480 primary tumourderived line. In addition, we report that, when present in combination, TGF-beta 1 and Hsp90 beta stimulate anchorageindependent growth, reduce adhesion and stimulate migration. This effect is potentiated by inhibition of the TGF-beta 1 receptor and occurs via an alternate TGF-beta 1 pathway, mediated by av beta 6 integrin. Interestingly, in the SW620 cells, activation of this alternate TGF-beta 1 signalling machinery does not appear to require inhibition of the canonical TGF-beta 1 receptor, which would allow them to respond more effectively to the pro-metastasis stimulus of a combination of Hsp90 beta and TGF-beta 1 and this could account for the increased migratory capacity of these cells. Conclusions: In this study we report an apparent synergy between TGF-beta 1 and Hsp90 beta in stimulating migratory behaviour of colon cancer cells when signalling occurs via av beta 6 integrin as opposed to the canonical TGF-beta 1 pathway.