Oral Presentation 14th International Biennial Conference on Metastasis Research 2012

The role of molecular chaperones in metastasis (#24)

Cara Lomas 1 , Marissa Powers 1 , Paul Workman 1 , Sue Eccles 1
  1. The Institute of Cancer Research, London, United Kingdom

Molecular chaperones are essential for the function of multiple ‘client’ proteins, particularly oncoproteins.  Adverse tumour microenvironmental conditions (e.g. hypoxia, glycolytic metabolism), have been linked to chaperone activation, metastasis and drug resistance.

Highly metastatic MDA-MB-231 and MDA-MB-435 cells were profiled for chaperone expression and response to inhibitors. HSP90, HSP70, GRP78 and GRP94 were abundant, whilst small chaperones (HSP27 and αB crystallin) were variable.   Chaperone inhibitors 17-AAG or NVP-AUY922 differentially affected cellular functions. MDA-MB-231 proliferation was relatively resistant to 17-AAG (due to low DT-diaphorase levels) but was sensitive to NVP-AUY922.  MDA-MB-231 chemotaxis was inhibited by both compounds, and reduced in hypoxia. Basal HSP27 was minimal, but robustly induced following HSP90 inhibition and in hypoxia.

MDA-MB-435 cell proliferation was sensitive to 17-AAG and NVP-AUY922 although chemotaxis was unaffected; furthermore, hypoxia enhanced chemotaxis. HSP27 was again up-regulated by HSP90 inhibition and hypoxia. αB crystallin was higher in a metastatic sublines and further induced by HSP90 inhibition and hypoxia. Interestingly, both HSP27 and αβ crystallin were also induced by 3D spheroid culture and this was again associated with reduced response to chaperone inhibitors. Thus upregulation of small (ATP-independent) chaperones under certain conditions may reduce the efficacy of HSP90 inhibitors. MDA-MB-231 orthotopic xenografts responded to 17-AAG, but bone metastases did not. The reduced sensitivity of bone metastases (or indeed growth enhancement according to some reports) may be due to the hypoxic nature of the marrow microenvironment.

Stress-inducible chaperones were explored further as potential confounders of response to inhibitors in 3D and under hypoxia. Stable knockdown of GRP78 or 94 by shRNA had no discernable phenotypic effects in vitro or in vivo. However, since knockdown induced compensatory reciprocal induction, dual depletion is required. Overall, it is clear that chaperones constitute a highly interdependent survival system allowing tumour cells to successfully achieve metastasis and circumvent therapeutic inhibition.