B53
Loss of protein folding gene expression in human tumours
Ern Yu Tan1, Leticia Campo1, Helen Turley1, Cheng Han2, Kevin Gatter1, Francesco Pezzella1
1Nuffield Department of Clinical Laboratory Sciences, Oxford, UK, 2CR-UK Molecular Oncology Laboratory, Oxford, UK, 3Tan Tock Seng Hospital, Singapore
Background
Tumour Necrosis Factor Receptor Associated Protein 1 (TRAP1) was noted to be downregulated in lung and pancreatic neuroendocrine tumours. TRAP1 is a molecular chaperone of the tumour suppressor Retinoblastoma (Rb), enhancing its regulation of G1/S transition. Loss of TRAP1 function may represent a novel oncogenic pathway in which inactivation of a tumour suppressor gene occurs as a result of the loss of its chaperone. We therefore aim to evaluate TRAP1 expression in solid tumours, and its effect on cell proliferation.
Method
TRAP1 expression was evaluated in a series of tumours using immunohistochemistry. The interaction between Rb and E2F1 and changes in the S phase fraction on flow cytometry were examined following TRAP1 silencing and over-expression. TRAP1 localisation was examined using immunofluorescence and cellular fractionation. Experiments were conducted in normoxia as well as in hypoxia (0.1% oxygen).
Results
Loss of TRAP1 expression was observed in a significant proportion of solid tumours. In breast tumours, nuclear TRAP1 expression was positively correlated with Rb expression (P < 0.0001), and was associated with poor prognostic factors and a shorter disease-free survival (P = 0.01). TRAP1 silencing attenuated Rb-E2F1 interaction in hypoxia and inhibited hypoxia-induced G1 arrest. The converse was observed following restoration of TRAP1 expression in TRAP1-deficient MDA231 breast carcinoma cells. TRAP1 was observed to translocate into the nucleus following hypoxic stress. Inhibition of this nuclear translocation resulted in reduced TRAP1 interaction with Rb, and consequently reduced Rb interaction with E2F1.
Conclusion
TRAP1 appears to modulate tumour behaviour by regulating cell cycle progression in hypoxia. TRAP1 loss was associated poor prognostic factors and a poorer clinical outcome in breast carcinoma, suggesting that TRAP1 may be have a significant role in the evolution of a more aggressive phenotype.
