title: The 78 kDa glucose regulated protein (GRP78) as a potential treatment predictive biomarker and therapeutic target in colorectal cancer adjuvant chemotherapy
Creators: name: Thornton, Michael
Publisher: name: University of Liverpool Repository
Year: 2014

description: Introduction: Glucose-regulated protein 78-kDa (GRP78) is an endoplasmic reticulum (ER)-resident molecular chaperone that is essential for correct protein folding and assembly in the ER lumen. Micro-environmental stress and a requirement for increased protein synthesis, typical of solid tumours, leads to a disruption of ER homeostasis, and accumulation of misfolded proteins. The ability of GRP78 to dissociate from several important ER-resident transmembrane proteins under conditions of ER stress leads to a cascade of signal transduction pathways, known as the unfolded protein response (UPR), that modulate cell survival or, if the stress is significantly severe, apoptosis. GRP78 has been found to be overexpressed in a variety of cancers compared with benign tissue and has been associated with poor outcome. In-vitro data indicate that GRP78 expression is often associated with aggressive phenotype and drug resistance. Thus, GRP78 has potential as a biomarker for tumour behaviour and treatment response. For stage III colorectal cancer, there is overwhelming evidence to recommend the use of fluoropyrimidine-based adjuvant chemotherapy. Unfortunately, a large proportion of patients do not benefit from adjuvant chemotherapy, and biomarkers that can determine the likelihood of response to chemotherapy remain elusive. The benefit of chemotherapy in stage II disease is less certain and markers that could reliably predict benefit would be particularly useful in this population. This study explores a potential mechanistic relationship between GRP78 and 5-FU sensitivity using both siRNA transfection and treatment with an engineered fusion protein, epidermal growth factor (EGF)-SubA, which has been demonstrated to cause highly selective cleavage of GRP78 at a single amino acid point. It was then examined whether GRP78 may have prognostic or predictive value in the context of colorectal cancer patients treated with fluoropyrimidine-based chemotherapy. The potential therapeutic value of targeting GRP78 in vitro using EGF-SubA is also examined. Methods: Colon cancer cell lines were used to examine response to 5-FU upon modulation of endogenous GRP78 using siRNA technology and EGF-SubA. Apoptosis and cell cycle progression were assessed using flow cytometry. Immunohistochemistry was used to characterise GRP78 expression in a large cohort of colorectal cancers on tissue microarrays and the results were correlated with clinicopathological parameters and with 5-year survival for the whole cohort and those treated with fluoropyrimidine-based (5-FU) adjuvant chemotherapy. The action of EGF-SubA upon colon cancer cells was examined using western blotting, MTT assay and flow cytometry. Results: GRP78 promotes apoptosis in response to 5-FU. Better overall 5-year survival was associated with high GRP78 expression (P=0.036). Stage III patients with high GRP78 showed significant benefit from adjuvant chemotherapy (P=0.026), whereas patients with low GRP78 failed to benefit (P=0.805). Low GRP78 was an independent poor prognostic indicator of overall 5-year survival (P=0.005; HR=1.536; 95%CI 1.139-2.122). Colon cancer cells expressing EGFR were highly sensitive to EGF-SubA, demonstrating reduced proliferation and cell cycle arrest. However, EGF-SubA did not induce significant apoptosis and reduced the effectiveness of 5-FU in vitro. Conclusion: This study demonstrates a mechanistic relationship between GRP78 expression and response to 5-FU. GRP78 expression may provide a useful additional risk stratification to inform the adjuvant treatment of colorectal cancer. EGF-SubA does not have therapeutic value in colorectal cancer but is a useful tool for studying GRP78 and the UPR.