Activation and clinical significance of the unfolded protein response in breast cancer.
BACKGROUND
The tumour microenvironment is hypoglycaemic, hypoxic and acidotic. This activates a stress signalling pathway: the unfolded protein response (UPR). The UPR is cytoprotective if the stressor is mild, but may initiate apoptosis if severe.Activation of the UPR in breast carcinoma is induced by microenvironmental stress such as glucose and oxygen deprivation, but may also be linked to oestrogen stimulation. It may be clinically significant as it may alter chemosensitivity to doxorubicin.


METHODS
395 human breast adenocarcinomas were immunohistochemically stained for UPR activation markers (glucose-regulated protein (GRP-78 and XBP-1). A model of UPR activation in vitro by glucose deprivation of T47D breast cancer cells was developed to determine how the UPR affects cellular sensitivity to doxorubicin and 5-fluorouracil. Cytotoxicity was assessed using a colorimetric cytotoxicity assay (MTT). The effect of oestrogen stimulation and tamoxifen exposure on UPR activation by T47D cells was determined by western blotting measurement of the key UPR protein, GRP-78.


RESULTS
Expression of GRP78 and XBP-1 was demonstrated in 76% and 90% of the breast cancers, respectively, and correlated with oestrogen receptor positivity (P=0.045 and 0.017, respectively). In vitro UPR activation induced resistance to both doxorubicin and 5-flurouracil, (P<0.05). Oestrogen stimulation induced GRP78 and XBP1 over-expression on western blotting. Tamoxifen did not block this response and may induce UPR activation in its own right.


CONCLUSIONS
The UPR is activated in the majority of breast cancers and confers resistance to chemotherapy. In vitro oestrogen stimulates UPR induction. UPR activation may contribute to breast cancer chemoresistance and interact with oestrogen response elements.
Academic Unit of Surgical Oncology, Department of Oncology, School of Medicine, Dentistry and Health, University of Sheffield, Beech Hill Road, Sheffield S10 2JP, UK.
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P
Scriven
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S
Coulson
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R
Haines
S
S
Balasubramanian
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S
Cross
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L
Wyld
D000230:Adenocarcinoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D000091342:Endoplasmic Reticulum Chaperone BiP; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D005260:Female; D005947:Glucose / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D013629:Tamoxifen / Q000494:pharmacology; D056811:Unfolded Protein Response
D000091342:Endoplasmic Reticulum Chaperone BiP; D020847:Estrogen Receptor Modulators; C000717247:HSPA5 protein, human; D013629:Tamoxifen; D005947:Glucose