Carcinogenesis Advance Access published online on October 8, 2008
Carcinogenesis, doi:10.1093/carcin/bgn220
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Glucose-Regulated Protein 78 Antagonizes Cisplatin and Adriamycin in Human Melanoma Cells
Immunology and Oncology Unit, Room 443, Newcastle Misericordiae Hospital, NSW, Australia
Address for Correspondence to: Dr. Peter Hersey or Dr. Xu Dong Zhang, Room 443, David Maddison Clinical Sciences Building, Cnr. King & Watt Streets, Newcastle, NSW 2300, Australia. Ph: 61 2 49 138174. Fax: 61 2 49138184. Email: Peter.Hersey{at}newcastle.edu.au or Xu.Zhang{at}newcastle.edu.au
Resistance of melanoma cells to chemotherapeutics remains a major obstacle to successful treatment of melanoma once it has spread beyond locoregional sites. We report in this study that activation of the unfolded protein response (UPR) is involved in resistance of melanoma cells to two chemotherapeutic drugs, cisplatin and adriamycin, and this is associated with glucose-regulated protein 78 (GRP78)-mediated inhibition of activation of caspase-4 and -7. The UPR was constitutively activated in cultured melanoma cell lines and fresh melanoma isolates as evidenced by elevated expression levels of the GRP78 protein and the active form of x-box-binding protein 1 (XBP1) mRNA. Treatment with cisplatin or adriamycin further increased the levels, indicative of induction of ER stress and activation of the UPR by the drugs. Inhibition of GRP78 by small interference RNA (siRNA) sensitized melanoma cells to cisplatin- and adriamycin-induced apoptosis. This was associated with enhanced caspase-4 and -7 activation as siRNA knockdown of the caspases blocked induction of apoptosis. In contrast, over-expression of GRP78 attenuated activation of caspase-4 and -7 and induction of apoptosis by the drugs. Cisplatin- and adriamycin-induced activation of caspase-4 and -7 appeared to be mediated by calpain activity in that it was blocked by the calpain inhibitors calpeptin and PD150606 even when GRP78 was inhibited by siRNA. These results provide new insights into resistance mechanisms of melanoma cells to cisplatin and adriamycin and identify GRP78 as a potential target for enhancing chemosensitivity in melanoma.
Key Words: Melanoma • GRP78 • the UPR • Apoptosis • Chemotherapy
This work was supported by the National Health and Medical Research Council, Australia. X.D. Zhang is a Cancer Institute NSW Fellow.
Received June 27, 2008; revised August 13, 2008; accepted September 12, 2008.