c-Myc-induced chemosensitization is mediated by suppression of cyclin D1 expression and nuclear factor-kappa B activity in pancreatic cancer cells.
OBJECTIVE
Pancreatic cancer is a highly aggressive disease that remains refractory to various chemotherapeutic agents. Because the proto-oncogene c-myc can modulate apoptosis in response to cytotoxic insults and is commonly overexpressed in pancreatic cancer, we investigated the value of c-myc as a potential modulator of cellular response to various chemotherapeutic agents.


METHODS
Stable overexpression or small interfering RNA (siRNA)-mediated knockdown of c-myc and restoration of cyclin D1 were done in the Ela-myc pancreatic tumor cell line. Cell viability after cisplatin treatment of c-myc-overexpressing, control, and siRNA-transfected cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and drug-induced apoptosis was measured by DNA fragmentation, sub-G(1), and poly(ADP-ribose) polymerase cleavage analyses. Protein expression profile after cisplatin treatment was determined by Western blotting and DNA binding activity of nuclear factor-kappaB was examined by electrophoretic mobility shift assay.


RESULTS
Ectopic overexpression of c-myc in murine and human pancreatic cancer cell lines, Ela-myc and L3.6pl, respectively, resulted in increased sensitivity to cisplatin and other chemotherapeutic drugs. Increased sensitivity to cisplatin in c-myc-overexpressing cells was due, in part, to the marked increase in cisplatin-induced apoptosis. Conversely, down-regulation of c-myc expression in stable c-myc-overexpressing cells by c-myc siRNA resulted in decreased sensitivity to cisplatin-induced cell death. These results indicate an important role of c-myc in chemosensitivity of pancreatic cancer cells. The c-myc-induced cisplatin sensitivity correlated with inhibition of nuclear factor kappaB activity, which was partially restored by ectopic cyclin D1 overexpression.


CONCLUSIONS
Our results suggest that the c-myc-dependent sensitization to chemotherapy-induced apoptosis involves suppression of cyclin D1 expression and nuclear factor kappaB activity.
Biliran
Hector
H
Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan, USA.
Banerjee
Sanjeev
S
Thakur
Archana
A
Sarkar
Fazlul H
FH
Bollig
Aliccia
A
Ahmed
Fakhara
F
Wu
Jiusheng
J
Sun
Yuan
Y
Liao
Joshua D
JD
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D019938:Cyclin D1 / Q000037:antagonists & inhibitors*; D053938:DNA Fragmentation; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D006801:Humans; D051379:Mice; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics
D000970:Antineoplastic Agents; C000715470:MAS1 protein, human; D016328:NF-kappa B; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D019938:Cyclin D1; D002945:Cisplatin