Activation of Akt and ERK signalling pathways induced by etoposide confer chemoresistance in gastric cancer cells.
OBJECTIVE
To identify whether phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular-regulated protein kinases signalling pathways are implicated in the chemoresistance of gastric cancer and to explore the possible mechanisms.


METHODS
Gastric cancer cell lines SGC7901 and BGC823 were exposed to etoposide, Wortmannin+etoposide or PD98059+etoposide. Cell cycle distribution and cell apoptosis were detected using flow cytometry and Hoechst 33258 staining. Cells viability was determined by a colourimetric assay utilising 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). Akt activity was detected using non-radioactive immunoprecipitation-kinase assay. Western blotting was exploited to evaluate the level of phosphorylated ERK1/2 and expressions of c-Myc and p53 protein.


RESULTS
Etoposide suppressed the viability of SGC7901 and BGC823 cells in a time- and dose-dependent manner; PD98059 and Wortmannin were able to enhance the cytotoxicity of etoposide. The apoptotic levels of cells treated with Wortmannin+etoposide or PD98059+etoposide were significantly higher than those of cells treated with etoposide only. Phospho-ERK1/2, Akt activity and expression of c-Myc were significantly induced by etoposide in a time-dependent manner; moreover, there was a weak effect on the expression of p53 protein. Both Wortmannin and PD98059 elevated the level of p53 expression strikingly, however, only PD98059 suppressed the up-regulation trend of c-Myc expression induced by etoposide.


CONCLUSIONS
Chemotherapy reagent activated phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular-regulated protein kinases signalling pathways, which decreased the chemotherapy sensitivity of gastric cancer cell lines SGC7901 and BGC823 via suppressing the expression of p53 and enhancing the expression of c-Myc. This may be one of the molecular mechanisms of gastric cancer chemoresistance.
Liu
S-Q
SQ
Department of Gastroenterology, Renmin Hospital of Wuhan University, Jiefang Road 238, Wuhan 430060, China.
Yu
J-P
JP
Yu
H-G
HG
Lv
P
P
Chen
H-l
HL
D000730:Androstadienes / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D013274:Stomach Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000077191:Wortmannin
D000730:Androstadienes; D000972:Antineoplastic Agents, Phytogenic; D005047:Etoposide; D048049:Extracellular Signal-Regulated MAP Kinases; D005419:Flavonoids; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; D000077191:Wortmannin; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one