BACKGROUNDIt has been known that oncogenesis and development of lung can- cer is a complex process regulated many genes and involved in multistages. Recent studies have demonstrated that signal transduction abnormality may play a very important role in these procedures. The aim of this study is to investigate the influence of exogenous MEK1/2 pathway inhibitor U0126 on the expression and activity of extracellular signal-regulated kinase (ERK1/2) of human high-metastatic large cell lung cancer cell line L9981 and its malignant biological behaviors.

METHODSThe expressive levels of total-ERK1/2, dually phosphorylated ERK1/2 and ERK1/2 relative activity of the human high-metastatic large cell lung cancer cell line L9981 (parent cell line with nm23-H1 gene hetero-deletion ) were detected by Western blot and immuno-precipitation technique after treating with different doses of U0126. The in vitro proliferative and invasive abilities of the lung cancer cell line were determined by MTT and modified Boyden chamber methods.

RESULTSThe ERK1/2 relative activity of L9981 gradually decreased accompanied with increase of U0126 doses, and a highly significant difference of phosphorylated ERK1/2 expression level existed among the different concentration groups of U0126 (P < 0.01), but no significant difference of total ERK1/2 expression was found among the different concentration groups of U0126 (P=0.387). After treatment with same concentration of U0126 for different time, the ERK1/2 relative activity of L9981 gradually decreased as the treatment time of U0126 prolonging, and a highly significant difference of phosphorylated ERK1/2 expression level was observed among different treatment time groups (P < 0.01). But no significant difference of total ERK1/2 expression level was found among different time groups (P=0.689). The inhibition of ERK1/2 pathway by MEK1/2 specific inhibitor U0126 targeting the ERK1/2 pathway of L9981 was dose- and time-dependent. After treatment with different concentration of U0126, the proliferation of L9981 gradually decreased accompanied with increase of U0126 concentration and a highly significant difference existed among different groups of U0126 concentration (P < 0.001). The in vitro invasion of L9981 gradually decreased accompanied with increase of U0126 concentration. No significant difference of in vitro invasion of L9981 was found among 0, 10 and 20μmol/l of U0126 (P > 0.05). A highly significant difference was observed when U0126 concentration increased to 40 and 60μmol/l compared with 0, 10 and 20μmol/l of U0126 (P < 0.001).

CONCLUSIONSThe inhibition of Ras-to-MAPK pathway by Ras-to-MAPK specific inhibitor U0126 targeting the Ras-to-MAPK pathway of the human high-metastatic large cell lung cancer cell line L9981 is dose-dependent and time-dependent. Suppressing or blocking of Ras-to-MAPK signal transduction pathway can reverse the invasive and metastatic phenotype of the human high-metastatic large cell lung cancer cell line L9981. These results suggest that the key kinase MEK1/2 of the ERK1/2 pathway may be a potent therapeutic target for human lung cancer.