Background: The results of our previous studies have proven that nm23-H1 gene can suppress metastasis of lung cancer, which may be associated with suppression of the Wnt signal pathway through up-regulating the activity of glycogen synthase kinase 3β (GSK-3β), the key kinase of the Wnt signal pathway. The aim of this study is to investigate the effect of point mutation of nm23-H1 gene on GSK-3β activity in cytoplasm and nucleus in human high-metastatic large cell lung cancer cell line L9981.
Methods: Using immunoprecipitation and a radioactive isotope scintillation counter, the activity of GSK-3β was detected in cytoplasm and nucleus of human low-metastatic large cell lung cancer cell line NL9980, human high-metastatic large cell lung cancer cell line L9981, L9981-pEGFP (transfected with vector), L9981-nm23-H1-pEGFP (transfected with wild type nm23-H1), L9981-nm23-H1 S44A -pEGFP mutant (transfected with serine 44 to alanineon of nm23-H1 gene), L9981-nm23-H1 P96S -pEGFP mutant (transfected with proline 96 to serine of nm23-H1 gene), L9981-nm23-H1 H118F -pEGFP mutant (transfected with histidine 118 to phenylalanine of nm23-H1 gene) and L9981-nm23-H1 S120G -pEGFP mutant (transfected with serine 120 to glycine of nm23-H1 gene).
Results: The GSK-3β activity in cytoplasm and nucleus was remarkably decreased in the transgene lung cancer cell lines transfected with mutant nm23-H1 cDNA (L9981-nm23-H1 S44A -pEGFP, L9981-nm23-H1 P96S -pEGFP, L9981-nm23-H1 H118F -pEGFP and L9981-nm23-H1 S120G -pEGFP). Significant differences of GSK-3β activity in cytoplasm and nucleus were observed (P < 0.05) when L9981-nm23-H1-pEGFP cell line was compared with L9981-nm23-H1 S44A -pEGFP, L9981-nm23-H1 P96S -pEGFP, L9981-nm23-H1 H118F -pEGFP and L9981-nm23-H1 S120G -pEGFP lung cancer cell lines. There was a highly significant difference in GSK-3β activity in the cytoplasm between L9981-nm23-H1-pEGFP cell line and L9981-nm23-H1 P96S -pEGFP lung cancer cell line (P < 0.01 ). A highly significant difference in GSK-3β activity in the nucleus was observed (P < 0.01) when L9981-nm23-H1-pEGFP lung cancer cell line was compared with L9981-nm23-H1 S44A -pEGFP, L9981-nm23-H1 P96S -pEGFP and L9981-nm23-H1 H118F -pEGFP lung cancer cell lines.
Conclusions: (1) Point mutation of nm23-H1 gene can significantly influence the regulating effects on the GSK-3β activity in the cytoplasm and nucleus in the human high-metastatic large cell lung cancer cell line L9981. (2) The effects of nm23-H1 gene on metastatic phenotype may be related to the upregulation of GSK-3β activity in human high-metastatic large cell lung cancer cell line L9981.