Suppression of 6A8 alpha-mannosidase gene expression reduced the potentiality of growth and metastasis of human nasopharyngeal carcinoma.

Suppression of alpha-mannosidases by chemicals has been shown to reduce the potentiality of growth and metastasis of various tumors. In our study, the effect of 6A8 alpha-mannosidase (MAN 6A8), recently discovered in our laboratory, on malignant behaviors of tumor cells was examined. Since the suppressive effect of chemicals on alpha-mannosidase is not specific, antisense technique was used to specifically inhibit expression of the MAN 6A8 in human nasopharyngeal carcinoma cells, CNE-2L2. Two cell clones, AS1 and AS2, with pronounced suppression of MAN 6A8 expression were developed. Wild-type (W), mock-transduced (M) and irrelevant DNA-transduced (IR) CNE-2L2 cells with normal expression of the enzyme were used as controls. Malignant behaviors of the cells were examined. Significant inhibition of growth of AS cells in vitro measured by MTT assay, colony formation and anchorage-independent colony formation was found. Pronounced inhibition of formation of tumors from AS cells inoculated into nude mice and metastasis was also observed. W, M and IR cells cultured in plate wells appeared dispersed with a fibroblastic or epithelial morphology, whereas AS cells were in compact sheets with an epithelioid organization. Since E-cadherin is the key factor in homophilic adhesion of epithelial cells, its expression on the surface of CNE-2L2 cells was determined. E-cadherin expression on AS cells was enhanced, whereas it was markedly diminished on W, M and IR cells. In addition, lamellipodia, which play an important role in cell spreading and mobility, almost disappeared on AS cells. The results demonstrate a significant suppressive effect of reduced expression of MAN 6A8 on malignant behaviors of CNE-2L2 cells.