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AIM:To investigate whether KAI1,as a metastasis suppressor gene,is associated with invasive and metastatic ability of pancreatic cancer cells.METHODS:KAI1 gene was transfected into pancreatic cancer cell line MiaPaCa Ⅱ by liposomes selected with G418.Expression of transfected cells was measured by West blotting,immunofluorescence and immunocytochemistry.Tumor cell invasion and metastatic ability were detected through gelatinase activity and reconstituted basement membrane (Matrigel) assay,pCMV-KAI1 was directly injected into the heterotopic human pancreatic adenocarcinoma successfully established in the groin of BALB/C nude mice,by subcutaneous injection of MiaPaCa Ⅱ pancreatic cancer cells.The statistical analysis between groups was determined by Student’s two tailed t test.RESULTS:By West blotting,NiaPaCa Ⅱ cells transfected by KAI1 gene indicated KAI1 expression at approximately 29.1 kDa.Cytoplasm staining was positive and uniformly spread in transfected cancer cells,using immunohistochemistry and immunofluorescence.The most obvious difference was present after 30 h (MiaPaca Ⅱ43.6±9.42,pCMV-MiaPaca Ⅱ 44.8±8.56,pCMVKAI1-MiaPaca Ⅱ 22.0±4.69,P＜0.05).Gelatinolysisrevealed a wider and clearer band of gelatinolytic activity in non-transfected than in transfected cells (MiaPaCa Ⅱ cells 30.8±0.57,transfected cells 28.1±0.65,P＜0.05).In vivo tumor growth rates of KAI1 transfectants with KAI1-Lipofectamine 1.22±0.31 in A group were lower than control 4.61±1.98 and pCMV-KAI 11.67±0.81.Analyses of metastases with and without KAI1 transfection in mice were different in liver and lung between controls 1.62±0.39,0.45±0.09,pCMVKAI 1.01±0.27,0.33±0.09 and KAI1-Lipofectamine 0.99±0.21,0.30±0.09 respectively (P＜0.05).CONCLUSION:High expression of KAI1 gene was found in transfected MiaPaCa Ⅱ human pancreatic cancer cells with lower metastatic ability.KAI1 gene plays an important role in inhibiting metastasis of pancreatic cancer after direct injection into pancreatic adenocarcinoma.These results show that the suppressed invasion and motor function of pancreatic cancer cells may be a key reason why the KAI1 gene controls pancreatic cancer cell metastasis.