Abstract: BACKGROUND ＆ AIM: To study the role of expression of Syk(Spleen tyrosine kinase) in the course of As2O3 induced brain tumor cell cycle defects. MATERIAL AND METHODS: To integrate syk gene into vector pIND and co_transfect tumor cell line U373 with mutated P53 gene together with regulator vector pVgRXR in order to induce the expression of Syk. The expression of cell cycle negative regulative factor P21 was measured by Western blot. The cell DNA content was assessed by FACS. The role of Syk's expression in As2 O3 inducing brain cell cycle defects was examined using the confocal laser scanning microscope system. RESULTS: U373 cells transfected with syk gene(U373 Syk_ind)could express Syk in the presence of inducing agent Pon A.As2O3 could make maintain U373 cells at G2/M stage,but the proportion was decreased when U373 expressed Syk.Syk could upregulate P21. CONCLUSION: As2O3 influenced brain tumor cell line U373 normal cycles,blocking them in G2/M stage.As2O3 could cause tumor cell apoptosis,while also inducing normal cells into tumor cells. The expression of Syk could decrease the proportion of blocked cells,so reducing the side_effects of As2O3 when used in treating cancer.

Key words: spleen tyrosine kinase, As2O3, cell cycle, cell apoptosis