2093

Nucleostemin (NS) is abundantly expressed while the cells are proliferating in an early multipotential state, but abruptly and almost entirely disappears at the start of differentiation and prior to cell-cycle exit. NS protein has been considered a kind of specific regulatory factor that across G2/M checkpoint. However, up to now no research has been done in the area of the association between NS gene and acute leukemia. In the present study, the expression of NS in human leukemic cells was evaluated by RT-PCR, immunocytochemistry and Western blot. NS-specific short hairpin RNA(NS-shRNA)was synthesized and transfected into the leukemia cell lines HL-60, then changes of cell-cycle, apoptosis as well as differentiation were analyzed by Flow cytometry (FCM), and myeloperoxidase (MPO) and α-naphthol acetate esterase (α-NAE) were detected. In vivo test the HL-60 cells transfected or non-transfected by NS-shRNA were inoculated into nude rats, then differences such as neoplasm forming, NS expression, apoptosis in tumor tissues were observed. The results revealed that high level of NS mRNA and protein was expressed in leukemic cells. The expression of NS gene was downregulated by NS-shRNA which resulted in the inhibition of HL-60 cells in the G2/M phase, the induction of apoptosis, as well as the induction of differentiation in HL-60 cells; moreover the enzyme activity of MPO and α-NAE were enhanced in HL-60 cells after transfection. In animal model the neoplasm volumes and weights from the nude rats inoculated by HL-60 cells transfected were lower than controls. NS protein expression from tumor tissues of the treatment group was remarkably reduced. Typical morphology characters of apoptosis such as apoptotic bodies were observed, Tunel test showed the apoptotic cells increased significantly. These findings presented that NS is overexpressed in leukemic cells, it play an important role in cell proliferation, differentiation and apoptosis which illustrate a potential molecular target for the therapy of leukemia.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA