上调c-myc基因的表达对U937白血病细胞的影响

Effects of up-regulation of c-myc expression on U937 cell line

目的:构建稳定表达外源c-myc基因的人单核细胞白血病细胞株U937,并初步分析其特性。方法:首先构建重组质粒MSCV-c-myc-IRES-GFP(MMIG)载体,分别用MMIG及空载体MSCV-IRES-GFP(MIG)包装病毒,并感染U937细胞,用流式细胞术分选绿色荧光细胞,获得U937/GFP和U937/MYC细胞,用荧光显微镜及流式细胞术检测GFP阳性率,用Western blotting测定细胞中c-Myc、survivin、X连锁凋亡抑制蛋白(XIAP)和Bcl-2的蛋白表达水平,流式细胞术检测U937/GFP和U937/MYC细胞周期,并用MTT法测定U937/GFP和U937/MYC细胞的生长情况,克隆形成实验检测克隆形成能力。结果:荧光显微镜观察,MIG和MMIG病毒感染后,2种细胞均表达绿色荧光蛋白;流式细胞术结果显示,MIG病毒感染的细胞荧光率为26.0%,MMIG病毒感染的细胞荧光率为27.7%;Western blotting的结果显示,c-Myc蛋白在MMIG病毒感染的细胞中表达水平升高。流式细胞术分选后,荧光显微镜观察可见绿色荧光蛋白表达明显增多,U937/GFP和U937/MYC细胞绿色荧光蛋白表达率分别达98.7%和93.7%。U937/MYC细胞中c-Myc蛋白表达较U937/GFP细胞显著升高,c-Myc蛋白下游的survivin表达增多,而凋亡相关蛋白XIAP及Bcl-2的表达则没有明显变化。细胞周期检测显示,U937/MYC细胞处于S期的细胞数增多。MTT实验结果显示,U937/MYC细胞的生长速率较U937/GFP细胞增快。U937/MYC细胞的克隆形成能力较U937/GFP细胞强。结论:成功构建了c-myc基因高表达的U937稳定细胞株U937/MYC。在U937/MYC细胞中,c-Myc及其下游的survivin表达明显上调,处于细胞周期S期的细胞数增多、细胞生长加快、克隆形成能力增强,提示c-Myc可能通过增强自我更新能力、加快细胞周期、促进相关抗凋亡蛋白表达从而提高细胞的存活率。

AIM： To establish a human monocytic leukemia cell line U937 stably expressing c-myc gene and to investigate the biological characteristics of this cell line. METHODS： The recombinant plasmid MSCV-c-myc-IRES-GFP （MMIG） was constructed. MMIG and MSCV-IRES-GFP （MIG） were used to package the viruses for infecting U937 cells. Fluorescence-activated cell sorter （FACS） was used for sorting U937/GFP and U937/MYC cells. The GFP-positive cells were detected by fluorescence microscopy and FACS. The protein expression of c-Myc, survivin, X-linked inhibitor of apoptosis protein （XIAP） and Bcl-2 was detected by Western blotting. Cell proliferation was evaluated by MTF assay. Propidium iodide （PI） staining was used to determine the cell cycle distribution. Self-renewal ability was observed by colony- forming assay. RESULTS： The GFP expression in the cells infected with MIG or MMIG virus was observed under fluorescence microscope. The green fluorescent rate of the cells infected with MIG was 26.0%, while that of the cells infected with MMIG was 27.7%. The protein expression of c-Myc in MMIG-infected U937 cells was higher than that in MIG-infected cells. After sorting, the green fluorescent rates of U937/GFP and U937/MYC ceils reached 98.7% and 93.7%, respectively. The protein expression of c-Myc in U937/MYC cells was higher than that in U937/GFP cells. In addition, survivin, a downstream protein of c-Myc, was up-regulated, while the protein expression of XIAP and Bcl-2 remained unchanged. Cell cycle analysis showed that the percentage of the cells in S phase increased in U937/MYC cells. Moreover, the proliferation and colony-forming ability of U937/MYC cells were also enhanced. CONCLUSION ： U937/MYC cell linestably expressing c-myc gene was successfully established, c-Myc may increase cell viability via enhancing the expression of anti-apoptotic protein survivin, the cell cycle transition and the self-renewal ability.