MECHANISMS OF TRANSFORMATION OF MURINE HEMATOPOIETIC CELLS BY ME26 VIRUS

小鼠模型系统用于确定含有逆转录病毒的 核癌基因可以转化造血细胞。MYB-ETS- 包含ME26的病毒编码一个135kD的Gag-MYB-ETS融合蛋白 可以与DNA结合。该病毒导致小鼠白血病的高发病率 并能诱导造血祖细胞在体外生长 促红细胞生成素(EPO)。病毒转化蛋白 先前被证明可以转录激活红系特异的 转录因子GATA-1，然后与GATA-1协同 反式激活EPO受体(EPOR)基因的蛋白质。使用 可选择的ME26病毒，我们研究了病毒的时间变化 ME26病毒激活红系基因前后的表达 这些细胞在只含有EPO的培养基上生长。GATA-1和EPOR 在细胞生长之前，基因被发现被病毒激活。 在EPO中，尽管这些基因的表达水平很高 细胞在促红细胞生成素中生长后升高。相比之下，珠蛋白基因 在感染ME26病毒的细胞中，直到细胞 已经在促红细胞生成素中生长了几天。其他红系的表现 包括核因子-E2、SPI-1和ID在内的基因没有被ME26病毒改变 感染。这表明EPO信号转导的组成部分 途径可能与ME26病毒蛋白协同增强 某些红系特异性基因的表达。构成表达 然而，EPOR基因的缺失抑制了GATA-1和珠蛋白的病毒激活 基因，这表明细胞表达结构性高水平的 EPOR基因表达抑制物或所需辅因子的限制量 来激活这些基因。GATA-基因缺失突变体的分析 1启动子在瞬时反式激活试验中表明ME26 病毒蛋白结合在病毒5‘端的391bp区域。 推动者。ME26病毒蛋白不同于c-病毒编码的蛋白。 MYB基因不阻断化学诱导的小鼠分化 红白血病细胞系。

Mouse model systems are used to determine how retroviruses containing nuclear oncogenes can transform hematopoietic cells. The myb-ets- containing ME26 virus encodes a 135 kD gag-myb-ets fusion protein that can bind to DNA. The virus causes a high incidence of leukemia in mice and can induce hematopoietic precursor cells to grow in vitro on the erythroid hormone erythropoietin (Epo). The viral transforming protein was previously shown to transcriptionally activate an erythroid-specific transcription factor, GATA-1, and then to cooperate with the GATA-1 protein to transactivate the Epo receptor (EpoR) gene. Using a selectable ME26 virus, we have examined the temporal changes in the expression of erythroid genes activated by ME26 virus before and after the cells are grown on medium containing only Epo. Both GATA-1 and EpoR genes were found to be activated by the virus before the cells were grown in Epo, although the level of expression of these genes was greatly elevated after the cells had been grown in Epo. In contrast, globin gene expression was not activated in ME26 virus-infected cells until the cells had been grown in Epo for several days. Expression of other erythroid genes, including NF-E2, Spi-1 and Id, were not altered by ME26 virus infection. This suggests that components of the Epo signal transduction pathway may cooperate with the ME26 viral protein to enhance the expression of certain erythroid-specific genes. Constitutive expression of the EpoR gene, however, inhibits viral activation of GATA-1 and globin genes, suggesting that cells expressing constitutively high levels of the EpoR gene express an inhibitor or limiting amounts of a co-factor needed for activation of these genes. Analysis of deletion mutants of the GATA- 1 promoter in transient transactivation assays indicates that the ME26 viral protein is binding to a 391 bp region in the 5' half of the promoter. The ME26 viral protein, unlike the protein encoded by the c- myb gene, does not block chemical-induced differentiation of mouse erythroleukemia cell lines.