Regulation of gene expression in erythropoiesis

小鼠红白血病(Mel)细胞的体外诱导分化是分析细胞分化过程中分子事件的一个很好的系统。我们发现，TSA8细胞是MEL细胞之一，在DMSO作用下，TSA8细胞对促红细胞生成素(EPO)有反应，并形成红系祖细胞的分化集落。在诱导过程中，EPO的表面受体的数量和亲和力没有变化，因此，细胞内诱导的因子是获得对EPO的反应性所必需的。两个独立因素的参与被证明是必需的，一个是在加入DMSO后立即出现的放线菌亚胺敏感因子，另一个是Na~+/H~+转运蛋白，它对任何氯衍生物敏感，出现在承诺的后期过程中。因此，承诺可能是由两个因素的顺序出现控制的，分析了EPO诱导的信号转导，结果表明cAMP途径主要参与EPO的作用。为了检测细胞癌基因在承诺过程中的参与，将甲硫蛋白启动子连接的c-myc基因导入MEL细胞，并分析了调控但过度生产的c-myc产物的作用。结果表明，c-myc的水平决定了MEL细胞分化的承诺概率，并且c-myc可能在组织特异性基因的承诺过程和表达时间上起着联系作用。

The induced differentiation of murine erythroleukemia(MEL) cells in vitro is a good system to analyze the molecular events underlining the commitment process of cell differentiation. We found that TSA8 cells, one of MEL cells were committed to respond to erythropoietin(epo) and to form the differentiated colonies of erythroid progenitor cells, when the cells were treated with DMSO. In the induced process, the surface receptors for epo did not change in their number and in their affinities, thus, the intracellular factors induced in the cells are required for the acquisition of responsiveness to epo. The involvement of two independent factors are shown to be required for the commitment; one is the cycloheximide-sensitive factor which appears just after the addition of DMSO, the other is the Na^+/H^+ transporter which is sensitive to anyloride derivatives and appears in the later process of commitment. Thus, the commitment may be controlled by the sequential appearance of two factors, The signal transduction induced by epo was analyzed and the results indicated that a cAMP pathway is mainly involved in the epo action.To examine the involvement of cellular onco genes in the commitment process, the methallothionein promoter-linked c-myc gene was introduced into MEL cells and the effect of the regulated, but over-produced c-myc products was analyzed. The results indicated that the level of c-myc determines the probability of commitment of differentiation of Mel cells, Furthermore, c-myc may function to link the commitment process and the timing of expression of tissue-specific genes.