Bies J, Mukhopadhyaya R, Pierce J, Wolff L
Laboratory of Genetics, National Cancer Institute, Bethesda, Maryland 20892.
Cell Growth Differ. 1995 Jan;6(1):59-68.
In murine leukemia virus-induced myeloid leukemias, insertional mutagenesis of the c-myb locus has been shown to occur frequently. Proto-oncogene activation is achieved in most leukemias by integration of murine leukemia virus upstream of exons 3 or 4 or by integration into exon 9 with consequent truncation of the protein. The present study investigates the effect of ectopic expression of full-length c-myb or c-myb containing amino- or carboxyl-terminal truncations (minus 47 and 248 amino acids, respectively) on granulocyte differentiation in vitro. Recombinant myb retroviruses were used to infect an interleukin 3-dependent progenitor cell line, 32Dcl3, which undergoes terminal differentiation to mature neutrophilic granulocytes in the presence of granulocyte colony-stimulating factor. Overexpression of c-myb did not abrogate the interleukin 3 dependency of the parental cell line. However, cells expressing all forms of c-myb were blocked at an intermediate stage of granulocyte differentiation and continued to proliferate in the presence of granulocyte colony-stimulating factor. After 14 days in medium with granulocyte colony-stimulating factor, myb-expressing cultures predominantly consisted of promyelocytes with some myelocytes and almost undetectable numbers of neutrophilic granulocytes. This suggested that early stages of granulocyte differentiation were not inhibited, a finding that was further supported by the induction of myeloperoxidase, a biochemical marker of promyelocytes. Interestingly, the expression of lactoferrin, known to be a marker of late stages of granulocyte differentiation, was completely inhibited in the cells infected with myb viruses. It was concluded that c-myb expression blocked granulocyte differentiation to the terminal mitotic stages and that deletion of the NH2-terminal 47 amino acids and/or the COOH-terminal 248 amino acids of c-myb neither enhanced nor diminished this effect.
在鼠白血病病毒诱导的髓系白血病中，已显示c-myb基因座的插入诱变频繁发生。在大多数白血病中，原癌基因激活是通过鼠白血病病毒整合到外显子3或4上游，或整合到外显子9中，从而导致蛋白质截短来实现的。本研究调查了全长c-myb或含有氨基或羧基末端截短（分别缺失47和248个氨基酸）的c-myb异位表达对体外粒细胞分化的影响。重组myb逆转录病毒用于感染白细胞介素3依赖的祖细胞系32Dcl3，该细胞系在粒细胞集落刺激因子存在下会发生终末分化成为成熟的嗜中性粒细胞。c-myb的过表达并未消除亲代细胞系对白细胞介素3的依赖性。然而，表达所有形式c-myb的细胞在粒细胞分化的中间阶段被阻断，并在粒细胞集落刺激因子存在下继续增殖。在含有粒细胞集落刺激因子的培养基中培养14天后，表达myb的培养物主要由早幼粒细胞组成，还有一些中幼粒细胞，嗜中性粒细胞数量几乎检测不到。这表明粒细胞分化的早期阶段未受抑制，这一发现得到了髓过氧化物酶（早幼粒细胞的生化标志物）诱导的进一步支持。有趣的是，乳铁蛋白（已知是粒细胞分化后期的标志物）的表达在感染myb病毒的细胞中完全受到抑制。得出的结论是，c-myb的表达阻断了粒细胞向终末有丝分裂阶段的分化，并且c-myb氨基末端47个氨基酸和/或羧基末端248个氨基酸的缺失既未增强也未减弱这种作用。
