Patel G, Tantravahi R, Oh I H, Reddy E P
The Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Oncogene. 1996 Sep 19;13(6):1197-208.
The myb gene has been shown to be an important regulator of hematopoietic cell proliferation, differentiation and apoptosis. Activation of the myb gene into an oncogenic form has involved structural alterations to the coding sequences. Thus, the v-myb gene encoded by the Avian Myeloblastosis Virus, is truncated at both the 5' and 3' ends. Additionally, tumor cells containing rearrangements in the myb locus, such as the ABPL tumors or NFS60 tumor cell line have recently been shown to display a heterogeneity of structure. In this study, we examined the growth and differentiation properties of clonal cell lines derived from 32Dcl3 which harbor myb transgenes; derived from v-myb, and the ABPL-1, ABPL-2, ABPL-4 and NFS-60 cell lines. Retroviral vectors containing the appropriate myb cDNAs were produced, transfected into packaging cell lines, and the viruses were used to generate the 32D derivative cell clones. Abrogation of IL-3 dependence was never observed in any cell line. Expression of c-myb, ABPL-1-myb and ABPL-2-myb isoforms in 32D cells resulted in a block to their ability to terminally differentiate into granulocytes at the pro-myelocytic stage. However, expression of ABPL-4-myb or NFS60-myb in these cells failed to result in a similar effect. These cells differentiated into granulocytes in the presence of G-CSF, albeit more slowly than control 32Dcl3 cells. We also examined the ability of various Myb-isoforms to transactivate transcription of reporter genes containing Myb-binding elements in their promoter/enhancer sequences, to determine whether the phenotypic effects produced by these various isoforms correlate with their ability to transactivate transcription. Our results show that while v-myb and c-myb transactivated transcription equally well, the NFS60-myb exhibited the highest levels of transcriptional transactivation. The ABPL-1, ABPL-2 and ABPL-4-myb isoforms showed very low levels of transcriptional transactivation potential with the same reporter genes. These results suggest that the ability of various Myb-isoforms to transactivate transcription does not by itself correlate with their ability to induce a block to G-CSF-induced terminal differentiation of myeloid precursor cells.
myb基因已被证明是造血细胞增殖、分化和凋亡的重要调节因子。myb基因激活为致癌形式涉及编码序列的结构改变。因此，禽成髓细胞瘤病毒编码的v-myb基因在5'和3'末端均被截断。此外，最近发现含有myb基因座重排的肿瘤细胞，如ABPL肿瘤或NFS60肿瘤细胞系，表现出结构异质性。在本研究中，我们检测了源自32Dcl3且携带myb转基因的克隆细胞系的生长和分化特性；这些克隆细胞系源自v-myb以及ABPL-1、ABPL-2、ABPL-4和NFS-60细胞系。构建了含有适当myb cDNA的逆转录病毒载体，转染到包装细胞系中，并用这些病毒生成32D衍生细胞克隆。在任何细胞系中均未观察到对IL-3依赖性的消除。32D细胞中c-myb、ABPL-1-myb和ABPL-2-myb异构体的表达导致它们在早幼粒细胞阶段终末分化为粒细胞的能力受阻。然而，这些细胞中ABPL-4-myb或NFS60-myb的表达并未产生类似效果。在G-CSF存在的情况下，这些细胞分化为粒细胞，尽管比对照32Dcl3细胞分化得更慢。我们还检测了各种Myb异构体在其启动子/增强子序列中反式激活含有Myb结合元件的报告基因转录的能力，以确定这些不同异构体产生的表型效应是否与其反式激活转录的能力相关。我们的结果表明，虽然v-myb和c-myb反式激活转录的效果相当，但NFS60-myb表现出最高水平的转录反式激活。ABPL-1、ABPL-2和ABPL-4-myb异构体对相同报告基因的转录反式激活潜力非常低。这些结果表明，各种Myb异构体反式激活转录的能力本身与其诱导髓系前体细胞对G-CSF诱导的终末分化产生阻滞的能力无关。
