Dvorakova M, Kralova J, Karafiat V, Bartunek P, Dvorak M
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Flemingovon. 2, Prague 6, 166 37, Czech Republic.
Blood Cells Mol Dis. 2001 Mar-Apr;27(2):437-45. doi: 10.1006/bcmd.2001.0402.
The v-myb(AMV) oncogene transforms myelomonocytic cells in vitro and induces acute monoblastic leukemia in chickens. We analyzed the activity of the evolutionarily conserved PEST-like domain (P1 domain) for biochemical and biological activities of v-Myb in ex vivo cultures and in vivo. Deletion of the P1 domain did not affect v-Myb transcriptional activity, intracellular stability, or subcellular localization. However, it resulted in subtle yet important changes in biological activities. Although the mutant DeltaP1 v-Myb protein blocked the terminal differentiation of the monocyte/macrophage lineage as efficiently as the wild type (wt) in ex vivo cultures, it failed to induce the acute phase of monoblastic leukemia, with its fatal consequences, in vivo. Interestingly, in DeltaP1 v-myb-infected animals large numbers of monoblasts, comparable to those induced by wt v-myb, were present in the bone marrow but very few were found in the peripheral blood. The comparison of ex vivo wt- and DeltaP v-Myb bone marrow cells revealed several important features of v-Myb transformation: (i) the proliferation of transformed monoblasts is not an apparent consequence of the differentiation block with these processes being at least in part independent; (ii) the P1 domain is required for proliferation of v-Myb-mediated transformed monoblasts; (iii) the mechanism which renders transformed cells growth factor independent does not involve activation of an autocrine growth factor loop; and (iv) deletion of the P1 domain affects self-adhesion properties of v-myb-transformed monoblasts as well as their interaction with bone marrow stromal cells. These data indicate that the DeltaP1 v-myb mutant and ex vivo bone marrow cell cultures represent a valuable tool for studies on the mechanisms of leukemia formation.
v-myb（禽成髓细胞瘤病毒，AMV）癌基因在体外可转化骨髓单核细胞，并在鸡中诱发急性单核细胞白血病。我们分析了进化上保守的类PEST结构域（P1结构域）对v-Myb在体外培养和体内的生化及生物学活性的作用。缺失P1结构域并不影响v-Myb的转录活性、细胞内稳定性或亚细胞定位。然而，它导致了生物学活性的细微但重要的变化。尽管在体外培养中，突变型ΔP1 v-Myb蛋白阻断单核细胞/巨噬细胞谱系终末分化的效率与野生型（wt）相同，但在体内它未能诱发具有致命后果的急性单核细胞白血病期。有趣的是，在感染ΔP1 v-myb的动物中，骨髓中存在大量与wt v-myb诱导的数量相当的单核母细胞，但在外周血中却很少发现。对体外wt和ΔP v-Myb骨髓细胞的比较揭示了v-Myb转化的几个重要特征：（i）转化的单核母细胞的增殖不是分化阻滞的明显结果，这些过程至少部分是独立的；（ii）P1结构域是v-Myb介导的转化单核母细胞增殖所必需的；（iii）使转化细胞不依赖生长因子的机制不涉及自分泌生长因子环的激活；（iv）缺失P1结构域影响v-myb转化的单核母细胞的自黏附特性及其与骨髓基质细胞的相互作用。这些数据表明，ΔP1 v-myb突变体和体外骨髓细胞培养物是研究白血病形成机制的有价值工具。
