Mantel C, Luo Z, Canfield J, Braun S, Deng C, Broxmeyer H E
Department of Medicine (Hematology/Oncology), Indiana University School of Medicine, Indianapolis 46202-5121, USA.
Blood. 1996 Nov 15;88(10):3710-9.
Steel factor (SLF) is a hematopoietic cytokine that synergizes with other growth factors to induce a greatly enhanced proliferative state of hematopoietic progenitor cells and factor-dependent cell lines. Even though the in vivo importance of SLF in the maintenance and responsiveness of stem and progenitor cells is well documented, the molecular mechanism involved in its synergistic effects are mainly unknown. Some factor-dependent myeloid cell lines respond to the synergistic proliferative effects of SLF plus other cytokines in a manner similar to that of normal myeloid progenitor cells from bone marrow and cord blood. We show here that SLF can synergize with granulocyte-macrophage colony-stimulating factor (GM-CSF) to induce an enhanced phosphorylation of the retinoblastoma gene product and a synergistic increase in the total intracellular protein level of the cyclin-dependent kinase inhibitor, p21cip-1, which is correlated with a simultaneous decrease in p27kip-1 in the human factor-dependent myeloid cell line, M07e. Moreover, these cytokines synergize to increase p21cip-1 binding and decrease p27kip-1 binding to cyclin-dependent kinase-2 (cdk2), an enzyme required for normal cell cycle progression; these inverse events correlated with increased cdk2 kinase activity. It is also shown that exogenous purified p21cip-1 can displace p27kip-1 already bound to cdk2 in vitro. These data implicate increased p21cip-1 and decreased p27kip-1 intracellular concentrations and their stoichiometric interplay in the enhanced proliferative status of cells stimulated by the combination of SLF and GM-CSF. In support of these findings, it is shown that hematopoietic progenitor cells from mice lacking p21cip-1 are defective in SLF synergistic proliferative response in vitro. Moreover, the cycling status of marrow and spleen progenitors and absolute numbers of marrow progenitors were significantly decreased in the p21cip-1 -/-, compared with the +/+ mice. We conclude that the cdk threshold regulators p21cip-1 and p27kip-1 play a critical role in the normal mitogenic response of M07e cells and murine myeloid progenitor cells to these cytokines and particularly in the SLF synergistic proliferative response that is important to the normal maintenance of the stem/progenitor cell compartment.
Steel因子（SLF）是一种造血细胞因子，它与其他生长因子协同作用，诱导造血祖细胞和因子依赖性细胞系进入增殖状态显著增强的状态。尽管SLF在体内对干细胞和祖细胞的维持及反应性的重要性已有充分记录，但其协同作用所涉及的分子机制仍主要未知。一些因子依赖性髓系细胞系对SLF与其他细胞因子的协同增殖作用的反应方式，类似于来自骨髓和脐血的正常髓系祖细胞。我们在此表明，SLF可与粒细胞 - 巨噬细胞集落刺激因子（GM - CSF）协同作用，诱导视网膜母细胞瘤基因产物的磷酸化增强，以及细胞周期蛋白依赖性激酶抑制剂p21cip - 1的细胞内总蛋白水平协同增加，这与人类因子依赖性髓系细胞系M07e中p27kip - 1的同时减少相关。此外，这些细胞因子协同作用，增加p21cip - 1与细胞周期蛋白依赖性激酶2（cdk2）的结合，并减少p27kip - 1与cdk2的结合，cdk2是正常细胞周期进程所需的一种酶；这些相反的事件与cdk2激酶活性增加相关。还表明，外源性纯化的p21cip - 1在体外可取代已与cdk2结合的p27kip - 1。这些数据表明，p21cip - 1增加和p27kip - 1细胞内浓度降低及其化学计量相互作用，参与了由SLF和GM - CSF联合刺激的细胞增殖增强状态。为支持这些发现，表明缺乏p21cip - 1的小鼠的造血祖细胞在体外对SLF协同增殖反应存在缺陷。此外，与 +/+ 小鼠相比，p21cip - 1 -/- 小鼠骨髓和脾脏祖细胞的循环状态以及骨髓祖细胞的绝对数量显著降低。我们得出结论，cdk阈值调节因子p21cip - 1和p27kip - 1在M07e细胞和小鼠髓系祖细胞对这些细胞因子的正常促有丝分裂反应中起关键作用，特别是在对干细胞/祖细胞区室的正常维持很重要的SLF协同增殖反应中。
