A cutting-edge approach unravels a novel role for CDK6 in leukemic progenitor cells

CDK6 induces a complex transcriptional program to block p53 in hematopoietic cells. CDK6 binds to the promoters of genes including p53-antagonists. Cells lacking CDK6 kinase function are required to mutate p53 to achieve a fully transformed immortalized state. Studies of molecular mechanisms of hematopoiesis and leukemogenesis are hampered by the unavailability of progenitor cell lines that accurately mimic the situation in vivo. We now report a robust method to generate and maintain LSK (lin-, Sca-1+, c-Kit+) cells which closely resemble MPP1 cells. HPCLSK reconstitute hematopoiesis in lethally irradiated recipient mice over more than eight months. Upon transformation with different oncogenes including BCR/ABL, FLT3-ITD or MLL-AF9 their leukemic counterparts maintain stem cell properties in vitro and recapitulate leukemia formation in vivo. The method to generate HPCLSK can be applied to transgenic mice and we illustrate it for CDK6-deficient animals. Upon BCR/ABLp210 transformation, Cdk6-/- HPCLSKs induce disease with a significantly enhanced latency and reduced incidence, showing the importance of CDK6 in leukemia formation. Studies of the CDK6 transcriptome in murine HPCLSK and human BCR/ABL+ cells have verified that certain pathways depend on CDK6 and have uncovered a novel CDK6-dependent signature, suggesting a role for CDK6 in leukemic progenitor cell homing. Loss of CDK6 may thus lead to a defect in homing. The HPCLSK system represents a unique tool for combined in vitro and in vivo studies and enables the production of large quantities of genetically modifiable hematopoietic or leukemic stem/progenitor cells.

细胞周期蛋白依赖性激酶6（CDK6）可诱导复杂的转录程序，在造血细胞中阻断p53（肿瘤蛋白53）。CDK6可结合包括p53拮抗剂在内的基因启动子区域。缺失CDK6激酶功能的细胞，必须发生p53突变才能达到完全转化的永生化状态。由于缺乏能够精准模拟体内生理状态的祖细胞系，造血作用与白血病发生的分子机制研究长期受阻。本研究现已报道一种稳健的方法，可稳定生成并维持LSK（谱系阴性、Sca-1阳性、c-Kit阳性）细胞，这类细胞与MPP1（多能祖细胞1）高度相似。LSK型造血祖细胞（HPCLSK）可在受致死剂量辐射的受体小鼠体内重建造血功能，且维持时长超过8个月。当用包括BCR/ABL、FLT3-ITD及MLL-AF9在内的不同癌基因转化后，其白血病转化子代细胞可在体外维持干细胞特性，并在体内重现白血病发生过程。该LSK型造血祖细胞的构建方法可应用于转基因小鼠，本研究以CDK6缺陷型小鼠为例进行了演示。经BCR/ABLp210转化后，Cdk6基因敲除的HPCLSK细胞所诱导的疾病，其潜伏期显著延长且发病率降低，这证实了CDK6在白血病发生中的重要作用。对小鼠HPCLSK细胞及人类BCR/ABL阳性细胞的CDK6转录组研究证实，部分信号通路依赖于CDK6，并发现了一种全新的CDK6依赖性基因特征，提示CDK6在白血病祖细胞归巢过程中发挥作用。因此，CDK6的缺失可能导致归巢功能缺陷。LSK型造血祖细胞系统是一款可同时用于体外与体内研究的独特工具，能够批量制备可进行遗传修饰的造血干细胞/祖细胞或白血病干细胞/祖细胞。