Wild-type Kras expands and exhausts hematopoietic stem cells.
Wild-type Kras expands and exhausts hematopoietic stem cells.
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野生型 Kras 会扩增并耗尽造血干细胞。
DOI：
10.1172/jci.insight.98197
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发表时间：
2018
期刊：
影响因子：
8
通讯作者：
Chute,JohnP
中科院分区：
文献类型：
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作者：
Sasine,JoshuaP;Himburg,HeatherA;Termini,ChristinaM;Roos,Martina;Tran,Evelyn;Zhao,Liman;Kan,Jenny;Li,Michelle;Zhang,Yurun;deBarros,StéphanieC;Rao,DineshS;Counter,ChristopherM;Chute,JohnP
致瘤性Kras在造血干细胞（HSC）中的特异性表达诱导小鼠快速致命的骨髓增生性肿瘤，表明Kras信号传导在正常造血中起主导作用。然而，这样的结论是基于Kras的致癌版本的表达。因此，我们试图确定简单地增加内源性野生型Kras的量对HSC命运的影响。为此，我们利用了我们开发的密码子优化版本的小鼠Kras基因（Krasex 3 op），其中外显子3中的沉默突变使编码的mRNA更有效地翻译，从而增加蛋白质表达而不破坏正常的基因结构。我们发现Krasex 3 op/ex 3 op小鼠骨髓（BM）HSC中的Kras蛋白水平显著增加，表明HSC中Kras的翻译通常受到稀有密码子的限制。Krasex 3 op/ex 3 op小鼠表现出BM HSC、祖细胞和B淋巴细胞的扩增，但在12个月的随访中没有小鼠骨髓增生性疾病或白血病的证据。来自Krasex 3 op/ex 3 op小鼠的BM HSC在初次竞争性移植试验中表现出增加的多谱系再生能力，但二次竞争性移植显示长期HSC的耗竭。全身照射后，Krasex 3 op/ex 3 op小鼠表现出加速的血液学恢复和增加的存活率。从机制上讲，Krasex 3 op/ex 3 op小鼠的HSC在基线时表现出增殖增加，Erk 1/2磷酸化和细胞周期蛋白依赖性激酶4和6（Cdk 4/6）活化相应增加。此外，Krasex 3 op/ex 3 op小鼠的HSC的增强的集落形成能力和体内重建能力都依赖于Cdk 4/6活化。最后，BM移植研究显示，增强的Kras表达以造血细胞自主的方式产生HSC、祖细胞和B细胞的扩增，而不依赖于对BM微环境的影响。本研究提供了哺乳动物中密码子使用具有生物学后果的基本证明，这可能说明密码子使用在哺乳动物生物学中的重要性。
Oncogenic Kras expression specifically in hematopoietic stem cells (HSCs) induces a rapidly fatal myeloproliferative neoplasm in mice, suggesting that Kras signaling plays a dominant role in normal hematopoiesis. However, such a conclusion is based on expression of an oncogenic version of Kras. Hence, we sought to determine the effect of simply increasing the amount of endogenous wild-type Kras on HSC fate. To this end, we utilized a codon-optimized version of the murine Kras gene (Krasex3op) that we developed, in which silent mutations in exon 3 render the encoded mRNA more efficiently translated, leading to increased protein expression without disruption to the normal gene architecture. We found that Kras protein levels were significantly increased in bone marrow (BM) HSCs in Krasex3op/ex3op mice, demonstrating that the translation of Kras in HSCs is normally constrained by rare codons. Krasex3op/ex3op mice displayed expansion of BM HSCs, progenitor cells, and B lymphocytes, but no evidence of myeloproliferative disease or leukemia in mice followed for 12 months. BM HSCs from Krasex3op/ex3op mice demonstrated increased multilineage repopulating capacity in primary competitive transplantation assays, but secondary competitive transplants revealed exhaustion of long-term HSCs. Following total body irradiation, Krasex3op/ex3op mice displayed accelerated hematologic recovery and increased survival. Mechanistically, HSCs from Krasex3op/ex3op mice demonstrated increased proliferation at baseline, with a corresponding increase in Erk1/2 phosphorylation and cyclin-dependent kinase 4 and 6 (Cdk4/6) activation. Furthermore, both the enhanced colony-forming capacity and in vivo repopulating capacity of HSCs from Krasex3op/ex3op mice were dependent on Cdk4/6 activation. Finally, BM transplantation studies revealed that augmented Kras expression produced expansion of HSCs, progenitor cells, and B cells in a hematopoietic cell–autonomous manner, independent from effects on the BM microenvironment. This study provides fundamental demonstration of codon usage in a mammal having a biological consequence, which may speak to the importance of codon usage in mammalian biology.