Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, Nine Cambridge Center, Cambridge, MA 02142, USA.
Haematologica. 2012 Nov;97(11):1713-21. doi: 10.3324/haematol.2011.061515. Epub 2012 Jun 11.
We previously described a t(2;11)(p21;q23) chromosomal translocation found in patients with myelodysplasia or acute myeloid leukemia that leads to over-expression of the microRNA miR-125b, and we showed that transplantation of mice with murine stem/progenitor cells overexpressing miR-125b is able to induce leukemia. In this study, we investigated the mechanism of myeloid transformation by miR-125b.
To investigate the consequences of miR-125b over-expression on myeloid differentiation, apoptosis and proliferation, we used the NB4 and HL60 human promyelocytic cell lines and the 32Dclone3 murine promyelocytic cell line. To test whether miR-125b is able to transform myeloid cells, we used the non-tumorigenic and interleukin-3-dependent 32Dclone3 cell line over-expressing miR-125b, in xenograft experiments in nude mice and in conditions of interleukin-3 deprivation. To identify new miR-125b targets, we compared, by RNA-sequencing, the transcriptome of cell lines that do or do not over-express miR-125b.
We showed that miR-125b over-expression blocks apoptosis and myeloid differentiation and enhances proliferation in both species. More importantly, we demonstrated that miR-125b is able to transform the 32Dclone3 cell line by conferring growth independence from interleukin-3; xenograft experiments showed that these cells form tumors in nude mice. Using RNA-sequencing and quantitative real-time polymerase chain reaction experiments, we identified multiple miR-125b targets. We demonstrated that ABTB1, an anti-proliferative factor, is a new direct target of miR-125b and we confirmed that CBFB, a transcription factor involved in hematopoiesis, is also targeted by miR-125b. MiR-125b controls apoptosis by down-regulating genes involved in the p53 pathway including BAK1 and TP53INP1.
This study demonstrates that in a myeloid context, miR-125b is an oncomiR able to transform cell lines. miR-125b blocks myeloid differentiation in part by targeting CBFB, blocks apoptosis through down-regulation of multiple genes involved in the p53 pathway, and confers a proliferative advantage to human and mouse myeloid cell lines in part by targeting ABTB1.
我们之前描述了一种在骨髓增生异常或急性髓系白血病患者中发现的 t(2;11)(p21;q23)染色体易位，该易位导致 microRNA miR-125b 过表达，并且我们表明过表达 miR-125b 的小鼠干细胞/祖细胞移植能够诱导白血病。在这项研究中，我们研究了 miR-125b 导致髓系转化的机制。
为了研究 miR-125b 过表达对髓系分化、凋亡和增殖的影响，我们使用了 NB4 和 HL60 人早幼粒细胞白血病细胞系和 32Dclone3 鼠早幼粒细胞白血病细胞系。为了测试 miR-125b 是否能够转化髓系细胞，我们使用非肿瘤性和依赖白细胞介素-3 的 32Dclone3 细胞系过表达 miR-125b，在裸鼠异种移植实验中和白细胞介素-3 剥夺条件下进行实验。为了鉴定新的 miR-125b 靶标，我们通过 RNA-seq 比较了过表达和不过表达 miR-125b 的细胞系的转录组。
我们表明 miR-125b 过表达在两种物种中均阻断凋亡和髓系分化并增强增殖。更重要的是，我们证明 miR-125b 通过赋予 32Dclone3 细胞系对白细胞介素-3 的生长独立性而能够转化该细胞系；异种移植实验表明这些细胞在裸鼠中形成肿瘤。通过 RNA-seq 和定量实时聚合酶链反应实验，我们鉴定了多个 miR-125b 靶标。我们表明，ABTB1，一种抗增殖因子，是 miR-125b 的新的直接靶标，并且我们证实，CBFB，一种参与造血的转录因子，也是 miR-125b 的靶标。miR-125b 通过下调参与 p53 途径的基因如 BAK1 和 TP53INP1 来控制凋亡。
这项研究表明，在髓系背景下，miR-125b 是一种能够转化细胞系的致癌 miRNA。miR-125b 通过靶向 CBFB 在一定程度上阻断髓系分化，通过下调多个参与 p53 途径的基因来阻断凋亡，并通过靶向 ABETB1 为人类和小鼠髓系细胞系赋予增殖优势。
