Department of Biochemistry, Faculty of Pharmacy, Keio University, 1-5-30 Shibakoen, Minato-ku, Tokyo 105-8512, USA.
J Biol Chem. 2010 Feb 19;285(8):5296-307. doi: 10.1074/jbc.M109.040733. Epub 2009 Dec 22.
It has been well established that disruption of JAK2 signaling regulation is involved in various hematopoietic disorders; however, the detailed mechanism by which abnormal activation of JAK2 exhibits transforming activity remains to be elucidated. Here, to clarify the functional role of the erythropoietin receptor (EpoR) and its downstream transcription factor STAT5 in the abnormal activation of JAK2-induced hematopoietic diseases, we generated a stable transfectant of Ba/F3 cells expressing EpoR and analyzed the molecular mechanism of how JAK2 mutation induces cell growth disorder. JAK2 V617F mutant exhibited transforming activity when EpoR was coexpressed. According to a study utilizing several truncated mutants of EpoR, the ability of EpoR to facilitate the transforming activity of JAK2 V617F mutant required the intracellular domain to interact with STAT5. Strikingly, once the truncated EpoR (EpoR-H) was mutated on Tyr-343, the phosphorylation of which is known to be important for interaction with STAT5, JAK2 V617F mutant failed to exhibit transforming activity, suggesting that STAT5 is critical for JAK2 mutant-induced hematopoietic disorder. Furthermore, the expression of the constitutively active STAT5 mutant exhibited transforming activity in Ba/F3 cells, and short hairpin RNA-mediated knockdown of STAT5 significantly inhibited the transforming activity of JAK2 V617F mutant. Taking these observations together, STAT5 plays an essential role in EpoR-JAK2 V617F mutant-induced hematopoietic disorder. Although it remains unclear why the presence of EpoR is required to activate oncogenic signaling via the JAK2 mutant and STAT5, its interacting ability is a target for the treatment of these hematopoietic diseases.
已经证实，JAK2 信号转导调节的破坏与各种造血系统紊乱有关；然而，异常激活的 JAK2 表现出转化活性的详细机制仍有待阐明。在这里，为了阐明促红细胞生成素受体（EpoR）及其下游转录因子 STAT5 在 JAK2 异常激活诱导的造血疾病中的功能作用，我们生成了表达 EpoR 的 Ba/F3 细胞的稳定转染子，并分析了 JAK2 突变如何诱导细胞生长紊乱的分子机制。当共表达 EpoR 时，JAK2 V617F 突变体表现出转化活性。根据对 EpoR 的几种截断突变体的研究，EpoR 促进 JAK2 V617F 突变体转化活性的能力需要其胞内域与 STAT5 相互作用。引人注目的是，一旦截短的 EpoR（EpoR-H）上 Tyr-343 发生突变，该突变对于与 STAT5 的相互作用很重要，JAK2 V617F 突变体就无法表现出转化活性，这表明 STAT5 对于 JAK2 突变体诱导的造血紊乱至关重要。此外，组成性激活的 STAT5 突变体的表达在 Ba/F3 细胞中表现出转化活性，而短发夹 RNA 介导的 STAT5 敲低显著抑制了 JAK2 V617F 突变体的转化活性。综上所述，STAT5 在 EpoR-JAK2 V617F 突变体诱导的造血紊乱中发挥着重要作用。尽管目前尚不清楚为什么存在 EpoR 是通过 JAK2 突变体和 STAT5 激活致癌信号所必需的，但它们的相互作用能力是治疗这些造血疾病的靶点。
