The MOE Key Laboratory of Biosystems Homeostasis & Protection and Zhejiang Provincial Key Laboratory of Cancer Molecular Cell Biology, Life Sciences Institute, Zhejiang University, Hangzhou, Zhejiang, 310058, China.
Center for Life Sciences, Shaoxing Institute, Zhejiang University, Shaoxing, Zhejiang, 321000, China.
Signal Transduct Target Ther. 2023 Mar 24;8(1):120. doi: 10.1038/s41392-023-01327-5.
Loss of TGF-β-mediated growth suppression is a major contributor to the development of cancers, best exemplified by loss-of-function mutations in genes encoding components of the TGF-β signaling pathway in colorectal and pancreatic cancers. Alternatively, gain-of-function oncogene mutations can also disrupt antiproliferative TGF-β signaling. However, the molecular mechanisms underlying oncogene-induced modulation of TGF-β signaling have not been extensively investigated. Here, we show that the oncogenic BCR-ABL1 of chronic myelogenous leukemia (CML) and the cellular ABL1 tyrosine kinases phosphorylate and inactivate Smad4 to block antiproliferative TGF-β signaling. Mechanistically, phosphorylation of Smad4 at Tyr195, Tyr301, and Tyr322 in the linker region interferes with its binding to the transcription co-activator p300/CBP, thereby blocking the ability of Smad4 to activate the expression of cyclin-dependent kinase (CDK) inhibitors and induce cell cycle arrest. In contrast, the inhibition of BCR-ABL1 kinase with Imatinib prevented Smad4 tyrosine phosphorylation and re-sensitized CML cells to TGF-β-induced antiproliferative and pro-apoptotic responses. Furthermore, expression of phosphorylation-site-mutated Y195F/Y301F/Y322F mutant of Smad4 in Smad4-null CML cells enhanced antiproliferative responses to TGF-β, whereas the phosphorylation-mimicking Y195E/Y301E/Y322E mutant interfered with TGF-β signaling and enhanced the in vivo growth of CML cells. These findings demonstrate the direct role of BCR-ABL1 tyrosine kinase in suppressing TGF-β signaling in CML and explain how Imatinib-targeted therapy restored beneficial TGF-β anti-growth responses.
TGF-β 介导的生长抑制丧失是癌症发展的主要原因，结直肠癌和胰腺癌中 TGF-β 信号通路成分的功能丧失性突变就是最好的例证。或者，致癌基因的获得性功能突变也可以破坏抗增殖 TGF-β 信号。然而，致癌基因诱导的 TGF-β 信号调节的分子机制尚未得到广泛研究。在这里，我们表明慢性髓性白血病 (CML) 的致癌 BCR-ABL1 和细胞 ABL1 酪氨酸激酶磷酸化并失活 Smad4，从而阻断抗增殖 TGF-β 信号。在机制上，连接区的 Smad4 Tyr195、Tyr301 和 Tyr322 位点的磷酸化干扰其与转录共激活因子 p300/CBP 的结合，从而阻断 Smad4 激活细胞周期蛋白依赖性激酶 (CDK) 抑制剂表达和诱导细胞周期停滞的能力。相比之下，用伊马替尼抑制 BCR-ABL1 激酶可防止 Smad4 酪氨酸磷酸化，并使 CML 细胞重新对 TGF-β 诱导的抗增殖和促凋亡反应敏感。此外，在 Smad4 缺失的 CML 细胞中表达磷酸化位点突变的 Y195F/Y301F/Y322F 突变型 Smad4 增强了对 TGF-β 的抗增殖反应，而磷酸化模拟的 Y195E/Y301E/Y322E 突变型则干扰了 TGF-β 信号并增强了 CML 细胞的体内生长。这些发现表明 BCR-ABL1 酪氨酸激酶在 CML 中直接抑制 TGF-β 信号，并解释了伊马替尼靶向治疗如何恢复有益的 TGF-β 抗生长反应。
