Sargin Bülent, Choudhary Chunaram, Crosetto Nicola, Schmidt Mirko H H, Grundler Rebekka, Rensinghoff Marion, Thiessen Christine, Tickenbrock Lara, Schwäble Joachim, Brandts Christian, August Benjamin, Koschmieder Steffen, Bandi Srinivasa Rao, Duyster Justus, Berdel Wolfgang E, Müller-Tidow Carsten, Dikic Ivan, Serve Hubert
Department of Medicine, Hematology and Oncology, and Interdisciplinary Center for Clinical Research, University Hospital Münster, Albert-Schweitzer-Strasse 33, 48129 Münster, Germany.
Blood. 2007 Aug 1;110(3):1004-12. doi: 10.1182/blood-2007-01-066076. Epub 2007 Apr 19.
In acute myeloid leukemia (AML), mutational activation of the receptor tyrosine kinase (RTK) Flt3 is frequently involved in leukemic transformation. However, little is known about a possible role of highly expressed wild-type Flt3 in AML. The proto-oncogene c-Cbl is an important regulator of RTK signaling, acting through its ubiquitin ligase activity and as a platform for several signaling adaptor molecules. Here, we analyzed the role of c-Cbl in Flt3 signal transduction and myeloid transformation. C-Cbl physically interacted with Flt3 and was tyrosine phosphorylated in the presence of Flt3-ligand (FL). Overexpression of a dominant-negative form of c-Cbl (Cbl-70Z) inhibited FL-induced Flt3 ubiquitylation and internalization, indicating involvement of c-Cbl in Flt3 signaling. DNA sequencing of AML bone marrow revealed a case with a c-Cbl point mutation (Cbl-R420Q). Cbl-R420Q inhibited Flt3 internalization and ubiquitylation. Coexpression of Cbl-R420Q or Cbl-70Z with Flt3 induced cytokine-independent growth and survival of 32Dcl3 cells in the absence of FL. Also, the mutant Cbl proteins altered the amplitude and duration of Flt3-dependent signaling events. Our results indicate an important role of Cbl proteins in Flt3 signal modulation. Also, the data suggest a novel mechanism of leukemic transformation in AML by mutational inactivation of negative RTK regulators.
在急性髓系白血病（AML）中，受体酪氨酸激酶（RTK）Flt3的突变激活常常参与白血病转化过程。然而，对于高表达野生型Flt3在AML中可能发挥的作用却知之甚少。原癌基因c-Cbl是RTK信号传导的重要调节因子，通过其泛素连接酶活性发挥作用，并作为几种信号衔接分子的平台。在此，我们分析了c-Cbl在Flt3信号转导和髓系转化中的作用。c-Cbl与Flt3发生物理相互作用，并在存在Flt3配体（FL）的情况下发生酪氨酸磷酸化。显性负性形式的c-Cbl（Cbl-70Z）的过表达抑制了FL诱导的Flt3泛素化和内化，表明c-Cbl参与Flt3信号传导。AML骨髓的DNA测序显示了一例c-Cbl点突变（Cbl-R420Q）的病例。Cbl-R420Q抑制了Flt3的内化和泛素化。Cbl-R420Q或Cbl-70Z与Flt3共表达在无FL的情况下诱导32Dcl3细胞的细胞因子非依赖性生长和存活。此外，突变的Cbl蛋白改变了Flt3依赖性信号事件的幅度和持续时间。我们的结果表明Cbl蛋白在Flt3信号调节中起重要作用。此外，数据提示了AML中通过RTK负调节因子的突变失活导致白血病转化的新机制。
