Schwäble Joachim, Choudhary Chunaram, Thiede Christian, Tickenbrock Lara, Sargin Bülent, Steur Claudia, Rehage Maike, Rudat Annika, Brandts Christian, Berdel Wolfgang E, Müller-Tidow Carsten, Serve Hubert
Department of Medicine, Hematology, and Oncology, and the Interdisciplinary Clinical Research Center (IZKF), University Hospital Münster, Albert-Schweitzer-Strasse 33, 48129 Münster, Germany.
Blood. 2005 Mar 1;105(5):2107-14. doi: 10.1182/blood-2004-03-0940. Epub 2004 Nov 9.
Activating fetal liver tyrosine kinase 3 (Flt3) mutations represent the most common genetic aberrations in acute myeloid leukemia (AML). Most commonly, they occur as internal tandem duplications in the juxtamembrane domain (Flt3-ITD) that transform myeloid cells in vitro and in vivo and that induce aberrant signaling and biologic functions. We identified RGS2, a regulator of G-protein signaling, as a gene specifically repressed by Flt3-ITD. Here we demonstrate an important role of RGS2 in Flt3-ITD-mediated transformation. RGS2 was repressed after forced expression of activating Flt3 mutations in 2 myeloid cell lines (32Dcl3 and NB4). Furthermore, RGS2 was repressed in Flt3-mutation-positive AML cases in comparison to Flt3-mutation-negative cases, especially in Flt3-ITD-positive cases with a high ITD-to-wild-type (WT) ratio. Coexpression of RGS2 with Flt3-ITD inhibited Flt3-ITD-induced autonomous proliferation and clonal growth of 32D cells. RGS2 also inhibited Flt3-ITD-induced phosphorylation of Akt and glycogen synthase kinase beta (Gsk3-beta) without influencing signal transducer and activator of transcription 5 (STAT5) activation. In addition, RGS2 reinduced the expression of Flt3-ITD-repressed CCAAT/enhancer-binding protein alpha (c/EBPalpha) and antagonized the Flt3-ITD-induced differentiation block in 32D cells. Expression analyses in myeloid cell lines revealed induction of RGS2 during granulocytic but not during monocytic differentiation. Taken together, RGS2 is a novel mediator of myeloid differentiation, and its repression is an important event in Flt3-ITD-induced transformation.
激活型胎儿肝酪氨酸激酶3（Flt3）突变是急性髓系白血病（AML）中最常见的基因畸变。最常见的情况是，它们以近膜结构域的内部串联重复形式出现（Flt3-ITD），这种突变在体外和体内均可转化髓系细胞，并诱导异常信号传导和生物学功能。我们鉴定出RGS2（一种G蛋白信号调节剂）是受Flt3-ITD特异性抑制的基因。在此我们证明了RGS2在Flt3-ITD介导的转化过程中发挥重要作用。在两种髓系细胞系（32Dcl3和NB4）中强制表达激活型Flt3突变后，RGS2受到抑制。此外，与Flt3突变阴性的AML病例相比，Flt3突变阳性的AML病例中RGS2受到抑制，尤其是在ITD与野生型（WT）比例高的Flt3-ITD阳性病例中。RGS2与Flt3-ITD共表达可抑制Flt3-ITD诱导的32D细胞自主增殖和克隆生长。RGS2还可抑制Flt3-ITD诱导的Akt和糖原合酶激酶β（Gsk3-β）磷酸化，而不影响信号转导及转录激活因子5（STAT5）的激活。此外，RGS2可重新诱导Flt3-ITD抑制的CCAAT/增强子结合蛋白α（c/EBPα）的表达，并拮抗Flt3-ITD诱导的32D细胞分化阻滞。髓系细胞系中的表达分析显示，RGS2在粒细胞分化过程中被诱导，但在单核细胞分化过程中未被诱导。综上所述，RGS2是髓系分化的新型调节因子，其抑制是Flt3-ITD诱导转化过程中的重要事件。
