An activated receptor tyrosine kinase, TEL/PDGFβR, cooperates with AML1/ETO to induce acute myeloid leukemia in mice

Abstract

The t(8;21)(q22;q22) translocation, occurring in 40% of patients with acute myeloid leukemia (AML) of the FAB-M2 subtype (AML with maturation), results in expression of the RUNX1-CBF2T1 [AML1-ETO (AE)] fusion oncogene. AML͞ETO may contribute to leukemogenesis by interacting with nuclear corepressor complexes that include histone deacetylases, which mediate the repression of target genes. However, expression of AE is not sufficient to transform primary hematopoietic cells or cause disease in animals, suggesting that additional mutations are required. Activating mutations in receptor tyrosine kinases (RTK) are present in at least 30% of patients with AML. To test the hypothesis that activating RTK mutations cooperate with AE to cause leukemia, we transplanted retrovirally transduced murine bone marrow coexpressing TEL-PDGFRB and AE into lethally irradiated syngeneic mice. These mice (19͞19, 100%) developed AML resembling M2-AML that was transplantable in secondary recipients. In contrast, control mice coexpressing with TEL-PDGFRB and a DNA-binding-mutant of AE developed a nontransplantable myeloproliferative disease identical to that induced by TEL-PDGFRB alone. We used this unique model of AML to test the efficacy of pharmacological inhibition of histone deacetylase activity by using trichostatin A and suberoylanilide hydroxamic acid alone or in combination with the tyrosine kinase inhibitor, imatinib mesylate. We found that although imatinib prolonged the survival of treated mice, histone deacetylase inhibitors provided no additional survival benefit. These data demonstrate that an activated RTK can cooperate with AE to cause AML in mice, and that this system can be used to evaluate novel therapeutic strategies.T he t(8;21)(q22;q22) translocation, which fuses the RUNX1 (AML1͞PEBP␣͞CBFA2) gene on chromosome 21 with the ETO (MTG8) gene on chromosome 8, is a common mutation associated with cases of acute myeloid leukemia (AML) of the FAB-M2 subtype (AML with maturation) (1). Expression of the resulting AML1-ETO (AE) fusion gene is detected in 40% of M2-AML patients and 12% of all newly diagnosed cases of AML (2, 3). The correlation between AE expression and the leukemic phenotype strongly suggests a causative role for AE in transformation. AE transcripts have been detected in nonneoplastic progenitors from AML patients in remission, suggesting that the translocation is an early event in the leukemogenic process (4). Furthermore, t(8;21) translocation and AE expression can be detected in neonatal Guthrie blood spots, implying an in utero origin of the translocation preceding development of AML in children by as much as 10 years (5,6).Several murine models have demonstrated that AE alone is not sufficient to induce leukemia. Mice expressing an inducible AE transgene in bone marrow cells remained disease-free for a normal life span of 24 mo (7). When expression of AE was targeted to the myeloid lineage by using the human MRP8 promoter, again the mice had no discernable phenotype (8). However, when additional random mu...

Gatekeeper pathways and cellular background in the pathogenesis and therapy of AML

“…Coexpression of AML1/ETO and TEL/PDGFR leads to a transplantable AML, while the receptor tyrosine kinase fusion protein by itself only induces a nontransplantable myeloproliferative disease arguing again for a role of AML1/ETO in maintaining self-renewal capacity and the requirement of this function in the pathogenesis of AML. 49 Similar observations about the requirement of gatekeeper inactivation prior to the proliferative signal have been made in epithelial tumors. KRAS2 mutations in the colonic epithelial cells can lead to self-limiting hyperplastic lesions that do not progress to cancer.…”

Review: genetic models of acute myeloid leukaemia

“…Subsequently, AML/ETO t(8;21) was transduced to bone marrow derived from mice deficient of the interferon regulatory factor ICSBP (Schwieger et al, 2002), implicated as a suppressor of myeloid neoplasia (Holtschke et al, 1996;Gabriele et al, 1999;Scheller et al, 1999) and was found to synergize with ICSBP deficiency to incite myeloblastic conditions evocative of AML. Furthermore, activating mutations in receptor tyrosine kinases, for example TEL/PDGFbR and Flt3, were found to cooperate with AML/ETO (Grisolano et al, 2003), NUP98/HOXA9 t(7;11) (Dash et al, 2002) and PML/RARa t(15;17) (Kelly et al, 2002) causing AML (FAB M2)-type leukaemia, AML and APL, respectively in transduced mice. Concurrently, cotransduction of murine HSCs with mutated tyrosine kinase BCR/ABL and translocation of NUP98/HOXA9 resulted in AML following transplantation into syngeneic mice (Dash et al, 2002).…”

Oncogenic pathways of AML1-ETO in acute myeloid leukemia: Multifaceted manipulation of marrow maturation

“…This role is more subtle than the differentiation blockade observed in transfected cell lines and argues against a simple unimodal model of transcriptional repression of RUNX1 target genes. Furthermore, in vivo models of AML1-ETO leukemogenesis have shown no disease responsiveness to HDAC inhibitors [5], raising questions regarding the relevance of HDAC recruitment, at least in the latter stages of the disease.…”

“…As will be discussed below, the impaired erythropoiesis seen in clinical cases of t(8;21)-positive AML has been recapitulated both in animal and in ex vivo model systems [3] Experimental and clinical studies underscore the importance of secondary mutations or events in AML1-ETO mediated leukemogenesis. For example, mice expressing AML1-ETO require exposure to a mutagen like N-ethyl-N-nitrosourea or coexpression of a constitutively active tyrosine kinase such as the TEL-PDGFRβ fusion in order to develop AML [4,5]. Similarly, the clinical data show a high incidence of secondary genetic alterations affecting tyrosine kinase signal transduction pathways in patients with t(8;21)-positive AML.…”