The ordered acquisition of Class II and Class I mutations directs formation of human t(8;21) acute myelogenous leukemia stem cell

Abstract

The cellular properties of leukemia stem cells (LSCs) are achieved at least through Class I and Class II mutations that generate signals for enhanced proliferation and impaired differentiation, respectively. Here we show that in t(8;21) acute myelogenous leukemia (AML), hematopoietic stem cells (HSCs) transform into LSCs via definitively-ordered acquisition of Class II (AML1/ETO) and then Class I (c-KIT mutant) abnormalities. Six t(8;21) AML patients with c-KIT mutants maintaining > 3 years of complete remission were analyzed. At diagnosis, all single LSCs had both AML1/ETO and c-KIT mutations. However, in remission, 16 out of 1,728 CD34(+)CD38(-) HSCs and 89 out of 7,187 single HSC-derived myeloerythroid colonies from these patients had AML1/ETO, whose breakpoints were identical to those found in LSCs. These cells had wild-type c-KIT, which expressed AML1/ETO at a low level, and could differentiate into mature blood cells, suggesting that they may be the persistent preleukemic stem cells. Microarray analysis suggested that mutated c-KIT signaling provides LSCs with enhanced survival and proliferation. Thus, in t(8;21) AML, the acquisition of AML1/ETO is not sufficient, and the subsequent upregulation of AML1/ETO and the additional c-KIT mutant signaling are critical steps for transformation into LSCs.

ASXL2 is essential for haematopoiesis and acts as a haploinsufficient tumour suppressor in leukemia

“…As noted earlier, despite being among the common fusions in AML patients, the AML1-ETO fusion protein by itself is not sufficient to promote overt leukemia2021222324. The fact that loss of even a single copy of Asxl2 promoted leukemogenesis mediated by endogenous Aml1-Eto expression strongly supports the concept that Asxl2 is a haploinsufficient tumour suppressor in the context of this subtype of AML.…”

“…Genetic analyses of patients with t(8;21) AML and extensive animal modelling of the haematopoietic effects of the AML1-ETO translocation have identified that AML1-ETO is expressed in early HSCs and increases self-renewal but is not sufficient for leukemogenesis alone202122. Substantial effort has therefore been spent to identify genetic events that collaborate with AML1-ETO to promote leukemogenesis.…”

“…At the same time, unlike mutations in ASXL1 , ASXL2 mutations are virtually absent in other forms of leukemia or in clonal haematopoiesis171819, suggesting a specific genetic interaction between ASXL2 and AML1-ETO . Given that expression of the AML1-ETO fusion is not sufficient to generate overt AML on its own2021222324, the unique enrichment of ASXL2 mutations in this subset of AML suggests that ASXL2 mutations may be an important cooperating genetic alteration in the pathogenesis of AML1-ETO AML. Currently however, very little is known about the role of ASXL2 in normal or malignant haematopoiesis.…”

Lentiviral vector system for coordinated constitutive and drug controlled tetracycline-regulated gene co-expression

“…Several mouse models have suggested that combined effects of enhanced proliferation (Class I abnormalities) and differentiation block (Class II) result in acute myelogenous leukemia (AML) [13e16]. In t(8; 21) human AML, it was recently shown that HSCs transform into leukemia stem cells (LSCs) via definitively-ordered acquisition of Class II (AML1/ETO) and Class I (c-KIT mutant) abnormalities [16].…”

Pre-malignant lymphoid cells arise from hematopoietic stem/progenitor cells in chronic lymphocytic leukemia

“…cells [21,22]. Additional mutations such as c-KIT mutations are critical for the formation of AML LSCs at the GMP stage [23]. Furthermore, NGS analyses have shown that pre-malignant clones carrying somatic mutations have been frequently found in HSCs of patients with AML without specific chromosomal abnormalities [24,25].…”