Level of RUNX1 activity is critical for leukemic predisposition but not for thrombocytopenia

Abstract

Key Points• A half loss of RUNX1 activity leads to defects in primitive erythropoiesis, megakaryopoiesis, and proplatelet formation.• An almost complete loss of RUNX1 activity leads to the amplification of the granulomonocytic compartment with increased genomic instability.To explore how RUNX1 mutations predispose to leukemia, we generated induced pluripotent stem cells (iPSCs) from 2 pedigrees with germline RUNX1 mutations. The first, carrying a missense R174Q mutation, which acts as a dominant-negative mutant, is associated with thrombocytopenia and leukemia, and the second, carrying a monoallelic gene deletion inducing a haploinsufficiency, presents only as thrombocytopenia. Hematopoietic differentiation of these iPSC clones demonstrated profound defects in erythropoiesis and megakaryopoiesis and deregulated expression of RUNX1 targets. iPSC clones from patients with the R174Q mutation specifically generated an increased amount of granulomonocytes, a phenotype reproduced by an 80% RUNX1 knockdown in the H9 human embryonic stem cell line, and a genomic instability. This phenotype, found only with a lower dosage of RUNX1, may account for development of leukemia in patients. Altogether, RUNX1 dosage could explain the differential phenotype according to RUNX1 mutations, with a haploinsufficiency leading to thrombocytopenia alone in a majority of cases whereas a more complete gene deletion predisposes to leukemia. (Blood. 2015; 125(6):930-940)

Inherited platelet dysfunction and hematopoietic transcription factor mutations

“…3 Most described RUNX1 mutations produce haplodeficiency, with approximately 50% of RUNX1 activity preserved, though some mutations may almost completely abrogate RUNX1 activity through a dominant negative effect, which has been postulated to markedly increase risk for leukemia development. 6,19,20 Patients with RUNX1 mutation have a phenotype characterized by thrombocytopenia, several platelet function defects, and a substantially increased risk of AML or MDS (over 40% at a median age of 33 years). 7,18,19,21 Patients typically only have a mild to moderate bleeding tendency despite the platelet dysfunction and mild to moderate thrombocytopenia, with usually normal-sized platelets.…”

Patient-derived induced pluripotent stem cells in cancer research and precision oncology

“…Incompletely reprogrammed ‘iPSC-like’ cells—cells that have not attained independence from exogenous expression of reprogramming TFs—have been generated from patients with pancreatic adenocarcinoma 33 . iPSCs have also been generated from patients with familial cancer predisposition syndromes resulting from germline mutations: Li–Fraumeni syndrome ( TP53 mutation) 34 , Fanconi anemia ( FANCA and FANCC mutations) 35 , familial platelet disorder (FPD) with a predisposition to acute myeloid leukemia (AML) (FPD/AML; RUNX1 mutation) 36 and breast cancer predisposition ( BRCA1 mutation) 37 . Li–Fraumeni syndrome iPSCs showed defective osteoblastic differentiation and tumorigenic potential, and they captured gene signatures of primary osteosarcomas, a tumor type that commonly develops in these patients 34 .…”

Acquired TET2 mutation in one patient with familial platelet disorder with predisposition to AML led to the development of pre‐leukaemic clone resulting in T2‐ALL and AML‐M0

“…We focus on a man with a familial history of RUNX1 R174Q mutation, previously referenced as AII‐1 , who developed at the age of 42 years an EGIL (European Group of Immunological Characterization of Leukemia) T2‐ALL with a loss of the 1p36 and 17q12 regions and the ASXL1 R693 * mutation in the leukaemic clone. The patient was pre‐treated with corticosteroids and then treated according to the French GRAALL2003 protocol based on a polychemotherapy .…”