Mutations of the PU.1 Ets domain are specifically associated with murine radiation-induced, but not human therapy-related, acute myeloid leukaemia

Abstract

Murine radiation-induced acute myeloid leukaemia (AML) is characterized by loss of one copy of chromosome 2. Previously, we positioned the critical haematopoietic-specific transcription factor PU.1 within a minimally deleted region. We now report a high frequency (>65%) of missense mutation at codon 235 in the DNAbinding Ets domain of PU.1 in murine AML. Earlier studies, outside the context of malignancy, determined that conversion of arginine 235 (R235) to any other amino-acid residue leads to ablation of DNA-binding function and loss of expression of downstream targets. We show that mutation of R235 does not lead to protein loss, and occurs specifically in those AMLs showing loss of one copy of PU.1 (P ¼ 0.001, Fisher's exact test). PU.1 mutations were not found in the coding region, UTRs or promoter of human therapy-related AMLs. Potentially regulatory elements upstream of PU.1 were located but no mutations found. In conclusion, we have identified the cause of murine radiation-induced AML and have shown that loss of one copy of PU.1, as a consequence of flanking radiation-sensitive fragile domains on chromosome 2, and subsequent R235 conversion are highly specific to this mouse model. Such a mechanism does not operate, or is extremely rare, in human AML.

Transcriptional dysregulation during myeloid transformation in AML

“…Mice with an engineered deletion of the upstream regulatory element (URE) of PU.1 had decreased PU.1 expression and subsequently developed AML (and lymphomas) (Rosenbauer et al, 2004). Moreover, mice with girradiation-induced myeloid leukemias acquired both a deletion in one copy of chromosome 2, which includes the PU.1 gene locus, and a point mutation in the ETS domain of PU.1, which impaired DNA binding of the other PU.1 allele (Cook et al, 2004;Suraweera et al, 2005). In addition, deletion of one PU.1 gene copy combined with suppression of the other copy by PML-RARA was reported as the mechanism in mouse APL (Walter et al, 2005).…”

Effect of transcription-factor concentrations on leukemic stem cells

“…A very similar observation was very recently reported by another group in an independent study. 69 C/EBP␣ is a second transcription-factor for which dosage sensitivity in leukemia can be suggested. First, although C/EBP␣ mutations occur frequently in patients with AML, no biallelic null mutations could be identified.…”

PU.1 is regulated by NF-κB through a novel binding site in a 17 kb upstream enhancer element

“…We recently reported that mutations of the PU.1 gene are found in some patients with acute myeloid leukemia (AML) (Mueller et al, 2002) and that PU.1 is suppressed in acute promyelocytic leukemia (Mueller et al, 2006). Others have shown that loss and/or mutation of the gene encoding PU.1 contributes to radiation-induced murine AML (Cook et al, 2004;Suraweera et al, 2005). PU.1 expression can be modulated by the balance of functional sense and antisense RNAs by a shared cis-regulatory element (Ebralidze et al, 2008).…”