Isoform-specific potentiation of stem and progenitor cell engraftment by AML1/RUNX1.
BACKGROUND
AML1/RUNX1 is the most frequently mutated gene in leukaemia and is central to the normal biology of hematopoietic stem and progenitor cells. However, the role of different AML1 isoforms within these primitive compartments is unclear. Here we investigate whether altering relative expression of AML1 isoforms impacts the balance between cell self-renewal and differentiation in vitro and in vivo.


RESULTS
The human AML1a isoform encodes a truncated molecule with DNA-binding but no transactivation capacity. We used a retrovirus-based approach to transduce AML1a into primitive haematopoietic cells isolated from the mouse. We observed that enforced AML1a expression increased the competitive engraftment potential of murine long-term reconstituting stem cells with the proportion of AML1a-expressing cells increasing over time in both primary and secondary recipients. Furthermore, AML1a expression dramatically increased primitive and committed progenitor activity in engrafted animals as assessed by long-term culture, cobblestone formation, and colony assays. In contrast, expression of the full-length isoform AML1b abrogated engraftment potential. In vitro, AML1b promoted differentiation while AML1a promoted proliferation of progenitors capable of short-term lymphomyeloid engraftment. Consistent with these findings, the relative abundance of AML1a was highest in the primitive stem/progenitor compartment of human cord blood, and forced expression of AML1a in these cells enhanced maintenance of primitive potential both in vitro and in vivo.


CONCLUSIONS
These data demonstrate that the "a" isoform of AML1 has the capacity to potentiate stem and progenitor cell engraftment, both of which are required for successful clinical transplantation. This activity is consistent with its expression pattern in both normal and leukaemic cells. Manipulating the balance of AML1 isoform expression may offer novel therapeutic strategies, exploitable in the contexts of leukaemia and also in cord blood transplantation in adults, in whom stem and progenitor cell numbers are often limiting.
Tsuzuki
Shinobu
S
Division of Molecular Medicine, Aichi Cancer Center Research Institute, Nagoya, Japan. stsuzuki@aichi-cc.jp
Hong
Dengli
D
Gupta
Rajeev
R
Matsuo
Keitaro
K
Seto
Masao
M
Enver
Tariq
T
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002470:Cell Survival; D018920:Coculture Techniques; D003114:Colony-Forming Units Assay; D050676:Core Binding Factor Alpha 2 Subunit / Q000502:physiology*; D016207:Cytokines / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics; D005434:Flow Cytometry; D015870:Gene Expression; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000502:physiology*; D016012:Poisson Distribution; D020033:Protein Isoforms / Q000502:physiology; D012190:Retroviridae / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018709:Statistics, Nonparametric; D014162:Transfection
D050676:Core Binding Factor Alpha 2 Subunit; D016207:Cytokines; D018076:DNA, Complementary; D015514:Oncogene Proteins, Fusion; D020033:Protein Isoforms; C493728:RUNX1 protein, human; D049452:Green Fluorescent Proteins