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RARA haploinsufficiency modestly influences the phenotype of APL.

ABSTRACT: RARA haploinsufficiency is an invariable consequence of t(15;17) reciprocal translocations in acute promyelocytic leukemia (APL). Furthermore, retinoids and RARA activity have been implicated in hematopoietic self-renewal, lineage commitment and neutrophil maturation. We and others therefore predicted that RARA haploinsufficiency would contribute to APL pathogenesis. To test this hypothesis we crossed RARA+/- mice with mice expressing PML-RARA from the Cathepsin G locus (mCG-PR). We found that RARA haploinsufficiency cooperated with PML-RARA, only modestly influencing the pre-leukemic and leukemic phenotype. Bone marrow from mCG-PR+/- x RARA+/- mice had decreased numbers of mature myeloid cells, increased ex vivo myeloid cell proliferation and an increased competitive advantage following transplantation. RARA haploinsufficiency did not alter mCG-PR dependent leukemic latency or penetrance, but did influence the distribution of leukemic cells; mCG-PR+/- x RARA+/- mice presented more commonly with low to normal white blood cell counts and with myeloid infiltration of lymph nodes. APL arising in these mice was responsive to ATRA, and had virtually no differences in expression profiling compared to tumors arising in mCG-PR+/- x RARA+/+ mice. These phenotypes were dependent on PML-RARA activity, since they were not detected in RARA+/- mice in the absence of the mCG-PR transgene. These data show that RARA haploinsufficiency (like PML haploinsufficiency and RARA-PML) can cooperate with PML-RARA to influence the pathogenesis and phenotype of APL in mice, but that PML-RARA is the driver of t(15;17) APL.

ORGANISM(S): Mus musculus

PROVIDER: GSE23291 | GEO | 2010/07/29

SECONDARY ACCESSION(S): PRJNA131353

REPOSITORIES: GEO

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Project description:The origin of aberrant DNA methylation in cancer remains largely unknown. In this study, we elucidated the DNA methylome in primary Acute Promyelocytic Leukemia (APL) and the role of PML-RARa in establishing these patterns. APL patients showed increased genome-wide DNA methylation with higher variability than healthy CD34+ cells, promyelocytes and remission bone marrow. A core set of differentially methylated regions in APL was identified. Age at diagnosis, Sanz score and Flt3-mutation status characterized methylation subtypes. Transcription factor binding sites, e.g. c-myc binding sites were associated with low methylation. SUZ12 and REST binding sites identified in embryonic stem cells were, however, preferentially DNA hypermethylated in APL. Unexpectedly, PML-RARa binding sites were also protected from aberrant DNA methylation in APL. In line, myeloid cells from pre-leukemic PML-RARa knock-in mice did not show altered DNA methylation and expression of PML-RARa in hematopoietic progenitor cells prevented differentiation without affecting DNA methylation. ATRA treatment of APL blasts did also not result in DNA methylation changes. These results suggest that aberrant DNA methylation is associated with leukemia phenotype but not required for PML-RARa-mediated initiation of leukemogenesis. We used Reduced Representation Bisulfite Sequencing (RRBS) to determine the genome-wide methylation signature of 18 primary APL patient samples. We then compared the APL methylation signature with methylation patterns found in CD34+ progenitor cells (n=4), promyelocytes (n=4) and remission bone marrow samples (n=8). Differentially methylated regions found in all three comparisons (APL vs. all three control specimens) were then further analyzed for genomic localization, variability and association with clinical parameters. Finally, the relationship between differentially methylated regions in APL and specific transcription factor binding sites was analyzed. For this purpose, ChiP-Sequencing of SUZ12 and REST was performed in primary APL patient blasts. To further determine the contribution of the leukemogenic transcription factor PML-RARa to methylation in APL, we also performed RRBS in pre-leukemic PML-RARa knock-in mice and hematopoetic progenitor cells retrovirally transduced with PML-RARa.

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RARA haploinsufficiency modestly influences the phenotype of APL.

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