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Distinct leukemogenic mechanism of acute promyelocytic leukemia based on genomic structure of PML-RARα fusion gene

ABSTRACT: Leukemic stem cells (LSCs) of acute myeloid leukemia (AML) are enriched in CD34+CD38- fraction, and self-renewing LSCs hierarchically organize and maintain the AML populations. In acute promyelocytic leukemia (APL), which is driven by PML-RARα fusion genes, the presence of LSCs has long been unidentified, due to the difficulty of efficient reconstitution of human APL in the immunodeficient mice. Here, we show that LSCs of short type isoform APL, subtype of APL defined by different breakpoint of PML gene, concentrate in CD34+CD38- fraction and express T cell immunoglobulin mucin-3 (TIM-3) as in other non-APL AML. Short type APL cells exhibited distinct gene expression signatures including LSCs-related genes from other types of APL. Moreover, CD34+CD38-TIM-3+ short type APL cells efficiently reconstituted huma APL in xenograft models with high penetration, whereas CD34- more differentiated APL cells did not. Furthermore, CD34+CD38-TIM-3+ short type APL cells also reconstituted leukemia in the serial transplantation. Thus, short type APL is showing hierarchically organized by self-renewing APL-LSCs same as in other types of AML. The identification of LSCs in a subset of APL and establishment of efficient patient derived xenograft model would contribute to further understanding of APL leukemogenesis and devising individual treatment for eradication of APL LSCs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE207432 | GEO | 2022/07/05

REPOSITORIES: GEO

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Project description:Differences in chemo-sensitivity of subpopulations of AML stem cells could have important clinical implications. Using in vitro cytotoxicity, xenograft models and colony forming assays, we compared chemotherapy sensitivity between Lineage (Lin-)CD34-CD38-, Lin-CD34-CD38+, Lin-CD34+CD38- and Lin-CD34+CD38+ populations from 26 primary AMLs (19 paediatric and 7 adult). We identified a common recurring pattern of chemo-response associated with a poor clinical outcome: In each of 16/26 (62%) AMLs, Lin-CD34-CD38- cells were the most chemoresistant of the four subpopulations to daunorubicin in vitro. Cytarabine-resistant colonies formed only from Lin-CD34-CD38- populations following tertiary passages through both NOG mice and methylcellulose in these AMLs The presence of chemo-resistant Lin-CD34-CD38- populations was signficantly associated with reduced relapse-free survival in childhood AML. Consistently, CD34 negativity was significantly associated with an increased risk of relapse in a larger retropsective cohort (n=89). Samples enriched for chemo-resistant Lin-CD34-CD38- LSCs with a stem cell profile and an undifferentiated genotype revealed pathways likely to confer chemo-resistance, These strongly indicated dependence of chemo-resistant Lin-CD34-CD38- LSCs on their niche environment as well as deregulated DNA damage responses, lipid and Notch1 signalling, Our findings have major implications for the risk stratification of childhood AML and could lead to the development of novel therapeutic approaches. 3 subpopulations of leukemia stem cells from 9 patients with primary childhood AML were analysed. We compared gene expression profiles of Lin-CD34+CD38- (Q1), Lin-CD34+CD38+ (Q2) and Lin-CD34-CD38- (Q3) cells between 3 AMLs in which the CD34+ cells were most chemo-resistant (AML-1P, AML-6P and AML-10P) and the same cells from the remaining AMLs in which the Lin-CD34-CD38- cells were the most chemo-resistant population. We also compared the gene expression profiles of Lin-CD34-CD38- (Q3) cells in the 3 samples with the highest LC50 values (AML-15P, AML-17P and AML-19P) with that of the 3 AMLs exhibiting the lowest LC50 values (AML-2P, AML-5P and AML-11P).

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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Distinct leukemogenic mechanism of acute promyelocytic leukemia based on genomic structure of PML-RARα fusion gene

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