Effect of Protease-resistant PML-RARα on the leukemogenic potential in a mouse model of Acute Promyelocytic Leukemia
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ABSTRACT: Previous studies in our laboratory demonstrated that the azurophil granule protease neutrophil elastase (NE) cleaves PML-RARA (PR), the fusion protein that initiates acute promyelocytic leukemia (APL). Further, NE deficiency reduces the penetrance of APL in a murine model of this disease. We therefore predicted that NE-mediated PR cleavage might be important for its ability to initiate APL. To test this hypothesis, we generated a mouse expressing NE-resistant PR. These mice developed APL indistinguishable from wild type PR, but with significantly reduced latency (median leukemia-free survival of 274 days versus 473 days for wild type PR, p<0.001). Resistance to proteolysis may increase the abundance of full length PR protein in early myeloid cells, and our previous data suggested that non-cleaved PR may be less toxic to early myeloid cells. Together, these effects appear to increase the leukemogenicity of NE-resistant PR, contrary to our previous prediction. We conclude that NE deficiency may reduce APL penetrance via indirect mechanisms that are still NE dependent. Keywords: Time course
Project description:Previous studies in our laboratory demonstrated that the azurophil granule protease neutrophil elastase (NE) cleaves PML-RARA (PR), the fusion protein that initiates acute promyelocytic leukemia (APL). Further, NE deficiency reduces the penetrance of APL in a murine model of this disease. We therefore predicted that NE-mediated PR cleavage might be important for its ability to initiate APL. To test this hypothesis, we generated a mouse expressing NE-resistant PR. These mice developed APL indistinguishable from wild type PR, but with significantly reduced latency (median leukemia-free survival of 274 days versus 473 days for wild type PR, p<0.001). Resistance to proteolysis may increase the abundance of full length PR protein in early myeloid cells, and our previous data suggested that non-cleaved PR may be less toxic to early myeloid cells. Together, these effects appear to increase the leukemogenicity of NE-resistant PR, contrary to our previous prediction. We conclude that NE deficiency may reduce APL penetrance via indirect mechanisms that are still NE dependent. Keywords: Time course U937 cells were transfected with one of three tagged constructs GFP,GFP-PR,GFP-PR-2VR sorted for GFP positivity at the indicated time points and harvested for RNA.
Project description: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.
Project description:Acute promyelocytic leukemia (APL) is characterized by a specific t(15;17) chromosome translocation that generates the promyelocytic leukemia/retinoic acid receptor-α (PML/RARα) fusion gene. However, the mechanism underlying PML/RARα mediated transcriptional dysregulation remain unclear. Here, we performed the transcription profiling in NB4, an APL patient-derived cell line.
Project description: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. RARA+/- mice were crossed with mice expressing PML-RARA from Cathepsin G locus (mCG-PR). Five leukemic mice were chosen from each of the mCG-PR+/-RARA+/- and mCG-PR+/-RARA+/+ strains and total RNA extracted from the spleen samples were analyzed using Affymetrics Mouse Exon 1.0 platform
Project description: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.
Project description:Acute promyelocytic leukemia (APL) is characterized by a specific t(15;17) chromosome translocation that generates the promyelocytic leukemia/retinoic acid receptor-α (PML/RARα) fusion gene. However, the global association between PML/RARα and transcriptional co-regulators, and the rules of their association in governing the key processes during the leukemogenesis remain unclear. Here, we performed the genome-wide binding profiling of PML/RARα and BRD4 in NB4, an APL patient-derived cell line. Moreover, we also performed ChIP-seq of PML/RARα and BRD4 upon genetic or pharmacological pertubation of PML/RARα or BRD4 to determine how they target regulatory elements.
Project description:Patients with newly diagnosed acute promyelocytic leukemia (APL) are often obese or overweight, accompanied by metabolic disorders, such as dyslipidemia. However, the link between dyslipidemia and leukemia development is obscure. Here, we conducted a retrospective study containing 1,412 medical records (319 APL, 393 non-APL acute myeloid leukemia (AML), and 700 non-tumor controls) and found that APL patients had higher triglyceride levels than non-APL AML and non-tumor controls. We revealed that triglyceride served as a risk factor of early death in APL patients, and there was a positive correlation between high triglyceride levels and high leukocyte counts. RNA-seq analysis on APL patients with high or normal triglyceride levels brought attention to peroxisome proliferator-activated receptor-alpha (PPARα) signaling, a crucial regulator of cell metabolism and a transcription factor involved in cancer development. We demonstrated that PPARα knockdown inhibited the proliferation of APL cells. Chromatin mapping data analysis with CUT&Tag revealed that PPARα coexisted with PML/RARα within the super-enhancer regions to maintain APL. Interventions to PPARα affected the transcription and protein level of FLT3. Moreover, in vivo results in mice having high-fat diet-induced high triglyceride levels supported the connection between high triglyceride levels and the leukemia burden, as well as the involvement of PPARα-mediated-FLT3 activation in the proliferation of APL cells. Our findings shed light on the association between APL cell proliferation and high triglyceride levels and established the contribution of an hyperlipidemia–PPARα–FLT3 axis to APL development.
Project description:Patients with newly diagnosed acute promyelocytic leukemia (APL) are often obese or overweight, accompanied by metabolic disorders, such as dyslipidemia. However, the link between dyslipidemia and leukemia development is obscure. Here, we conducted a retrospective study containing 1,412 medical records (319 APL, 393 non-APL acute myeloid leukemia (AML), and 700 non-tumor controls) and found that APL patients had higher triglyceride levels than non-APL AML and non-tumor controls. We revealed that triglyceride served as a risk factor of early death in APL patients, and there was a positive correlation between high triglyceride levels and high leukocyte counts. RNA-seq analysis on APL patients with high or normal triglyceride levels brought attention to peroxisome proliferator-activated receptor-alpha (PPARα) signaling, a crucial regulator of cell metabolism and a transcription factor involved in cancer development. We demonstrated that PPARα knockdown inhibited the proliferation of APL cells. Chromatin mapping data analysis with CUT&Tag revealed that PPARα coexisted with PML/RARα within the super-enhancer regions to maintain APL. Interventions to PPARα affected the transcription and protein level of FLT3. Moreover, in vivo results in mice having high-fat diet-induced high triglyceride levels supported the connection between high triglyceride levels and the leukemia burden, as well as the involvement of PPARα-mediated-FLT3 activation in the proliferation of APL cells. Our findings shed light on the association between APL cell proliferation and high triglyceride levels and established the contribution of an hyperlipidemia–PPARα–FLT3 axis to APL development.
Project description:Epigenetic abnormalities are frequently involved in the initiation and progression of cancers including acute myeloid leukemia (AML). A subtype of AML, Acute promyelocytic leukemia (APL), is mainly driven by a specific oncogenic fusion event of PML-RARα. PML-RARα was reported as a transcription repressor through the interaction with NCoR/HDAC complexes leading to the mis-suppression of its target genes and differentiation blockage. While previous studies were mainly focused on the connection of histone acetylation, it is still largely unknown whether alternative epigenetics mechanisms are involved in APL progression. KDM5A is a demethylase of histone H3 lysine 4 di- and tri- methylations (H3K4me2/3) and a transcription corepressor. Here, we found that the loss of KDM5A led to APL NB4 cell differentiation and retarded growth. Mechanistically, through epigenomics and transcriptomics analyses, we detected KDM5A binding in 1,889 genes, with the majority of the binding events at promoter regions. KDM5A suppressed the expression of 621 genes, including 42 PML-RARα target genes primarily by controlling the H3K4me2 in the promoters and 5’ end intragenic regions. In addition, a recently reported pan-KDM5 inhibitor, CPI-455 on its own could phenocopy the differentiation effects as KDM5A loss in NB4 cells. CPI-455 treatment or KDM5A knockout could greatly sensitize NB4 cells to ATRA induced differentiation. Our findings indicated that KDM5A contributed to the differentiation blockage in the APL cell line NB4, and inhibition of KDM5A could greatly potentiate NB4 differentiation.
Project description:Acute promyelocytic leukemia (APL) is characterized by a specific t(15;17) chromosome translocation that generates the promyelocytic leukemia/retinoic acid receptor-α (PML/RARα) fusion gene. However, the global association between PML/RARα and transcriptional co-regulators, and the rules of their association in governing the key processes during the leukemogenesis remain obscure. Here, we performed the genome-wide binding profiling of PML/RARα, HDAC1 and P300, in NB4, an APL patient-derived cell line. We found that PML/RARα targets could be classified into two classes. Moreover, we also performed ChIP-seq of H3K27ac to determine super-enhancers in NB4. We identified a novel function of PML/RARα in super-enhancer regulation during the leukemogenesis of APL.