Chen, B., Chan, W. (2014). The de novo DNA methyltransferase DNMT3A in development and cancer. Epigenetics. 9(5): 669-677
This 2014 review by Chen and Chan compares and contrasts the role of DNMT3A in development and cancer. The structure, variants, localization, and expression patterns of the DNMT3A gene are described in detail. DNMT3A plays a critical role in primordial germ cells, helping to re-establish the parental imprints that are needed for meiosis, spermatogenesis, and oogenesis. Studies have shown that DNMT3A is also involved in the de novo methylation that takes place post-implantation, with Dnmt3a knockout murine ESCs failing to differentiate normally. In addition to the frequent mutation of DNMT3A in AML, DNMT3A is also mutated in hepatic cellular cancer (HCC), melanoma, and lung cancers.
Collins, C.T., Hess, J.L. (2016). Role of HOXA9 in leukemia: dysregulation, cofactors, and essential targets. Oncogene. 35(9):1090-8.
This review summarizes the role of the homeobox family protein HOXA9 in leukemia. HOXA9 is a transcription factor that plays several important roles in development, specifically in the expansion of hematopoietic stem cells (HSCs). The molecular mechanisms through which HOXA9 can induce leukemia are not yet understood, and it is hypothesized that several additional upstream genetic alterations leading to overexpression of HOXA9 have yet to be identified. Given that HOXA9 has also been found to be hypomethylated in DNMT3A-null cancers, this paper brought up the question of whether loss of DNMT3A and HOXA9 hypomethylation are connected to the gene’s overexpression and leukemogenic activity.
Estey, E. (2006). Acute myeloid leukemia. The Lancet. 368(9550):1894-1907.
This review in The Lancet describes the key clinical, molecular, and pathogenic features of acute myeloid leukemia. AML is a heterogeneous disorder affecting the hematopoietic stem cells, characterized by a differentiation block that leads to accumulation of immature “blasts” in the bone marrow. AML is the most common myeloid malignancy in adults, and is particularly common in adults over age 65. Many older adults develop the cancer as a consequence of cytotoxic therapy for another type of cancer. The cancer is called “acute” as it progresses fairly rapidly, with a five-year survival rate of less than 25%. Prognosis is even more dire for older adults, with elderly patients surviving for an average of a few months. This paper provided me with a background in the clinical features of the disease, and helped me to understand the relevance of my research question.
Figueroa, M.E., Lugthart, S., Li, Y., Erpelinck-Verschueren, C., Deng, X., Christos, P.J., et al. (2010). DNA methylation signatures identify biologically distinct subtypes in acute myeloid leukemia. Cancer Cell. 17:13-27.
DNA methylation patterns are known to be aberrant in cancers. In this study, the authors investigated whether DNA methylation could be used to classify distinct subtypes in acute myeloid leukemia (AML), which may be relevant for treatment. The methylation profiles of over 300 patients with AML were examined, and several different subgroups were identified on the basis of DNA methylation signatures. This paper demonstrates that DNA methylation patterns have the potential to be clinically significant, and supports the significance of my research question.
Kim, M.S., Kim, Y.R., Yoo, N.J., Lee, S.H. (2013). Mutational analysis of DNMT3A gene in acute leukemias and common solid cancers. APMIS. 121(2):85-94.
This study by Kim et al. examined mutations in DNMT3A in several common solid cancers and acute lymphoblastic leukemia (ALL) to see if the mutation was common in other malignancies in addition to AML. Using a single-strand conformation polymorphism assay, 916 cancers from >400 blood malignancies were examined, as were >500 solid tumours. DNMT3A mutations were identified in most of the cancer types that were analyzed, including gastric cancers, lung cancers, and lymphomas. Different types of alterations in DNMT3A were observed, including allelic loss, somatic mutations, and loss of expression. This suggests that DNMT3A likely plays a critical role in multiple cancer types, and that it may initiate tumorigenesis through a multitude of mechanisms.
Qu, Y. et al. (2014). Differential methylation in CN-AML preferentially targets non-CGI regions and is dictated by DNMT3A mutational status and associated with predominant hypomethylation of HOX genes. Epigenetics. 9(8):1108-1119.
This primary research study characterized the genome-wide methylation differences between cytogenically normal AML (CN-AML) cells and healthy control bone marrow cells. A key finding from this study was that homeodomain-containing (HOX) genes experienced the most significant changes in methylation, with hypomethylation occurring in genes including HOXA5 and HOXA9. While this study showed only a correlation between DNMT3A mutation and hypomethylation of homeobox genes, it provides an intriguing potential mechanism through which DNMT3A may initiate cancer.
Redecke, V., Wu, R., Zhou, J., Finkelstein, D., Chaturvedi, V., High, A.A., Hacker, H. (2013). Hematopoietic progenitor cell lines with myeloid and lymphoid potential. Nature Methods. 10:795-803.
This group reports the development of a novel hematopoietic stem cell-derived line that is capable of differentiating into both myeloid and lymphoid lineages, but not erythrocytes or megakaryocytes. The potential to differentiate into cells of the myeloid lineage is assessed through differentiation with GM-CSF and M-CSF, which promote differentiation into dendritic cells and granulocytes, and macrophages, respectively. The differentiated cells expressed the surface markers characteristic of the myeloid cell lineage, and had similar immune function and properties. I decided to use this cell line as my model system in my project, since I needed cells to be predisposed towards a myeloid lineage and did not want to use HSCs.
Shan, W., Ma, X. (2013). How to establish acute myeloid leukemia xenograft models using immunodeficient mice. Asian Pacific Journal of Cancer Prevention. 14(12):7057-7063.
This review from Shan and Ma examined the various mouse models that are used in xenograft experiments for acute myeloid leukemia (AML). Xenografts require immunodeficient mice, as the cells come from another species and therefore are prone to rejection from the host. The authors detail the various positive aspects and challenges involved in using different immunodeficient mice, such as NOD/SCID, NSG, and NOG mice. I ultimately decided to use the NSG strain, since the authors note that it has the highest engraftment success rate when modelling acute myeloid leukemia in vivo.
Shlush, L. I. et al. (2014). Identification of pre-leukaemic haematopoietic stem cells in acute leukaemia. Nature. 506: 328–333.
This study investigated whether a pre-leukemic state prior to blast development could be observed in AML samples, as this could help with early detection and treatment. Upon examination of the hematopoietic stem cells (HSCs) of patients with AML, a high allele frequency of DNMT3A mutations were observed. This occurred, surprisingly, in the absence of the NPM1 mutations that typically coincide with DNMT3A mutation in AML blasts. DNMT3A was therefore one of the first mutations to arise in the AML clones. The DNMT3A mutant cells were also found to differentiate into a variety of lineages, and could survive chemotherapy. The authors concluded that HSCs bearing DNMT3A mutations clonally expand into a population of pre-leukemic cells that ultimately evolve into AML.
Yang, L., Rau, R., Goodell, M.A. (2015). DNMT3A in hematological malignancies. Nature Reviews Cancer. 15:152-165.
This review summarizes the research connecting mutations in the DNA methyltransferase 3A (DNMT3A) enzyme to blood malignancies such as acute myeloid leukemia (AML). This paper provided crucial information surrounding the structure of the DNMT3A enzyme, its catalytic activity, and the role it plays during development. The authors also examine the research implicating DNMT3A mutations in various blood malignancies of the myeloid and leukoid lineage, and propose a model for leukemia development in which DNMT3A acts to transform cells into a “pre-leukemic” state, and subsequent mutations in key proteins such as NPM1 result in different types of blood malignancies. This model greatly informed my own hypothesis and predictions for my research project.