View metadata, citation and similar papers at core.ac.uk brought to you by CORE

provided by Elsevier - Publisher Connector Cancer Cell Previews

Breaking the LSD1/KDM1A Addiction: Therapeutic Targeting of the Epigenetic Modifier in AML

Alyson A. Lokken1 and Nancy J. Zeleznik-Le1,2,* 1Oncology Institute 2Department of Medicine Loyola University Chicago, Maywood, IL 60153, USA *Correspondence: [email protected] DOI 10.1016/j.ccr.2012.03.027

KDM1A/LSD1, a H3K4/K9 and epigenetic regulator with roles in both activation and repression, has increased expression in multiple cancer types. Harris et al., in this issue of Cancer Cell, and Schenk et al. show that KDM1A may be a viable therapeutic target in treating AML.

Epigenetic regulation of gene expression, II), pTEFb, AF4, and AFF4 (Biswas et al., ture leukemic cells into mature myeloid through both histone modification and 2011). Additionally, KDM1A is a compo- cells. In the majority of APLs, chromo- DNA methylation, provides cells with a nent of an MLL supercomplex associated somal translocations involving the retinoic heritable mechanism for controlling gene with active transcription (Nakamura et al., acid receptor alpha gene (RARA) and expression without altering the DNA 2002). MLL itself is an epigenetic modifier the promyelocytic leukemia gene (PML) nucleotide sequence. KDM1A/ spe- as a histone methyltransferase with spec- produce the PML-RARa fusion . cific demethylase 1 (LSD1) was discov- ificity for H3K4. PML-RARa aberrantly interacts with co- ered in 2004 as the first histone deme- In normal hematopoietic development, repressor molecules such as NCOR and thylase, with specificity for mono- and hematopoietic stem cells undergo a series HDAC to prevent expression of RAR dimethyl histone H3 lysine 4 and mono- of changes in gene expression which both target necessary for differentiation. and dimethyl histone H3 lysine 9. Prior to promote differentiation to mature blood The use of all-trans retinoic acid (ATRA) its identification, methylation of cell lineages and repress genes neces- can lift the differentiation block by pro- was thought to be a relatively permanent sary for maintaining stem cell identity. moting expression of RAR-responsive epigenetic mark. KDM1A is a member of These changes are mediated, in part, by genes. However, the ability of ATRA to the flavin adenine dinucleotide (FAD)- epigenetic modifiers such as KDM1A promote differentiation of PML-RARa dependent family of amine oxidases, and MLL (Figure 1B). In leukemia, this nor- AML cells is specific to this subset of which require FAD to oxidize the mono- mal process of cellular maturation goes leukemia; non-APL AML, such as AML or dimethyl lysine to an imine intermediate awry; the leukemic stem cells (LSCs) do harboring a MLL translocation, requires that is further hydrolyzed to unmodified not differentiate appropriately, with resul- other treatment modalities. lysine and formaldehyde (Shi et al., 2004). tant accumulation of immature blast cells. In this issue of Cancer Cell, Harris et al. KDM1A was originally identified as a The mixed lineage leukemia gene (MLL) (2012) used microarray data from murine member of the CoREST repressor com- is frequently involved in chromosomal models of MLL leukemia to determine plex (You et al., 2001)(Figure 1A). When translocation with one of a variety of part- a correlation between KDM1A expression this complex is targeted to lineage- ner genes in acute leukemias of myeloid level and the leukemia colony-forming specific genes, KDM1A demethylates (AML) or lymphoid lineage. As a result, ability, often used as a surrogate assay the activating H3K4me2 mark to silence functional oncogenic fusion are to quantify LSC potential. Using both their expression. Additional repressive produced that promote the constitutive shRNAs and pharmacological inhibitors complexes containing KDM1A have since expression of MLL target genes, thereby synthesized to target the enzymatic been identified (Wang et al., 2007). blocking differentiation and promoting activity of KDM1A, the authors show that Conversely, KDM1A has been found to proliferation of immature blast cells. Re- inhibition of KDM1A results in induction interact with multiple proteins/complexes cent studies have shown increased of differentiation in both murine and pri- that function in gene activation (Figure 1A). KDM1A expression in AML regardless of mary human MLL-fusion cells (Figure 1C). KDM1A is required for transcription of subtype/cytogenetic status (http://www. Cells without active KDM1A were unable (AR) and estrogen proteinatlas.org; Berglund et al., 2008) to form colonies (indicative of loss of receptor (ER) target genes, where it is as well as in a variety of other tumor types LSC potential), exhibited differentiated recruited via interaction with AR or ER, (Hayami et al., 2011). This raises the cell morphology and could not cause respectively, and is thought to demethy- hypothesis that KDM1A may be an attrac- leukemia when introduced into mice. late the repressive H3K9me2 mark to tive target for therapeutic development. Gene expression analysis suggested allow for gene activation (Metzger et al., One therapeutic approach that has that KDM1A is responsible for promoting 2005). KDM1A is also a member of a tran- been successful in treating the acute pro- the oncogenic gene program associated scription elongation complex composed myelocytic leukemia (APL) subset of leu- with MLL-AF9 leukemia. KDM1A co- of ELL (elongation factor RNA polymerase kemias is forced differentiation of imma- localized to genes bound by MLL-AF9,

Cancer Cell 21, April 17, 2012 ª2012 Elsevier Inc. 451 Cancer Cell Previews

Figure 1. KDM1A/LSD1 Maintains a Balance in Gene Expression through Activating and Repressive Mechanisms that Are Disrupted in Acute Myeloid Leukemia (A and B) In normal cells, KDM1A activates or represses genes through its histone demethylase activity (A), maintaining the balance between hematopoietic stem cells and differentiation to mature myeloid cells (B). (C) In AML, increased KDM1A expression promotes an oncogenic gene expression program, causing a block in differentiation associated with increased H3K4me3 to H3K4me2 ratio at the promoter of target genes. Inhibition of KDM1A restores this balance, promoting blast cell differentiation. and the presence of KDM1A correlated decreased leukemia-initiating activity decreases the H3K4me2 to H3K4me3 with a decreased ratio of H3K4me2 to (i.e., engraftment) as well as decreased ratio, but how does KDM1A demethyla- H3K4me3 on these target genes. Upon tumor burden in human xenograft models. tion of H3K4me2/me1 lead to an increase inhibition of KDM1A, no global changes These combination-treated cells demon- in H3K4me3? Additionally, what proteins/ in H3K4me2 were evident, but the genes strated increased expression of genes protein complexes are recruited to these targeted by MLL-AF9 showed an increase associated with myeloid-lineage differ- loci when KDM1A is present? Finally, in the H3K4me2 mark at their promoter entiation and a concomitant increase in what will be the long-term effect on nor- and 50 gene regions. This regional in- H3K4me2 at their promoters. mal hematopoietic stem cells and hema- crease in H3K4me2 marks increased the Together, these two studies illustrate topoietic cell homeostasis and differ- ratio of H3K4me2 to H3K4me3 at the the importance of KDM1A in maintaining entiation programs when treated with locus, making the prevalence of the marks expression of oncogenic gene programs KDM1A inhibitors? Harris et al. (2012) more equal. and blocking differentiation in multiple start to address this question in their Complementary findings were recently subtypes of AML and highlight the poten- article. They found that while the overall reported in Nature Medicine (Schenk tial therapeutic implications of targeting frequency of colony forming cells remains et al., 2012). The authors examined the this important epigenetic regulator in leu- the same upon KDM1A inhibition, ery- effect of combining ATRA differentiation kemia. Despite these exciting findings, throid lineage differentiation is decreased. therapy with KDM1A inhibition in AML some very important questions remain In mice, this manifested as lethal anemia. cells. They found that KDM1A inhibition, to be addressed. First, what is the mech- How will these in vitro and in vivo re- in combination with ATRA therapy, could anism by which KDM1A functions at sults translate to patients that may be sensitize otherwise ATRA-insensitive these target genes in AML? The presence treated long-term with KDM1A inhibitors? cells toward differentiation. This caused of KDM1A at MLL-AF9 target genes Although the questions are plentiful in this

452 Cancer Cell 21, April 17, 2012 ª2012 Elsevier Inc. Cancer Cell Previews

emerging field of targeting epigenetic re- R.G. (2011). Proc. Natl. Acad. Sci. USA 108, Croce, C.M., and Canaani, E. (2002). Mol. Cell 10, gulators in cancer, the results presented 15751–15756. 1119–1128. in these articles highlight the potential of Harris, W.J., Huang, X., Lynch, J.T., Spencer, G.J., Schenk, T., Chen, W.C., Go¨ llner, S., Howell, L., Jin, using such therapies, not only in AML, Hitchin, J.R., Li, Y., Cicero, F., Blaser, J.G., L., Hebestreit, K., Klein, H.U., Popescu, A.C., but perhaps in other cancers that are Greystroke, B.F., Jordan, A.M., et al. (2012). Burnett, A., Mills, K., et al. (2012). Nature Medicine. Cancer Cell 21, this issue, 473–487. Published online March 11, 2012. 10.1038/nm. dependent on aberrant epigenetic activity 2661. for survival. Hayami, S., Kelly, J.D., Cho, H.S., Yoshimatsu, M., Shi, Y., Lan, F., Matson, C., Mulligan, P., Whets- Unoki, M., Tsunoda, T., Field, H.I., Neal, D.E., tine, J.R., Cole, P.A., Casero, R.A., and Shi, Y. Yamaue, H., Ponder, B.A.J., et al. (2011). Int. J. REFERENCES (2004). Cell 119, 941–953. Cancer 128, 574–586.

Berglund, L., Bjo¨ rling, E., Oksvold, P., Fagerberg, Wang, J., Scully, K., Zhu, X., Cai, L., Zhang, J., Pre- Metzger, E., Wissmann, M., Yin, N., Mu¨ ller, J.M., L., Asplund, A., Szigyarto, C.A., Persson, A., Ottos- fontaine, G.G., Krones, A., Ohgi, K.A., Zhu, P., Gar- Schneider, R., Peters, A.H., Gu¨ nther, T., Buettner, son, J., Werne´ rus, H., Nilsson, P., et al. (2008). Mol. cia-Bassets, I., et al. (2007). Nature 446, 882–887. R., and Schu¨ le, R. (2005). Nature 437, 436–439. Cell. Proteomics 7, 2019–2027. You, A., Tong, J.K., Grozinger, C.M., and Biswas, D., Milne, T.A., Basrur, V., Kim, J., Nakamura, T., Mori, T., Tada, S., Krajewski, W., Schreiber, S.L. (2001). Proc. Natl. Acad. Sci. USA Elenitoba-Johnson, K.S., Allis, C.D., and Roeder, Rozovskaia, T., Wassell, R., Dubois, G., Mazo, A., 98, 1454–1458.

Hijacking T Cell Differentiation: New Insights in TLX Function in T-ALL

Bryan King,1 Panagiotis Ntziachristos,1 and Iannis Aifantis1,* 1Howard Hughes Medical Institute and Department of Pathology, NYU School of Medicine, New York, NY 10016, USA *Correspondence: [email protected] DOI 10.1016/j.ccr.2012.03.026

TLX1 and TLX3 are two closely-related homeobox transcriptional repressors frequently misexpressed and translocated in T cell acute lymphoblastic leukemia (T-ALL). In this issue of Cancer Cell, Dadi et al. provide new insights into how these factors are recruited by ETS-1 to the TCRa enhancer and actively repress differ- entiation.

In the majority of human cancers, tumor (T-ALL) (Mullighan and Downing, 2009). process, controlled by cell intrinsic (tran- cells tend to share aspects of their identity Such findings have suggested that certain scription factors) and cell extrinsic with a corresponding cell of origin, a prop- oncogenic lesions have the ability to (antigen, cytokines, and chemokines) erty that has proved useful for diagnosis ‘‘freeze’’ at distinct factors. Uncommitted, multipotent pro- in the clinic and provided researchers stages. Therefore, a thorough under- genitors enter the thymus through the with a wide range of potential therapeutic standing of how oncogenes halt develop- cortico-medullary junction, sense Notch targets. In particular, acute lymphoblastic mental processes will provide clues ligands, and initiate commitment to the leukemia (ALL) often presents as a snap- toward the reinforcement of differentiation T cell lineage. At this point the T cell shot of lymphocyte differentiation, based and, presumably, the desired outcomes of receptor (TCR) b, g, and d loci become on surface marker expression and charac- cell cycle exit and/or programmed cell accessible and the outcome of rearrange- teristic molecular genetic signatures death. In this issue of Cancer Cell, Dadi ment leads to either the differentiation (Aifantis et al., 2008). A large amount of et al. (2012) reveal how two such onco- toward the gd lineage or (as it happens data over the last decade has underlined genes (TLX1 and TLX3) manage to inter- with the vast majority of T cells) the the connection between physiological fere with a critical stage of T cell differenti- expression of the pre-TCR, which helps lymphocyte differentiation and the trans- ation, leading to development of a subset drive cellular proliferation and leads to formation events that lead to ALL. of T-ALL. the CD4+8+ stage. At this stage, the Whole-genome profiling and sequencing T cell differentiation and ALL are TCRa locus undergoes recombination studies have suggested that some of the ideal models to study such oncogenic which leads to the surface expression most common mutational targets in ALL effects due to our detailed knowledge on of a TCRab and subsequent selection are also key regulators of normal differen- the phenotypic and molecular programs events (Sleckman et al., 1998). RAG- tiation, including IKZF1 and PAX5 in B-ALL of differentiation. T cells mature in the mediated rearrangement of the TCRa and NOTCH1 and GATA3 in T cell ALL thymus following a highly orchestrated locus is a process controlled by distinct

Cancer Cell 21, April 17, 2012 ª2012 Elsevier Inc. 453