The treatment of specific tumor cell lines with poly- and oligoamine analogues results in a super-induction of polyamine catabolism that is associated with cytotoxicity; however, other tumor cells demonstrate resistance to analogue treatment. Recent data indicate that some of these analogues also have direct epigenetic effects. We therefore sought to determine the effects of combining specific analogues with an epigenetic targeting agent in phenotypically resistant human lung cancer cell lines. We demonstrate that the histone deacetylase inhibitor MS-275 when combined with (N1, N11)-bisethylnorspermine (BENSpm) or (N1, N12)-bis(ethyl)-cis-6,7-dehydrospermine tetrahydrochloride (PG-11047) synergistically induces the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT), a major determinant of sensitivity to the antitumor analogues. Evidence indicates that the mechanism of this synergy includes reactivation of miR-200a, which targets and destabilizes kelch-like ECH-associated protein 1 (KEAP1) mRNA, resulting in the translocation and binding of nuclear factor (erythroid-derived 2)-like 2 (NRF2) to the polyamine-responsive element of the SSAT promoter. This transcriptional stimulation combined with positive regulation of SSAT mRNA and protein by the analogues results in decreased intracellular concentrations of natural polyamines and growth inhibition. The finding that an epigenetic targeting agent is capable of inducing a rate-limiting step in polyamine catabolism to overcome resistance to the antitumor analogues represents a completely novel chemotherapeutic approach. This is also the first demonstration of miRNA-mediated regulation of the polyamine catabolic pathway. Furthermore, the individual agents used in this study have been investigated clinically; therefore, translation of these combinations into the clinical setting holds promise.
miR-200a; NRF2; spermidine/spermine N1-acetyltransferase SSAT; MS-275; KEAP1
Epigenetic silencing of gene expression is important in cancer. Aberrant DNA CpG island hypermethylation and histone modifications are involved in the aberrant silencing of tumour-suppressor genes. LSD1 (lysine-specific demethylase 1) is a H3K4 (histone H3 Lys4) demethylase associated with gene repression and is overexpressed in multiple cancer types. LSD1 has also been implicated in targeting p53 and DNMT1 (DNA methyltransferase 1), with data suggesting that the demethylating activity of LSD1 on these proteins is necessary for their stabilization. To examine the role of LSD1 we generated LSD1 heterozygous (LSD1+/−) and homozygous (LSD1−/−) knockouts in the human colorectal cancer cell line HCT116. The deletion of LSD1 led to a reduced cell proliferation both in vitro and in vivo. Surprisingly, the knockout of LSD1 in HCT116 cells did not result in global increases in its histone substrate H3K4me2 (dimethyl-H3K4) or changes in the stability or function of p53 or DNMT1. However, there was a significant difference in gene expression between cells containing LSD1 and those null for LSD1. The results of the present study suggested that LSD1 is critical in the regulation of cell proliferation, but also indicated that LSD1 is not an absolute requirement for the stabilization of either p53 or DNMT1.
chromatin; epigenetics; FAD-dependent oxidase; histone modification; transcriptional repression; AAV, adeno-associated viral; AOL, amine oxidase-like; ATRA, all-trans retinoic acid; ChIP, chromatin immunoprecipitation; COBRA, combined bisulfite restriction analysis; CoREST, RE1-silencing transcription factor corepressor 1; DNMT1, DNA methyltransferase 1; ES, embryonic stem; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HA, homology arm; HDAC, histone deacetylase; HEK, human embryonic kidney; H3K4, histone H3 Lys4; H3K9, histone H3 Lys9; H3K9ac, H3K9 acetylation; JARID1, Jumonji, AT rich interactive domain 1; LINE-1, long interspersed nucleotide element 1; LSD, lysine-specific demethylase; me1, monomethyl; me2, dimethyl; me3, trimethyl; pAAV, AAV plasmid; PCNA, proliferating cell nuclear antigen; qPCR, quantitative PCR; SEPT, synthetic exon promoter trap; SET7/9, SET domain-containing histone methyltransferase 7/9; SWIRM, Swi3p/Rsc8p/Moira; TSS, transcriptional start site; VAT1L, vesicle amine transport protein 1 homologue-like; VIM, vimentin
Cancer progression is accompanied by widespread transcriptional changes and metabolic alterations. While it is widely accepted that the origin of cancer can be traced to the mutations that accumulate over time, relatively recent evidence favors a similarly fundamental role for alterations in the epigenome during tumorigenesis. Changes in epigenetics that arise from post-translational modifications of histones and DNA are exploited by cancer cells to upregulate and/or downregulate the expression levels of oncogenes and tumor suppressors, respectively. Although the mechanisms behind these modifications, in particular how they lead to gene silencing and activation, are still being understood, most of the enzymatic machinery of epigenetics require metabolites as substrates or cofactors. As a result, their activities can be influenced by the metabolic state of the cell. The purpose of this review is to give an overview of cancer epigenetics and metabolism and provide examples of where they converge.
Warburg effect; metabolic signaling; NAD metabolism; α-ketoglutarate and cancer; TCA cycle; histone modifications; IDH mutations