SPERMINE OXIDATION AND EPIGENETIC REGULATION: IMPLICATIONS FOR INFLAMMATION/INFECTION-ASSOCIATED CARCINOGENESIS

polyamine;spermine oxidase;Helicobacter pylori;gastric cancer;inflammation;infection;epigenetic;microRNA;miR-124;methylation;gastritis;Colombia;Nariño;not listed

Murray Stewart, TracyPapadopoulos, Nickolas ;

Johns Hopkins University

关键词: polyamine;    spermine oxidase;    Helicobacter pylori;    gastric cancer;    inflammation;    infection;    epigenetic;    microRNA;    miR-124;    methylation;    gastritis;    Colombia;    Nariño;    not listed;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/40679/MURRAYSTEWART-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Intracellular mammalian polyamine catabolism occurs through 2 distinct pathways, both of which culminate in oxidation reactions that generate highly reactive, potentially toxic byproducts. In the back-conversion to spermidine, spermine can either undergo direct oxidation by spermine oxidase (SMOX) or be acetylated by spermidine/spermine N1-acetyltransferase (SSAT), followed by subsequent oxidation by acetylpolyamine oxidase (APAO). Polyamines are absolutely essential for cell viability and proliferation, and polyamine metabolism and intracellular concentrations are frequently dysregulated in hyperproliferative conditions such as cancer. As a result, many studies have successfully focused on the induction of polyamine catabolism as a rational target for antiproliferative chemotherapeutic intervention. However, it has also become apparent that chronically elevated levels of polyamine catabolism, particularly through SMOX activity, can have disease implications in non-tumorigenic cells. A variety of stimuli, including microbial pathogens and inflammatory signals, induce SMOX activity, generating the reactive oxygen species precursor hydrogen peroxide as a byproduct that, along with the reduction in protective spermine and spermidine levels, can have deleterious physiological effects resulting in the manifestation and promotion of multiple pathologies. The studies presented in this dissertation investigate some of the mechanisms involved in the induction of SMOX in gastric epithelial cells exposed to Helicobacter pylori. This induction and subsequent oxidative DNA damage has been causally associated with the development of gastric cancer from chronic gastritis. We identify a miRNA (hsa-miR-124) that directly targets the 3’-UTR of spermine oxidase, thereby repressing the expression of SMOX mRNA and protein. Importantly, this miRNA becomes silenced via DNA hypermethylation in several epithelial cancers that are associated with chronic inflammation and/or infection, including H. pylori-associated gastric cancer. We demonstrate that overexpressing miR-124 in gastric adenocarcinoma cells abrogates the induction of SMOX mRNA and activity that occurs upon exposure to H. pylori. Importantly, we present preliminary data from human samples suggesting that increased methylation of miR-124 identifies populations at high risk for gastric carcinogenesis through its modulation of SMOX expression. Additionally, using a conditional SMOX overexpression system, we develop an in vitro model to investigate the molecular mechanisms through which SMOX-generated oxidative DNA damage contributes to tumorigenesis. We demonstrate that SMOX overexpression results in the down-regulation of the MGMT tumor suppressor gene and propose the recruitment of epigenetic chromatin modifiers to regions of oxidative DNA damage as a mechanism for SMOX-dependent tumor suppressor gene silencing. Combined, these studies suggest a mechanism by which pathogen-induced SMOX can result in epigenetic silencing of critical genes and possibly even feed-forward through a miRNA regulatory mechanism to exacerbate this phenomenon.