Mutational impact of chronic alcohol use on stem cells in cirrhotic liver

Abstract

27Excessive alcohol consumption increases the risk of developing liver cancer, but the 28 mechanism through which alcohol drives carcinogenesis is as yet unknown. Here, we 29 determined the mutational consequences of chronic alcohol use on the genome of human liver 30 stem cells prior to cancer development. No change in base substitution rate or spectrum could 31 be detected. Analysis of the trunk mutations in an alcohol-related liver tumor by multi-site 32 whole-genome sequencing confirms the absence of specific alcohol-induced mutational 33 signatures driving the development of liver cancer. However, we did identify an enrichment of 34 nonsynonymous base substitutions in cancer genes in stem cells of the cirrhotic livers, such as 35 recurrent nonsense mutations in PTPRK that disturb Epidermal Growth Factor (EGF)-36 signaling. Our results thus suggest that chronic alcohol use does not contribute to 37 carcinogenesis through altered mutagenicity, but instead induces microenvironment changes 38 which provide a 'fertile ground' for selection of cells with oncogenic mutations. 39 40 45hypotheses. The first hypothesis suggests that alcohol consumption may contribute to the 46 development of cancer through an increased mutation accumulation in the genome 4 . 47Consistently, the first metabolite of ethanol, acetaldehyde, is highly carcinogenic 5-7 and can 48 also contribute to the formation of mutagenic reactive oxygen species (ROS) [8][9][10][11] . Analysis of a 49 large number of tumor exomes and genomes showed that alcohol intake is associated with an 50 increased mutation load and different mutational characteristics [12][13][14][15] . The second hypothesis 51 2 suggests that an alcohol-induced change of microenvironment is an essential driver for 52 tumorigenesis by providing a fertile ground for cells with oncogenic mutations [16][17][18] . Indeed, 53 development of HCC is preceded by chronic inflammation and cirrhosis in about 80% of 54 patients and this cell-extrinsic damage appears a prerequisite for the formation of the majority 55 of liver cancers 18-20 . Additionally, Hepatitis C Virus (HCV)-induced cirrhotic livers show an 56 increase in the number and size of clonal patches with mutations in genes that are frequently 57 mutated in HCC 21 . Alcohol use itself has been associated with an increased number of cancer-58 stem-cell-like epithelial cell adhesion molecule (EpCAM)-positive cells in the cirrhotic liver 22 , 59 which may be driven by epithelial to mesenchymal transition through activation of the Wnt 60 pathway 23 , confirming that cellular composition changes can be induced by alcohol use. Yet, 61it is still uncertain whether an altered cellular environment is sufficient to drive the 62 development of cancer, or whether an increase in the mutation load is also required. The here 63 mentioned hypotheses are thus not mutually exclusive. 64 We have demonstrated previously that mutations accumulate linearly with age in liver 65 adult stem cells (ASCs) of healthy individuals, without controlling for...