Epigenetic Changes Induced by Environment and Diet in Cancer

The term ‘epigenetic’ refers to all heritable changes in gene expression and associated phenotypic traits that are not coded in the DNA sequence itself. Epigenetic inheritance includes DNA methylation, histone modifications, and micro-RNAs, all of which are essential mechanisms that allow the stable propagation of gene activity states from one generation of cells to the next. Many epidemiological and laboratory-based studies either confirm or implicate epigenetic changes induced by environmental, nutritional, and lifestyle factors in a variety of human cancer. Environmental factors known to play important roles in the etiology of human cancer include chemical carcinogens, such as those found in cigarette smoke; dietary contaminants, such as the aflatoxin B1; and physical carcinogen, such as UV radiation. Lifestyles such as smoking, alcohol consumption, excess exposure to sunlight, and fat consumption are environmental factors that contribute to human malignancies. Epigenetic mechanisms play a critical role in normal physiological responses to environmental stimuli that establish an appropriate gene expression pattern by altering the epigenetic state of the genome. Exposure to environmental, physical, and chemical carcinogens, infectious agents, and lifestyle may induce epigenetic changes that alter critical cellular processes including silencing of tumor suppressor genes, activation of oncogenes, aberrant cell cycle, defects in DNA repair, and deregulation of cell death, all of which may promote the development of cancer.