Persistent transcriptional changes induced by nickel through epigenetic alterations

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Project Summary Nickel (Ni) compounds are environmental toxicants, prevalent in the atmosphere due to their use in several industrial processes, as well as extensive consumption of Ni containing products such as stainless steel, batteries, medical devices and medical implants. In addition, combustion of fossil fuels is a major source of Ni contamination in the atmosphere. Exposure to Ni is a major human health hazard, associated with a multitude of health risks including allergic contact dermatitis, bronchitis, pulmonary fibrosis, and pulmonary edema. Moreover, epidemiological studies indicate cancer development as a major outcome of Ni exposure. However, the molecular basis of Ni-induced diseases remains poorly understood. To better understand the molecular mechanisms underlying Ni-induced diseases, we investigated the effects of Ni-exposure on human epithelial cells. Our studies show that Ni-exposure-induced gene expression changes persist long after the cessation of exposure. This resulted in the cells undergoing epithelial-mesenchymal transition (EMT), and the EMT phenotype continued long after the termination of exposure. EMT is the process in which polarized epithelial cells lose cell-cell adhesion and acquire invasive and migratory mesenchymal properties. EMT is implicated in a number of diseases associated with Ni-exposure including asthma, fibrosis, cancer and metastasis. Therefore, our results suggest that persistent transcriptional changes caused by Ni exposure are likely important in the etiology of Ni-exposure associated diseases. The overarching goal of this grant is to understand the mechanisms that drive long-term transcriptional changes caused by Ni exposure. Our preliminary results suggest that Ni-exposure disrupts chromatin regulation mediated by the histone modification, H3K27me3 and the zinc finger protein, CTCF. Based on our preliminary results, we hypothesize that Ni-exposure increases chromatin accessibility through H3K27me3 loss, causing gene upregulation. CTCF binds the newly accessible chromatin and prevents H3K27me3 re-establishment after termination of Ni-exposure, thereby persistently altering gene expression. In Aim 1, we will investigate the role of H3K27me3-loss in Ni- induced persistent gene expression alterations in human lung epithelial cells. In Aim 2, we will investigate the mechanisms underlying Ni-induced persistent chromatin alterations by knocking-down CTCF and by disrupting CTCF binding sites using CRISPR/Cas9 system to examine if loss of CTCF binding could reverse Ni-induced persistent transcriptional changes. In Aim 3, we will examine the functional outcome of Ni-induced persistent transcriptional changes by investigating the tumor generating potential of Ni-exposed cells in in mice. The overall impact of our study will be the identification of the mechanisms underlying long-term transcriptional changes caused by nickel exposure, which will reveal the molecular basis of its pathogenicity, and will have major human health implications.