Arsenic exposure is a worldwide environmental health problem causing multiple chronic diseases including cancer. Cancer results from mutations in, and epigenetic modifications of, oncogenes and tumor suppressor genes. The molecular mechanisms driving arsenic (iAs)-induced carcinogenesis are likely a complex interplay of multiple factors contributing to yet unidentified genetic changes responsible for tumorigenesis. One mechanism is the epigenetic effect of miRNA dysregulation. iAs-exposure induces chromosomal instability (CIN) and CIN contributes to carcinogenesis. We focused on mechanism and effects of overexpression of hsa- miR-186 on CIN in the previous funding period. miR-186 is an intronic miRNA and is overexpressed in iAs- induced squamous cell carcinoma (SCC). The parent gene encodes an alternative mRNA splicing factor that is disrupted by iAs-exposure. miR-186 overexpression in human keratinocytes suppresses two mitotic regulators and gives rise to aneuploidy, a hallmark of cancer. This investigation led to establishment of a new human keratinocyte model for iAs-induced carcinogenesis using Ker-CT cells that is more amenable to karyotype analysis necessary to analyze CIN for leads into carcinogenic mutations. We identified 5 additional miRNAs that are overexpressed in iAs-induced SCC and also in human keratinocytes (HaCaT) chronically exposed to low dose iAs. These miRNAs are predicted to target multiple proteins also targeted by known oncogenic miRNAs. This continuation application focuses on miRNAs dysregulated in iAs-induced SCC and proposes to identify additional miR-186 targets contributing to CIN and to characterize the impact of the additional 5 overexpressed miRNAs on carcinogenesis. The hypothesis underlying these studies is that dysregulation of RNA metabolism contributes to iAs-induced carcinogenesis by modulating gene expression and inducing CIN. The specific aims are: 1) Determine the mechanism of hsa-miR-186 overexpression inducing aneuploidy and CIN in new Ker-CT model; 2) Characterize the new Ker-CT model of iAs-induced skin carcinogenesis; 3) Investigate role in cellular transformation of miRNAs common to SCC and arsenite-exposed HaCaT cells. Mutations in cancer genes in cells transformed by miR-186 overexpression and arsenic exposure will be characterized providing information to fill a knowledge gap. Demonstrating that these miRNAs overexpressed in human iAs-induced SCC share targets with known oncogenic miRNAs will establish an epigenetic mechanism and be a major step forward in our understanding of the mechanism of iAs-induced carcinogenesis, thus filling a critical knowledge gap in our understanding. The principles learned will provide a translational framework for understanding the molecular mechanisms operative in iAs-induced carcinogenesis in other tissues and cell types. Identification of mutations in, or epigenetic silencing of, cancer genes induced by iAs exposure will be a major step forward in our understanding of the mechanism of iAs-induced carcinogenesis.

Narrative Some microRNAs can act as oncogenes or tumor suppressors by suppressing the expression of tumor suppressor or oncogene proteins. The proposed studies will determine whether microRNAs overexpressed in skin cancers caused by chronic arsenic exposure contribute to the development of skin cancer by targeting proteins in common with known oncogenic microRNAs.