Short Title: Arsenic induces inactivation of p53 by mot-2 Page 1 of 29 Toxicological Sciences

Page 2 Inorganic arsenic is a ubiquitous environmental contaminant associated with an increased risk of skin hyperkeratosis and cancer. Although several hypotheses that relate to arsenic-induced carcinogenesis have been suggested, the mechanism of action remains obscure. In the present study, molecular mechanisms underlying the inactivation of p53 function and the genomic instability in malignant transformation of the human keratinocyte cell line, HaCaT, induced by low levels of arsenic were investigated. Our results show that long-term exposure of HaCaT cells to sodium arsenite (1.0 µM) increases their proliferation, causes DNA double-strand breaks, and induce anchorage-independent growth. In arsenite-exposed cells, the levels of phospho-p53, p21, and mdm2 increase at early times after exposure. The levels, however, decrease with longer times. Interaction of the promoter of mot-2 (a p53 inhibitor) with nuclear factor κB (NF-κB) was established by Southwestern and Western blot assays. Blockage of NF-κB prevents the increases of arsenite-induce