Long-term exposure to arsenic, esp. the inorganic trivalent arsenic (iAs), a human carcinogen that
occurs naturally in the earth's crust or work place due to industrial settings, has been linked to various
types of cancers, esp. lung cancer. It has been known for decades that multiple different mechanisms
might be involved in iAs-induced malignant transformation. However, whether and how iAs induces
cancer stem-like cells (CSCs) from non-stem cells hadn’t been studied. We had previously shown that
consecutive treatment of the human bronchial epithelial cells with 0.125 to 0.25 ¿M (~9 to 18ppb) iAs
for six months induced generation of the CSCs. In addition to the higher expression of the stemness
circuit genes, including Oct4, Sox2, myc, Klf4, etc., these iAs-induced CSCs also exhibited a unique
metabolic pattern featured with an active glycolysis and diminished mitochondrial oxidative
phosphorylation (OXPHOS). ChIP-seq analysis of the parental cells and the iAs-induced CSCs
revealed a substantial increase in the enrichment of histone H3 lysine4 trimethylation (H3K4me3), an
active epigenetic marker for gene transcription, among genes critical for the stemness and glycolysis
of the CSCs. To understand how iAs induces these metabolic and epigenetic changes and the
generation of the CSCs, we recently also investigated the capability of iAs on the activation of Nrf2 and
HIF1¿ signaling through both biochemical and ChIP-seq approaches. The data indicate that Nrf2 and
HIF1¿ may serve as initiators for the metabolic and epigenetic reprograming, and the acquisition of the
CSC features. Accordingly, we hypothesize that iAs-activated Nrf2 is an upstream activator for HIF1¿
signaling linked to glycolysis, and the subsequent epigenetic reprogramming and generation of the
CSCs. To test this hypothesis, the following three specific aims will be pursued: Aim1, dissecting Nrf2
activation pathways with an emphasis on the iAs-induced ubiquitination and degradation of Keap1, the
endogenous inhibitor of Nrf2; Aim 2, investigating mechanisms of Nrf2-dependent initiation of HIF1¿
signaling in the cells in response to iAs; and Aim 3, understanding how iAs-induced Nrf2-HIF1¿
signaling shifts the metabolism from mitochondrial TCA cycle to glycolysis that linked to reprogramming
of the histone methylation profiles and the generation of CSCs. We expect that the data from the
completion of this research plan will be the first to reveal the importance of Nrf2 and HIF1¿ in iAs-
induced CSCs, which may be translated into new strategies of cancer therapy by targeting the Nrf2-
HIF1¿ signaling and the CSCs.
