Arsenic carcinogenicity: Metabolic disruption leads to loss of PTEN function

描述（由申请人提供）：人类砷暴露被认为是现代人类历史上最严重的环境中毒。砷对人体的毒性会导致多种靶组织发生癌症，包括肺、膀胱和皮肤。尽管无可争议的流行病学反复证实了砷的致癌性，但没有明确的机制解释砷的致癌作用。磷酸酶和紧张素同系物（PTEN）基因是一种肿瘤抑制基因，在人类癌症研究中占有独特的地位，因为它可以说是唯一的肿瘤抑制基因，通常通过家族性和散发性癌症的功能丧失而参与。PTEN的主要肿瘤抑制机制是通过它使Akt通路失活，Akt通路是细胞存活和增殖的主要效应因子。Akt激活是体外慢性砷暴露的常见结果，包括砷诱导恶性转化的细胞培养模型。本项目旨在测试砷暴露可使PTEN失活的新机制，从而导致其肿瘤抑制功能丧失，导致Akt活化和砷诱导的致癌。使用适合于体外恶性转化研究的细胞培养模型，我们的初步数据建立了无机三价砷的一般效应

DESCRIPTION (provided by applicant): Human arsenic exposure has been referred to as the worst environmental poisoning in modern human history. Arsenic toxicity in exposed humans causes cancer in diverse target tissues, including lung, bladder and skin. Despite incontrovertible epidemiology that repeatable confirms arsenic carcinogenicity, no definitive mechanism explaining the carcinogenic action of arsenic exists. The phosphatase and tensin homologue (PTEN) gene is a tumor suppressor gene that holds a unique place in human cancer research, in that it is arguably the only tumor suppressor gene that is commonly involved through loss of function in both familial and sporadic cancers. The principal tumor-suppressive mechanism of PTEN is through it inactivation of the Akt pathway, a central effector of cell survival and proliferation. Akt activation is a frequently reported consequence of chronic arsenic exposure in vitro, including cell culture models of arsenic-induced malignant transformation. This project seeks to test a novel mechanism by which arsenic exposure could inactivate PTEN, leading to loss of its tumor-suppressive function, leading to Akt activation and arsenic-induced carcinogenesis. Using a cell culture model amenable to in vitro studies of malignant transformation, our preliminary data establish that a general effect of inorganic trivalent arsenic (arsenite) exposure is the disruption of cellular metabolism, including the induction of aerobic glycolysis and elevation of intracellular NADH level. This is intriguing because PTEN activity has been demonstrated to be inhibited by elevated NADH. We hypothesize that an important mechanism of arsenic's carcinogenic action is its ability to disturb fundamental cell metabolism, leading to elevated NADH levels, and the functional loss of the tumor suppressor, PTEN. Two specific aims will test this hypothesis. Aim 1 will define the temporal relationship and associations between PTEN activity, Akt activation, and key phenotypes associated with the acquisition of malignancy in BEAS-2B cells chronically exposed to a non-cytotoxic, environmentally relevant concentration of arsenite. Aim 2 is designed to incorporate data collected in Aim 1 to affect sustained, experimentally modulated, increased and decreased NADH level in derived BEAS-2B cell lines. These BEAS-2B cell lines will be subjected to the malignant transformation protocol used in Aim 1 (1 um arsenite for approximately 17 weeks). Our hypothesis predicts that upward or downward modulation of NADH level will result in enhanced or diminished malignant transformation, respectively. This R03 project proposes an initial test of a novel mechanism involving metabolic control of cell signaling in environmental carcinogenesis.