Int. J. Environ. Res. Public Health 2012, 9, 474-495; doi:10.3390/ijerph9020474 OPEN ACCESS International Journal of Environmental Research and Public Health ISSN 1660-4601 www.mdpi.com/journal/ijerph Article Microtubules as a Critical Target for Arsenic Toxicity in Lung Cells in Vitro and in Vivo Yinzhi Zhao, Paul Toselli and Wande Li * Department of Biochemistry, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA; E-Mails: yinzhi@bu.edu (Y.Z.); paulacs@bu.edu (P.T.) * Author to whom correspondence should be addressed; E-Mail: wandeli@bu.edu; Tel.: +1-617-638-5485, Fax: +1-617-638-5339. Received: 29 December 2011; in revised form: 29 January 2012 / Accepted: 30 January 2012 / Published: 1 February 2012 Abstract: To understand mechanisms for arsenic toxicity in the lung, we examined effects of sodium m-arsenite (As3+) on microtubule (MT) assembly in vitro (0–40 µM), in cultured rat lung fibroblasts (RFL6, 0–20 µM for 24 h) and in the rat animal model (intratracheal instillation of 2.02 mg As/kg body weight, once a week for 5 weeks). As3+ induced a dose-dependent disassembly of cellular MTs and enhancement of the free tubulin pool, initiating an autoregulation of tubulin synthesis manifest as inhibition of steady-state mRNA levels of I-tubulin in dosed lung cells and tissues. Spindle MT injuries by As3+ were concomitant with chromosomal disorientations. As3+ reduced the binding to tubulin of [3H]N-ethylmaleimide (NEM), an -SH group reagent, resulting in inhibition of MT polymerization in vitro with bovine brain tubulins which was abolished by addition of dithiothreitol (DTT) suggesting As3+ action upon tubulin through -SH groups. In response to As3+, cells elevated cellular thiols such as metallothionein. Taxol, a tubulin polymerization agent, antagonized both As3+ and NEM induced MT depolymerization. MT–associated proteins (MAPs) essential for the MT stability were markedly suppressed in As3+-treated cells. Thus, tubulin sulfhydryls and MAPs are major molecular targets for As3+ damage to the lung triggering MT disassembly cascades. Keywords: trivalent arsenic (As3+); microtubules (MTs); tubulin; tubulin mRNA; tubulin sulfhydryl groups (-SH); microtubule-associated proteins (MAPs); chromosomal disorientations; metallothionein; taxol