To understand mechanisms for arsenic toxicity in the lung, we examined effects of sodium m-arsenite (As3+) on microtubule (MT) assembly in vitro (0â40 ÂµM), in cultured rat lung fibroblasts (RFL6, 0â20 ÂµM for 24 h) and in the rat
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To understand mechanisms for arsenic toxicity in the lung, we examined effects of sodium m
) 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 βI-tubulin in dosed lung cells and tissues. Spindle MT injuries by As3+
were concomitant with chromosomal disorientations. As3+
reduced the binding to tubulin of [3
H]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.