Microtubules as a Critical Target for Arsenic Toxicity in Lung Cells in Vitro and in Vivo

Yinzhi Zhao,Wande Li,Paul Toselli

doi:10.3390/ijerph9020474

Yinzhi Zhao, Wande Li + Show 1 more

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https://doi.org/10.3390/ijerph9020474

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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 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 [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.

Highlights

Arsenic (As) is an abundant metalloid element in the Earth’s crust
Exposure of cells to 5 μM As3+ for 24 h induced partial loss of MTs and no-organized tubulins with brightly staining accumulated in the perinuclear area where the MT organizing center (MTOC) is generally located [Figure 1(B)]
Mast cells exhibited high-density of depolymerized tubulin mass concentrated in the central area of cells

Summary

Introduction

Arsenic (As) is an abundant metalloid element in the Earth’s crust. Its compounds are widely used in industries, agricultures, and medicines [1]. In addition to occupational contact, consumption of contaminated drinking water is a major source of As exposure for humans. The lung is one of the major target organs of As, either from contaminated air or from polluted water, and leading to the development of bronchiectasis, bronchitis, chronic obstructive pulmonary disease (COPD), and malignancies [2,7]. Environmental exposure to As is generally in the form of either arsenite (As3+) or arsenate (As5+) [6,8,9], with As3+ being more potent in its biological effects than As5+ [9,10]. Since As3+ displays high affinity for -SH groups perturbing essential proteins [11,12], As3+ compounds are of major human health concern. The precise mechanisms leading to lung damages and cancinogenesis by As3+ remain unclear and should be further investigated

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