Arsenite-induced mitotic death involves stress response and is independent of tubulin polymerization

Abstract

Arsenite, a known mitotic disruptor, causes cell cycle arrest and cell death at anaphase. The mechanism causing mitotic arrest is highly disputed. We compared arsenite to the spindle poisons nocodazole and paclitaxel. Immunofluorescence analysis of α-tubulin in interphase cells demonstrated that, while nocodazole and paclitaxel disrupt microtubule polymerization through destabilization and hyperpolymerization, respectively, microtubules in arsenite-treated cells remain comparable to untreated cells even at supra-therapeutic concentrations. Immunofluorescence analysis of α-tubulin in mitotic cells showed spindle formation in arsenite-and paclitaxel-treated cells but not in nocodazole-treated cells. Spindle formation in arsenite-treated cells appeared irregular and multi-polar. γ-tubulin staining showed that cells treated with nocodazole and therapeutic concentrations of paclitaxel contained two centrosomes. In contrast, most arsenite-treated mitotic cells contained more than two centrosomes, similar to centrosome abnormalities induced by heat shock. Of the three drugs tested, only arsenite treatment increased expression of the inducible isoform of heat shock protein 70 (HSP70i). HSP70 and HSP90 proteins are intimately involved in centrosome regulation and mitotic spindle formation. HSP90 inhibitor 17-DMAG sensitized cells to arsenite treatment and increased arsenite-induced centrosome abnormalities. Combined treatment of 17-DMAG and arsenite resulted in a supra-additive effect on viability, mitotic arrest, and centrosome abnormalities. Thus, arsenite-induced abnormal centrosome amplification and subsequent mitotic arrest is independent of effects on tubulin polymerization and may be due to specific stresses that are protected against by HSP90 and HSP70.

Aneuploidy as an early mechanistic event in metal carcinogenesis

“…The induction of lagging chromosomes [14,16] suggests a disruption of microtubule assembly dynamics; however, two more recent studies suggest that arsenic does not affect spindle formation [7,21]. The second possibility is effects on the SAC, arsenic-induced mitotic cell death requires the activation of the SAC indicated by the activation and proper localization of BubR1, Mad2 and Cdc27 and the stabilization of securin and cyclin B, [7,17,18].…”

“…Centrosome amplification is induced by arsenic treatment, and it has been detected indirectly through the formation of multi polar spindles and directly by immunoflourescent staining of centrosomes [18,20,21,23,24,25]. Arsenite-induced centrosome amplification does not require dysfunctional p53, but the loss of p53 results in a significant increase in centrosome amplification which would lead inevitably to further instability [21,24]. Co-treatment with other carcinogens, such as nicotine-derived nitrosamine ketone (NNK) which reduces p53 in the nucleus, synergistically increases centrosome amplification [25].…”

JWA enhances As2O3-induced tubulin polymerization and apoptosis via p38 in HeLa and MCF-7 cells

“…In HeLa cells, the microtubule poison nocodazole partially blocks accumulation of condensed chromatin within surface blebs, and confocal imaging revealed that microtubules associate closely with chromatin within late apoptotic surface blebs [19,20]. However, Taylor et al [21] reported that arsenite-induced mitotic death was independent of tubulin polymerization. Beside arsenic, a number of anti-cancer drugs produce proapoptotic effects by their microtubule-toxicity.…”

Mechanisms of metal-induced centrosome amplification

“…Arsenic-induced centrosome amplification occurs in mitotic cells but does not appear to occur in interphase cells [7] and is associated with a prolonged mitotic arrest [5–7]. Arsenic-induced mitotic arrest and subsequent centrosome amplification and multipolar spindle formation requires the spindle assembly checkpoint as data show that inhibition of BubR1 and Mad2 attenuate arsenic-induced centrosome amplification [7,8]. In addition, data show that the amplified centrosomes caused by arsenic contain either abnormal centriole numbers or no centrioles at all, suggesting centrosome fragmentation and/or overexpression of pericentriolar proteins are involved in the underlying mechanism [7].…”