Unprecedented inhibition of tubulin polymerization directed by gold nanoparticles inducing cell cycle arrest and apoptosis

Abstract

The effect of gold nanoparticles (AuNPs) on the polymerization of tubulin has not been examined till now. We report that interaction of weakly protected AuNPs with microtubules (MTs) could cause inhibition of polymerization and aggregation in the cell free system. We estimate that single citrate capped AuNPs could cause aggregation of ∼10(5) tubulin heterodimers. Investigation of the nature of inhibition of polymerization and aggregation by Raman and Fourier transform-infrared (FTIR) spectroscopies indicated partial conformational changes of tubulin and microtubules, thus revealing that AuNP-induced conformational change is the driving force behind the observed phenomenon. Cell culture experiments were carried out to check whether this can happen inside a cell. Dark field microscopy (DFM) combined with hyperspectral imaging (HSI) along with flow cytometric (FC) and confocal laser scanning microscopic (CLSM) analyses suggested that AuNPs entered the cell, caused aggregation of the MTs of A549 cells, leading to cell cycle arrest at the G0/G1 phase and concomitant apoptosis. Further, Western blot analysis indicated the upregulation of mitochondrial apoptosis proteins such as Bax and p53, down regulation of Bcl-2 and cleavage of poly(ADP-ribose) polymerase (PARP) confirming mitochondrial apoptosis. Western blot run after cold-depolymerization revealed an increase in the aggregated insoluble intracellular tubulin while the control and actin did not aggregate, suggesting microtubule damage induced cell cycle arrest and apoptosis. The observed polymerization inhibition and cytotoxic effects were dependent on the size and concentration of the AuNPs used and also on the incubation time. As microtubules are important cellular structures and target for anti-cancer drugs, this first observation of nanoparticles-induced protein's conformational change-based aggregation of the tubulin-MT system is of high importance, and would be useful in the understanding of cancer therapeutics and safety of nanomaterials.

Inhibition of colon cancer cell growth by nanoemulsion carrying gold nanoparticles and lycopene

“…Also, with AN treatment, both Bax and P53 expressions were upregulated, while both Bcl-2 and PARP-1 expressions were downregulated. 35 In our experiment with the treatment of the nanoemulsion containing AN (0.16 ppm) plus LP (0.4 µM), the expressions of procaspases 8, 3, and 9, as well as PARP-1 and Bcl-2 declined, while the Bax expression rose. Thus, it was postulated that the AN-LP nanoemulsion could accelerate apoptosis through the activation of caspases 8, 9, and 3, and through regulation by the mitochondria.…”

“…34 In a similar study, Tsai et al 20 also reported that AN could activate caspase 3 to induce apoptosis after the treatment of leukemia cell, k562, with AN (5-6 nm) for 24 hours. More recently, Choudhury et al 35 further pointed out that AN could penetrate into lung cancer cell, A549, for conjugation with micro-organelle to induce apoptosis with arrest at G0/G1. Also, with AN treatment, both Bax and P53 expressions were upregulated, while both Bcl-2 and PARP-1 expressions were downregulated.…”

Characterization and in vitro studies on anticancer, antioxidant activity against colon cancer cell line of gold nanoparticles capped with Cassia tora SM leaf extract

“…Such a color transition is often indicative of changes in the metal oxidation state (Fujiwara et al 2007). The increase in the background may be due to the aggregation happened in the synthesized non-purified AuNPs-C. tora leaf conjugates (Choudhury et al 2013). It is well known that the particles aggregate the background scattering.…”

Potential Links between Cytoskeletal Disturbances and Electroneurophysiological Dysfunctions Induced in the Central Nervous System by Inorganic Nanoparticles

“…Plenty of evidence has shown that NPs can induce cell cycle arrest at different phases of the cell cycle. Some studies have indicated that gold NPs treatments could induce significantly increased cell-doubling times and more cell cycle arrest at the sub-G0/G1 phase [18] or S phase [29] than the control treatments, indicating that not all cells could complete the whole cell cycle after being exposed to gold NPs. Cell cycle analyses have suggested that Fe 3 O 4 NPs [32] and SiO 2 NPs [24] both resulted in G2/M arrest in PC12 cells, as well as an increase in the rate of apoptosis.…”

“…Inorganic NPs can range in size from 1-100 nm and have a high surface area-to-volume ratio; thus, they have marked reactivity and particle-to-cell contact and can be internalized by nerve cells, subsequently affecting the cytoskeleton system [18,19], which is important for sustaining fundamental cellular morphology. The cytoskeleton is composed of MTs, microfilaments (MFs), and intermediate filaments (IFs).…”