p53 Mediates Colistin-Induced Autophagy and Apoptosis in PC-12 Cells

The mechanism of colistin-induced neurotoxicity is still unknown. Our recent study (L.Zhang,Y.H.Zhao,W.J. Ding,G.Z. Jiang, Z.Y. Lu, L. Li, J. L. Wang, J.Li, and J.C. Li, Antimicrob Agents Chemother 59:2189-2197, 2015, http://dx.doi.org/10.1128/AAC.04092-14; H. Jiang, J. C. Li,T.Zhou, C. H. Wang, H. Zhang, and H. Wang, Int J Mol Med 33: 1298-1304, 2014, http://dx.doi.org/10.3892/ijmm. 2014.1684) indicates that colistin induces autophagy and apoptosis in rat adrenal medulla PC-12 cells, and there is interplay between both cellular events. As an important cellular stress sensor, phosphoprotein p53 can trigger cell cycle arrest and apoptosis and regulate autophagy. The aim of the present study was to investigate the involvement of the p53 pathway in colistin-induced neurotoxicity in PC-12 cells. Specifically, cells were treated with colistin (125 mu g/ml) in the absence and presence of a p53 inhibitor, pifithrin-alpha(PFT- alpha; 20 nM), for 12 h and 24 h, and the typical hallmarks of autophagy and apoptosis were examined by fluorescence/immunofluorescence microscopy and electron microscopy, real-time PCR, and Western blotting. The results indicate that colistin had a stimulatory effect on the expression levels of the target genes and proteins involved in autophagy and apoptosis, including LC3-II/ I, p53, DRAM (damage-regulated autophagy modulator), PUMA (p53 upregulated modulator of apoptosis), Bax, p-AMPK (activated form of AMP-activated protein kinase), and caspase-3. In contrast,colistin appeared to have an inhibitory effect on the expression of p-mTOR (activated form of mammalian target of rapamycin), which is another target protein in autophagy. Importantly, analysis of the levels of p53 in the cells treated with colistin revealed an increase in nuclear p53 at 12 h and cytoplasmic p53 at 24 h. Pretreatment of colistin-treated cells with PFT-alpha inhibited autophagy and promoted colistin-induced apoptosis. This is the first study to demonstrate that colistin-induced autophagy and apoptosis are associated with the p53-mediated pathway.