DNA damage is believed to be the main cause of the antiproliferative effect of cisplatin, a cornerstone agent in anticancer therapy. However, cisplatin can be expected to react also with nucleophiles other than DNA. Using enucleated cells (cytoplasts) we demonstrate here that cisplatin-induced apoptotic signaling may occur independently of DNA damage. Cisplatin-induced caspase-3 activation in cytoplasts required calcium and the activity of the calcium-dependent protease calpain. It is known that calpain activation may be associated with endoplasmic reticulum (ER) stress, suggesting that the ER is a cytosolic target of cisplatin. Consistent with this hypothesis, cisplatin induced calpain-dependent activation of the ER-specific caspase-12 in cytoplasts as well as in intact cells. Cisplatin also induced increased expression of Grp78/BiP, another marker of ER stress. By contrast, the DNA-damaging topoisomerase II inhibitor etoposide did not induce apoptotic signaling in cytoplasts nor ER stress in intact cells. We have thus identified a novel mechanism of action of cisplatin. The results have implications for the understanding of resistance mechanisms as well as the unique efficiency of this drug.Cisplatin is a widely used chemotherapeutic agent generally recognized as a DNA-damaging drug. The molecular mechanisms that link the formation of DNA adducts to cell deathinducing signaling are not well understood. We have previously reported that cisplatin induces at least two apoptotic signaling pathways. One involves calpain activation and calpain-mediated cleavage of the proapoptotic BH3-only protein Bid. The other one results in MEKK1 1 -dependent modulation of the proapoptotic protein Bak (1, 2). Both pathways contribute to cytochrome c release and subsequent caspase activation.In aqueous solutions, the chloride ligands of cisplatin are replaced by water molecules generating a positively charged electrophile. This electrophile reacts with nucleophilic sites on intracellular macromolecules to form DNA, RNA, and protein adducts (3). Approximately 1% of intracellular cisplatin reacts with DNA resulting in intra-and interstrand cross-links, with an intrastrand cross-link between adjacent guanines as the most common adduct (4, 5). DNA adducts are considered the key toxic lesions induced by cisplatin; however, some studies have not shown a clear correlation between DNA adducts and cisplatin cytotoxicity (6, 7). The potential contribution of cisplatin-induced RNA or protein damage to cytotoxicity has not been examined in this respect (8).This prompted us to investigate the ability of cisplatin to induce apoptosis independently of DNA damage, and we here report the ability of cisplatin to induce apoptosis in enucleated cells. The cisplatin response was also found to involve endoplasmic reticulum (ER) stress. Altogether, we have here identified an apoptotic pathway induced by cisplatin independently of its DNA-damaging activity. This novel mechanism of action may contribute to the understanding of the causes of sensitivity an...

Calpain is a ubiquitous protease with potential involvement in apoptosis. We report that in human melanoma cells, cisplatin-induced calpain activation occurs early in apoptosis. Calpain activation and subsequent apoptosis were inhibited by calpeptin and PD150606, two calpain inhibitors with different modes of action. Furthermore, cisplatin induced cleavage of the BH3-only protein Bid, yielding a 14-kDa fragment similar to proapoptotic, caspase-cleaved Bid. However, Bid cleavage was inhibited by inhibitors of calpain, but not by inhibitors of caspases or of cathepsin L. Recombinant Bid was cleaved in vitro by both recombinant calpain and by lysates of cisplatin-treated cells. Cleavage was calpeptin sensitive, and the cleavage site was mapped between Gly70 and Arg71. Calpain-cleaved Bid induced cytochrome c release from isolated mitochondria. While calpeptin did not affect cisplatin-induced modulation of Bak to its proapoptotic conformation, a dominant-negative mutant of MEKK1 (dnMEKK) inhibited Bak modulation. dnMEKK did not, however, block Bid cleavage. The combination of dnMEKK and calpeptin had an additive inhibitory effect on apoptosis. In summary, calpain-mediated Bid cleavage is important in drug-induced apoptosis, and cisplatin induces at least two separate apoptotic signaling pathways resulting in Bid cleavage and Bak modulation, respectively.

In a panel of four human melanoma cell lines, equitoxic doses of cisplatin induced the proapoptotic conformation of the Bcl-2 family protein Bak prior to the execution phase of apoptosis. Because cisplatininduced modulation of the related Bax protein was seen in only one cell line, a degree of specificity in the signal to Bak is indicated. Little is known about upstream regulation of Bak activity. In this study, we examined whether the apoptosis-specific pathway mediated by a kinase fragment of MEKK1 (⌬MEKK1)

Relatively low travel costs and abundant opportunities for research funding in Switzerland and other developed countries allow researchers large amounts of international travel and collaborations, leading to a substantial carbon footprint. Increasing willingness to tackle this issue, in combination with the desire of many academic institutions to become carbon-neutral, calls for an in-depth understanding of academic air travel. In this study, we quantified and analyzed the carbon footprint of air travel by researchers from the École Polytechnique Fédérale de Lausanne (EPFL) from 2014 to 2016, which is responsible for about one third of EPFL’s total CO2 emissions. We find that the air travel impact of individual researchers is highly unequally distributed, with 10% of the EPFL researchers causing almost 60% of the total emissions from EPFL air travel. The travel footprint increases drastically with researcher seniority, increasing 10-fold from PhD students to professors. We found that simple measures such as restricting to economy class, replacing short trips by train and avoiding layovers already have the potential to reduce emissions by 36%. These findings can help academic institutions to implement travel policies which can mitigate the climate impact of their air travel.