5). Yeast

cells exposed to environmental Cd2+ take up this metal through essential metal divalent transporters, including the Cch1p/Mid1p high affinity Ca2+ channel. Cd2+ competes with essential ions and, in the case of Ca2+, some kind of intracellular signaling that improves the affinity of Cch1p/Mid1p by its natural substrate can drive early Ca2+ capture. After some time, the reduction of external available Ca2+ favors the MK-2206 molecular weight entry of Cd2+ into the cells, due to minor competition between the two ions. Once inside cells, Cd2+ can bind two GSH molecules, forming Cd-[GS]2 complexes, which, in turn, are removed from the cytosol by Ycf1p or other GS-pumps such as the newly identified Vmr1p (Wawrzycka et al., 2010), which is not included in

the model. Alternatively, Cd2+ can be detoxified by GSH-independent pathways, such as those mediated by Pmr1p or Pmc1p. The pathway used is probably related to a balance between Cd2+ toxicity and metabolic status of the cells. Low Cd2+ concentration and/or high intracellular requirements for GSH are expected to drive more Cd2+ to Pmr1p or Pmc1p. The latter situation can occur, for example, during respiratory metabolism when YCF1 is down-regulated ( Mielniczki-Pereira et al., 2008). Cd2+ captured by Pmr1p into the Golgi will be released to the extracellular medium by the secretory pathway. In contrast, high Pmc1p expression will promote Cd2+ sequestration into the vacuole. In cells with high basal expression of Pmc1p compared to Pmr1p, the first carrier will be more responsive to Cd2+. When Cd2+ concentrations are high, simultaneous activation AZD6244 of GSH-dependent (e.g. Ycf1p) and independent detoxification systems can occur. If one of these mechanisms is impaired, cells may compensate by up-regulating

those that are still operative. This situation could produce a high degree of cell injury, including inhibition of mismatch repair, lipid peroxidation, and extensive oxidation of proteins. As a result, cells could trigger ER stress and activate the UPR mediated by Cod1p. We also speculate that Ycv1p can produce Ca2+ signals in response to Cd2+, which could activate biochemical pathways to cope with the toxicity. Ultimately, Cd2+ can be exported out of the cells directly by membrane proteins, such as also Yor1p, Alr1p or Pca1p (Nagy et al., 2006, Kern et al., 2005, Adle et al., 2007 and Adle et al., 2009). The authors declare that there are no conflicts of interest. This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Programa Nacional de Cooperação Acadêmica/Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (PROCAD/CAPES, Grant no. 0306053) and GENOTOX/Instituto ROYAL (CBiot-UFRGS). We thank Dr. Jacqueline Moraes Cardone and Dr. Cassiana Macagnan Viau for help with expression analysis. We also thank Dr. Delmo Santiago Vaistmann for help with atomic absorption procedures.