Regulating cytoplasmic calcium homeostasis can reduce aluminum toxicity in yeast

Our previous study suggested that increased cytoplasmic calcium (Ca) signals may mediate aluminum (Al) toxicity in yeast (Saccharomyces cerevisiae). In this report, we found that a yeast mutant, pmc1, lacking the vacuolar calcium ion (Ca²⁺) pump Ca²⁺-ATPase (Pmc1p), was more sensitive to Al treatment than the wild-type strain. Overexpression of either PMC1 or an anti-apoptotic factor, such as Bcl-2, Ced-9 or PpBI-1, decreased cytoplasmic Ca²⁺ levels and rescued yeast from Al sensitivity in both the wild-type and pmc1 mutant. Moreover, pretreatment with the Ca²⁺ chelator BAPTA-AM sustained cytoplasmic Ca²⁺ at low levels in the presence of Al, effectively making the cells more tolerant to Al exposure. Quantitative RT-PCR revealed that the expression of calmodulin (CaM) and phospholipase C (PLC), which are in the Ca²⁺ signaling pathway, was down-regulated under Al stress. This effect was largely counteracted when cells overexpressed anti-apoptotic Ced-9 or were pretreated with BAPTA-AM. Taken together, our results suggest that the negative regulation of Al-induced cytoplasmic Ca signaling is a novel mechanism underlying internal resistance to Al toxicity.