Loss of ERAD bridging factor UBX2 modulates lipid metabolism and leads to ER stress-associated apoptosis during cadmium toxicity in Saccharomyces cerevisiae

The endoplasmic reticulum (ER) stress potentially activates the unfolded protein response (UPR) and ER-associated protein degradation (ERAD) as quality-control mechanisms. During ERAD process, the ERAD adaptor protein Ubx2 serves as a bridging factor and transports the misfolded proteins from the ER to the cytosol for subsequent ubiquitylation and proteasomal degradation. Cadmium (Cd) is a toxic metal that initiates ER stress and has an impact on lipid homeostasis and this study focuses on the synergistic impact of Cd exposure and ERAD (usingubx2 increment strain). With Cd exposure inubx2 increment strain, we observed stunted growth and induction of ER stress. The ER stress was confirmed by measuring the expression of UPR marker (Kar2p), and mRNA expression of ER stress-responsive genes (HAC1, IRE1, ERO1,andPDI1), heat shock responsive genes (HSP104andHSP60), ERAD pathway genes (DOA10, CDC48, HRD1, andYOS9), and proteasome regulators (UBI14,andRPN4). We also observed aberrant membrane morphology with DiOC6 staining, and interrupted mitochondria with mitotracker dye using microscopic analysis. The cell's inability to relieve stress through adaptive response results in apoptosis and was assessed using acridine orange (AO)-ethidium bromide (EtBr) staining. Inubx2 increment strain, there was reduction in triacylglycerol (TAG) and lipid droplets (LDs), and increase in the phospholipids. The mRNA expression of lipid metabolic genes (LRO1, DGA1, ARE1, ARE2, andOLE1) supported the lipid pattern observed. Collectively, our data suggest that inSaccharomyces cerevisiae, the Cd exposure onubx2 increment strain induced cellular stress and has an impact on ERAD, UPR, and LD homeostasis.