Medium-chain fatty acids mitigate endoplasmic reticulum stress in yeast cells

Upon endoplasmic reticulum (ER) stress, eukaryotic cells commonly trigger cytoprotective transcriptome changes, namely the unfolded protein response (UPR). In yeast Saccharomyces cerevisiae , the UPR is mediated by the transcription factor Hac1, which is induced in response to ER stress. Since Hac1 controls hundreds of genes, the biological phenomena that result from UPR are not yet fully understood. Here, we show that cells carrying a mutation to constitutively express Hac1 abundantly contained C10:0 and C12:0 fatty acids, known as medium-chain fatty acids (MCFs). UPR induction by some ER stress stimuli was attenuated by externally supplied MCFs in cells in which fatty acid elongation was genetically or pharmacologically halted. The cell survival assay also indicated the mitigation of ER stress by the MCFs. Moreover, we demonstrated that MCFs leads to the diffusion of a mutant transmembrane protein aggregated in the ER. We propose that, as a biologically beneficial outcome of UPR, MCFs are produced to change the properties of the ER membrane, such as fluidity, in ER-stressed yeast cells.