Endoplasmic reticulum stress

The accumulation of unfolded or misfolded proteins in endoplasmic reticulum (ER) leads to ER stress and the activation of unfolded protein response (UPR). Recent studies show that ER stress or UPR are associated with many diseases such as diabetes, hepatitis type C, prion disease, different kinds of tumors or Alzheimer's, Parkinson's and Huntington's disease and also with physiological processes like cell differentiation. When UPR is activated in yeast Saccharomyces cerevisiae, Ire1 protein oligomerizes, transautophosphorylates and activates itself. After this, Ire1 cleaves HAC1 mRNA to remove an intron. The spliced form of HAC1 mRNA is translated into the Hac1 transcription factor, which induces transcription of genes for chaperones of lumen ER, proteins involved in ERAD, synthesis of lipids etc. The cell uses this to reestablish homeostasis in ER. In mammals, the UPR is more complex and except Ire1 dependent pathway, it comprises Perk and Atf6 pathways, which are missing in yeast. Nevertheless, Perk is activated and regulated by the similar mechanism as Ire1 in S. cerevisiae. In consideration of broad spectrum of methods for genetic manipulation, rapid growth and well annotated genome, the yeast S. cerevisiae is a useful model for study of general mechanisms of UPR in mammals