Kinetochore genes are required to fully activate secretory pathway expansion in S. cerevisiae under induced ER stress

Abstract

Basal ER stress occurs when proteins misfold in normal physiological conditions and are corrected by the unfolded protein response (UPR). Elevated ER stress occurs when misfolding is refractory as found in numerous diseases such as atherosclerosis, Type II diabetes and some cancers. In elevated ER stress it is unclear whether cells utilise the same or different networks of genes as in basal levels of ER stress. To probe this question, we used secretory pathway reporters Yip3p-GFP, Erv29p-GFP, Orm2p-GFP and UPREpr-GFP placed on the yeast deletion mutant array (DMA) genetic background. The reporter's expression levels, measured by automated microscopy, at basal versus elevated ER stress induced by the over-expression of CPY* were compared. A novel group of kinetochore genes (CTF19 complex) were found to be uniquely required for full induction of all four ER stress reporters in elevated stress. A follow-up reporter screen was developed by mating the ctf19Δ kinetochore gene deletion strain into the genome-wide XXXp-GFP tagged library then testing with over-expressed CPY*. This screen identified Bcy1p and Bfr1p as possible signalling points that down-regulate the UPR and secretory pathway when kinetochore proteins are absent under elevated stress conditions. Bfr1p appears to be a checkpoint that monitors the integrity of kinetochores at increased levels of ER stress. This study concludes that functional kinetochores are required for full activation of the secretory pathway in elevated ER stress and that the responses to basal and elevated levels of ER stress require different networks of genes.

Genetic interaction networks mediate individual statin drug response in Saccharomyces cerevisiae

“…The EMC complex use per se is worthy of comment because in S288C subunits individually have an effect on intracellular traffic 38 and it is possible the number of subunits used are proportional to ER stress in S288C compared to the statin-resistant strains. Thirdly, induced ER stress requires secretory pathway gene interactions with kinetochore genes 60 and here we detected the COMA complex (Ctf19p, Okp1p, Mcm21p and Ame1p) for atorvastatin and cerivastatin response in all genetic backgrounds (except YPS606 in cerivastatin) in one specific community (Supplementary Table S9). Fourthly, we demonstrated that UPR-specific communities containing CWH41, IRE1 and/or HAC1 had different complements of other UPR-related genes depending on genetic background and also on whether the statin drug was atorvastatin or cerivastatin.…”

Local translation of yeastERG4mRNA at the endoplasmic reticulum requires the brefeldin A resistance protein Bfr1

“…The non-canonical RBP Bfr1p is involved in several cellular processes including transfer and 123 retention of mRNAs to P-bodies (Simpson et al 2014;Weidner et al 2014), translation (Lang 124 et al 2001), and response to functional failure of the yeast spindle pole body or kinetochore 125 (Sezen et al 2009;Low et al 2014). We generated bfr1 mutants in order to address the 126 question of whether RNA-binding is required for all processes.…”

The endoplasmic reticulum-associated mRNA-binding proteins ERBP1 and ERBP2 interact in bloodstream-formTrypanosoma brucei

“…In yeast, it is associated with over 1,000 different mRNAs, enriched for those encoding ribosomal proteins and mRNAs that are translated at the ER (Lapointe et al, 2015). In addition to a role in stress granules, Bfr1 has been implicated in ER quality control (Low et al, 2014) and correct nuclear segregation (Xue et al, 1996). The physical interaction map (https://www.yeastgenome.org/locus/S000005724/interaction) includes five proteins related to mRNA decay: with Xrn1p, Dcp2p, Scp160p, Puf3p, and Asc1p (an orthologue of RACK1 that inhibits translation).…”