Project description:The unfolded protein response (UPR) maintains endoplasmic reticulum (ER) proteostasis through the activation of transcription factors such as XBP1s and ATF6. The functional consequences of these transcription factors for ER proteostasis remain poorly defined. Here, we describe methodology that enables orthogonal, small molecule-mediated activation of the UPR-associated transcription factors XBP1s and/or ATF6 in the same cell independent of stress. We employ transcriptomics and quantitative proteomics to evaluate ER proteostasis network remodeling owing to the XBP1s and/or ATF6 transcriptional programs. Furthermore, we demonstrate that the three ER proteostasis environments accessible by activating XBP1s and/or ATF6 differentially influence the folding, trafficking, and degradation of destabilized ER client proteins without globally affecting the endogenous proteome. Our data reveal how the ER proteostasis network is remodeled by the XBP1s and/or ATF6 transcriptional programs at the molecular level and demonstrate the potential for selectively restoring aberrant ER proteostasis of pathologic, destabilized proteins through arm-selective UPR-activation. The unfolded protein response adapts endoplasmic reticulum (ER) proteostasis via stress-responsive transcription factors including XBP1s and ATF6. Here, R. Luke Wiseman and colleagues implement technology for the orthogonal, ligand-dependent activation of XBP1s and/or ATF6 in a single cell. They characterize how XBP1s and/or ATF6 activation impacts ER proteostasis pathway composition and function. Adapted ER environments influence the proteostasis of destabilized protein variants without affecting the endogenous proteome. The work informs the development of proteostasis environment-adapting therapeutics for protein misfolding-related diseases. In order to activate both XBP1s and ATF6 in the same cell, we incorporated DHFR.ATF6 and tet-inducible XBP1s into a HEK293T-REx cell line stably expressing the tet-repressor. The HEK293DYG control cell line expresses tet-inducible eGFP and DHFR.YFP and is used as a control to demonstrate that the addition of doxycycline (dox) and trimethoprim (TMP) do not induce UPR genes. HEK293DYG cells were treated for 12 h with vehicle or 1 μg/mL dox and 10 μM TMP in biological triplicate. Cells were harvested and RNA was extracted using the RNeasy Mini Kit (Qiagen). Genomic DNA was removed by on-column digestion using the RNase-free DNase Set (Qiagen). Data from HEK293DYG cells showed no significant overlap in the ligand-treated transcriptomes obtained from HEK293DAX cells.

Project description:The unfolded protein response (UPR) maintains endoplasmic reticulum (ER) proteostasis through the activation of transcription factors such as XBP1s and ATF6. The functional consequences of these transcription factors for ER proteostasis remain poorly defined. Here, we describe methodology that enables orthogonal, small molecule-mediated activation of the UPR-associated transcription factors XBP1s and/or ATF6 in the same cell independent of stress. We employ transcriptomics and quantitative proteomics to evaluate ER proteostasis network remodeling owing to the XBP1s and/or ATF6 transcriptional programs. Furthermore, we demonstrate that the three ER proteostasis environments accessible by activating XBP1s and/or ATF6 differentially influence the folding, trafficking, and degradation of destabilized ER client proteins without globally affecting the endogenous proteome. Our data reveal how the ER proteostasis network is remodeled by the XBP1s and/or ATF6 transcriptional programs at the molecular level and demonstrate the potential for selectively restoring aberrant ER proteostasis of pathologic, destabilized proteins through arm-selective UPR-activation. The unfolded protein response adapts endoplasmic reticulum (ER) proteostasis via stress-responsive transcription factors including XBP1s and ATF6. Here, R. Luke Wiseman and colleagues implement technology for the orthogonal, ligand-dependent activation of XBP1s and/or ATF6 in a single cell. They characterize how XBP1s and/or ATF6 activation impacts ER proteostasis pathway composition and function. Adapted ER environments influence the proteostasis of destabilized protein variants without affecting the endogenous proteome. The work informs the development of proteostasis environment-adapting therapeutics for protein misfolding-related diseases. In order to activate both XBP1s and ATF6 in the same cell, we incorporated DHFR.ATF6 and tet-inducible XBP1s into a HEK293T-REx cell line stably expressing the tet-repressor. Selection of a single colony resulted in the HEK293DAX cell line in which XBP1s is induced by doxycycline and DHFR.ATF6 is activated by trimethoprim (TMP; TMP-dependent DHFR.ATF6 activation in HEK293DAX cells will henceforth be referred to as ATF6 activation for simplicity). HEK293DAX cells were treated for 12 h with vehicle, 1 ?g/mL dox, 10 ?M TMP, or both in biological triplicate. Cells were harvested and RNA was extracted using the RNeasy Mini Kit (Qiagen). Genomic DNA was removed by on-column digestion using the RNase-free DNase Set (Qiagen). Data from HEK293DYG cells showed no significant overlap in the ligand-treated transcriptomes obtained from the control HEK293DYG cells.

Project description:BACKGROUND:The protein homeostasis (proteostasis) network maintains balanced protein synthesis, folding, transport, and degradation within a cell. Failure to maintain proteostasis is associated with aging and disease, leading to concerted efforts to study how the network responds to various proteotoxic stresses. This is often accomplished using ectopic overexpression of well-characterized, model misfolded protein substrates. However, how cells tolerate large-scale, diverse burden to the proteostasis network is not understood. Aneuploidy, the state of imbalanced chromosome content, adversely affects the proteostasis network by dysregulating the expression of hundreds of proteins simultaneously. Using aneuploid haploid yeast cells as a model, we address whether cells can tolerate large-scale, diverse challenges to the proteostasis network. RESULTS:Here we characterize several aneuploid Saccharomyces cerevisiae strains isolated from a collection of stable, randomly generated yeast aneuploid cells. These strains exhibit robust growth and resistance to multiple drugs which induce various forms of proteotoxic stress. Whole genome re-sequencing of the strains revealed this was not the result of genetic mutations, and transcriptome profiling combined with ribosome footprinting showed that genes are expressed and translated in accordance to chromosome copy number. In some strains, various facets of the proteostasis network are mildly upregulated without chronic activation of environmental stress response or heat shock response pathways. No severe defects were observed in the degradation of misfolded proteins, using model misfolded substrates of endoplasmic reticulum-associated degradation or cytosolic quality control pathways, and protein biosynthesis capacity was not impaired. CONCLUSIONS:We show that yeast strains of some karyotypes in the genetic background studied here can tolerate the large aneuploidy-associated burden to the proteostasis machinery without genetic changes, dosage compensation, or activation of canonical stress response pathways. We suggest that proteotoxic stress, while common, is not always an obligate consequence of aneuploidy, but rather certain karyotypes and genetic backgrounds may be able to tolerate the excess protein burden placed on the protein homeostasis machinery. This may help clarify how cancer cells are paradoxically both highly aneuploid and highly proliferative at the same time.

Project description:The unfolded protein response (UPR) maintains endoplasmic reticulum (ER) proteostasis through the activation of transcription factors such as XBP1s and ATF6. The functional consequences of these transcription factors for ER proteostasis remain poorly defined. Here, we describe methodology that enables orthogonal, small molecule-mediated activation of the UPR-associated transcription factors XBP1s and/or ATF6 in the same cell independent of stress. We employ transcriptomics and quantitative proteomics to evaluate ER proteostasis network remodeling owing to the XBP1s and/or ATF6 transcriptional programs. Furthermore, we demonstrate that the three ER proteostasis environments accessible by activating XBP1s and/or ATF6 differentially influence the folding, trafficking, and degradation of destabilized ER client proteins without globally affecting the endogenous proteome. Our data reveal how the ER proteostasis network is remodeled by the XBP1s and/or ATF6 transcriptional programs at the molecular level and demonstrate the potential for selectively restoring aberrant ER proteostasis of pathologic, destabilized proteins through arm-selective UPR-activation. The unfolded protein response adapts endoplasmic reticulum (ER) proteostasis via stress-responsive transcription factors including XBP1s and ATF6. Here, R. Luke Wiseman and colleagues implement technology for the orthogonal, ligand-dependent activation of XBP1s and/or ATF6 in a single cell. They characterize how XBP1s and/or ATF6 activation impacts ER proteostasis pathway composition and function. Adapted ER environments influence the proteostasis of destabilized protein variants without affecting the endogenous proteome. The work informs the development of proteostasis environment-adapting therapeutics for protein misfolding-related diseases. In order to activate both XBP1s and ATF6 in the same cell, we incorporated DHFR.ATF6 and tet-inducible XBP1s into a HEK293T-REx cell line stably expressing the tet-repressor. The HEK293DYG control cell line expresses tet-inducible eGFP and DHFR.YFP and is used as a control to demonstrate that the addition of doxycycline (dox) and trimethoprim (TMP) do not induce UPR genes.

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Aneuploidy-induced proteotoxic stress can be effectively tolerated without dosage compensation, genetic mutations or stress responses

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