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  • 1.
    Gowda, Naveen Kumar Chandappa
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kaimal, Jayasankar Mohanakrishnan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Masser, Anna E.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kang, Wenjing
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Friedländer, Marc R.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Andréasson, Claes
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Cytosolic splice isoform of Hsp70 nucleotide exchange factor Fes1 is required for the degradation of misfolded proteins in yeast2016In: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 27, no 8, p. 1210-1219Article in journal (Refereed)
    Abstract [en]

    Cells maintain proteostasis by selectively recognizing and targeting misfolded proteins for degradation. In Saccharomyces cerevisiae, the Hsp70 nucleotide exchange factor Fes1 is essential for the degradation of chaperone-associated misfolded proteins by the ubiquitin-proteasome system. Here we show that the FES1 transcript undergoes unique 3' alternative splicing that results in two equally active isoforms with alternative C-termini, Fes1L and Fes1S. Fes1L is actively targeted to the nucleus and represents the first identified nuclear Hsp70 nucleotide exchange factor. In contrast, Fes1S localizes to the cytosol and is essential to maintain proteostasis. In the absence of Fes1S, the heat-shock response is constitutively induced at normally non-stressful conditions. Moreover, cells display severe growth defects when elevated temperatures, amino acid analogues or the ectopic expression of misfolded proteins, induce protein misfolding. Importantly, misfolded proteins are not targeted for degradation by the ubiquitin-proteasome system. These observations support the notion that cytosolic Fes1S maintains proteostasis by supporting the removal of toxic misfolded proteins by proteasomal degradation. This study provides key findings for the understanding of the organization of protein quality control mechanisms in the cytosol and nucleus.

  • 2.
    Masser, Anna E.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Controlling protein homeostasis through regulation of Heat shock factor 12019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In order to thrive in a changing environment all organisms need to ensure protein homeostasis (proteostasis). Proteostasis is ensured by the proteostasis system that monitors the folding status of the proteome and regulates cell physiology and gene expression to counteract any perturbations. An increased burden on the proteostasis system activates Heat shock factor 1 (Hsf1) to induce transcription of the heat shock response (HSR), a transiently induced transcriptional program including core proteostasis genes, importantly those encoding the Hsp70 class of molecular chaperones. The HSR assists cells in counteracting the harmful effects of protein folding stress and restoring proteostasis. The work presented in this thesis is based on experiments with the Saccharomyces cerevisiae (yeast) model with the overall goal of deciphering how Hsp70 detects and impacts on perturbations of cellular proteostasis and controls Hsf1 activity.

    In Study I we describe the fundamental mechanism by which Hsp70 maintains Hsf1 in its latent state by controlling its ability to bind DNA. We found that Hsf1 and unfolded proteins directly compete for binding to the Hsp70 substrate-binding domain. During heat shock the pool of unfolded proteins mainly consist of misfolded, newly synthesized proteins. Severe out-titration of Hsp70 by misfolded substrates resulted in unrestrained Hsf1 activity inducing a previously uncharacterized genetic hyper-stress program. More insight into regulation of Hsp70 availability was gained in Study II where the two splice isoforms of the Hsp70 nucleotide exchange factor Fes1 were characterized. We found that the cytosolic splice isoform Fes1S is crucial to release unfolded proteins from Hsp70 and that impaired release results in strong Hsf1 activation.

    In Study III we developed methodology to easily measure the rapid changes in Hsf1 activity upon proteostatic perturbations and to monitor protein turnover using the novel bioluminescent reporter NanoLuc optimized for yeast expression (yNluc). In Study IV we report that yNluc also functions as an in vivo reporter that detects severe perturbations of de novo protein folding by its failure to fold to an active conformation under such conditions.

    Finally, in Study V we investigated how organellar proteostasis impacts on the availability of cytosolic Hsp70. We found that a lowered mitochondrial proteostatic load as a result of high translation accuracy extended lifespan and improved cytosolic proteostasis capacity, evidenced by more rapid stress recovery and less sensitivity to toxic misfolded proteins. In contrast, lowered mitochondrial translation accuracy decreased lifespan and impaired management of cytosolic protein aggregates as well as elicited a general transcriptional stress response.

    Taken together, the findings presented in this thesis advance our understanding of how the regulatory mechanisms of the proteostasis system function. Furthermore, they provide novel methodology that will facilitate future studies to improve our understanding how cells integrate internal and external stress cues to control proteostasis.

  • 3.
    Masser, Anna E.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Induction of the heat-shock response by misfolded proteins2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cells respond to stress by transcriptional changes intended for stress survival and adaption to further stresses. Heat shock is an intensively studied stress condition that induces in a plethora of physiological changes including increased protein misfolding. The heat-shock response (HSR) is an evolutionary conserved transcriptional response to elevated temperatures. In yeast, the HSR is governed by the transcription factors Hsf1 and Msn2/4. The HSR counteracts protein-folding stress by upregulating the expression of proteins involved in the proteostasis network including molecular chaperones and proteins involved in proteasomal degradation. Msn2/4 activity is controlled through complex signal transduction pathways involving Protein Kinase A (PKA). Hsf1 is thought to be regulated by chaperone titration, a model adapted from bacterial stress-sensing, but the mechanisms underlying its regulation are poorly understood. Here we investigate the influence that accumulated misfolded proteins have on the HSR. In study I, we evaluate a novel bioluminescent reporter system, Nanoluciferase (Nluc), for studies of the HSR in yeast. We find that codon-optimized Nluc faithfully reports on the rapid changes associated with gene induction during stress. In study II, we investigate the Hsp70 nucleotide exchange factor Fes1 and find that its nuclear splice-isoform Fes1S is involved in the degradation of misfolded proteins and a negative regulator of the HSR. In study III, we build on study II and make use of fes1Δ cells as a model for cells that have accumulated misfolded proteins. We find that accumulated misfolded proteins specifically activate Hsf1 and not Msn2/4. Interestingly, accumulated misfolded proteins potently modify both the amplitude and range of the HSR. Our findings lay the groundwork for further studies on the mechanisms that make accumulated proteins rewire cellular stress responses and Hsf1 activation.

  • 4.
    Masser, Anna E.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Andréasson, Claes
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    A co-translational folding reporter to monitor proteostasisManuscript (preprint) (Other academic)
  • 5.
    Masser, Anna E.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kandasamy, Ganapathi
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kaimal, Jayasankar Mohanakrishnan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Andréasson, Claes
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Luciferase NanoLuc as a reporter for gene expression and protein levels in Saccharomyces cerevisiae2016In: Yeast, ISSN 0749-503X, E-ISSN 1097-0061, Vol. 33, no 5, p. 191-200Article in journal (Refereed)
    Abstract [en]

    Reporter proteins are essential tools in the study of biological processes and are employed to monitor changes in gene expression and protein levels. Luciferases are reporter proteins that enable rapid and highly sensitive detection with an outstanding dynamic range. Here we evaluated the usefulness of the 19 kDa luciferase NanoLuc (Nluc), derived from the deep sea shrimp Oplophorus gracilirostris, as a reporter protein in yeast. Cassettes with codon-optimized genes expressing yeast Nluc (yNluc) or its destabilized derivative yNlucPEST have been assembled in the context of the dominant drug resistance marker kanMX. The reporter proteins do not impair the growth of yeast cells and exhibit half-lives of 40 and 5 min, respectively. The commercial substrate Nano-Glo (R) is compatible with detection of yNluc bioluminescence in < 50 cells. Using the unstable yNlucPEST to report on the rapid and transient expression of a heat-shock promoter (PCYC1-HSE), we found a close match between the intensity of the bioluminescent signal and mRNA levels during both induction and decay. We demonstrated that the bioluminescence of yNluc fused to the C-terminus of a temperature-sensitive protein reports on its protein levels. In conclusion, yNluc and yNlucPEST are valuable new reporter proteins suitable for experiments with yeast using standard commercial substrate.

  • 6.
    Masser, Anna E.
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Kang, Wenjing
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Friedländer, Marc R.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Andréasson, Claes
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Cytoplasmic protein misfolding titrates nuclear Hsp70 to unleash active Hsf1Manuscript (preprint) (Other academic)
  • 7.
    Nejedla, Michaela
    et al.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Li, Zhilun
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Masser, Anna E.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Biancospino, Matteo
    Spiess, Matthias
    Mackowiak, Sebastian D.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Friedländer, Marc R.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Karlsson, Roger
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    A Fluorophore Fusion Construct of Human Profilin I with Non-Compromised Poly(L-Proline) Binding Capacity Suitable for Imaging2017In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 429, no 7, p. 964-976Article in journal (Refereed)
    Abstract [en]

    Profilin is vital for actin organisation in eukaryotic cells. It controls actin filament formation by binding monomeric actin and numerous proteins involved in polarised actin assembly. Important for the latter is the interaction surface formed by the N- and C-terminal helices, which pack close to each other on one side of the molecule at a distance from the actin site and mediate binding to poly-proline sequences present in many of the targeted proteins. Via these interactions, profilin contributes to the spatiotemporal control of actin filament growth. Studies of profilin dynamics in living cells by imaging techniques have been hampered by problems to generate fusion constructs with fluorophore proteins without negatively impacting on its poly-proline binding. With the object to circumvent this problem, we have generated an internal fusion of profilin with the green fluorescent variant citrine, here referred to as citrine profilin. The characterisation of citrine profilin (CIT-Pfn) demonstrates that it has full capacity to interact with poly-proline and also binds phosphatidylinositol lipids and actin, albeit with 10 times reduced affinity for the latter. Imaging of living cells expressing CIT-Pfn showed a distribution of the fusion protein similar to endogenous profilin. Furthermore, CIT-Pfn rescued the phenotypes observed after the Crispr/Cas9 knockout of the profilin 1 gene, including the lost migratory capacity characterising the knockout cells. Based on this, we conclude that the CIT-Pfn construct will be useful as a tool for displaying profilin localisation in living cells and obtaining information on its dynamic organisation under different conditions and activations of the actin microfilament and microtubule systems.

  • 8.
    Suhm, Tamara
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Kaimal, Jayasankar Mohanakrishnan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Dawitz, Hannah
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Peselj, Carlotta
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Masser, Anna E.
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Hanzén, Sarah
    Ambrožič, Matevž
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Smialowska, Agata
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Björck, Markus L.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nyström, Thomas
    Büttner, Sabrina
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute. University of Graz, Austria.
    Andréasson, Claes
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Ott, Martin
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mitochondrial Translation Efficiency Controls Cytoplasmic Protein Homeostasis2018In: Cell Metabolism, ISSN 1550-4131, E-ISSN 1932-7420, Vol. 27, no 6, p. 1309-1322Article in journal (Refereed)
    Abstract [en]

    Cellular proteostasis ismaintained via the coordinated synthesis, maintenance, and breakdown of proteins in the cytosol and organelles. While biogenesis of the mitochondrial membrane complexes that execute oxidative phosphorylation depends on cytoplasmic translation, it is unknown how translation within mitochondria impacts cytoplasmic proteostasis and nuclear gene expression. Here we have analyzed the effects of mutations in the highly conserved accuracy center of the yeast mitoribosome. Decreased accuracy of mitochondrial translation shortened chronological lifespan, impaired management of cytosolic protein aggregates, and elicited a general transcriptional stress response. In striking contrast, increased accuracy extended lifespan, improved cytosolic aggregate clearance, and suppressed a normally stress-induced, Msn2/4-dependent interor-ganellar proteostasis transcription program (IPTP) that regulates genes important for mitochondrial proteostasis. Collectively, the data demonstrate that cytosolic protein homeostasis and nuclear stress signaling are controlled by mitochondrial translation efficiency in an inter-connected organelle quality control network that determines cellular lifespan.

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