bims-unfpre 2019-07-07 papers

Issue of 2019–07–07
three papers selected by
Susan Logue, University of Manitoba

Nat Cell Biol. 2019 Jul;21(7): 889-899

ATF4 couples MYC-dependent translational activity to bioenergetic demands during tumour progression.

Feven Tameire, Ioannis I Verginadis, Nektaria Maria Leli, Christine Polte, Crystal S Conn, Rani Ojha, Carlo Salas Salinas, Frank Chinga, Alexandra M Monroy, Weixuan Fu, Paul Wang, Andrew Kossenkov, Jiangbin Ye, Ravi K Amaravadi, Zoya Ignatova, Serge Y Fuchs, J Alan Diehl, Davide Ruggero, Constantinos Koumenis.

The c-Myc oncogene drives malignant progression and induces robust anabolic and proliferative programmes leading to intrinsic stress. The mechanisms enabling adaptation to MYC-induced stress are not fully understood. Here we reveal an essential role for activating transcription factor 4 (ATF4) in survival following MYC activation. MYC upregulates ATF4 by activating general control nonderepressible 2 (GCN2) kinase through uncharged transfer RNAs. Subsequently, ATF4 co-occupies promoter regions of over 30 MYC-target genes, primarily those regulating amino acid and protein synthesis, including eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), a negative regulator of translation. 4E-BP1 relieves MYC-induced proteotoxic stress and is essential to balance protein synthesis. 4E-BP1 activity is negatively regulated by mammalian target of rapamycin complex 1 (mTORC1)-dependent phosphorylation and inhibition of mTORC1 signalling rescues ATF4-deficient cells from MYC-induced endoplasmic reticulum stress. Acute deletion of ATF4 significantly delays MYC-driven tumour progression and increases survival in mouse models. Our results establish ATF4 as a cellular rheostat of MYC activity, which ensures that enhanced translation rates are compatible with survival and tumour progression.

DOI: https://doi.org/10.1038/s41556-019-0347-9

Science. 2019 Jul 05. pii: eaaw4144. [Epub ahead of print]365(6448):

The heme-regulated inhibitor is a cytosolic sensor of protein misfolding that controls innate immune signaling.

Multiple cytosolic innate sensors form large signalosomes after activation, but this assembly needs to be tightly regulated to avoid accumulation of misfolded aggregates. We found that the eIF2α kinase heme-regulated inhibitor (HRI) controls NOD1 signalosome folding and activation through a process requiring eukaryotic initiation factor 2α (eIF2α), the transcription factor ATF4, and the heat shock protein HSPB8. The HRI/eIF2α signaling axis was also essential for signaling downstream of the innate immune mediators NOD2, MAVS, and TRIF but dispensable for pathways dependent on MyD88 or STING. Moreover, filament-forming α-synuclein activated HRI-dependent responses, which suggests that the HRI pathway may restrict toxic oligomer formation. We propose that HRI, eIF2α, and HSPB8 define a novel cytosolic unfolded protein response (cUPR) essential for optimal innate immune signaling by large molecular platforms, functionally homologous to the PERK/eIF2α/HSPA5 axis of the endoplasmic reticulum UPR.

DOI: https://doi.org/10.1126/science.aaw4144

Science. 2019 Jul 05. 365(6448): 53-60

A COPII subunit acts with an autophagy receptor to target endoplasmic reticulum for degradation.

Yixian Cui, Smriti Parashar, Muhammad Zahoor, Patrick G Needham, Muriel Mari, Ming Zhu, Shuliang Chen, Hsuan-Chung Ho, Fulvio Reggiori, Hesso Farhan, Jeffrey L Brodsky, Susan Ferro-Novick.

The COPII-cargo adaptor complex Lst1-Sec23 selectively sorts proteins into vesicles that bud from the endoplasmic reticulum (ER) and traffic to the Golgi. Improperly folded proteins are prevented from exiting the ER and are degraded. ER-phagy is an autophagic degradation pathway that uses ER-resident receptors. Working in yeast, we found an unexpected role for Lst1-Sec23 in ER-phagy that was independent from its function in secretion. Up-regulation of the stress-inducible ER-phagy receptor Atg40 induced the association of Lst1-Sec23 with Atg40 at distinct ER domains to package ER into autophagosomes. Lst1-mediated ER-phagy played a vital role in maintaining cellular homeostasis by preventing the accumulation of an aggregation-prone protein in the ER. Lst1 function appears to be conserved because its mammalian homolog, SEC24C, was also required for ER-phagy.

DOI: https://doi.org/10.1126/science.aau9263