Protein translation and folding are coupled by an endoplasmic-reticulum-resident kinase
TL;DR: The cloning of perk is described, a gene encoding a type I transmembrane ER-resident protein that contains a protein-kinase domain most similar to that of the known eIF2α kinases, PKR and HRI that implicate PERK in a signalling pathway that attenuates protein translation in response to ER stress.
Abstract: Protein synthesis and the folding of the newly synthesized proteins into the correct three-dimensional structure are coupled in cellular compartments of the exocytosis pathway by a process that modulates the phosphorylation level of eukaryotic initiation factor-2alpha (eIF2alpha) in response to a stress signal from the endoplasmic reticulum (ER). Activation of this process leads to reduced rates of initiation of protein translation during ER stress. Here we describe the cloning of perk, a gene encoding a type I transmembrane ER-resident protein. PERK has a lumenal domain that is similar to the ER-stress-sensing lumenal domain of the ER-resident kinase Ire1, and a cytoplasmic portion that contains a protein-kinase domain most similar to that of the known eIF2alpha kinases, PKR and HRI. ER stress increases PERK's protein-kinase activity and PERK phosphorylates eIF2alpha on serine residue 51, inhibiting translation of messenger RNA into protein. These properties implicate PERK in a signalling pathway that attenuates protein translation in response to ER stress.
Citations
More filters
TL;DR: Dysfunction of the immune response and metabolic regulation interface can be viewed as a central homeostatic mechanism, dysfunction of which can lead to a cluster of chronic metabolic disorders, particularly obesity, type 2 diabetes and cardiovascular disease.
Abstract: Metabolic and immune systems are among the most fundamental requirements for survival. Many metabolic and immune response pathways or nutrient- and pathogen-sensing systems have been evolutionarily conserved throughout species. As a result, immune response and metabolic regulation are highly integrated and the proper function of each is dependent on the other. This interface can be viewed as a central homeostatic mechanism, dysfunction of which can lead to a cluster of chronic metabolic disorders, particularly obesity, type 2 diabetes and cardiovascular disease. Collectively, these diseases constitute the greatest current threat to global human health and welfare.
7,536 citations
Cites background from "Protein translation and folding are..."
...The principal branches of UPR signalling are mediated through three molecules: inositol-requiring enzyme 1 (IRE-1), PKR-like endoplasmic-reticulum kinase (PERK) and activating transcription factor 6 (ATF6...
[...]
TL;DR: Together, at least three mechanistically distinct arms of the UPR regulate the expression of numerous genes that function within the secretory pathway but also affect broad aspects of cell fate and the metabolism of proteins, amino acids and lipids.
Abstract: The endoplasmic reticulum (ER) responds to the accumulation of unfolded proteins in its lumen (ER stress) by activating intracellular signal transduction pathways - cumulatively called the unfolded protein response (UPR). Together, at least three mechanistically distinct arms of the UPR regulate the expression of numerous genes that function within the secretory pathway but also affect broad aspects of cell fate and the metabolism of proteins, amino acids and lipids. The arms of the UPR are integrated to provide a response that remodels the secretory apparatus and aligns cellular physiology to the demands imposed by ER stress.
5,701 citations
TL;DR: It is shown that obesity causes endoplasmic reticulum (ER) stress, which leads to suppression of insulin receptor signaling through hyperactivation of c-Jun N-terminal kinase (JNK) and subsequent serine phosphorylation of insulin receptors substrate–1 (IRS-1).
Abstract: Obesity contributes to the development of type 2 diabetes, but the underlying mechanisms are poorly understood. Using cell culture and mouse models, we show that obesity causes endoplasmic reticulum (ER) stress. This stress in turn leads to suppression of insulin receptor signaling through hyperactivation of c-Jun N-terminal kinase (JNK) and subsequent serine phosphorylation of insulin receptor substrate-1 (IRS-1). Mice deficient in X-box-binding protein-1 (XBP-1), a transcription factor that modulates the ER stress response, develop insulin resistance. These findings demonstrate that ER stress is a central feature of peripheral insulin resistance and type 2 diabetes at the molecular, cellular, and organismal levels. Pharmacologic manipulation of this pathway may offer novel opportunities for treating these common diseases.
3,484 citations
TL;DR: Protein kinases that phosphorylate the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) are activated in stressed cells and negatively regulate protein synthesis, resulting in the induction of the downstream gene CHOP (GADD153).
2,988 citations
Cites background from "Protein translation and folding are..."
...Gcn4p is a transcription factor that binds to and acti-the mammalian eIF2 kinases PERK and GCN2 repress translation of most mRNAs but selectively increase vates the target genes of this pathway (Hinnebusch, 1997).translation of Activating Transcription Factor 4 (ATF4), resulting in the induction of the downstream gene The striking conservation in structure and function between mammalian and yeast eIF2a and eIF2a kinasesCHOP (GADD153)....
[...]
...…on the The cellular response to unfolded proteins in the ER protein folding and degradation apparatus in the organ- (UPR) has two known functional components: inhibition elle (Harding et al., 1999; Harding et al., 2000; Sood et of protein synthesis and activation of gene expression. al., 2000a)....
[...]
...HRI attenuates protein synthesis in heme- Two distinct signaling pathways mediated by IRE1a & deficient erythroid precursors, matching hemoglobin b and ATF6 have been implicated in activating gene synthesis with iron availability (Chen and London, 1995). expression, whereas PERK was believed to be responsiIn cells deprived of nutrients, activation of mammalian ble for translational regulation in the UPR (reviewed in GCN2 conserves scarce amino acids for use in essential Kaufman, 1999)....
[...]
...PERK was required for ATF4 accumulation duringexpressed GCN4 mRNA contains several short up- stream open reading frames (uORFs)....
[...]
...In the absence of PERK, cells experimetabolic processes (Berlanga et al., 1999; Sood et al., ence more ER stress and are hypersensitive to its lethal 2000b)....
[...]
TL;DR: In the endoplasmic reticulum (ER), secretory and transmembrane proteins fold into their native conformation and undergo posttranslational modifications important for their activity and structure as mentioned in this paper.
Abstract: In the endoplasmic reticulum (ER), secretory and transmembrane proteins fold into their native conformation and undergo posttranslational modifications important for their activity and structure. When protein folding in the ER is inhibited, signal transduction pathways, which increase the biosynthetic capacity and decrease the biosynthetic burden of the ER to maintain the homeostasis of this organelle, are activated. These pathways are called the unfolded protein response (UPR). In this review, we briefly summarize principles of protein folding and molecular chaperone function important for a mechanistic understanding of UPR-signaling events. We then discuss mechanisms of signal transduction employed by the UPR in mammals and our current understanding of the remodeling of cellular processes by the UPR. Finally, we summarize data that demonstrate that UPR signaling feeds into decision making in other processes previously thought to be unrelated to ER function, e.g., eukaryotic starvation responses and differentiation programs.
2,892 citations
References
More filters
TL;DR: Molecular genetic and biochemical studies described here suggest that, as in the case of growth factor receptors of higher eukaryotic cells, Ire1p oligomerizes in response to the accumulation of unfolded proteins in the ER and is phosphorylated in trans by otherIre1p molecules as a result of oligomerization.
Abstract: The transmembrane kinase Ire1p is required for activation of the unfolded protein response (UPR), the increase in transcription of genes encoding endoplasmic reticulum (ER) resident proteins that occurs in response to the accumulation of unfolded proteins in the ER. Ire1p spans the ER membrane (or the nuclear membrane with which the ER is continuous), with its kinase domain localized in the cytoplasm or in the nucleus. Consistent with this arrangement, it has been proposed that Ire1p senses the accumulation of unfolded proteins in the ER and transmits the signal across the membrane toward the transcription machinery, possibly by phosphorylating downstream components of the UPR pathway. Molecular genetic and biochemical studies described here suggest that, as in the case of growth factor receptors of higher eukaryotic cells, Ire1p oligomerizes in response to the accumulation of unfolded proteins in the ER and is phosphorylated in trans by other Ire1p molecules as a result of oligomerization. In addition to its kinase domain, a C-terminal tail domain of Ire1p is required for induction of the UPR. The role of the tail is probably to bind other proteins that transmit the unfolded protein signal to the nucleus.
12,185 citations
TL;DR: Folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.
Abstract: In the cell, as in vitro, the final conformation of a protein is determined by its amino-acid sequence. But whereas some isolated proteins can be denatured and refolded in vitro in the absence of other macromolecular cellular components, folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.
4,181 citations
TL;DR: Testing the hypothesis that the presence of malfolded proteins may be the primary signal for induction of GRPs by expressing wild-type and mutant forms of influenza virus haemagglutinin in simian cells shows that malfoldingper se, rather than abnormal glycosylation1, is the proximal inducer of this family of stress proteins.
Abstract: Two glucose-regulated proteins, GRP78 and GRP94, are major constituents of the endoplasmic reticulum (ER) of mammalian cells. These proteins are synthesized constitutively in detectable amounts under normal growth conditions; they can also be induced under a variety of conditions of stress including glucose starvation and treatment with drugs that inhibit cellular glycosylation, with calcium ionophores or with amino-acid analogues. Unlike the closely-related heat shock protein (HSP) family, the GRPs are not induced significantly by high temperature. Recently, GRP78 has been identified as the immunoglobulin heavy chain binding protein (BiP) (ref. 5 and Y.K. et al., in preparation) which binds transiently to a variety of nascent, wild-type secretory and transmembrane proteins and permanently to malfolded proteins that accumulate within the ER. We have tested the hypothesis that the presence of malfolded proteins may be the primary signal for induction of GRPs by expressing wild-type and mutant forms of influenza virus haemagglutinin (HA) in simian cells. Only malfolded HAs, whose transport from the ER is blocked, induced the synthesis of GRPs 78 and 94. Additional evidence is presented that malfolding per se, rather than abnormal glycosylation, is the proximal inducer of this family of stress proteins.
1,245 citations
TL;DR: IRE1 encodes a transmembrane serine/threonine kinase that it is proposed transmits the unfolded protein signal across the ER or inner nuclear membrane, suggesting that the induction of ER resident proteins is coupled to the biogenesis of new ER membrane.
1,186 citations
TL;DR: HIre1p is an essential proximal sensor of the unfolded protein response pathway in mammalian cells and is demonstrated to be highly conserved to the yeast counterpart having a Ser/Thr protein kinase domain and a domain homologous to RNase L.
Abstract: Eukaryotes respond to the presence of unfolded protein in the endoplasmic reticulum (ER) by up-regulating the transcription of genes encoding ER protein chaperones, such as BiP. We have isolated a novel human cDNA encoding a homolog to Saccharomyces cerevisiae Ire1p, a proximal sensor for this signal transduction pathway in yeast. The gene product hIre1p is a type 1 transmembrane protein containing a cytoplasmic domain that is highly conserved to the yeast counterpart having a Ser/Thr protein kinase domain and a domain homologous to RNase L. However, the luminal domain has extensively diverged from the yeast gene product. hIre1p expressed in mammalian cells displayed intrinsic autophosphorylation activity and an endoribonuclease activity that cleaved the 5′ splice site of yeast HAC1 mRNA, a substrate for the endoribonuclease activity of yeast Ire1p. Overexpressed hIre1p was localized to the ER with particular concentration around the nuclear envelope and some colocalization with the nuclear pore complex. Expression of Ire1p mRNA was autoregulated through a process that required a functional hIre1p kinase activity. Finally, overexpression of wild-type hIre1p constitutively activated a reporter gene under transcriptional control of the rat BiP promoter, whereas expression of a catalytically inactive hIre1p acted in a trans-dominant-negative manner to prevent transcriptional activation of the BiP promoter in response to ER stress induced by inhibition of N-linked glycosylation. These results demonstrate that hIre1p is an essential proximal sensor of the unfolded protein response pathway in mammalian cells.
892 citations