SUMO modification regulates the transcriptional activity of XBP1

The UPR (unfolded protein response), a cellular defence mechanism against misfolded protein accumulation in the ER (endoplasmic reticulum), is associated with many human diseases such as aging, cancer and diabetes. XBP1 (X-box-binding protein 1), a key transcription factor of the UPR, is critical in maintaining ER homoeostasis. Nevertheless, the mechanism by which XBP1 transcriptional activity is regulated remains unexplored. In the present study we show that XBP1s, the active spliced form of XBP1 protein, is SUMOylated, mainly by PIAS2 [protein inhibitor of activated STAT (signal transducer and activator of transcription) 2] at two lysine residues located in the C-terminal transactivation domain. Ablation of these SUMOylation events significantly enhances the transcriptional activity of XBP1s towards UPR target genes. Thus our results reveal an unexpected role for SUMO (small ubiquitin-related modifier) in the regulation of UPR activation and ER homoeostasis.

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Lysine acetyltransferase Tip60 acetylates the APP adaptor Fe65 to increase its transcriptional activity

Biological Chemistry ◽

10.1515/hsz-2020-0279 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Sabine Probst ◽

Florian Riese ◽

Larissa Kägi ◽

Maik Krüger ◽

Natalie Russi ◽

...

Keyword(s):

Transcriptional Activity ◽

Target Genes ◽

Adaptor Protein ◽

Proteolytic Processing ◽

Class Iii ◽

Lysine Deacetylase ◽

Lysine Residues ◽

Lysine Acetyltransferase ◽

Complex Forms ◽

Spot Formation

AbstractProteolytic processing of the amyloid precursor protein (APP) releases the APP intracellular domain (AICD) from the membrane. Bound to the APP adaptor protein Fe65 and the lysine acetyltransferase (KAT) Tip60, AICD translocates to the nucleus. Here, the complex forms spherical condensates at sites of endogenous target genes, termed AFT spots (AICD-Fe65-Tip60). We show that loss of Tip60 KAT activity prevents autoacetylation, reduces binding of Fe65 and abolishes Fe65-mediated stabilization of Tip60. Autoacetylation is a prerequisite for AFT spot formation, with KAT-deficient Tip60 retained together with Fe65 in speckles. We identify lysine residues 204 and 701 of Fe65 as acetylation targets of Tip60. We do not detect acetylation of AICD. Mutation of Fe65 K204 and K701 to glutamine, mimicking acetylation-induced charge neutralization, increases the transcriptional activity of Fe65 whereas Tip60 inhibition reduces it. The lysine deacetylase (KDAC) class III Sirt1 deacetylates Fe65 and pharmacological modulation of Sirt1 activity regulates Fe65 transcriptional activity. A second acetylation/deacetylation cycle, conducted by CBP and class I/II KDACs at different lysine residues, regulates stability of Fe65. This is the first report describing a role for acetylation in the regulation of Fe65 transcriptional activity, with Tip60 being the only KAT tested that supports AFT spot formation.

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Differential Regulation of Estrogen-Inducible Proteolysis and Transcription by the Estrogen Receptor α N Terminus

Molecular and Cellular Biology ◽

10.1128/mcb.25.13.5417-5428.2005 ◽

2005 ◽

Vol 25 (13) ◽

pp. 5417-5428 ◽

Cited By ~ 67

Author(s):

Christopher C. Valley ◽

Raphaël Métivier ◽

Natalia M. Solodin ◽

Amy M. Fowler ◽

Mara T. Mashek ◽

...

Keyword(s):

Estrogen Receptor ◽

Transcriptional Activity ◽

Target Genes ◽

Estrogen Receptor Α ◽

Transactivation Domain ◽

Related Factors ◽

Additional Element ◽

Transactivation Domains ◽

Ubiquitin Proteasome ◽

Transcriptional Complex

ABSTRACT The ubiquitin-proteasome pathway has emerged as an important regulatory mechanism governing the activity of several transcription factors. While estrogen receptor α (ERα) is also subjected to rapid ubiquitin-proteasome degradation, the relationship between proteolysis and transcriptional regulation is incompletely understood. Based on studies primarily focusing on the C-terminal ligand-binding and AF-2 transactivation domains, an assembly of an active transcriptional complex has been proposed to signal ERα proteolysis that is in turn necessary for its transcriptional activity. Here, we investigated the role of other regions of ERα and identified S118 within the N-terminal AF-1 transactivation domain as an additional element for regulating estrogen-induced ubiquitination and degradation of ERα. Significantly, different S118 mutants revealed that degradation and transcriptional activity of ERα are mechanistically separable functions of ERα. We find that proteolysis of ERα correlates with the ability of ERα mutants to recruit specific ubiquitin ligases regardless of the recruitment of other transcription-related factors to endogenous model target genes. Thus, our findings indicate that the AF-1 domain performs a previously unrecognized and important role in controlling ligand-induced receptor degradation which permits the uncoupling of estrogen-regulated ERα proteolysis and transcription.

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XBP-1 Regulates a Subset of Endoplasmic Reticulum Resident Chaperone Genes in the Unfolded Protein Response

Molecular and Cellular Biology ◽

10.1128/mcb.23.21.7448-7459.2003 ◽

2003 ◽

Vol 23 (21) ◽

pp. 7448-7459 ◽

Cited By ~ 1306

Author(s):

Ann-Hwee Lee ◽

Neal N. Iwakoshi ◽

Laurie H. Glimcher

Keyword(s):

Endoplasmic Reticulum ◽

Unfolded Protein Response ◽

Target Genes ◽

Gene Profiling ◽

Minor Role ◽

Compensatory Mechanism ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

A Minor ◽

Protein Response

ABSTRACT The mammalian unfolded protein response (UPR) protects the cell against the stress of misfolded proteins in the endoplasmic reticulum (ER). We have investigated here the contribution of the UPR transcription factors XBP-1, ATF6α, and ATF6β to UPR target gene expression. Gene profiling of cell lines lacking these factors yielded several XBP-1-dependent UPR target genes, all of which appear to act in the ER. These included the DnaJ/Hsp40-like genes, p58IPK, ERdj4, and HEDJ, as well as EDEM, protein disulfide isomerase-P5, and ribosome-associated membrane protein 4 (RAMP4), whereas expression of BiP was only modestly dependent on XBP-1. Surprisingly, given previous reports that enforced expression of ATF6α induced a subset of UPR target genes, cells deficient in ATF6α, ATF6β, or both had minimal defects in upregulating UPR target genes by gene profiling analysis, suggesting the presence of compensatory mechanism(s) for ATF6 in the UPR. Since cells lacking both XBP-1 and ATF6α had significantly impaired induction of select UPR target genes and ERSE reporter activation, XBP-1 and ATF6α may serve partially redundant functions. No UPR target genes that required ATF6β were identified, nor, in contrast to XBP-1 and ATF6α, did the activity of the UPRE or ERSE promoters require ATF6β, suggesting a minor role for it during the UPR. Collectively, these results suggest that the IRE1/XBP-1 pathway is required for efficient protein folding, maturation, and degradation in the ER and imply the existence of subsets of UPR target genes as defined by their dependence on XBP-1. Further, our observations suggest the existence of additional, as-yet-unknown, key regulators of the UPR.

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Enforced dimerization between XBP1s and ATF6f enhances the protective effects of the unfolded protein response (UPR) in models of neurodegeneration

10.1101/2020.11.17.387480 ◽

2020 ◽

Author(s):

René L. Vidal ◽

Denisse Sepulveda ◽

Paulina Troncoso-Escudero ◽

Paula Garcia-Huerta ◽

Constanza Gonzalez ◽

...

Keyword(s):

Gene Expression ◽

Unfolded Protein Response ◽

Target Genes ◽

Cell Function ◽

Alpha Synuclein ◽

Protective Effects ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response

AbstractAlteration to endoplasmic reticulum (ER) proteostasis is observed on a variety of neurodegenerative diseases associated with abnormal protein aggregation. Activation of the unfolded protein response (UPR) enables an adaptive reaction to recover ER proteostasis and cell function. The UPR is initiated by specialized stress sensors that engage gene expression programs through the concerted action of the transcription factors ATF4, ATF6f, and XBP1s. Although UPR signaling is generally studied as unique linear signaling branches, correlative evidence suggests that ATF6f and XBP1s may physically interact to regulate a subset of UPR-target genes. Here, we designed an ATF6f-XBP1s fusion protein termed UPRplus that behaves as a heterodimer in terms of its selective transcriptional activity. Cell-based studies demonstrated that UPRplus has stronger an effect in reducing the abnormal aggregation of mutant huntingtin and alpha-synuclein when compared to XBP1s or ATF6 alone. We developed a gene transfer approach to deliver UPRplus into the brain using adeno-associated viruses (AAVs) and demonstrated potent neuroprotection in vivo in preclinical models of Parkinson’s and Huntington’s disease. These results support the concept where directing UPR-mediated gene expression toward specific adaptive programs may serve as a possible strategy to optimize the beneficial effects of the pathway in different disease conditions.

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Inhibition of IRE1α-mediated XBP1 mRNA cleavage by XBP1 reveals a novel regulatory process during the unfolded protein response

Wellcome Open Research ◽

10.12688/wellcomeopenres.11764.1 ◽

2017 ◽

Vol 2 ◽

pp. 36 ◽

Cited By ~ 8

Author(s):

Fiona Chalmers ◽

Bernadette Sweeney ◽

Katharine Cain ◽

Neil J. Bulleid

Keyword(s):

Transcription Factor ◽

Unfolded Protein Response ◽

Target Genes ◽

Feedback Mechanism ◽

Ribonuclease Activity ◽

Stable Cell Line ◽

Factor X ◽

Unfolded Protein ◽

Xbp1 Mrna ◽

Protein Response

Background: The mammalian endoplasmic reticulum (ER) continuously adapts to the cellular secretory load by the activation of an unfolded protein response (UPR). This stress response results in expansion of the ER, upregulation of proteins involved in protein folding and degradation, and attenuation of protein synthesis. The response is orchestrated by three signalling pathways each activated by a specific signal transducer, either inositol requiring enzyme α (IRE1α), double-stranded RNA-activated protein kinase-like ER kinase (PERK) or activating transcription factor 6 (ATF6). Activation of IRE1α results in its oligomerisation, autophosphorylation and stimulation of its ribonuclease activity. The ribonuclease initiates the splicing of an intron from mRNA encoding the transcription factor, X-box binding protein 1 (XBP1), as well as degradation of specific mRNAs and microRNAs. Methods: To investigate the consequence of expression of exogenous XBP1, we generated a stable cell-line expressing spliced XBP1 mRNA under the control of an inducible promotor. Results: Following induction of expression, high levels of XBP1 protein were detected, which allowed upregulation of target genes in the absence of induction of the UPR. Remarkably under stress conditions, the expression of exogenous XBP1 repressed splicing of endogenous XBP1 mRNA without repressing the activation of PERK. Conclusions: These results illustrate that a feedback mechanism exists to attenuate activation of the Ire1α ribonuclease activity in the presence of XBP1.

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Involvement of STAT5 in Oncogenesis

Biomedicines ◽

10.3390/biomedicines8090316 ◽

2020 ◽

Vol 8 (9) ◽

pp. 316

Author(s):

Clarissa Esmeralda Halim ◽

Shuo Deng ◽

Mei Shan Ong ◽

Celestial T. Yap

Keyword(s):

Cell Proliferation ◽

Cancer Progression ◽

Transcriptional Activity ◽

Target Genes ◽

Kinase Inhibitors ◽

Cyclin D ◽

Signal Transducer ◽

Stat Proteins ◽

Constitutive Activation ◽

Target Molecules

Signal transducer and activator of transcription (STAT) proteins, and in particular STAT3, have been established as heavily implicated in cancer. Recently, the involvement of STAT5 signalling in the pathology of cancer has been shown to be of increasing importance. STAT5 plays a crucial role in the development of the mammary gland and the homeostasis of the immune system. However, in various cancers, aberrant STAT5 signalling promotes the expression of target genes, such as cyclin D, Bcl-2 and MMP-2, that result in increased cell proliferation, survival and metastasis. To target constitutive STAT5 signalling in cancers, there are several STAT5 inhibitors that can prevent STAT5 phosphorylation, dimerisation, or its transcriptional activity. Tyrosine kinase inhibitors (TKIs) that target molecules upstream of STAT5 could also be utilised. Consequently, since STAT5 contributes to tumour aggressiveness and cancer progression, inhibiting STAT5 constitutive activation in cancers that rely on its signalling makes for a promising targeted treatment option.

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Inhibition of IRE1α-mediated XBP1 mRNA cleavage by XBP1 reveals a novel regulatory process during the unfolded protein response

Wellcome Open Research ◽

10.12688/wellcomeopenres.11764.2 ◽

2017 ◽

Vol 2 ◽

pp. 36 ◽

Cited By ~ 4

Author(s):

Fiona Chalmers ◽

Marcel van Lith ◽

Bernadette Sweeney ◽

Katharine Cain ◽

Neil J. Bulleid

Keyword(s):

Transcription Factor ◽

Unfolded Protein Response ◽

Target Genes ◽

Feedback Mechanism ◽

Ribonuclease Activity ◽

Stable Cell Line ◽

Factor X ◽

Unfolded Protein ◽

Xbp1 Mrna ◽

Protein Response

Background: The mammalian endoplasmic reticulum (ER) continuously adapts to the cellular secretory load by the activation of an unfolded protein response (UPR). This stress response results in expansion of the ER, upregulation of proteins involved in protein folding and degradation, and attenuation of protein synthesis. The response is orchestrated by three signalling pathways each activated by a specific signal transducer, either inositol requiring enzyme α (IRE1α), double-stranded RNA-activated protein kinase-like ER kinase (PERK) or activating transcription factor 6 (ATF6). Activation of IRE1α results in its oligomerisation, autophosphorylation and stimulation of its ribonuclease activity. The ribonuclease initiates the splicing of an intron from mRNA encoding the transcription factor, X-box binding protein 1 (XBP1), as well as degradation of specific mRNAs and microRNAs. Methods: To investigate the consequence of expression of exogenous XBP1, we generated a stable cell-line expressing spliced XBP1 mRNA under the control of an inducible promotor. Results: Following induction of expression, high levels of XBP1 protein were detected, which allowed upregulation of target genes in the absence of induction of the UPR. Remarkably under stress conditions, the expression of exogenous XBP1 repressed splicing of endogenous XBP1 mRNA without repressing the activation of PERK. Conclusions: These results illustrate that a feedback mechanism exists to attenuate Ire1α ribonuclease activity in the presence of XBP1.

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Induction of secretory pathway components in yeast is associated with increased stability of their mRNA

The Journal of Cell Biology ◽

10.1083/jcb.200112008 ◽

2002 ◽

Vol 156 (6) ◽

pp. 993-1001 ◽

Cited By ~ 30

Author(s):

Maureen Hyde ◽

Laura Block-Alper ◽

Jahaira Felix ◽

Paul Webster ◽

David I. Meyer

Keyword(s):

Transcriptional Activity ◽

Secretory Pathway ◽

Terminal Differentiation ◽

Mrna Turnover ◽

Functional Changes ◽

Unfolded Protein ◽

Single Protein ◽

The Unfolded Protein Response ◽

Protein Response ◽

Specific Mrna

The overexpression of certain membrane proteins is accompanied by a striking proliferation of intracellular membranes. One of the best characterized inducers of membrane proliferation is the 180-kD mammalian ribosome receptor (p180), whose expression in yeast results in increases in levels of mRNAs encoding proteins that function in the secretory pathway, and an elevation in the cell's ability to secrete proteins. In this study we demonstrate that neither the unfolded protein response nor increased transcription accounts for membrane proliferation or the observed increase in secretory pathway mRNAs. Rather, p180-induced up-regulation of certain secretory pathway transcripts is due to a p180-mediated increase in the longevity of these mRNA species, as determined by measurements of transcriptional activity and specific mRNA turnover. Moreover, we show that the longevity of mRNA in general is substantially promoted through the process of its targeting to the membrane of the endoplasmic reticulum. With respect to the terminal differentiation of secretory tissues, results from this model system provide insights into how the expression of a single protein, p180, could result in substantial morphological and functional changes.

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Endoplasmic reticulum stress regulation of the Kar2p/BiP chaperone alleviates proteotoxicity via dual degradation pathways

Molecular Biology of the Cell ◽

10.1091/mbc.e11-04-0297 ◽

2012 ◽

Vol 23 (4) ◽

pp. 630-641 ◽

Cited By ~ 6

Author(s):

Chia-Ling Hsu ◽

Rupali Prasad ◽

Christie Blackman ◽

Davis T. W. Ng

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Target Genes ◽

Regulatory Element ◽

Unfolded Protein ◽

Single Target ◽

Transcriptional Regulatory ◽

The Unfolded Protein Response ◽

Protein Response ◽

Stress Activation

The unfolded protein response (UPR) monitors and maintains protein homeostasis in the endoplasmic reticulum (ER). In budding yeast, the UPR is a transcriptional regulatory pathway that is quiescent under normal conditions. Under conditions of acute ER stress, activation of UPR targets is essential for cell viability. How individual target genes contribute to stress tolerance is unclear. Uncovering these roles is hampered because most targets also play important functions in the absence of stress. To differentiate stress-specific roles from everyday functions, a single target gene was uncoupled from UPR control by eliminating its UPR-specific regulatory element. Through this approach, the UPR remains intact, aside from its inability to induce the designated target. Applying the strategy to the major ER chaperone Kar2p/BiP revealed the physiological function of increasing its cellular concentration. Despite hundreds of target genes under UPR control, we show that activation of KAR2 is indispensable to alleviate some forms of ER stress. Specifically, activation is essential to dispose misfolded proteins that are otherwise toxic. Surprisingly, induced BiP/Kar2p molecules are dedicated to alleviating stress. The inability to induce KAR2 under stress had no effect on its known housekeeping functions.

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Signal integration at the PI3K-p85-XBP1 hub endows coagulation protease activated protein C with insulin-like function

Blood ◽

10.1182/blood-2017-02-767921 ◽

2017 ◽

Vol 130 (12) ◽

pp. 1445-1455 ◽

Cited By ~ 9

Author(s):

Thati Madhusudhan ◽

Hongjie Wang ◽

Sanchita Ghosh ◽

Wei Dong ◽

Varun Kumar ◽

...

Keyword(s):

Insulin Signaling ◽

Protein C ◽

Target Genes ◽

Activated Protein C ◽

Regulatory Subunits ◽

Downstream Signaling ◽

Unfolded Protein ◽

Filtration Barrier ◽

Transcriptional Regulatory ◽

Protein Response

Abstract Coagulation proteases have increasingly recognized functions beyond hemostasis and thrombosis. Disruption of activated protein C (aPC) or insulin signaling impair function of podocytes and ultimately cause dysfunction of the glomerular filtration barrier and diabetic kidney disease (DKD). We here show that insulin and aPC converge on a common spliced-X-box binding protein-1 (sXBP1) signaling pathway to maintain endoplasmic reticulum (ER) homeostasis. Analogous to insulin, physiological levels of aPC maintain ER proteostasis in DKD. Accordingly, genetically impaired protein C activation exacerbates maladaptive ER response, whereas genetic or pharmacological restoration of aPC maintains ER proteostasis in DKD models. Importantly, in mice with podocyte-specific deficiency of insulin receptor (INSR), aPC selectively restores the activity of the cytoprotective ER-transcription factor sXBP1 by temporally targeting INSR downstream signaling intermediates, the regulatory subunits of PI3Kinase, p85α and p85β. Genome-wide mapping of condition-specific XBP1-transcriptional regulatory patterns confirmed that concordant unfolded protein response target genes are involved in maintenance of ER proteostasis by both insulin and aPC. Thus, aPC efficiently employs disengaged insulin signaling components to reconfigure ER signaling and restore proteostasis. These results identify ER reprogramming as a novel hormonelike function of coagulation proteases and demonstrate that targeting insulin signaling intermediates may be a feasible therapeutic approach ameliorating defective insulin signaling.

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