UXT (Ubiquitously Expressed Transcript) causes mitochondrial aggregation

UXT oligomerization is essential for its role as an autophagy adaptor

SQSTM1/p62 serves as an autophagy receptor that binds to ubiquitinated misfolded proteins and delivers them to the phagophores for removal. This function can be augmented by autophagy adaptors, such as UXT. Here, by in silico structural homology modeling, we demonstrated that UXT can potentially form a hexameric structure to bind to misfolded proteins. Importantly, the UXT hexamer can assemble into a high-order oligomer via β hairpins positioned outside of each hexamer, facilitating the formation and efficient removal of protein aggregates. Consistently, the high-order oligomer of UXT was found to be essential for inducing the efficient clearance of SOD1(A4V) aggregates, in both in vitro and in vivo. Collectively, our research emphasizes the crucial importance of UXT oligomerization in its role as an autophagy adaptor and explains why the structurally and functionally similar prefoldin, which lacks such high-order oligomerization capacity, is employed for the refolding of individual misfolded proteins, but not autophagy.

MYB regulates the SUMO protease SENP1 and its novel interaction partner UXT, modulating MYB target genes and the SUMO landscape

SUMOylation is a post-translational modification frequently found on nuclear proteins, including transcription factors (TFs) and coactivators. By controlling the activity of several TFs, SUMOylation may have far-reaching effects. MYB is an example of a developmental TF subjected to SUMO-mediated regulation, through both SUMO conjugation and SUMO binding. How SUMO affects MYB target genes is unknown. Here, we explored the global effect of reduced SUMOylation of MYB on its downstream gene programs. RNA-Seq in K562 cells after MYB knockdown and rescue with mutants having an altered SUMO status revealed a number of differentially regulated genes and distinct gene ontology term enrichments. Clearly, the SUMO status of MYB both quantitatively and qualitatively affects its regulome. The transcriptome data further revealed that MYB upregulates the SUMO protease SENP1, a key enzyme that removes SUMO conjugation from SUMOylated proteins. Given this role of SENP1 in the MYB regulome, we expanded the analysis, mapped interaction partners of SENP1, and identified UXT as a novel player affecting the SUMO system by acting as a repressor of SENP1. MYB inhibits the expression of UXT suggesting that MYB is able not only to control a specific gene program directly but also indirectly by affecting the SUMO landscape through SENP1 and UXT. These findings suggest an autoactivation loop whereby MYB, through enhancing SENP1 and reducing UXT, is itself being activated by a reduced level of repressive SUMOylation. We propose that overexpressed MYB, seen in multiple cancers, may drive this autoactivation loop and contribute to oncogenic activation of MYB.

UXT at the crossroads of cell death, immunity and neurodegenerative diseases

The ubiquitous expressed transcript (UXT), a member of the prefoldin-like protein family, modulates regulated cell death (RCD) such as apoptosis and autophagy-mediated cell death through nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), P53, P62, and methylation, and is involved in the regulation of cell metabolism, thereby affecting tumor progression. UXT also maintains immune homeostasis and reduces proteotoxicity in neuro-degenerative diseases through selective autophagy and molecular chaperones. Herein, we review and further elucidate the mechanisms by which UXT affects the regulation of cell death, maintenance of immune homeostasis, and neurodegenerative diseases and discuss the possible UXT involvement in the regulation of ferroptosis and immunogenic cell death, and targeting it to improve cancer treatment outcomes by regulating cell death and immune surveillance.

The E3 ubiquitin ligase SCF(Fbxo7) mediates proteasomal degradation of UXT isoform 2 (UXT-V2) to inhibit the NF-κB signaling pathway

Background

Ubiquitously eXpressed Transcript isoform 2 (UXT—V2) is a prefoldin-like protein involved in NF-κB signaling, apoptosis, and the androgen and estrogen response. UXT-V2 is a cofactor in the NF-κB transcriptional enhanceosome, and its knockdown inhibits TNF-α -induced NF-κB activation. Fbxo7 is an F-box protein that interacts with SKP1, Cullin1 and RBX1 proteins to form an SCF(Fbxo7) E3 ubiquitin ligase complex. Fbxo7 negatively regulates NF-κB signaling through TRAF2 and cIAP1 ubiquitination.

Methods

We combine co-immunoprecipitation, ubiquitination in vitro and in vivo, cycloheximide chase assay, ubiquitin chain restriction analysis and microscopy to investigate interaction between Fbxo7 and overexpressed UXT-V2-HA.

Results

The Ubl domain of Fbxo7 contributes to interaction with UXT—V2. This substrate is polyubiquitinated by SCF(Fbxo7) with K48 and K63 ubiquitin chain linkages in vitro and in vivo. This post-translational modification decreases UXT-V2 stability and promotes its proteasomal degradation. We further show that UXT—V1, an alternatively spliced isoform of UXT, containing 12 additional amino acids at the N-terminus as compared to UXT—V2, also interacts with and is ubiquitinated by Fbxo7. Moreover, FBXO7 knockdown promotes UXT-V2 accumulation, and the overexpression of Fbxo7-ΔF-box protects UXT-V2 from proteasomal degradation and enhances the responsiveness of NF-κB reporter. We find that UXT-V2 colocalizes with Fbxo7 in the cell nucleus.

Conclusions

Together, our study reveals that SCF(Fbxo7) mediates the proteasomal degradation of UXT-V2 causing the inhibition of the NF-κB signaling pathway.

General significance

Discovering new substrates of E3 ubiquitin-ligase SCF(Fbxo7) contributes to understand its function in different diseases such as cancer and Parkinson.

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UXT-V2 is a canonical substrate of SCF(Fbxo7) E3 ubiquitin ligase.

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Fbxo7 interacts with both UXT-V1 and UXT—V2.

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UXT-V2 recruits Fbxo7 to the cell nuclei.

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Fbxo7 inhibit NF-kB pathway through degradation of UXT-V2.

UXT is required for spermatogenesis in mice

Male mammals must simultaneously produce prodigious numbers of sperm and maintain an adequate reserve of stem cells to ensure continuous production of gametes throughout life. Failures in the mechanisms responsible for balancing germ cell differentiation and spermatogonial stem cell (SSC) self-renewal can result in infertility. We discovered a novel requirement for Ubiquitous Expressed Transcript (UXT) in spermatogenesis by developing the first knockout mouse model for this gene. Constitutive deletion of Uxt is embryonic lethal, while conditional knockout in the male germline results in a Sertoli cell-only phenotype during the first wave of spermatogenesis that does not recover in the adult. This phenotype begins to manifest between 6 and 7 days post-partum, just before meiotic entry. Gene expression analysis revealed that Uxt deletion downregulates the transcription of genes governing SSC self-renewal, differentiation, and meiosis, consistent with its previously defined role as a transcriptional co-factor. Our study has revealed the first in vivo function for UXT in the mammalian germline as a regulator of distinct transcriptional programs in SSCs and differentiating spermatogonia.

UXT Is a LOX-PP Interacting Protein That Modulates Estrogen Receptor Alpha Activity in Breast Cancer Cells

The lysyl oxidase proenzyme propeptide region (LOX-PP) is a tumor suppressor protein whose mechanism of action is not completely understood. Here, the Ubiquitously expressed Transcript (UXT) was identified in a yeast two-hybrid assay with LOX-PP as bait and confirmed as a novel LOX-PP associating protein. UXT, a prefoldin-like protein, is ubiquitous in human and mouse. Since UXT modulates androgen receptor transcriptional activity in prostate cancer, we studied its role in breast cancer. Breast tumors and derived cell lines overexpressed UXT. UXT was able to associate with the estrogen receptor alpha (ER) and decrease its transcriptional activity and target gene expression. Conversely, UXT knockdown increased ER element-dependent transcriptional activity. Ectopic LOX-PP relocalized UXT to the cytoplasm and decreased its stability. UXT ubiquitination and depletion in the presence of LOX-PP was rescued by a proteasomal inhibitor. In summary, proteasome-mediated turnover of UXT upon interaction with LOX-PP releases repression of ER transcriptional activity. J. Cell. Biochem. 118: 2347-2356, 2017. © 2017 Wiley Periodicals, Inc.

Ubiquitously expressed transcript is a novel interacting protein of protein inhibitor of activated signal transducer and activator of transcription 2

Protein inhibitor of activated signal transducer and activator of transcription 2 (PIAS2) is a member of the PIAS protein family. This protein family modulates the activity of several transcription factors and acts as an E3 ubiquitin ligase in the sumoylation pathway. To improve understanding of the physiological roles of PIAS2, the current study used a yeast two-hybrid system to screen mouse stem cell cDNA libraries for proteins that interact with PIAS2. The screening identified an interaction between PIAS2 and ubiquitously expressed transcript (UXT). UXT, also termed androgen receptor trapped clone-27, is an α-class prefoldin-type chaperone that acts as a coregulator for various transcription factors, including nuclear factor-κB and androgen receptor (AR). A direct interaction between PIAS2 and UXT was confirmed by direct yeast two-hybrid analysis. In vitro evidence of the association of UXT with PIAS2 was obtained by co-immunoprecipitation. Colocalization between PIAS2 and UXT was identified in the nucleus and cytoplasm of HEK 293T and human cervical carcinoma HeLa cells. The results of the current study suggested that UXT is a binding protein of PIAS2, and interaction between PIAS2 and UXT may be important for the transcriptional activation of AR.

Art27 interacts with GATA4, FOG2 and NKX2.5 and is a novel co-repressor of cardiac genes

Transcription factors play a crucial role in regulation of cardiac biology. FOG-2 is indispensable in this setting, predominantly functioning through a physical interaction with GATA-4. This study aimed to identify novel co-regulators of FOG-2 to further elaborate on its inhibitory activity on GATA-4. The Art27 transcription factor was identified by a yeast-2-hybrid library screen to be a novel FOG-2 protein partner. Characterisation revealed that Art27 is co-expressed with FOG-2 and GATA-4 throughout cardiac myocyte differentiation and in multiple structures of the adult heart. Art27 physically interacts with GATA-4, FOG-2 and other cardiac transcription factors and by this means, down-regulates their activity on cardiac specific promoters α-myosin heavy chain, atrial natriuretic peptide and B-type natriuretic peptide. Regulation of endogenous cardiac genes by Art27 was shown using microarray analysis of P19CL6-Mlc2v-GFP cardiomyocytes. Together these results suggest that Art27 is a novel transcription factor that is involved in downregulation of cardiac specific genes by physically interacting and inhibiting the activity of crucial transcriptions factors involved in cardiac biology.

Regulation of the transcriptional activation of the androgen receptor by the UXT-binding protein VHL

Loss and/or inactivation of the VHL (von Hippel-Lindau) tumour suppressor causes various tumours. Using a yeast two-hybrid system, we have identified the AR (androgen receptor) co-activator UXT (ubiquitously expressed transcript), as a VHL-interacting protein. GST pull-down and co-immunoprecipitation assays show that UXT interacts with VHL. In addition, UXT recruits VHL to the nucleus. VHL associates with the DBD (DNA-binding domain) and hinge domains of the AR and induces AR ubiquitination. Moreover, VHL interaction with the AR activates AR transactivation upon DHT (dihydrotestosterone) treatment. VHL knockdown inhibits AR ubiquitination and decreases transcriptional activation of the AR. Our data suggest that the VHL-UXT interaction and VHL-induced ubiquitination of AR regulate transcriptional activation of the AR.

UXT plays dual opposing roles on SARM-induced apoptosis

Apoptosis is a vital defense mechanism for the clearance of infected cells. Ubiquitously expressed transcript (UXT), which exists in two isoforms (V1 and V2), interact with both apoptotic and cellular proteins. By yeast two-hybrid analysis, we found that UXT interacts with SARM (sterile α and HEAT armadillo motif-containing protein). Since SARM is a TLR adaptor which induces intrinsic apoptosis following immune activation, we were prompted to query whether UXT and SARM might co-regulate apoptosis. We found that the UXT isoforms elicit dual opposing regulatory effects on SARM-induced apoptosis; while UXT V1, co-expressed with SARM, caused a reduction in caspase 8 activity, UXT V2 strongly increased caspase 8 activity and enhanced SARM-induced apoptosis by activating the extrinsic pathway and depolarizing the mitochondria.

Gene expression profile differences in embryos derived from prepubertal and adult Japanese Black cattle during in vitro development

The present study was carried out to compare the gene expression profiles of in vitro-generated embryos derived from adult and prepubertal Japanese Black cattle oocytes using GeneChip Bovine Genome Array (containing 24072 probe sets representing over 23000 transcripts). Microarray experiments were performed on populations of 8- to 16-cell stage embryos and blastocysts derived from adult (24-35 months old) versus prepubertal (9-10 months old) Japanese Black cattle oocytes matured and fertilised in vitro. In total, 591 (2.4%) and 490 (2.0%) genes were differentially expressed in prepubertal and adult bovine in 8- to 16-cell and blastocyst stage embryos, respectively. Out of these, 218 and 248 genes were upregulated, while 373 and 242 were downregulated in prepubertal and adult 8- to 16-cell and blastocysts stage embryos, respectively. Gene ontology classification regarding biological process, molecular functions and cellular component revealed diversity in transcript abundances between prepubertal and adult groups in both the distinct developmental stages. Quantitative reverse transcription-PCR validated the expression differences of some selected transcripts as identified by microarray analysis. To our knowledge, this is the first report indicating the significant number of genes differentially expression (>2-fold, P<0.01) in preimplantition embryos between adult and prepubertal Japanese Black cattle during in vitro development.

Redox state-dependent aggregation of mitochondria induced by cytochrome c

Cytochrome c is known to play central role in apoptosis. Here, it is shown that ferricytochrome c, but not ferrocytochrome c is able to directly induce the aggregation of rat liver mitochondria, similar to the effect caused by magnesium ions at high concentrations. The aggregation was revealed by a decrease in light dispersion of mitochondrial suspension and it was confirmed by the optical microscopy. In the medium containing NADH and cytochrome c, mitochondrial aggregation was initiated only after exhaustion of NADH leading to oxidation of cytochrome c. The aggregation induced by 30 μM ferricytochrome c, but not by 5 mM MgCl(2), was completely inhibited by 30-100 μM ferricyanide, thus indicating that ferricyanide-cytochrome c specific interaction prevents mitochondrial aggregation. After completion of the aggregation caused by ferricytochrome c, this effect cannot be readily reversed by subsequent reduction of cytochrome c. The aggregation induced by ferricytochrome c and/or magnesium ions explains masking of the external NADH-oxidase activity of mitochondria in vitro reported in the literature. This new cytochrome c redox state-dependent phenomenon might also be involved in more complex mechanisms controlling aggregation (clustering) of mitochondria in vivo under the influence of pro-apoptotic factors and requires further study.

Alfa-class prefoldin protein UXT is a novel interacting partner of Amyotrophic Lateral Sclerosis 2 (Als2) protein

Mutations in Als2 gene cause several autosomal recessive forms of motor neuron diseases including Juvenile Amyotrophic Lateral Sclerosis (JALS), Juvenile Primary Lateral Sclerosis (PLSJ) and Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP). To find novel protein-protein interactions of Als2 protein we performed a yeast two hybrid screen and fished out the Ubiquitously Expressed Transcript (UXT) protein. UXT is a novel gene encoding for an α-class prefoldin type chaperone which acts as a co-activator for various transcriptional factors such as Nf-κB and AR. The interaction between Als2 and UXT was confirmed by co-immunoprecipitation. Co-localization between endogenous Als2 and UXT was mainly found in the cytoplasm of neuronal Neuro2a cells with immunofluorescence microscopy. Cell cycle arrest of Neuro2a cells showed that Als2 and Uxt transcriptional levels are synchronously changing. Our results suggest that Als2 is a binding partner of Uxt and Als2/Uxt interaction could be important for the activation of Nf-κB pathway. These results provides basis for future research to investigate the role of Nf-κB pathway in the development of motor neuron diseases.

New insights into the biogenesis of nuclear RNA polymerases?

More than 30 years of research on nuclear RNA polymerases (RNAP I, II, and III) has uncovered numerous factors that regulate the activity of these enzymes during the transcription reaction. However, very little is known about the machinery that regulates the fate of RNAPs before or after transcription. In particular, the mechanisms of biogenesis of the 3 nuclear RNAPs, which comprise both common and specific subunits, remains mostly uncharacterized and the proteins involved are yet to be discovered. Using protein affinity purification coupled to mass spectrometry (AP-MS), we recently unraveled a high-density interaction network formed by nuclear RNAP subunits from the soluble fraction of human cell extracts. Validation of the dataset using a machine learning approach trained to minimize the rate of false positives and false negatives yielded a high-confidence dataset and uncovered novel interactors that regulate the RNAP II transcription machinery, including a set of proteins we named the RNAP II-associated proteins (RPAPs). One of the RPAPs, RPAP3, is part of an 11-subunit complex we termed the RPAP3/R2TP/prefoldin-like complex. Here, we review the literature on the subunits of this complex, which points to a role in nuclear RNAP biogenesis.

Death by committee: organellar trafficking and communication in apoptosis

Apoptosis proceeds through a set of evolutionarily conserved processes that co-ordinate the elimination of damaged or unneeded cells. This program of cell death is carried out by organelle-directed regulators, including the Bcl-2 proteins, and ultimately executed by proteases of the caspase family. Although the biochemical mechanisms of apoptosis are increasingly understood, the underlying cell biology orchestrating programmed cell death remains enigmatic. In this review, we summarize the current understanding of Bcl-2 protein regulation and caspase activation while examining cell biological mechanisms and consequences of apoptotic induction. Organellar contributions to apoptotic induction include death receptor endocytosis, mitochondrial and lysosomal permeabilization, endoplasmic reticulum calcium release and fragmentation of the Golgi apparatus. These early apoptotic events are accompanied by stabilization of the microtubule cytoskeleton and translocation of organelles to the microtubule organizing center. Together, these phenomena establish a model of apoptotic induction whereby a cytoskeletal-dependent coalescence and 'scrambling' of organelles in the paranuclear region co-ordinates apoptotic communication, caspase activation and cell death.

Nuclear factor kappa B and hepatitis viruses

BACKGROUND

Hepatitis can be caused by a number of viruses, which have similar clinical manifestations and render infected individuals at high risk of death from cirrhosis and liver cancer. Current therapies for hepatitis have limited effects and unsatisfactory patient outcomes. Nuclear factor kappa B (NF-kappaB) is critical for immune and inflammatory responses. During its lifetime the cell demands specific and highly regulated control of NF-kappaB activity.

OBJECTIVE

To develop novel strategies to overcome various hepatitides and related liver cancer with NF-kappaB as the key point.

METHODS

All aspects of NF-kappaB control with regard to hepatitis are covered.

RESULTS/CONCLUSION

NF-kappaB plays an important role in the process of hepatitis and is hypothesized to be an anti-cancer factor in the subsequent inflammation-associated hepatocarcinogenesis.