The signalling from endoplasmic reticulum-resident bZIP transcription factors involved in diverse cellular physiology

The Protective Role of Transcript-Induced in Spermiogenesis 40 in Cerebral Ischemia-Reperfusion Injury

Prompt reperfusion after cerebral ischemia is important to maintain neuronal survival and reduce permanent disability and death. However, the resupply of blood can induce oxidative stress, inflammatory response and apoptosis, further leading to tissue damage. Here, we report the versatile biological roles of transcript-induced in spermiogenesis 40 (Tisp40) in ischemic stroke. We found that the expression of Tisp40 was upregulated in ischemia/reperfusion-induced brain tissues and oxygen glucose deprivation/returned -stimulated neurons. Tisp40 deficiency increased the infarct size and neurological deficit score, and promoted inflammation and apoptosis. Tisp40 overexpression played the opposite role. In vitro, the oxygen glucose deprivation/returned model was established in Tisp40 knockdown and overexpression primary cultured cortical neurons. Tisp40 knockdown can aggravate the process of inflammation and apoptosis, and Tisp40 overexpression ameliorated the aforementioned processes. Mechanistically, Tisp40 protected against ischemic stroke via activating the AKT signaling pathway. Tisp40 may be a new therapeutic target in brain ischemia/reperfusion injury.

Lack of Nuclear Localization of the Creb3l1 Transcription Factor Causes Defects in Caudal Fin Bifurcation in Zebrafish Danio rerio

INTRODUCTION

The formation of normal bone and bone healing requires the cAMP-responsive element binding protein 3-like-1 (Creb3l1) transmembrane transcription factor, as deletion of the murine CREB3L1 results in osteopenic animals with limited capacity to repair bone after a fracture. Creb3l1 undergoes regulated intramembrane proteolysis (RIP) to release the N-terminal transcription activating (TA) fragment that enters the nucleus and regulates the expression of target genes.

METHODS

To expand our understanding of Creb3l1's role in skeletal development and skeletal patterning, we aimed to generate animals expressing only the TA fragment of Creb3l1 lacking the transmembrane domain and thereby not regulated through RIP. However, the CRISPR/Cas9-mediated genome editing in zebrafish Danio rerio caused a frameshift mutation that added 56 random amino acids at the C-terminus of the TA fragment (TA+), making it unable to enter the nucleus. Thus, TA+ does not regulate transcription, and the creb3l1TA+/TA+ fish do not mediate creb3l1-dependent transcription.

RESULTS

We document that the creb3l1TA+/TA+ fish exhibit defects in the patterning of caudal fin lepidotrichia, with significantly distalized points of proximal bifurcation and decreased secondary bifurcations. Moreover, using the caudal fin amputation model, we show that creb3l1TA+/TA+ fish have decreased regeneration and that their regenerates replicate the distalization and bifurcation defects observed in intact fins of creb3l1TA+/TA+ animals. These defects correlate with altered expression of the shha and ptch2 components of the Sonic Hedgehog signaling pathway in creb3l1TA+/TA+ regenerates.

CONCLUSION

Together, our results uncover a previously unknown intersection between Creb3l1 and the Sonic Hedgehog pathway and document a novel role of Creb3l1 in tissue patterning.

Endoplasmic reticulum stress and associated apoptosis are linked with the pathogenesis of white striping in broiler breast muscles

White striping (WS) that appears as white stripes parallel to the muscle fibrils is an emerging growth-related abnormality of broiler breast meat. The pathomechanism of this defect has not been fully understood despite intensive studies over the past decade. In the present study, endoplasmic reticulum (ER) stress and its associated apoptotic pathways were investigated to elucidate the potential role of these pathways in the development of WS. To this end, a total of 60 Pectoralis major (Pm) muscle samples were collected from 55-d-old Ross 308 male broiler chickens according to the severity of gross WS lesions (normal, mild, and severe). Histopathological and molecular analyses were conducted to evaluate the lesions and genes involved in the ER stress and related apoptosis. All the Pm samples, both with and without macroscopic WS lesions, showed varying degrees of myodegenerative lesions. Molecular analysis revealed that the transcript abundances of many components related to protein kinase R-like ER kinase (PERK) and inositol-requiring enzyme type 1 (IRE-1) signals of the ER stress response were significantly greater in severely WS-affected breast tissues compared to their mildly affected and normal counterparts. Similarly, the transcript abundances of apoptotic markers related to both signaling pathways were significantly greater in severe WS lesions than those of mildly affected and normal Pm tissues. Besides these, a significant increase in caspase-3 transcript abundance was seen in severe WS lesions in comparison with mild WS and normal breast muscles. Findings of this study suggest that ER stress response and its related apoptotic pathways are possibly activated in the breast muscle of broiler chickens with severe WS lesions. Based on these findings, it is speculated that ER stress-mediated apoptosis occupies a central role in the progression of WS in broiler chickens.

Disruption of the creb3l1 gene causes defects in caudal fin regeneration and patterning in zebrafish Danio rerio

BACKGROUND

The gene cAMP-Responsive Element Binding protein 3-like-1 (CREB3L1) has been implicated in bone development in mice, with CREB3L1 knock-out mice exhibiting fragile bones, and in humans, with CREB3L1 mutations linked to osteogenesis imperfecta. However, the mechanism through which Creb3l1 regulates bone development is not fully understood.

RESULTS

To probe the role of Creb3l1 in organismal physiology, we used CRISPR-Cas9 genome editing to generate a Danio rerio (zebrafish) model of Creb3l1 deficiency. In contrast to mammalian phenotypes, the Creb3l1 deficient fish do not display abnormalities in osteogenesis, except for a decrease in the bifurcation pattern of caudal fin. Both, skeletal morphology and overall bone density appear normal in the mutant fish. However, the regeneration of caudal fin postamputation is significantly affected, with decreased overall regenerate and mineralized bone area. Moreover, the mutant fish exhibit a severe patterning defect during regeneration, with a significant decrease in bifurcation complexity of the fin rays and distalization of the bifurcation sites. Analysis of genes implicated in bone development showed aberrant patterning of shha and ptch2 in Creb3l1 deficient fish, linking Creb3l1 with Sonic Hedgehog signaling during fin regeneration.

CONCLUSIONS

Our results uncover a novel role for Creb3l1 in regulating tissue growth and patterning during regeneration.

G protein-coupled receptor 84 gene expression is regulated by the ER stress response in the liver

G protein-coupled receptor 84 (Gpr84) is reportedly activated by medium-chain fatty acids and is involved in the pathology of liver fibrosis. Inflammatory stimulants, such as lipopolysaccharide and tumor necrosis factor-α, upregulate Gpr84 expression. However, the detailed molecular mechanism by which Gpr84 is induced remains unknown. Inflammatory stimulation also evokes endoplasmic reticulum (ER) stress, but there has been no direct evidence to link Gpr84 expression and the ER stress response. Administration of tunicamycin (Tm) provokes ER stress and acute steatosis in the liver tissue of mice. Here, in situ hybridization analysis revealed that induction of Gpr84 expression occurred in parenchymal cells in the liver tissue following Tm administration. Gene expression analysis using a reporter assay showed that the intron 1 region of Gpr84 was involved in induction of the gene under ER stress conditions. Furthermore, Tm-dependent upregulation of Gpr84 was blocked by the small chemical compound AEBSF, an inhibitor of ER stress transducers, in vitro and in vivo. In conclusion, the current study marks the discovery that the ER stress agent Tm induces the expression of Gpr84.

Oncofetal SNRPE promotes HCC tumorigenesis by regulating the FGFR4 expression through alternative splicing

BACKGROUND

Due to insufficient knowledge about key molecular events, Hepatocellular carcinoma (HCC) lacks effective treatment targets. Spliceosome-related genes were significantly altered in HCC. Oncofetal proteins are ideal tumor therapeutic targets. Screening of differentially expressed Spliceosome-related oncofetal protein in embryonic liver development and HCC helps discover effective therapeutic targets for HCC.

METHODS

Differentially expressed spliceosome genes were analysis in fetal liver and HCC through bioinformatics analysis. Small nuclear ribonucleoprotein polypeptide E (SNRPE) expression was detected in fetal liver, adult liver and HCC tissues. The role of SNRPE in HCC was performed multiple assays in vitro and in vivo. SNRPE-regulated alternative splicing was recognized by RNA-Seq and confirmed by multiple assays.

RESULTS

We herein identified SNRPE as a crucial oncofetal splicing factor, significantly associated with the adverse prognosis of HCC. SOX2 was identified as the activator for SNRPE reactivation. Efficient knockdown of SNRPE resulted in the complete cessation of HCC tumorigenesis and progression. Mechanistically, SNRPE knockdown reduced FGFR4 mRNA expression by triggering nonsense-mediated RNA decay. A partial inhibition of SNRPE-induced malignant progression of HCC cells was observed upon FGFR4 knockdown.

CONCLUSIONS

Our findings highlight SNRPE as a novel oncofetal splicing factor and shed light on the intricate relationship between oncofetal splicing factors, splicing events, and carcinogenesis. Consequently, SNRPE emerges as a potential therapeutic target for HCC treatment. Model of oncofetal SNRPE promotes HCC tumorigenesis by regulating the AS of FGFR4 pre-mRNA.

Lineage-determining transcription factor-driven promoters regulate cell type-specific macrophage gene expression

Mammalian promoters consist of multifarious elements, which make them unique and support the selection of the proper transcript variants required under diverse conditions in distinct cell types. However, their direct DNA-transcription factor (TF) interactions are mostly unidentified. Murine bone marrow-derived macrophages (BMDMs) are a widely used model for studying gene expression regulation. Thus, this model serves as a rich source of various next-generation sequencing data sets, including a large number of TF cistromes. By processing and integrating the available cistromic, epigenomic and transcriptomic data from BMDMs, we characterized the macrophage-specific direct DNA-TF interactions, with a particular emphasis on those specific for promoters. Whilst active promoters are enriched for certain types of typically methylatable elements, more than half of them contain non-methylatable and prototypically promoter-distal elements. In addition, circa 14% of promoters-including that of Csf1r-are composed exclusively of 'distal' elements that provide cell type-specific gene regulation by specialized TFs. Similar to CG-rich promoters, these also contain methylatable CG sites that are demethylated in a significant portion and show high polymerase activity. We conclude that this unusual class of promoters regulates cell type-specific gene expression in macrophages, and such a mechanism might exist in other cell types too.

AIbZIP/CREB3L4 Promotes Cell Proliferation via the SKP2-p27 Axis in Luminal Androgen Receptor Subtype Triple-Negative Breast Cancer

Breast cancer ranks first in incidence and fifth in cancer-related deaths among all types of cancer globally. Among breast cancer, triple-negative breast cancer (TNBC) has few known therapeutic targets and a poor prognosis. Therefore, new therapeutic targets and strategies against TNBC are required. We found that androgen-induced basic leucine zipper (AIbZIP), also known as cyclic AMP-responsive element-binding protein 3-like protein 4 (CREB3L4), which is encoded by Creb3l4, is highly upregulated in a particular subtype of TNBC, luminal androgen receptor (LAR) subtype. We analyzed the function of AIbZIP through depletion of AIbZIP by siRNA knockdown in LAR subtype TNBC cell lines, MFM223 and MDAMB453. In AIbZIP-depleted cells, the proliferation ratios of cells were greatly suppressed. Moreover, G1-S transition was inhibited in AIbZIP-depleted cells. We comprehensively analyzed the expression levels of proteins that regulate G1-S transition and found that p27 was specifically upregulated in AIbZIP-depleted cells. Furthermore, we identified that this p27 downregulation was caused by protein degradation modulated by the ubiquitin-proteasome system via F-box protein S-phase kinase-associated protein 2 (SKP2) upregulation. Our findings demonstrate that AIbZIP is a novel p27-SKP2 pathway-regulating factor and a potential molecule that contributes to LAR subtype TNBC progression.

IMPLICATIONS

This research shows a new mechanism for the proliferation of LAR subtype TNBC regulated by AIbZIP, that may provide novel insight into the LAR subtype TNBC progression and the molecular mechanisms involved in cell proliferation.

Molecular mechanism of ATF6 in unfolded protein response and its role in disease

Activating transcription factor 6 (ATF6), an important signaling molecule in unfolded protein response (UPR), plays a role in the pathogenesis of several diseases, including diseases such as congenital retinal disease, liver fibrosis and ankylosing spondylitis. After endoplasmic reticulum stress (ERS), ATF6 is activated after separation from binding immunoglobulin protein (GRP78/BiP) in the endoplasmic reticulum (ER) and transported to the Golgi apparatus to be hydrolyzed by site 1 and site 2 proteases into ATF6 fragments, which localize to the nucleus and regulate the transcription and expression of ERS-related genes. In these diseases, ERS leads to the activation of UPR, which ultimately lead to the occurrence and development of diseases by regulating the physiological state of cells through the ATF6 signaling pathway. Here, we discuss the evidence for the pathogenic importance of ATF6 signaling in different diseases and discuss preclinical results.

Regulatory mechanisms of the cAMP-responsive element binding protein 3 (CREB3) family in cancers

The CREB3 family of proteins, encompassing CREB3 and its four homologs (CREB3L1, CREB3L2, CREB3L3, and CREB3L4), exerts pivotal control over cellular protein metabolism in response to unfolded protein reactions. Under conditions of endoplasmic reticulum stress, activation of the CREB3 family occurs through regulated intramembrane proteolysis within the endoplasmic reticulum membrane. Perturbations in the function and expression of the CREB3 family have been closely associated with the development of diverse diseases, with a particular emphasis on cancer. Recent investigations have shed light on the indispensable role played by CREB3 family members in modulating the onset and progression of various human cancers. This comprehensive review endeavors to provide an in-depth examination of the involvement of CREB3 family members in distinct human cancer types, accentuating their significance in the pathogenesis of cancer and the manifestation of malignant phenotypes.

Achromatopsia Showing Compound Heterozygous Mutations in ATF6 by Whole Exome Sequencing: A Rare Case Report

Achromatopsia, inherited in an autosomal recessive manner, is a rare condition featured by dysfunction of cone photoreceptors responsible for high-acuity vision in daylight. To date, its pathogenesis and genetic mechanism are still not well defined due to the rarity of cases. In this study, the authors describe a patient with achromatopsia who was diagnosed based on the combination of whole exome sequencing, ocular examination, fundus photography, and fundus fluorescein angiography. A 1-year-old girl presented due to absence of the foveal reflex, severe photophobia, and pigment mottling. Fundus photography and fundus fluorescein angiography were performed on admission. Blood samples were extracted from the proband and her parents. Whole exome sequencing detected two ATF6 variants (c.533C>A and c.82+1G>T), which were confirmed through Sanger sequencing. According to the American College of Medical Genetics guidelines, both c.533C>A and c.82+1G>T variants in ATF6 were predicted as pathogenic mutations (PVS1, PM2, PM3). The patient was diagnosed as having achromatopsia with pathogenicity of ATF6 variants (c.533C>A and c.82+1G>T). [J Pediatr Ophthalmol Strabismus. 2023;60(5):e65-e69.].

Anticancer Activity of ST101, A Novel Antagonist of CCAAT/Enhancer Binding Protein β

CCAAT/enhancer binding protein β (C/EBPβ) is a basic leucine zipper (bZIP) family transcription factor, which is upregulated or overactivated in many cancers, resulting in a gene expression profile that drives oncogenesis. C/EBPβ dimerization regulates binding to DNA at the canonical TTGCGCAA motif and subsequent transcriptional activity, suggesting that disruption of dimerization represents a powerful approach to inhibit this previously "undruggable" oncogenic target. Here we describe the mechanism of action and antitumor activity of ST101, a novel and selective peptide antagonist of C/EBPβ that is currently in clinical evaluation in patients with advanced solid tumors. ST101 binds the leucine zipper domain of C/EBPβ, preventing its dimerization and enhancing ubiquitin-proteasome dependent C/EBPβ degradation. ST101 exposure attenuates transcription of C/EBPβ target genes, including a significant decrease in expression of survival, transcription factors, and cell-cycle-related proteins. The result of ST101 exposure is potent, tumor-specific in vitro cytotoxic activity in cancer cell lines including glioblastoma, breast, melanoma, prostate, and lung cancer, whereas normal human immune and epithelial cells are not impacted. Further, in mouse xenograft models ST101 exposure results in potent tumor growth inhibition or regression, both as a single agent and in combination studies. These data provide the First Disclosure of ST101, and support continued clinical development of ST101 as a novel strategy for targeting C/EBPβ-dependent cancers.

CREB3L1 and CREB3L2 control Golgi remodelling during decidualization of endometrial stromal cells

Upon progesterone stimulation, Endometrial Stromal Cells (EnSCs) undergo a differentiation program into secretory cells (decidualization) to release in abundance factors crucial for embryo implantation. We previously demonstrated that decidualization requires massive reshaping of the secretory pathway and, in particular, of the Golgi complex. To decipher the underlying mechanisms, we performed a time-course transcriptomic analysis of in vitro decidualizing EnSC. Pathway analysis shows that Gene Ontology terms associated with vesicular trafficking and early secretory pathway compartments are the most represented among those enriched for upregulated genes. Among these, we identified a cluster of co-regulated genes that share CREB3L1 and CREB3L2 binding elements in their promoter regions. Indeed, both CREB3L1 and CREB3L2 transcription factors are up-regulated during decidualization. Simultaneous downregulation of CREB3L1 and CREB3L2 impairs Golgi enlargement, and causes dramatic changes in decidualizing EnSC, including Golgi fragmentation, collagen accumulation in dilated Endoplasmic Reticulum cisternae, and overall decreased protein secretion. Thus, both CREB3L1 and CREB3L2 are required for Golgi reshaping and efficient protein secretion, and, as such, for successful decidualization.

Expression analysis and functional characterization of thioredoxin domain-containing protein 11

BACKGROUNDS

The endoplasmic reticulum (ER) is a crucial organelle that regulates both the folding, modification and transport of many proteins and senses certain stimuli inside and outside of cells. ER-associated degradation (ERAD), including SEL1L is a crucial mechanism to maintain homeostasis. In this study, we performed comparative proteome analysis in wild-type (wt) and SEL1L-deficient cells.

METHODS AND RESULTS

We found constitutively high expression of thioredoxin domain-containing protein 11 (TXNDC11) mRNA and protein in our SEL1L-deficient HEK293 cells by RT-PCR and Western blot analysis. The TXNDC11 gene possesses a well-conserved unfolded protein response element (UPRE) around its transcription start site, and ER stress increased TXNDC11 mRNA and luciferase reporter activity via this putative UPRE in HEK293 cells. The amounts of TXNDC11 protein in wild-type and SEL1L-deficient cells with or without thapsigargin (Tg) treatment were parallel to their mRNAs in these cells, which was almost proportional to spliced XBP1 (sXBP1) mRNA expression. The establishment and characterization of TXNDC11-deficient HEK293 cells revealed that the expression of three different ER resident stress sensors, ATF6α, CREB3 and CREB3L2, is regulated by TXNDC11. The rate of disappearance of the three proteins by CHX treatment in wt cells was remarkably different, and the full-length CREB3L2 protein was almost completely degraded within 15 min after CHX treatment. TXNDC11 deficiency increased the expression of each full-length form under resting conditions and delayed their disappearance by CHX treatment. Interestingly, the degree of increase in full-length CREB3/CREB3L2 by TXNDC11 deficiency was apparently higher than that in full-length ATF6α. The increase in these proteins by TXNDC11 deficiency was hardly correlated with the expression of each mRNA. Treatment with ER stress inducers influenced each full-length mature form, and the difference in each full-length form observed in wt and TXNDC11-deficient cells was smaller.

CONCLUSION

This study demonstrated that TXNDC11 is an ER stress-inducible gene regulated by the IRE1-sXBP1 pathway. In addition, TXNDC11 is involved in the regulation of ATF6α, CREB3 and CREB3L2 protein expression, although the contribution to the stability of these proteins is quite variable. Therefore, its further characterization will provide new insights for understanding protein homeostasis in ER physiology and pathology.

Regulation of endoplasmic reticulum stress by hesperetin: Focus on antitumor and cytoprotective effects

BACKGROUND

Cancer is still an all-times issue due to a large and even increasing number of deaths. Impaired genes regulating cell proliferation and apoptosis are targets for the development of novel cancer treatments.

HYPOTHESIS

Increased transcription of NADPH oxidase activator (NOXA), Bcl2-like11 (BIM), BH3-only proteins and p53 unregulated apoptosis modulator (PUMA) is caused by the imbalance between pro- and anti-apoptotic Bcl-2 proteins due to endoplasmic reticulum (ER) stress. The membranous network of ER is present in all eukaryotic cells. ER stress facilitates the interaction between Bax and PUMA, triggering the release of cytochrome C. As a main intracellular organelle, ER is responsible for translocation as well as post-translation modification and protein folding.

RESULTS

Hesperetin is a cytoprotective flavonone, which acts against ER stress and protects from cell damage induced by reactive oxygen species (ROS) and reactive nitrogen species (RNS). Hesperetin inhibits lipid peroxidation induced by Fe²⁺ and l-ascorbic acid in rat brain homogenates.

CONCLUSION

This review deals with the anticancer effects of hesperetin regarding the regulation of ER stress as a principal mechanism in the pathogenesis of tumors.

Unveiling OASIS family as a key player in hypoxia-ischemia cases induced by cocaine using generative adversarial networks

Repeated cocaine use poses many serious health risks to users. One of the risks is hypoxia and ischemia (HI). To restore the biological system against HI, complex biological mechanisms operate at the gene level. Despite the complexity of biological mechanisms, there are common denominator genes that play pivotal roles in various defense systems. Among these genes, the cAMP response element-binding (Creb) protein contributes not only to various aspects of drug-seeking behavior and drug reward, but also to protective mechanisms. However, it is still unclear which Creb members are key players in the protection of cocaine-induced HI conditions. Herein, using one of the state-of-the-art deep learning methods, the generative adversarial network, we revealed that the OASIS family, one of the Creb family, is a key player in various defense mechanisms such as angiogenesis and unfolded protein response against the HI state by unveiling hidden mRNA expression profiles. Furthermore, we identified mysterious kinases in the OASIS family and are able to explain why the prefrontal cortex and hippocampus are vulnerable to HI at the genetic level.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.

Genome-wide DNA methylation analysis of pulmonary function in middle and old-aged Chinese monozygotic twins

BACKGROUND

Previous studies have determined the epigenetic association between DNA methylation and pulmonary function among various ethnics, whereas this association is largely unknown in Chinese adults. Thus, we aimed to explore epigenetic relationships between genome-wide DNA methylation levels and pulmonary function among middle-aged Chinese monozygotic twins.

METHODS

The monozygotic twin sample was drawn from the Qingdao Twin Registry. Pulmonary function was measured by three parameters including forced expiratory volume the first second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio. Linear mixed effect model was used to regress the methylation level of CpG sites on pulmonary function. After that, we applied Genomic Regions Enrichment of Annotations Tool (GREAT) to predict the genomic regions enrichment, and used comb-p python library to detect differentially methylated regions (DMRs). Gene expression analysis was conducted to validate the results of differentially methylated analyses.

RESULTS

We identified 112 CpG sites with the level of P < 1 × 10^-4 which were annotated to 40 genes. We identified 12 common enriched pathways of three pulmonary function parameters. We detected 39 DMRs located at 23 genes, of which PRDM1 was related to decreased pulmonary function, and MPL, LTB4R2, and EPHB3 were related to increased pulmonary function. The gene expression analyses validated DIP2C, ASB2, SLC6A5, and GAS6 related to decreased pulmonary function.

CONCLUSION

Our DNA methylation sequencing analysis on identical twins provides new references for the epigenetic regulation on pulmonary function. Several CpG sites, genes, biological pathways and DMRs are considered as possible crucial to pulmonary function.

The Interplay between the Unfolded Protein Response, Inflammation and Infection in Cystic Fibrosis

In cystic fibrosis (CF), p.Phe508del is the most frequent mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The p.Phe508del-CFTR protein is retained in the ER and rapidly degraded. This retention likely triggers an atypical Unfolded Protein Response (UPR) involving ATF6, which reduces the expression of p.Phe508del-CFTR. There are still some debates on the role of the UPR in CF: could it be triggered by the accumulation of misfolded CFTR proteins in the endoplasmic reticulum as was proposed for the most common CFTR mutation p.Phe508del? Or, is it the consequence of inflammation and infection that occur in the disease? In this review, we summarize recent findings on UPR in CF and show how infection, inflammation and UPR act together in CF. We propose to rethink their respective role in CF and to consider them as a whole.

Molecular characterization of mouse CREB3 regulatory factor in Neuro2a cells

We performed expression and functional analysis of mouse CREB3 regulatory factor (CREBRF) in Neuro2a cells by constructing several expression vectors. Overexpressed full-length (FL) CREBRF protein was stabilized by MG132; however, the intrinsic CREBRF expression in Neuro2a cells was negligible under all conditions. On the other hand, N- or C-terminal deletion of CREBRF influenced its stability. Cotransfection of CREBRF together with GAL4-tagged FL CREB3 increased luciferase reporter activity, and only the N-terminal region of CREBRF was sufficient to potentiate luciferase activity. Furthermore, this positive effect of CREBRF was also observed in cells expressing GAL4-tagged cleaved CREB3, although CREBRF hardly influenced the protein stability of NanoLuc-tagged cleaved CREB3 or intracellular localization of EGFP-tagged one. In conclusion, this study suggests that CREBRF, a quite unstable proteasome substrate, positively regulates the CREB3 pathway, which is distinct from the canonical ER stress pathway in Neuro2a cells.

OASIS/CREB3L1 is a factor that responds to nuclear envelope stress

The nuclear envelope (NE) safeguards the genome and is pivotal for regulating genome activity as the structural scaffold of higher-order chromatin organization. NE had been thought as the stable during the interphase of cell cycle. However, recent studies have revealed that the NE can be damaged by various stresses such as mechanical stress and cellular senescence. These types of stresses are called NE stress. It has been proposed that NE stress is closely related to cellular dysfunctions such as genome instability and cell death. Here, we found that an endoplasmic reticulum (ER)-resident transmembrane transcription factor, OASIS, accumulates at damaged NE. Notably, the major components of nuclear lamina, Lamin proteins were depleted at the NE where OASIS accumulates. We previously demonstrated that OASIS is cleaved at the membrane domain in response to ER stress. In contrast, OASIS accumulates as the full-length form to damaged NE in response to NE stress. The accumulation to damaged NE is specific for OASIS among OASIS family members. Intriguingly, OASIS colocalizes with the components of linker of nucleoskeleton and cytoskeleton complexes, SUN2 and Nesprin-2 at the damaged NE. OASIS partially colocalizes with BAF, LEM domain proteins, and a component of ESCRT III, which are involved in the repair of ruptured NE. Furthermore, OASIS suppresses DNA damage induced by NE stress and restores nuclear deformation under NE stress conditions. Our findings reveal a novel NE stress response pathway mediated by OASIS.

Elucidation of brefeldin A-induced ER and Golgi stress responses in Neuro2a cells

Brefeldin A (BFA) disrupts the structure of the Golgi apparatus to trigger ER stress signaling pathways. On the other hand, treatment with BFA induces the activation of CREB3, the protein structure of which is similar to that of ATF6. In this study, we established Neuro2a cells in which three different transcription factors, namely, ATF4, ATF3 and CREB3, were deficient using the CRISPR/Cas9 approach, and we investigated the BFA-induced ER and Golgi stress response in these cells. BFA treatment rapidly induced ATF4, ATF3, Herp and GADD153 protein expression in Neuro2a cells. ATF4-deficient Neuro2a cells exhibited significantly decreased mRNA and protein expression of ATF3 and Herp but not GADD153; however, cells deficient in ATF3 exhibited minimal effects on GADD34, GADD153 and Herp expression. The cleavage of CREB3 in Neuro2a cells was triggered by BFA; however, the expression of several ER and Golgi stress-related factors was hardly influenced by the CREB3 deficiency in these Neuro2a cells. This study shows that CREB3 minimally associates with typical ER stress-inducible responses in Neuro2a cells. Therefore, identification and characterization of the downstream transcriptional targets of CREB3 is required to clarify not only Golgi stress response but also its relationship with ER stress signaling pathways.

Redox and Inflammatory Signaling, the Unfolded Protein Response, and the Pathogenesis of Pulmonary Hypertension

Protein folding overload and oxidative stress disrupt endoplasmic reticulum (ER) homeostasis, generating reactive oxygen species (ROS) and activating the unfolded protein response (UPR). The altered ER redox state induces further ROS production through UPR signaling that balances the cell fates of survival and apoptosis, contributing to pulmonary microvascular inflammation and dysfunction and driving the development of pulmonary hypertension (PH). UPR-induced ROS production through ER calcium release along with NADPH oxidase activity results in endothelial injury and smooth muscle cell (SMC) proliferation. ROS and calcium signaling also promote endothelial nitric oxide (NO) synthase (eNOS) uncoupling, decreasing NO production and increasing vascular resistance through persistent vasoconstriction and SMC proliferation. C/EBP-homologous protein further inhibits eNOS, interfering with endothelial function. UPR-induced NF-κB activity regulates inflammatory processes in lung tissue and contributes to pulmonary vascular remodeling. Conversely, UPR-activated nuclear factor erythroid 2-related factor 2-mediated antioxidant signaling through heme oxygenase 1 attenuates inflammatory cytokine levels and protects against vascular SMC proliferation. A mutation in the bone morphogenic protein type 2 receptor (BMPR2) gene causes misfolded BMPR2 protein accumulation in the ER, implicating the UPR in familial pulmonary arterial hypertension pathogenesis. Altogether, there is substantial evidence that redox and inflammatory signaling associated with UPR activation is critical in PH pathogenesis.

Enforced dimerization between XBP1s and ATF6f enhances the protective effects of the UPR in models of neurodegeneration

Alteration to endoplasmic reticulum (ER) proteostasis is observed in 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. In this study, 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 a stronger effect in reducing the abnormal aggregation of mutant huntingtin and α-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 disease and Huntington's disease. These results support the concept in which 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.

CrebA increases secretory capacity through direct transcriptional regulation of the secretory machinery, a subset of secretory cargo, and other key regulators

Specialization of many cells, including the acinar cells of the salivary glands and pancreas, milk-producing cells of mammary glands, mucus-secreting goblet cells, antibody-producing plasma cells, and cells that generate the dense extracellular matrices of bone and cartilage, requires scaling up both secretory machinery and cell-type specific secretory cargo. Using tissue-specific genome-scale analyses, we determine how increases in secretory capacity are coordinated with increases in secretory load in the Drosophila salivary gland (SG), an ideal model for gaining mechanistic insight into the functional specialization of secretory organs. Our findings show that CrebA, a bZIP transcription factor, directly binds genes encoding the core secretory machinery, including protein components of the signal recognition particle and receptor, ER cargo translocators, Cop I and Cop II vesicles, as well as the structural proteins and enzymes of these organelles. CrebA directly binds a subset of SG cargo genes and CrebA binds and boosts expression of Sage, a SG-specific transcription factor essential for cargo expression. To further enhance secretory output, CrebA binds and activates Xbp1 and Tudor-SN. Thus, CrebA directly upregulates the machinery of secretion and additional factors to increase overall secretory capacity in professional secretory cells; concomitant increases in cargo are achieved both directly and indirectly.

Potential Roles of Endoplasmic Reticulum Stress and Cellular Proteins Implicated in Diabesity

The role of the endoplasmic reticulum (ER) has evolved from protein synthesis, processing, and other secretory pathways to forming a foundation for lipid biosynthesis and other metabolic functions. Maintaining ER homeostasis is essential for normal cellular function and survival. An imbalance in the ER implied stressful conditions such as metabolic distress, which activates a protective process called unfolded protein response (UPR). This response is activated through some canonical branches of ER stress, i.e., the protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). Therefore, chronic hyperglycemia, hyperinsulinemia, increased proinflammatory cytokines, and free fatty acids (FFAs) found in diabesity (a pathophysiological link between obesity and diabetes) could lead to ER stress. However, limited data exist regarding ER stress and its association with diabesity, particularly the implicated proteins and molecular mechanisms. Thus, this review highlights the role of ER stress in relation to some proteins involved in diabesity pathogenesis and provides insight into possible pathways that could serve as novel targets for therapeutic intervention.

Comparative Analysis of CREB3 and CREB3L2 Protein Expression in HEK293 Cells

We performed a comparative analysis of two ER-resident CREB3 family proteins, CREB3 and CREB3L2, in HEK293 cells using pharmacological and genome editing approaches and identified several differences between the two. Treatment with brefeldin A (BFA) and monensin induced the cleavage of full-length CREB3 and CREB3L2; however, the level of the full-length CREB3 protein, but not CREB3L2 protein, was not noticeably reduced by the monensin treatment. On the other hand, treatment with tunicamycin (Tm) shifted the molecular weight of the full-length CREB3L2 protein downward but abolished CREB3 protein expression. Thapsigargin (Tg) significantly increased the expression of only full-length CREB3L2 protein concomitant with a slight increase in the level of its cleaved form. Treatment with cycloheximide and MG132 revealed that both endogenous CREB3 and CREB3L2 are proteasome substrates. In addition, kifunensine, an α-mannosidase inhibitor, significantly increased the levels of both full-length forms. Consistent with these findings, cells lacking SEL1L, a crucial ER-associated protein degradation (ERAD) component, showed increased expression of both full-length CREB3 and CREB3L2; however, cycloheximide treatment downregulated full-length CREB3L2 protein expression more rapidly in SEL1L-deficient cells than the full-length CREB3 protein. Finally, we investigated the induction of the expression of several CREB3 and CREB3L2 target genes by Tg and BFA treatments and SEL1L deficiency. In conclusion, this study suggests that both endogenous full-length CREB3 and CREB3L2 are substrates for ER-associated protein degradation but are partially regulated by distinct mechanisms, each of which contributes to unique cellular responses that are distinct from canonical ER signals.

Monogenic and syndromic diabetes due to endoplasmic reticulum stress

The endoplasmic reticulum (ER) lies at the crossroads of protein folding, calcium storage, lipid metabolism, and the regulation of autophagy and apoptosis. Accordingly, dysregulation of ER homeostasis leads to β-cell dysfunction in type 1 and type 2 diabetes that ultimately culminates in cell death. The ER is therefore an emerging target for understanding the mechanisms of diabetes mellitus that captures the complex etiologies of this multifactorial class of metabolic disorders. Our strategy for developing ER-targeted diagnostics and therapeutics is to focus on monogenic forms of diabetes related to ER dysregulation in an effort to understand the exact contribution of ER stress to β-cell death. In this manner, we can develop personalized genetic medicine for ERstress-related diabetic disorders, such as Wolfram syndrome. In this article, we describe the phenotypes and molecular pathogenesis of ERstress-related monogenic forms of diabetes.

Luman/CREB3 knock-down inhibit hCG induced MLTC-1 apoptosis

Luman has been reported to be involved in the formation of COP II-mediated transport vesicles that affect protein transportation and secretion. Western blotting, immunohistochemistry, immunofluorescence, and RT-qPCR indicated that Luman is widely expressed in the male mouse reproductive system. In sperm, Luman was mainly located in the sperm tail, and the expression level increased with sperm maturity. In the testis, Luman was located in Leydig cells. In MLTC-1, a high-concentration hCG treatment significantly increased GRP78, ATF6, p-IRE1, and p-EIF2S1 expression but had no effect on Luman expression. To investigate the role of Luman in hCG-induced ER stress (ERS), experiments were conducted to examine the consequences of short hairpin RNA (shRNA)-mediated Luman knockdown in MLTC-1 cells. Luman knockdown decreased the percentage of S phase cells and up-regulated Cyclin A1, Cyclin B1, and Cyclin D2 expression. ELISA and WB results showed that with Luman knockdown, Cyp11a1, p-IRE1, and p-EIF2S1 expression and testosterone secretion were significantly increased, while GRP78 and CHOP expression were decreased. Flow cytometry results showed that Luman knockdown reduced MLTC-1 cell apoptosis. RT-qPCR and WB results showed that Luman knockdown significantly up-regulated BCL-2 expression and decreased Caspase-3 and BAX expression. These data suggest that Luman is widely expressed in the male mouse reproductive system. In MLTC-1 cells, Luman knockdown up-regulated p-IRE1, p-EIF2S1, and BCL-2 expression and decreased GRP78, CHOP, BAX, and Caspase-3 expression. We propose that Luman knockdown reduces cell apoptosis through the ERS pathway, thereby promoting cell survival and testosterone secretion. These findings provide new insights into the role of Luman in hCG-induced ERS.

Transcription factor old astrocyte specifically induced substance is a novel regulator of kidney fibrosis

Prevention of kidney fibrosis is an essential requisite for effective therapy in preventing chronic kidney disease (CKD). Here, we identify Old astrocyte specifically induced substance (OASIS)/cAMP responsive element‐binding protein 3‐like 1 (CREB3l1), a CREB/ATF family transcription factor, as a candidate profibrotic gene that drives the final common pathological step along the fibrotic pathway in CKD. Although microarray data from diseased patient kidneys and fibrotic mouse model kidneys both exhibit OASIS/Creb3l1 upregulation, the pathophysiological roles of OASIS in CKD remains unknown. Immunohistochemistry revealed that OASIS protein was overexpressed in human fibrotic kidney compared with normal kidney. Moreover, OASIS was upregulated in murine fibrotic kidneys, following unilateral ureteral obstruction (UUO), resulting in an increase in the number of OASIS‐expressing pathological myofibroblasts. In vitro assays revealed exogenous TGF‐β1 increased OASIS expression coincident with fibroblast‐to‐myofibroblast transition and OASIS contributed to TGF‐β1–mediated myofibroblast migration and increased proliferation. Significantly, in vivo kidney fibrosis induced via UUO or ischemia/reperfusion injury was ameliorated by systemic genetic knockout of OASIS, accompanied by reduced myofibroblast proliferation. Microarrays revealed that the transmembrane glycoprotein Bone marrow stromal antigen 2 (Bst2) expression was reduced in OASIS knockout myofibroblasts. Interestingly, a systemic anti‐Bst2 blocking antibody approach attenuated kidney fibrosis in normal mice but not in OASIS knockout mice after UUO, signifying Bst2 functions downstream of OASIS. Finally, myofibroblast‐restricted OASIS conditional knockouts resulted in resistance to kidney fibrosis. Taken together, OASIS in myofibroblasts promotes kidney fibrosis, at least in part, via increased Bst2 expression. Thus, we have identified and demonstrated that OASIS signaling is a novel regulator of kidney fibrosis.

Endoplasmic reticulum stress serves an important role in cardiac ischemia/reperfusion injury (Review)

Although acute myocardial infarction is one of the most common fatal diseases worldwide, the understanding of its underlying pathogenesis continues to develop. Myocardial ischemia/reperfusion (I/R) can restore myocardial oxygen and nutrient supply. However, a large number of studies have demonstrated that recovery of blood perfusion after acute ischemia causes reperfusion injury to the heart. With progress made in the understanding of the underlying mechanisms of myocardial I/R and oxidative stress, a novel area of research that merits greater study has been identified, that of I/R-induced endoplasmic reticulum (ER) stress (ERS). Cardiac I/R can alter the function of the ER, leading to the accumulation of unfolded/misfolded proteins. The resulting ERS then induces the activation of signal transduction pathways, which in turn contribute to the development of I/R injury. The mechanism of I/R injury, and the causal relationship between I/R and ERS are reviewed in the present article.

Promotion of Axon Growth by the Secreted End of a Transcription Factor

Axon growth is regulated externally by attractive and repulsive cues generated in the environment. In addition, intrinsic pathways govern axon development, although the extent to which axons themselves can influence their own growth is unknown. We find that dorsal root ganglion (DRG) axons secrete a factor supporting axon growth and identify it as the C terminus of the ER stress-induced transcription factor CREB3L2, which is generated by site 2 protease (S2P) cleavage in sensory neurons. S2P and CREB3L2 knockdown or inhibition of axonal S2P interfere with the growth of axons, and C-terminal CREB3L2 is sufficient to rescue these effects. C-terminal CREB3L2 forms a complex with Shh and stabilizes its association with the Patched-1 receptor on developing axons. Our results reveal a neuron-intrinsic pathway downstream of S2P that promotes axon growth.

Combined transcriptome and proteome profiling of the pancreatic β-cell response to palmitate unveils key pathways of β-cell lipotoxicity

BACKGROUND

Prolonged exposure to elevated free fatty acids induces β-cell failure (lipotoxicity) and contributes to the pathogenesis of type 2 diabetes. In vitro exposure of β-cells to the saturated free fatty acid palmitate is a valuable model of lipotoxicity, reproducing features of β-cell failure observed in type 2 diabetes. In order to map the β-cell response to lipotoxicity, we combined RNA-sequencing of palmitate-treated human islets with iTRAQ proteomics of insulin-secreting INS-1E cells following a time course exposure to palmitate.

RESULTS

Crossing transcriptome and proteome of palmitate-treated β-cells revealed 85 upregulated and 122 downregulated genes at both transcript and protein level. Pathway analysis identified lipid metabolism, oxidative stress, amino-acid metabolism and cell cycle pathways among the most enriched palmitate-modified pathways. Palmitate induced gene expression changes compatible with increased free fatty acid mitochondrial import and β-oxidation, decreased lipogenesis and modified cholesterol transport. Palmitate modified genes regulating endoplasmic reticulum (ER) function, ER-to-Golgi transport and ER stress pathways. Furthermore, palmitate modulated cAMP/protein kinase A (PKA) signaling, inhibiting expression of PKA anchoring proteins and downregulating the GLP-1 receptor. SLC7 family amino-acid transporters were upregulated in response to palmitate but this induction did not contribute to β-cell demise. To unravel critical mediators of lipotoxicity upstream of the palmitate-modified genes, we identified overrepresented transcription factor binding sites and performed network inference analysis. These identified LXR, PPARα, FOXO1 and BACH1 as key transcription factors orchestrating the metabolic and oxidative stress responses to palmitate.

CONCLUSIONS

This is the first study to combine transcriptomic and sensitive time course proteomic profiling of palmitate-exposed β-cells. Our results provide comprehensive insight into gene and protein expression changes, corroborating and expanding beyond previous findings. The identification of critical drivers and pathways of the β-cell lipotoxic response points to novel therapeutic targets for type 2 diabetes.

Tisp40 Induces Tubular Epithelial Cell GSDMD-Mediated Pyroptosis in Renal Ischemia-Reperfusion Injury via NF-κB Signaling

Renal ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI). As a transcription factor, the Transcript induced in spermiogenesis 40 (Tisp40) has been found to be involved in renal IRI. However, the role of Tisp40 in tubular epithelial cell (TEC) pyroptosis of renal IRI remains unknown. In this study, we investigated effects of Tisp40 on Gasdermin D (GSDMD)-mediated TEC pyroptosis in renal IRI and underlying molecular mechanisms in I/R-induced kidney by hematoxylin and eosin (HE) staining, Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay,immunohistochemistry (IHC), reverse transcription-quantitative PCR (RT-qPCR) and western blot analysis in vivo and oxygen-glucose deprivation/reoxygenation (OGD/R)-stimulated TCMK-1 cells by lactate dehydrogenase (LDH) release assay, CCK-8 assay,enzyme-linked immunosorbent assay (ELISA), flow cytometric analysis, immunofluorescence staining,RT-qPCRand western blot analysis in vitro. We found that the levels of Tisp40 and GSDMD-N expression increased gradually, and peaked at 30 min ischemia/24 h reperfusion in vivo and 24 h OGD/R/6 h reoxygenation in vitro, simultaneously, the levels of TEC pyroptosis and renal injury were correspondingly increased. The data of Pearson’s correlation analysis showed that the expression of Tisp40 and GSDMD-N was positively correlated. Furthermore, Tisp40 overexpression aggravated TEC pyroptosis rate and increased the expressions of related proteins, including GSDMD-N, NLRP3, caspase-1, IL-1β, and IL-18 in the OGD/R-stimulated TCMK-1 cell line, whereas the opposite occurred in cells treated with small interfeing RNA (siRNA) targeting Tisp40. Tisp40-deficient mice showed attenuated renal IRI and pyroptosis compared with wild-type mice. In addition, Tisp40 knockout remarkably decreased the levels of GSDMD-N, IL-1β, IL-18, NLRP3, and caspase-1 expression, and alleviated renal pyroptosis induced by I/R. Importantly, Tisp40 overexpression significantly increased TECs pyroptosis via p-p65 activation, however, the effects of Tisp40 overexpression were partially blocked by parthenolide (PTL). Collectively, our findings provide insight into the mechanism of how Tisp40 regulated GSDMD-mediated pyroptosis in renal IRI.

Metabolic coessentiality mapping identifies C12orf49 as a regulator of SREBP processing and cholesterol metabolism

Coessentiality mapping has been useful to systematically cluster genes into biological pathways and identify gene functions1-3. Here, using the debiased sparse partial correlation (DSPC) method3, we construct a functional coessentiality map for cellular metabolic processes across human cancer cell lines. This analysis reveals 35 modules associated with known metabolic pathways and further assigns metabolic functions to unknown genes. In particular, we identify C12orf49 as an essential regulator of cholesterol and fatty acid metabolism in mammalian cells. Mechanistically, C12orf49 localizes to the Golgi, binds membrane-bound transcription factor peptidase, site 1 (MBTPS1, site 1 protease) and is necessary for the cleavage of its substrates, including sterol regulatory element binding protein (SREBP) transcription factors. This function depends on the evolutionarily conserved uncharacterized domain (DUF2054) and promotes cell proliferation under cholesterol depletion. Notably, c12orf49 depletion in zebrafish blocks dietary lipid clearance in vivo, mimicking the phenotype of mbtps1 mutants. Finally, in an electronic health record (EHR)-linked DNA biobank, C12orf49 is associated with hyperlipidaemia through phenome analysis. Altogether, our findings reveal a conserved role for C12orf49 in cholesterol and lipid homeostasis and provide a platform to identify unknown components of other metabolic pathways.

Cleavage of cyclic AMP-responsive element-binding protein H aggravates myocardial hypoxia reperfusion injury in a hepatocyte-myocardial cell co-culture system

OBJECTIVE

This study aimed to determine whether proinflammatory cytokines have an effect on myocardial cells (MCs) and hepatocytes during myocardial ischemia to induce cyclic AMP-responsive element-binding protein H (CREBH) cleavage, activate the acute phase response in the liver, and cause a superimposed injury in MCs.

METHODS

In this study, a hepatocyte-MC transwell co-culture system was used to investigate the relationship between myocardial hypoxia/reperfusion injury and CREBH cleavage. MCs and hepatocytes of neonatal rats were obtained from the ventricles and livers of Sprague-Dawley rats, respectively. MCs were inoculated into the lower chamber of transwell chambers for 12 hours under hypoxia. Levels of the endoplasmic reticulum stress protein glucose-regulated protein 78 in MCs, CREBH in hepatocytes, inflammatory factor (tumor necrosis factor-α and interleukin-6) levels, and cell viability were evaluated. The effect of CREBH knockdown was also studied using a CREBH-specific short hairpin RNA (Ad-CREBHi).

RESULTS

We found that proinflammatory cytokines affect MCs and hepatocytes during myocardial ischemia to induce CREBH cleavage, activate the acute phase response in the liver, and cause superimposed injury in MCs.

CONCLUSIONS

Expression of CREBH aggravates myocardial injury during myocardial ischemia.

Transcription factor Creb3l1 regulates the synthesis of prohormone convertase enzyme PC1/3 in endocrine cells

Transcription factor cAMP responsive element-binding protein 3 like 1 (Creb3l1) is a non-classical endoplasmic reticulum stress molecule that is emerging as an important component for cellular homeostasis, particularly within cell types with high peptide secretory capabilities. We have previously shown that Creb3l1 serves an important role in body fluid homeostasis through its transcriptional control of the gene coding for antidiuretic hormone arginine vasopressin in the neuropeptide-rich magnocellular neurones of the supraoptic nucleus. In response to osmotic stimuli such as dehydration, vasopressin magnocellular neurones undergo remarkable transcriptome changes, including increased Creb3l1 expression, to ensure that the supply of vasopressin meets demand. To determine where else Creb3l1 fits into the secretory cell supply chain, we performed RNA-sequencing of Creb3l1 knockdown anterior pituitary mouse corticotroph cell line AtT20. The target chosen for further investigation was Pcsk1, which encodes proprotein convertase enzyme 1 (PC1/3). PC1/3 is crucial for processing of neuropeptides and peptide hormones such as pro-opiomelanocortin (POMC), proinsulin, proglucagon, vasopressin and oxytocin. Viral manipulations in supraoptic nuclei by over-expression of Creb3l1 increased Pcsk1, whereas Creb3l1 knockdown decreased Pcsk1 expression. In vitro promoter activity and binding studies showed that Creb3l1 was a transcription factor of the Pcsk1 gene binding directly to a G-box motif in the promoter. In the dehydrated rat anterior pituitary, Creb3l1 and Pcsk1 expression decreased in parallel compared to control, supporting our findings from manipulations in AtT20 cells and the supraoptic nucleus. No relationship was observed between Creb3l1 and Pcsk1 expression in the neurointermediate lobe of the pituitary, indicating a different mechanism of PC1/3 synthesis by these POMC-synthesising cells. Therefore, Creb3l1, by regulating the expression of Pcsk1, does not control the processing of POMC peptides in the intermediate lobe.

Natural Products Targeting ER Stress, and the Functional Link to Mitochondria

The endoplasmic reticulum (ER) is a dynamic organelle essential for intracellular homeostasis maintenance, controlling synthesis, the folding of secreted and membrane-bound proteins, and transport of Ca²⁺. During cellular stress, ER dysfunction leads to the activation of unfolded protein response (UPR) due to accumulated misfolded proteins in the ER. This condition is referred as ER stress. Mitochondria and ER form a site of close contact (the mitochondria-associated membrane, MAM) which is a major platform exerting important physiological roles in the regulation of intracellular Ca²⁺ homeostasis, lipid metabolism, mitochondrial fission, autophagosome formation, and apoptosis progression. Natural products have been receiving increasing attention for their ability to interfere with ER stress. Research works have focused on the capacity of these bioactive compounds to induce apoptosis by activating ER stress through the ER stress-mediated mitochondrial apoptotic pathway. In this review we discuss the role of natural products in the signaling communication between ER and mitochondria, focusing on the effects induced by ER stress including Ca²⁺ permeability transition and UPR signaling (protein kinase R-like ER kinase/mitofusin 2).

Sledgehammer to Scalpel: Broad Challenges to the Heart and Other Tissues Yield Specific Cellular Responses via Transcriptional Regulation of the ER-Stress Master Regulator ATF6α

There are more than 2000 transcription factors in eukaryotes, many of which are subject to complex mechanisms fine-tuning their activity and their transcriptional programs to meet the vast array of conditions under which cells must adapt to thrive and survive. For example, conditions that impair protein folding in the endoplasmic reticulum (ER), sometimes called ER stress, elicit the relocation of the ER-transmembrane protein, activating transcription factor 6α (ATF6α), to the Golgi, where it is proteolytically cleaved. This generates a fragment of ATF6α that translocates to the nucleus, where it regulates numerous genes that restore ER protein-folding capacity but is degraded soon after. Thus, upon ER stress, ATF6α is converted from a stable, transmembrane protein, to a rapidly degraded, nuclear protein that is a potent transcription factor. This review focuses on the molecular mechanisms governing ATF6α location, activity, and stability, as well as the transcriptional programs ATF6α regulates, whether canonical genes that restore ER protein-folding or unexpected, non-canonical genes affecting cellular functions beyond the ER. Moreover, we will review fascinating roles for an ATF6α isoform, ATF6β, which has a similar mode of activation but, unlike ATF6α, is a long-lived, weak transcription factor that may moderate the genetic effects of ATF6α.

Dysregulation in the Unfolded Protein Response in the FGR Rat Pancreas

Accumulating evidence suggests that fetal growth restriction (FGR) leads to the development of diabetes mellitus in adults. The aim of this study was to investigate the effect of protein malnutrition in utero on the pancreatic unfolded protein response (UPR) pathway in FGR offspring. An FGR model was developed by feeding a low-protein diet to pregnant rats throughout gestation. Eighty-four UPR pathway components in the pancreas were investigated by quantitative PCR arrays and confirmed by qPCR and western blotting. Activating transcription factor (Atf4 and Atf6), herpud1, protein kinase R-like endoplasmic reticulum kinase (Perk), X-box binding protein 1 (Xbp1), and the phosphorylation of eIF2α were upregulated, while cyclic AMP-responsive element-binding protein 3-like protein was markedly downregulated in FGR fetuses compared with controls. Investigation in adult offspring revealed temporal changes, for most UPR factors restored to normal, except that dysregulation of Atf6 and Creb3l3 maintained until adulthood. Moreover, autophagy was suppressed in FGR fetal pancreas and may be associated with decreased activation of AMP-activated protein kinase (Ampk). Apoptosis regulators Bax and cleaved-caspase 3 and 9 were upregulated in FGR fetal pancreas. Given that islet size and number were decreased in FGR fetus, we speculated that the aberrant intrauterine milieu impaired UPR signaling in fetal pancreas development. Whether these alterations early in life contribute to the predisposition of FGR fetuses to adult metabolic disorders invites further exploration.

A Review of Mouse Models of Monogenic Diabetes and ER Stress Signaling

Diabetes is a major public health problem: it is estimated that 420 million people are affected globally. Monogenic forms of diabetes are less common, but variants in monogenic diabetes genes have been shown to contribute to type 2 diabetes risk. In vitro and in vivo models of monogenic forms of diabetes related to the endoplasmic reticulum (ER) stress response provided compelling evidence on the role of ER stress and dysregulated ER stress signaling on β cell demise in type 1 and type 2 diabetes. In this chapter, we describe the genetics, background, and phenotype of ER stress-related monogenic diabetes mouse models, and we comment on their advantages and disadvantages. We conclude that these mouse models are very useful tools for monogenic diabetes molecular pathogenesis studies, although there is a variability on the methodology that is used. Regarding the use of these models for therapeutic testing of ER stress modulators, a specific consideration should be given to the fact that they recapitulate some, but not all, the phenotypic characteristics of the human disease.

Mechanisms of action of amyloid-beta and its precursor protein in neuronal cell death

Extracellular senile plaques and intracellular neurofibrillary tangles are the neuropathological findings of the Alzheimer's disease (AD). Based on the amyloid cascade hypothesis, the main component of senile plaques, the amyloid-beta (Aβ) peptide, and its derivative called amyloid precursor protein (APP) both have been found to place their central roles in AD development for years. However, the recent therapeutics have yet to reverse or halt this disease. Previous evidence demonstrates that the accumulation of Aβ peptides and APP can exert neurotoxicity and ultimately neuronal cell death. Hence, we discuss the mechanisms of excessive production of Aβ peptides and APP serving as pathophysiologic stimuli for the initiation of various cell signalling pathways including apoptosis, necrosis, necroptosis and autophagy which lead to neuronal cell death. Conversely, the activation of such pathways could also result in the abnormal generation of APP and Aβ peptides. An elucidation of actions of APP and its metabolite, Aβ, could be vital in suggesting novel therapeutic opportunities.

Crebl2 regulates cell metabolism in muscle and liver cells

We previously identified Drosophila REPTOR and REPTOR-BP as transcription factors downstream of mTORC1 that play an important role in regulating organismal metabolism. We study here the mammalian ortholog of REPTOR-BP, Crebl2. We find that Crebl2 mediates part of the transcriptional induction caused by mTORC1 inhibition. In C2C12 myoblasts, Crebl2 knockdown leads to elevated glucose uptake, elevated glycolysis as observed by lactate secretion, and elevated triglyceride biosynthesis. In Hepa1-6 hepatoma cells, Crebl2 knockdown also leads to elevated triglyceride levels. In sum, this works identifies Crebl2 as a regulator of cellular metabolism that can link nutrient sensing via mTORC1 to the metabolic response of cells.

Herpesviruses and the Unfolded Protein Response

Herpesviruses usurp cellular stress responses to promote viral replication and avoid immune surveillance. The unfolded protein response (UPR) is a conserved stress response that is activated when the protein load in the ER exceeds folding capacity and misfolded proteins accumulate. The UPR aims to restore protein homeostasis through translational and transcriptional reprogramming; if homeostasis cannot be restored, the UPR switches from "helper" to "executioner", triggering apoptosis. It is thought that the burst of herpesvirus glycoprotein synthesis during lytic replication causes ER stress, and that these viruses may have evolved mechanisms to manage UPR signaling to create an optimal niche for replication. The past decade has seen considerable progress in understanding how herpesviruses reprogram the UPR. Here we provide an overview of the molecular events of UPR activation, signaling and transcriptional outputs, and highlight key evidence that herpesviruses hijack the UPR to aid infection.

Control of Protein Homeostasis in the Early Secretory Pathway: Current Status and Challenges

: Discrimination between properly folded proteins and those that do not reach this state is necessary for cells to achieve functionality. Eukaryotic cells have evolved several mechanisms to ensure secretory protein quality control, which allows efficiency and fidelity in protein production. Among the actors involved in such process, both endoplasmic reticulum (ER) and the Golgi complex play prominent roles in protein synthesis, biogenesis and secretion. ER and Golgi functions ensure that only properly folded proteins are allowed to flow through the secretory pathway while improperly folded proteins have to be eliminated to not impinge on cellular functions. Thus, complex quality control and degradation machineries are crucial to prevent the toxic accumulation of improperly folded proteins. However, in some instances, improperly folded proteins can escape the quality control systems thereby contributing to several human diseases. Herein, we summarize how the early secretory pathways copes with the accumulation of improperly folded proteins, and how insufficient handling can cause the development of several human diseases. Finally, we detail the genetic and pharmacologic approaches that could be used as potential therapeutic tools to treat these diseases.

Knockdown of CREB3 activates endoplasmic reticulum stress and induces apoptosis in glioblastoma

Glioblastoma is a highly malignant type of central nervous system tumor. In the present study, the results of RNA sequencing indicated that cAMP responsive element binding protein 3 (CREB3) was upregulated in tumor tissues from patients with GBM. The cAMP responsive element binding protein 3 (CREB3) pathway is a major contributor to the malignant progression of glioblastoma. In this study, we explored the mechanisms by which CREB3 regulates the proliferation, invasion and apoptosis of glioblastoma. Pairs of glioblastoma and normal tissues were subjected to RNA sequencing. Then, qRT-PCR and Western blotting were used to detect CREB3 levels in glioblastoma tissues and cell lines, respectively. CREB3 was upregulated in glioblastoma tissues and cell lines. Overexpression of CREB3 promoted the proliferation and invasion of SHG-44 cells, while downregulation of CREB3 inhibited the invasion of U251MG cells. Knockdown of CREB3 also induced apoptosis in U251MG cells and increased the protein levels of BAX, active caspase 3, p-PERK, p-eIF2α and ATF4. An in vivo study in nude mice bearing U251MG cell xenografts confirmed these results. Our findings indicate that CREB3 functions as a tumor promoter in glioblastoma, and thus could serve as a treatment target in glioblastoma patients.

Pituitary cell translation and secretory capacities are enhanced cell autonomously by the transcription factor Creb3l2

Translation is a basic cellular process and its capacity is adapted to cell function. In particular, secretory cells achieve high protein synthesis levels without triggering the protein stress response. It is unknown how and when translation capacity is increased during differentiation. Here, we show that the transcription factor Creb3l2 is a scaling factor for translation capacity in pituitary secretory cells and that it directly binds ~75% of regulatory and effector genes for translation. In parallel with this cell-autonomous mechanism, implementation of the physiological UPR pathway prevents triggering the protein stress response. Knockout mice for Tpit, a pituitary differentiation factor, show that Creb3l2 expression and its downstream regulatory network are dependent on Tpit. Further, Creb3l2 acts by direct targeting of translation effector genes in parallel with signaling pathways that otherwise regulate protein synthesis. Expression of Creb3l2 may be a useful means to enhance production of therapeutic proteins.

Regulation of the ER-bound transcription factor Luman/CREB3 in HEK293 cells

CREB3 is a transcription factor localized to the ER. Here, we investigated endogenous CREB3 expression in HEK293 cells using pharmacological and genome editing approaches. Full-length CREB3 detected under resting conditions disappeared following treatment with tunicamycin, brefeldin A and nigericin. Treatment with cycloheximide and MG132 indicated that endogenous CREB3 is a proteasome substrate. Using cells deficient for the ER-associated protein degradation (ERAD) factors SEL1L and Herp, we demonstrate that SEL1L, but not Herp, plays a crucial role in the posttranslational regulation of full-length CREB3 expression. In addition, kifunensine, an α-mannosidase inhibitor, remarkably increased full-length CREB3 expression. Our study suggests that endogenous full-length CREB3 is a novel substrate for ERAD and identifies unique cellular signals distinct from those in canonical ER stress.