Protein quality control in the early secretory pathway

Molecular insights in the pathogenesis of classical Ehlers-Danlos syndrome from transcriptome-wide expression profiling of patients' skin fibroblasts

Classical Ehlers-Danlos syndrome (cEDS) is a dominant inherited connective tissue disorder mainly caused by mutations in the COL5A1 and COL5A2 genes encoding type V collagen (COLLV), which is a fibrillar COLL widely distributed in a variety of connective tissues. cEDS patients suffer from skin hyperextensibility, abnormal wound healing/atrophic scars, and joint hypermobility. Most of the causative variants result in a non-functional COL5A1 allele and COLLV haploinsufficiency, whilst COL5A2 mutations affect its structural integrity. To shed light into disease mechanisms involved in cEDS, we performed gene expression profiling in skin fibroblasts from four patients harboring haploinsufficient and structural mutations in both disease genes. Transcriptome profiling revealed significant changes in the expression levels of different extracellular matrix (ECM)-related genes, such as SPP1, POSTN, EDIL3, IGFBP2, and C3, which encode both matricellular and soluble proteins that are mainly involved in cell proliferation and migration, and cutaneous wound healing. These gene expression changes are consistent with our previous protein findings on in vitro fibroblasts from other cEDS patients, which exhibited reduced migration and poor wound repair owing to COLLV disorganization, altered deposition of fibronectin into ECM, and an abnormal integrin pattern. Microarray analysis also indicated the decreased expression of DNAJB7, VIPAS39, CCPG1, ATG10, SVIP, which encode molecular chaperones facilitating protein folding, enzymes regulating post-Golgi COLLs processing, and proteins acting as cargo receptors required for endoplasmic reticulum (ER) proteostasis and implicated in the autophagy process. Patients’ cells also showed altered mRNA levels of many cell cycle regulating genes including CCNE2, KIF4A, MKI67, DTL, and DDIAS. Protein studies showed that aberrant COLLV expression causes the disassembly of itself and many structural ECM constituents including COLLI, COLLIII, fibronectin, and fibrillins. Our findings provide the first molecular evidence of significant gene expression changes in cEDS skin fibroblasts highlighting that defective ECM remodeling, ER homeostasis and autophagy might play a role in the pathogenesis of this connective tissue disorder.

IFNγ and TNFα synergistically induce apoptosis of mesenchymal stem/stromal cells via the induction of nitric oxide

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) have been widely used to treat various inflammatory diseases. The immunomodulatory capabilities of MSCs are usually licensed by inflammatory cytokines and may vary depending on the levels and the types of inflammatory cytokines. However, how the inflammatory microenvironment affects the fate of MSCs remains elusive. Here we characterized the molecular mechanism underlying the apoptosis of mouse MSCs triggered by the synergistic action of IFNγ and TNFα.

METHODS

We isolated and expanded MSCs by flushing the femoral and tibial bone marrow of wild-type, iNOS^-/-, and Fas^-/- mice. BM-MSCs were treated with IFNγ and TNFα in vitro, and cell viability was evaluated by a CCK-8 kit. Apoptosis was assessed by Annexin V/propidium iodide-stained flow cytometry. Expression of genes related to apoptosis and endoplasmic reticulum (ER) stress was measured by reverse transcription-polymerase chain reaction (RT-PCR). Apoptosis and autophagy-related proteins were examined by Western blot analysis.

RESULTS

IFNγ and TNFα synergistically trigger apoptosis of mouse BM-MSCs. The two cytokines were shown to stimulate the expression of inducible nitric oxide synthase (iNOS) and consequently the generation of nitric oxide (NO), which is required for the apoptosis of mouse BM-MSCs. The two cytokines similarly induced apoptosis in Fas^-/- BM-MSCs. iNOS and NO were shown to upregulate Fas in mouse MSCs and sensitize them to Fas agonist-induced apoptosis. Moreover, NO stimulated by IFNγ/TNFα impairs autophagy, which aggravates ER stress and promotes apoptosis.

CONCLUSIONS

IFNγ/TNFα-induced apoptosis in mouse MSCs is mediated by NO. Our findings shed new light on cytokine-induced apoptosis of MSCs and have implications in MSC-based therapy of inflammatory diseases.

Myosin 1F Regulates M1-Polarization by Stimulating Intercellular Adhesion in Macrophages

Intestinal macrophages are highly mobile cells with extraordinary plasticity and actively contribute to cytokine-mediated epithelial cell damage. The mechanisms triggering macrophage polarization into a proinflammatory phenotype are unknown. Here, we report that during inflammation macrophages enhance its intercellular adhesion properties in order to acquire a M1-phenotype. Using in vitro and in vivo models we demonstrate that intercellular adhesion is mediated by integrin-αVβ3 and relies in the presence of the unconventional class I myosin 1F (Myo1F). Intercellular adhesion mediated by αVβ3 stimulates M1-like phenotype in macrophages through hyperactivation of STAT1 and STAT3 downstream of ILK/Akt/mTOR signaling. Inhibition of integrin-αVβ3, Akt/mTOR, or lack of Myo1F attenuated the commitment of macrophages into a pro-inflammatory phenotype. In a model of colitis, Myo1F deficiency strongly reduces the secretion of proinflammatory cytokines, decreases epithelial damage, ameliorates disease activity, and enhances tissue repair. Together our findings uncover an unknown role for Myo1F as part of the machinery that regulates intercellular adhesion and polarization in macrophages.

Influence of N-glycosylation on effector functions and thermal stability of glycoengineered IgG1 monoclonal antibody with homogeneous glycoforms

Glycosylation of the conserved asparagine residue in each heavy chain of IgG in the CH2 domain is known as N-glycosylation. It is one of the most common post-translational modifications and important critical quality attributes of monoclonal antibody (mAb) therapeutics. Various studies have demonstrated the effects of the Fc N-glycosylation on safety, Fc effector functions, and pharmacokinetics, both dependent and independent of neonatal Fc receptor (FcRn) pathway. However, separation of various glycoforms to investigate the biological and functional relevance of glycosylation is a major challenge, and existing studies often discuss the overall impact of N-glycans, without considering the individual contributions of each glycoform when evaluating mAbs with highly heterogeneous distributions. In this study, chemoenzymatic glycoengineering incorporating an endo-β-N-acetylglucosaminidase (ENGase) EndoS2 and its mutant with transglycosylation activity was used to generate mAb glycoforms with highly homogeneous and well-defined N-glycans to better understand and precisely evaluate the effect of each N-glycan structure on Fc effector functions and protein stability. We demonstrated that the core fucosylation, non-reducing terminal galactosylation, sialylation, and mannosylation of IgG1 mAb N-glycans impact not only on FcγRIIIa binding, antibody-dependent cell-mediated cytotoxicity, and C1q binding, but also FcRn binding, thermal stability and propensity for protein aggregation.

MiR-378 modulates energy imbalance and apoptosis of mitochondria induced by doxorubicin

Doxorubicin (DOX) is an effective anticancer drug, however its clinical application is limited due to its cardiotoxicity. Therefore, understanding the mechanisms of cardiotoxicity induced by DOX is essential. We found that the level of miR-378 was decreased in the hearts of DOX-treated rats. Increasing the expression of miR-378 resulted in a decrease of lactate dehydrogenase (LDH) upon DOX treatment in vitro by targeting lactate dehydrogenase A (LDHA). Furthermore, bioinformatics analysis indicated that cyclophilin A (PPIA), a regulator of apoptosis, is also a direct target gene of miR-378. We confirmed this by Western blot. Our results also showed that the overexpression of miR-378 inhibited the hyperactivation of ER stress signaling induced by DOX. In addition, MiR-378 overexpression was found to protect cardiomyocytes from DOX-induced energy imbalance and apoptosis of mitochondria. These results may allow for a therapeutic approach that overcomes the cardiotoxicity of DOX-based treatments for cancer.

Attempt to Untangle the Prion-Like Misfolding Mechanism for Neurodegenerative Diseases

The misfolding and aggregation of proteins is the neuropathological hallmark for numerous diseases including Alzheimer's disease, Parkinson's disease, and prion diseases. It is believed that misfolded and abnormal β-sheets forms of wild-type proteins are the vectors of these diseases by acting as seeds for the aggregation of endogenous proteins. Cellular prion protein (PrP^C) is a glycosyl-phosphatidyl-inositol (GPI) anchored glycoprotein that is able to misfold to a pathogenic isoform PrP^Sc, the causative agent of prion diseases which present as sporadic, dominantly inherited and transmissible infectious disorders. Increasing evidence highlights the importance of prion-like seeding as a mechanism for pathological spread in Alzheimer's disease and Tauopathy, as well as other neurodegenerative disorders. Here, we report the latest findings on the mechanisms controlling protein folding, focusing on the ER (Endoplasmic Reticulum) quality control of GPI-anchored proteins and describe the "prion-like" properties of amyloid-β and tau assemblies. Furthermore, we highlight the importance of pathogenic assemblies interaction with protein and lipid membrane components and their implications in both prion and Alzheimer's diseases.

Cab45s inhibits neuronal apoptosis following intracerebral hemorrhage in adult rats

Recent studies have shown that Cab45s, belonging to the CREC family, can fight against apoptosis in the cancer cell lines. Here, we report that Cab45s may involve in neuronal apoptosis at the early stage of intracerebral hemorrhage (ICH) in pathophysiology. We found that expression of Cab45s was enhanced in areas contiguous to hematoma following ICH in adult rats, and that so were the expressions of Glucose-regulated protein 78 (GRP78), pro-apoptotic Bcl-2-associated X protein (Bax) and active caspase-3. In vitro, coimmunoprecipitation analysis indicated the interaction between Cab45s and GRP78. Depletion of Cab45s attenuated the expression of GRP78, but increased the expressions of Bax and caspase-3 in PC12 cells treated with hemin, which finally promoted apoptosis. Together, these results reveal that Cab45s might exert its anti-apoptotic function against neuronal apoptosis. Thus, the study may provide evidences for regulating Cab45s as a potentially reliable treatment for the secondary damage following ICH.

Intermediate compartment (IC): from pre-Golgi vacuoles to a semi-autonomous membrane system

Despite its discovery more than three decades ago and well-established role in protein sorting and trafficking in the early secretory pathway, the intermediate compartment (IC) has remained enigmatic. The prevailing view is that the IC evolved as a specialized organelle to mediate long-distance endoplasmic reticulum (ER)–Golgi communication in metazoan cells, but is lacking in other eukaryotes, such as plants and fungi. However, this distinction is difficult to reconcile with the high conservation of the core machineries that regulate early secretory trafficking from yeast to man. Also, it has remained unclear whether the pleiomorphic IC components—vacuoles, tubules and vesicles—represent transient transport carriers or building blocks of a permanent pre-Golgi organelle. Interestingly, recent studies have revealed that the IC maintains its compositional, structural and spatial properties throughout the cell cycle, supporting a model that combines the dynamic and stable aspects of the organelle. Moreover, the IC has been assigned novel functions, such as cell signaling, Golgi-independent trafficking and autophagy. The emerging permanent nature of the IC and its connections with the centrosome and the endocytic recycling system encourage reconsideration of its relationship with the Golgi ribbon, role in Golgi biogenesis and ubiquitous presence in eukaryotic cells.

Antitumor effect of ginsenoside Rg3 on gallbladder cancer by inducing endoplasmic reticulum stress-mediated apoptosis in vitro and in vivo

Recent studies have highlighted the importance of the endoplasmic reticulum (ER) in apoptotic processes. In the present study, the traditional herbal medicine ginsenoside Rg3 was used to treat gallbladder cancer in vitro and in vivo. The underlying signaling mechanisms were investigated using various molecular biology techniques, including flow cytometry, western blot analysis, ELISA and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). It was indicated that Rg3 exerted pro-apoptotic activity against the gallbladder cancer cell line GBC-SD through the ER stress-mediated signaling pathway. This was demonstrated by increased expression of phosphorylation of eukaryotic translation-initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4), CCAAT/enhancer-binding protein homologous protein and lipocalin 2. In addition, eIF2α and ATF4 knockdown attenuated the pro-apoptotic effect of Rg3 by inhibiting reactive oxygen species. Furthermore, the results of RT-qPCR analysis indicated that long intergenic non-protein coding RNA-p21 was significantly upregulated following Rg3 treatment. In conclusion, the results of the present study demonstrated that Rg3 inhibited tumor growth in a GBC-SD gallbladder cancer xenograft, by upregulating the ER stress-mediated signaling pathway. Therefore, ER stress activation is suggested to mediate the antitumor effect of Rg3 in gallbladder cancer activity in vitro and in vivo.

Sigma Receptors as Endoplasmic Reticulum Stress "Gatekeepers" and their Modulators as Emerging New Weapons in the Fight Against Cancer

Despite the interest aroused by sigma receptors (SRs) in the area of oncology, their role in tumor biology remains enigmatic. The predominant subcellular localization and main site of activity of SRs are the endoplasmic reticulum (ER). Current literature data, including recent findings on the sigma 2 receptor subtype (S2R) identity, suggest that SRs may play a role as ER stress gatekeepers. Although SR endogenous ligands are still unknown, a wide series of structurally unrelated compounds able to bind SRs have been identified. Currently, the identification of novel antiproliferative molecules acting via SR interaction is a challenging task for both academia and industry, as shown by the fact that novel anticancer drugs targeting SRs are in the preclinical-stage pipeline of pharmaceutical companies (i.e., Anavex Corp. and Accuronix). So far, no clinically available anticancer drugs targeting SRs are still available. The present review focuses literature advancements and provides a state-of-the-art overview of SRs, with emphasis on their involvement in cancer biology and on the role of SR modulators as anticancer agents. Findings from preclinical studies on novel anticancer drugs targeting SRs are presented in brief.

Repurposing drugs to target the malaria parasite unfolding protein response

Drug resistant Plasmodium falciparum parasites represent a major obstacle in our efforts to control malaria, a deadly vector borne infectious disease. This situation creates an urgent need to find and validate new drug targets to contain the spread of the disease. Several genes associated with the unfolded protein response (UPR) including Glucose-regulated Protein 78 kDa (GRP78, also known as BiP) have been deemed potential drug targets. We explored the drug target potential of GRP78, a molecular chaperone that is a regulator of the UPR, for the treatment of P. falciparum parasite infection. By screening repurposed chaperone inhibitors that are anticancer agents, we showed that GRP78 inhibition is lethal to drug-sensitive and -resistant P. falciparum parasite strains in vitro. We correlated the antiplasmodial activity of the inhibitors with their ability to bind the malaria chaperone, by characterizing their binding to recombinant parasite GRP78. Furthermore, we determined the crystal structure of the ATP binding domain of P. falciparum GRP78 with ADP and identified structural features unique to the parasite. These data suggest that P. falciparum GRP78 can be a valid drug target and that its structural differences to human GRP78 emphasize potential to generate parasite specific compounds.

Endoplasmic reticulum stress in autoimmune diseases: Can altered protein quality control and/or unfolded protein response contribute to autoimmunity? A critical review on Sjögren's syndrome

For many years, researchers in the field of autoimmunity have focused on the role of the immune components in the etiopathogenesis of autoimmune diseases. However, some studies have demonstrated the importance of target tissues in their pathogenesis and the breach of immune tolerance. The immune system as well as target tissue cells (plasmatic, β-pancreatic, fibroblast-like synoviocytes, thyroid follicular and epithelial cells of the lachrymal glands, salivary glands, intestine, bronchioles and renal tubules) share the characteristic of secretory cells with an extended endoplasmic reticulum (ER). The function of these cells depends considerably on a normal ER function and calcium homeostasis, so they can produce and secrete their main components, which include glycoproteins involved in antigenic presentation such as major histocompatibility complex (MHC) class I and II. All these proteins are synthesized and modified in the ER, and for this reason disturbances in the normal functions of this organelle such as protein folding, protein quality control, calcium homeostasis and redox balance, promote accumulation of unfolded or misfolded proteins, a condition known as ER stress. Autoimmune diseases are characterized by inflammation, which has been associated with an ER stress condition. Interestingly, patients with these diseases contain circulating auto-antibodies against chaperone proteins (such as Calnexin and GRP94), thus affecting the folding and assembly of MHC class I and II glycoproteins and their loading with peptide. The main purpose of this article is to review the involvement of the protein quality control and unfolded protein response (UPR) in the ER protein homeostasis (proteostasis) and their alterations in autoimmune diseases. In addition, we describe the interaction between ER stress and inflammation and evidences are shown of how autoimmune diseases are associated with an ER stress condition, with a special emphasis on the second most prevalent autoimmune rheumatic disease, Sjögren's syndrome.

The functional effects and mechanisms by which fibroblast growth factor 2 (FGF2) controls bovine mammary epithelial cells: Implications for the development and functionality of the bovine mammary gland

Fibroblast growth factor (FGF) signaling plays essential roles in tissue development and homeostasis. Accumulating evidence reveals that fibroblast growth factor 2 (FGF2) regulates ductal elongation, which requires cell proliferation and epithelial expansion in the mammary gland. However, the function and mechanisms by which FGF2 controls functionality of epithelial cells is less well defined. Here, we demonstrate the functional effects of FGF2 on bovine mammary epithelial (MAC-T) cells and the intracellular signaling mechanisms for these FGF2-induced actions. The current results show that treatment of MAC-T cells with a recombinant FGF2 induced cell proliferation and cell-cycle progression with increased expression of proliferating cell nuclear antigen and cyclin D1. Moreover, FGF2 increased phosphorylation of serine/threonine protein kinase (protein kinase B [AKT]), extracellular signal-regulated kinases 1 and 2 (ERK1/2), Jun N-terminal kinase (JNK), 70 kDa ribosomal S6 kinase (P70S6K), 90 kDa ribosomal S6 kinase (P90S6K), ribosomal protein S6 (S6), and cyclin D1 proteins. These FGF2-induced activations of signaling pathway proteins were inhibited by blocking AKT, ERK1/2, or JNK phosphorylation. The effect of FGF2 to stimulate MAC-T cell proliferation was mediated by activation of FGF receptors (FGFR) and AKT, ERK1/2, and JNK mitogen-activated protein kinase pathways in response to FGF2 stimulation. Furthermore, expression and activation of endoplasmic reticulum (ER) stress-related factors and ER stress-induced MAC-T cell death was reduced by FGF2. Together, these results suggest that the FGF2-FGFR-intracellular signaling cascades may contribute to maintaining and/or increasing numbers of mammary epithelial cells by inducing proliferation of mammary epithelial cells and by protecting cells from ER stress responses. Therefore, this study provides evidence that FGF2 signaling is a positive factor for mammary gland remodeling and for increasing persistency of milk production.

IRE1α Implications in Endoplasmic Reticulum Stress-Mediated Development and Pathogenesis of Autoimmune Diseases

Inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) is the most prominent and evolutionarily conserved endoplasmic reticulum (ER) membrane protein. This transduces the signal of misfolded protein accumulation in the ER, named as ER stress, to the nucleus as “unfolded protein response (UPR).” The ER stress-mediated IRE1α signaling pathway arbitrates the yin and yang of cell life. IRE1α has been implicated in several physiological as well as pathological conditions, including immune disorders. Autoimmune diseases are caused by abnormal immune responses that develop due to genetic mutations and several environmental factors, including infections and chemicals. These factors dysregulate the cell immune reactions, such as cytokine secretion, antigen presentation, and autoantigen generation. However, the mechanisms involved, in which these factors induce the onset of autoimmune diseases, are remaining unknown. Considering that these environmental factors also induce the UPR, which is expected to have significant role in secretory cells and immune cells. The role of the major UPR molecule, IRE1α, in causing immune responses is well identified, but its role in inducing autoimmunity and the pathogenesis of autoimmune diseases has not been clearly elucidated. Hence, a better understanding of the role of IRE1α and its regulatory mechanisms in causing autoimmune diseases could help to identify and develop the appropriate therapeutic strategies. In this review, we mainly center the discussion on the molecular mechanisms of IRE1α in the pathophysiology of autoimmune diseases.

Characterization of Novel Missense Variants of SERPINA1 Gene Causing Alpha-1 Antitrypsin Deficiency

The SERPINA1 gene is highly polymorphic, with more than 100 variants described in databases. SERPINA1 encodes the alpha-1 antitrypsin (AAT) protein, and severe deficiency of AAT is a major contributor to pulmonary emphysema and liver diseases. In Spanish patients with AAT deficiency, we identified seven new variants of the SERPINA1 gene involving amino acid substitutions in different exons: PiSDonosti (S+Ser14Phe), PiTijarafe (Ile50Asn), PiSevilla (Ala58Asp), PiCadiz (Glu151Lys), PiTarragona (Phe227Cys), PiPuerto Real (Thr249Ala), and PiValencia (Lys328Glu). We examined the characteristics of these variants and the putative association with the disease. Mutant proteins were overexpressed in HEK293T cells, and AAT expression, polymerization, degradation, and secretion, as well as antielastase activity, were analyzed by periodic acid-Schiff staining, Western blotting, pulse-chase, and elastase inhibition assays. When overexpressed, S+S14F, I50N, A58D, F227C, and T249A variants formed intracellular polymers and did not secrete AAT protein. Both the E151K and K328E variants secreted AAT protein and did not form polymers, although K328E showed intracellular retention and reduced antielastase activity. We conclude that deficient variants may be more frequent than previously thought and that their discovery is possible only by the complete sequencing of the gene and subsequent functional characterization. Better knowledge of SERPINA1 variants would improve diagnosis and management of individuals with AAT deficiency.

Advanced glycation end products-induced insulin resistance involves repression of skeletal muscle GLUT4 expression

Little is known about advanced glycation end products (AGEs) participation in glucose homeostasis, a process in which skeletal muscle glucose transporter GLUT4 (Scl2a4 gene) plays a key role. This study investigated (1) the in vivo and in vitro effects of AGEs on Slc2a4/GLUT4 expression in skeletal muscle of healthy rats, and (2) the potential involvement of endoplasmic reticulum and inflammatory stress in the observed regulations. For in vivo analysis, rats were treated with advanced glycated rat albumin (AGE-albumin) for 12 weeks; for in vitro analysis, soleus muscles from normal rats were incubated with bovine AGE-albumin for 2.5 to 7.5 hours. In vivo, AGE-albumin induced whole-body insulin resistance; decreased (~30%) Slc2a4 mRNA and GLUT4 protein content; and increased (~30%) the nuclear content of nuclear factor NF-kappa-B p50 subunit (NFKB1), and cellular content of 78 kDa glucose-regulated protein (GRP78). In vitro, incubation with AGE-albumin decreased (~50%) the Slc2a4/GLUT4 content; and increased cellular content of GRP78/94, phosphorylated-IKK-alpha/beta, nuclear content of NFKB1 and RELA, and the nuclear protein binding into Slc2a4 promoter NFKB-binding site. The data reveal that AGEs impair glucose homeostasis in non-diabetic states of increased AGEs concentration; an effect that involves activation of endoplasmic reticulum- and inflammatory-stress and repression of Slc2a4/GLUT4 expression.

Renal aquaporin-4 associated pathology in TG-26 mice

Human immunodeficiency virus-associated nephropathy (HIVAN) is a leading cause of end-stage renal disease in HIV patients, which is characterized by glomerulosclerosis and renal tubular dysfunction. Aquaporin-4 (AQP-4) is a membrane bound water channel protein that plays a distinct role in water reabsorption from renal tubular fluid. It has been proven that failure of AQP-4 insertion into the renal tubular membrane leads to renal dysfunction. However, the role of AQP-4 in HIVAN is unclear. We hypothesize that impaired water reabsorption leads to renal injury in HIVAN, where AQP-4 plays a crucial role. Renal function is assessed by urinary protein and serum blood urea nitrogen (BUN). Kidneys from HIV Transgenic (TG26) mice (HIVAN animal model) were compared to wild type mice by immunostaining, immunoblotting and quantitative RT-PCR. TG26 mice had increased proteinuria and BUN. We found decreased AQP-4 levels in the renal medulla, increased endothelin-1, endothelin receptor A and reduced Sirtuin1 (SIRT-1) levels in TG26 mice. Also, oxidative and endoplasmic reticulum stress was enhanced in kidneys of TG26 mice. We provide the first evidence that AQP-4 is inhibited due to induction of HIV associated stress in the kidneys of TG26 mice which limits water reabsorption in the kidney which may be one of the cause associated with HIVAN, impairing kidney physiology. AQP-4 dysregulation in TG26 mice suggests that similar changes may occur in HIVAN patients. This work may identify new therapeutic targets to be evaluated in HIVAN.

The convergent roles of NF-κB and ER stress in sunitinib-mediated expression of pro-tumorigenic cytokines and refractory phenotype in renal cell carcinoma

Renal cell carcinoma (RCC) is the most common form of kidney cancer. While cure remains exceptionally infrequent in RCC patients with systemic or recurrent disease, current targeted molecular strategies, including multi-targeted tyrosine kinase inhibitors (TKIs), notably changed the treatment paradigm of advanced renal cancer. Yet, complete and durable responses have been noted in only a few cases. Our studies reveal that sunitinib triggers two resistance-promoting signaling pathways in RCC cells, which emanate from the endoplasmic reticulum (ER) stress response: a PERK-driven ER stress response that induces expression of the pro-tumorigenic cytokines IL-6, IL-8, and TNF-α, and a TRAF2-mediated NF-κB survival program that protects tumor cells against cell death. PERK blockade completely prevents sunitinib-induced expression of IL-6, IL-8 and TNF-α, whereas NF-κB inhibition reinstates sensitivity of RCC cells to sunitinib both in vitro and in vivo. Taken together, our findings indicate that ER stress response may contribute to sunitinib resistance in RCC patients.

Impaired Processing of Prohormones in Secretogranin III-Null Mice Causes Maladaptation to an Inadequate Diet and Stress

Secretogranin III (SgIII), a member of the granin family, binds both to another granin, chromogranin A (CgA), and to a cholesterol-rich membrane that is destined for secretory granules (SGs). The knockdown of SgIII in adrenocorticotropic hormone (ACTH)-producing AtT-20 cells largely impairs the regulated secretion of CgA and ACTH. To clarify the physiological roles of SgIII in vivo, we analyzed hormone secretion and SG biogenesis in newly established SgIII-knockout (KO) mice. Although the SgIII-KO mice were viable and fertile and exhibited no overt abnormalities under ordinary rearing conditions, a high-fat/high-sucrose diet caused pronounced obesity in the mice. Furthermore, in the SgIII-KO mice compared with wild-type (WT) mice, the stimulated secretion of active insulin decreased substantially, whereas the storage of proinsulin increased in the islets. The plasma ACTH was also less elevated in the SgIII-KO mice than in the WT mice after chronic restraint stress, whereas the storage level of the precursor proopiomelanocortin in the pituitary gland was somewhat increased. These findings suggest that the lack of SgIII causes maladaptation of endocrine cells to an inadequate diet and stress by impairing the proteolytic conversion of prohormones in SGs, whereas SG biogenesis and the basal secretion of peptide hormones under ordinary conditions are ensured by the compensatory upregulation of other residual granins or factors.

Transcriptome analysis of skin fibroblasts with dominant negative COL3A1 mutations provides molecular insights into the etiopathology of vascular Ehlers-Danlos syndrome

Vascular Ehlers-Danlos syndrome (vEDS) is a dominantly inherited connective tissue disorder caused by mutations in the COL3A1 gene that encodes type III collagen (COLLIII), which is the major expressed collagen in blood vessels and hollow organs. The majority of disease-causing variants in COL3A1 are glycine substitutions and in-frame splice mutations in the triple helix domain that through a dominant negative effect are associated with the severe clinical spectrum potentially lethal of vEDS, characterized by fragility of soft connective tissues with arterial and organ ruptures.

To shed lights into molecular mechanisms underlying vEDS, we performed gene expression profiling in cultured skin fibroblasts from three patients with different structural COL3A1 mutations. Transcriptome analysis revealed significant changes in the expression levels of several genes involved in maintenance of cell redox and endoplasmic reticulum (ER) homeostasis, COLLs folding and extracellular matrix (ECM) organization, formation of the proteasome complex, and cell cycle regulation. Protein analyses showed that aberrant COLLIII expression is associated with the disassembly of many structural ECM constituents, such as fibrillins, EMILINs, and elastin, as well as with the reduction of the proteoglycans perlecan, decorin, and versican, all playing an important role in the vascular system. Furthermore, the altered distribution of the ER marker protein disulfide isomerase PDI and the strong reduction of the COLLs-modifying enzyme FKBP22 are consistent with the disturbance of ER-related homeostasis and COLLs biosynthesis and post-translational modifications, indicated by microarray analysis. Our findings add new insights into the pathophysiology of this severe vascular disorder, since they provide a picture of the gene expression changes in vEDS skin fibroblasts and highlight that dominant negative mutations in COL3A1 also affect post-translational modifications and deposition into the ECM of several structural proteins crucial to the integrity of soft connective tissues.

The endoplasmic reticulum is a hub to sort proteins toward unconventional traffic pathways and endosymbiotic organelles

The discovery that much of the extracellular proteome in eukaryotic cells consists of proteins lacking a signal peptide, which cannot therefore enter the secretory pathway, has led to the identification of alternative protein secretion routes bypassing the Golgi apparatus. However, proteins harboring a signal peptide for translocation into the endoplasmic reticulum can also be transported along these alternative routes, which are still far from being well elucidated in terms of the molecular machineries and subcellular/intermediate compartments involved. In this review, we first try to provide a definition of all the unconventional protein secretion pathways in eukaryotic cells, as those pathways followed by proteins directed to an 'external space' bypassing the Golgi, where 'external space' refers to the extracellular space plus the lumen of the secretory route compartments and the inner space of mitochondria and plastids. Then, we discuss the role of the endoplasmic reticulum in sorting proteins toward unconventional traffic pathways in plants. In this regard, various unconventional pathways exporting proteins from the endoplasmic reticulum to the vacuole, plasma membrane, apoplast, mitochondria, and plastids are described, including the short routes followed by the proteins resident in the endoplasmic reticulum.

Periostin has a protective role in melatonin‑induced cell apoptosis by inhibiting the eIF2α‑ATF4 pathway in human osteoblasts

The present study aimed to investigate the role of periostin (POSTN) and high melatonin concentrations in the apoptosis of hFOB 1.19 human normal fetal osteoblastic cells. hFOB 1.19 human osteoblastic cells were stably cultured and treated in different concentrations of melatonin for different durations of action. Apoptosis was assessed quantitatively using flow cytometric analysis. The results of western blot analysis demonstrated that the treatment of cells with different concentrations of melatonin for different durations of action revealed a positive association between melatonin and the expression levels of glucose‑regulated protein (GRP)78, GRP94, phosphorylated (p‑) eukaryotic initiation factor 2α (eIF2α), activating transcription factor (ATF)4, CCAAT/enhanced binding protein homologous protein (CHOP), cleaved caspase‑3, p‑c‑Jun N‑terminal kinase (JNK) and POSTN. When POSTN was inhibited, the levels of p‑JNK, CHOP, p‑eIF2α, ATF4 and cleaved caspase‑3 were significantly increased, whereas other proteins associated with the endoplasmic reticulum stress (ERS) pathways, including ATF6 and X‑box binding protein 1 (XBP1), were not significantly altered. Reverse transcription‑quantitative polymerase chain reaction analysis was also performed to assess the relative mRNA levels of ATF4, ATF6 and XBP1. The results of the present study are the first, to the best of our knowledge, to demonstrate that melatonin induced apoptosis in hFOB 1.19 human osteoblastic cells by activating the ERS‑associated eIF2α‑ATF4 pathway and subsequently triggered the cascade effects of CHOP, caspase‑3 and JNK. POSTN may function as a protective factor for osteoblasts during this process by inhibiting the eIF2α‑ATF4 pathway.

Membrane-anchored stalk domain of influenza HA enhanced immune responses in mice

Current strategies for influenza virus vaccines primarily aim to elicit immune responses towards the globular head domain of the hemagglutinin (HA) protein so that binding of the virus to membrane receptors on the host cells is inhibited. In the present study, we show a novel strategy to generate immunity against the highly conserved region of the influenza virus. The globular head domain was replaced by different linkers to generate a headless HA (stalk domain) and then coexpressed with influenza M1 proteinin Tni insect cells. The expression was validated by western blot analysis, and stalk domain with peptides (GGGGS)4 linkers was identified to anchor in a stable way to the cell membrane. An immunoelectron microscope showed that stalk domain with (GGGGS)4 linkers were steadily incorporated to the surface of influenza virus-like particles (VLPs). Mice immunized with these VLPs exhibited enhanced systemic antibody responses with increased binding avidity and study found high titers of ADCC antibodies to the influenza virus, these VLPs also induced mucosal immune responses and produced antigen-specific IgG and IgA in nasal and lung washes. In addition, antigen-specific IgG antibody-secreting cells (ASCs) increased significantly in the spleen and lymph node. The results of this study suggest that the headless HA is a useful target in developing a universal vaccine against influenza virus.

Targeting protein quality control pathways in breast cancer

The efficient production, folding, and secretion of proteins is critical for cancer cell survival. However, cancer cells thrive under stress conditions that damage proteins, so many cancer cells overexpress molecular chaperones that facilitate protein folding and target misfolded proteins for degradation via the ubiquitin-proteasome or autophagy pathway. Stress response pathway induction is also important for cancer cell survival. Indeed, validated targets for anti-cancer treatments include molecular chaperones, components of the unfolded protein response, the ubiquitin-proteasome system, and autophagy. We will focus on links between breast cancer and these processes, as well as the development of drug resistance, relapse, and treatment.

Misfolding leads the way to unraveling signaling pathways in the pathophysiology of prion diseases

A misfolded version of the prion protein represents an essential component in the pathophysiology of fatal neurodegenerative prion diseases, which affect humans and animals alike. They may be of sporadic origin, acquired through exogenous introduction of infectious misfolded prion protein, or caused by genetic alterations in the prion protein coding gene. We have recently described a novel pathway linking retention of mutant prion protein in the early secretory pathway to activation p38-MAPK and a neurodegenerative phenotype in transgenic mice. Here we review the consequences that mutations in prion protein have on intracellular transport and stress responses focusing on protein quality control. We also discuss the neurotoxic signaling elicited by the accumulation of mutant prion protein in the endoplasmic reticulum and the Golgi apparatus. Improved knowledge about these processes will help us to better understand complex pathogenesis of prion diseases, a prerequisite for therapeutic strategies.

Differential expression and functional roles of chemokine (C-C motif) ligand 23 and its receptor chemokine (C-C motif) receptor type 1 in the uterine endometrium during early pregnancy in pigs

Many chemokines expressed by cells of the uterine endometrium of mammals are involved in cell-cell interactions. However, little is known about expression and functional roles of chemokine (C-C motif) ligand 23 (CCL23) in the uterine endometrium. Results of this study demonstrated that CCL23 and its receptor, chemokine (C-C motif) receptor type 1 (CCR1), are up-regulated in porcine endometria during pregnancy. CCL23 and CCR1 mRNAs were strongly expressed in endometrial glandular (GE) and luminal (LE) epithelial cells. Treatment of porcine uterine luminal epithelial (pLE) cells with recombinant CCL23 increased the abundances of PCNA and cyclin D1, and enhanced proliferation and cell cycle progression in pLE cells. CCL23 also stimulated phosphorylation of cell signaling molecules including AKT and MAPKs in pLE cells. Furthermore, ER stress-related molecules were reduced by CCL23. These results suggest that CCL23-CCR1 signaling is important for endometrial development and establishment of pregnancy in pigs.

A large-scale expression strategy for multimeric extracellular protein complexes using Drosophila S2 cells and its application to the recombinant expression of heterodimeric ligand-binding domains of taste receptor

Many of the extracellular proteins or extracellular domains of plasma membrane proteins exist or function as homo- or heteromeric multimer protein complexes. Successful recombinant production of such proteins is often achieved by co-expression of the components using eukaryotic cells via the secretory pathway. Here we report a strategy addressing large-scale expression of hetero-multimeric extracellular domains of plasma membrane proteins and its application to the extracellular domains of a taste receptor. The target receptor consists of a heterodimer of T1r2 and T1r3 proteins, and their extracellular ligand binding domains (LBDs) are responsible for the perception of major taste substances. However, despite the functional importance, recombinant production of the heterodimeric proteins has so far been unsuccessful. We achieved the successful preparation of the heterodimeric LBD by use of Drosophila S2 cells, which have a high secretory capacity, and by the establishment of a stable high-expression clone producing both subunits at a comparable level. The method overcame the problems encountered in the conventional transient expression of the receptor protein in insect cells using baculovirus or vector lipofection, which failed in the proper heterodimer production because of the biased expression of T1r3LBD over T1r2LBD. The large-scale expression methodology reported here may serve as one of the considerable strategies for the preparation of multimeric extracellular protein complexes.

Curcumin and Curcuma longa L. extract ameliorate lipid accumulation through the regulation of the endoplasmic reticulum redox and ER stress

For this study, we examined the effects of curcumin against acute and chronic stress, paying specific attention to ROS. We also aimed to clarify the differences between acute and chronic stress conditions. We investigated the effects of curcumin against acute stress (once/1 day CCl4 treatment) and chronic-stress (every other day/4week CCl4 treatment). Compared with acute stress, in which the antioxidant system functioned properly and aspartate transaminase (AST) and ROS production increased, chronic stress increased AST, alanine aminotransferase (ALT), hepatic enzymes, and ROS more significantly, and the antioxidant system became impaired. We also found that ER-originated ROS accumulated in the chronic model, another difference between the two conditions. ER stress was induced consistently, and oxidative intra-ER protein folding status, representatively PDI, was impaired, especially in chronic stress. The PDI-associated client protein hepatic apoB accumulated with the PDI-binding status in chronic stress, and curcumin recovered the altered ER folding status, regulating ER stress and the resultant hepatic dyslipidemia. Throughout this study, curcumin and curcumin-rich Curcuma longa L. extract promoted recovery from CCl4-induced hepatic toxicity in both stress conditions. For both stress-associated hepatic dyslipidemia, curcumin and Curcuma longa L. extract might be recommendable to recover liver activity.

Secreted Proteins Defy the Expression Level-Evolutionary Rate Anticorrelation

The rates of evolution of the proteins of any organism vary across orders of magnitude. A primary factor influencing rates of protein evolution is expression. A strong negative correlation between expression levels and evolutionary rates (the so-called E-R anticorrelation) has been observed in virtually all studied organisms. This effect is currently attributed to the abundance-dependent fitness costs of misfolding and unspecific protein-protein interactions, among other factors. Secreted proteins are folded in the endoplasmic reticulum, a compartment where chaperones, folding catalysts, and stringent quality control mechanisms promote their correct folding and may reduce the fitness costs of misfolding. In addition, confinement of secreted proteins to the extracellular space may reduce misinteractions and their deleterious effects. We hypothesize that each of these factors (the secretory pathway quality control and extracellular location) may reduce the strength of the E-R anticorrelation. Indeed, here we show that among human proteins that are secreted to the extracellular space, rates of evolution do not correlate with protein abundances. This trend is robust to controlling for several potentially confounding factors and is also observed when analyzing protein abundance data for 6 human tissues. In addition, analysis of mRNA abundance data for 32 human tissues shows that the E-R correlation is always less negative, and sometimes nonsignificant, in secreted proteins. Similar observations were made in Caenorhabditis elegans and in Escherichia coli, and to a lesser extent in Drosophila melanogaster, Saccharomyces cerevisiae and Arabidopsis thaliana. Our observations contribute to understand the causes of the E-R anticorrelation.

Piezo1 protein induces the apoptosis of human osteoarthritis-derived chondrocytes by activating caspase-12, the signaling marker of ER stress

The present study was carried out to determine whether the mechanically activated cation channel Piezo1 protein plays a role as a signaling pathway which causes the apoptosis of human chondrocytes. The chondrocytes were isolated, cultured, and then subjected to mechanical stretch force for 0, 2, 12, 24 and 48 h, respectively. The expression levels of Piezo1 and the apoptosis-related protein caspase-12 were assessed by reverse transcription-quantitative polymerase chain reaction, as well as the apoptosis-related genes, B cell lymphoma/leukemia-2 (Bcl-2), Bcl-associated X protein (Bax) and Bcl-2-associated death promoter (BAD). Lactate dehydrogenase (LDH) activity was used to discern dead cells. Piezo1 expression was determined by immunofluorescence. In addition, Piezo1 inhibitor, GsMTx4, was used to block the mechanically activated (MA) cation channel Piezo1, and served as a positive control. The results showed that the osteoarthritis (OA)-derived chondrocytes showed a tendency to undergo late-stage apoptosis under compressive loading. Piezo1 and caspase-12 were significantly upregulated under static compressive stimuli and the expression was related to the rate of apoptosis of the OA-derived chondrocytes during compressive loading. The expression of caspase-12 and late-stage apoptosis of the human OA-derived chondrocytes were repressed by GsMTx4, the specific inhibitor of Piezo1, while the expression of Piezo1 and the induction of the apoptosis of the OA-derived chondrocytes during compressive loading was not totally blocked. Thus, we conclude that Piezo1 plays an important role in the apoptosis of human OA-derived chondrocytes through a caspase-12-dependent pathway. The expression of Piezo1 protein was not totally inhibited by GsMTx4.

The Piezo1 protein ion channel functions in human nucleus pulposus cell apoptosis by regulating mitochondrial dysfunction and the endoplasmic reticulum stress signal pathway

The Piezo1 protein ion channel is a novel mechanical stretch-activated ion channel (SAC) closely related to mechanical signals. Mechanotransduction plays a crucial role in organ development and homeostasis. Previous studies identified Piezo1 and demonstrated that it is distinct from other ion channels with well-established roles in lower organisms. Mechanical stretch-activated ion channels from other organisms are not conserved in mammals or do not act as mechanically activated channels in mammals. In the current study, we explored the role of the Piezo1 ion channel in human nucleus pulposus cell (NP cell) apoptosis through mechanical force-induced mitochondrial dysfunction and endoplasmic reticulum stress. Reverse Transcription Polymerase chain reaction (RT-PCR), immunofluorescence, immunohistochemistry and Annexin V binding and propidium iodide analyses revealed that the Piezo1 protein ion channel was highly expressed in human NP cells, which are the primary cells that comprise the intervertebral disc. In patients with intervertebral disc degeneration (IVDD), the Piezo1 protein may play a crucial role in human NP cell apoptosis through mitochondrial dysfunction and endoplasmic reticulum stress under abnormal loading conditions. This study also verified that human NP cells have an intimate connection with the cytoskeleton upon treatment of the cells with the Piezo1 blocking peptide GsMTx4 from tarantula venom. In summary, Piezo1 functions in human NP cell apoptosis, which may be one underlying mechanism of apoptosis induced by abnormal loading in IVDD patients.

Calumenin relieves cardiac injury by inhibiting ERS-initiated apoptosis during viral myocarditis

Viral myocarditis (VMC) is a common disease causing heart failure (HF) for which no specific treatments are available. As apoptosis of cardiomyoctes is a hallmark of VMC and HF, strategies targeting apoptosis are an effective way of prevention and treatment of HF. Recent studies found endoplasmic reticulum stress (ERS) reaction is a new signal transduction pathway mediating apoptosis. Calumenin protein (CP) is located within the endoplasmic reticulum Ca²⁺ binding proteins, and is important in ER-initiated apoptosis. The aim of this study was to investigate whether the function of CP was influenced in cardiomyocytes infected by coxsackievirus B3. The expression of CP was down-regulated in cardiomyocytes infected by coxsackievirus B3. TUNEL studies showed that apoptosis was increased in CP-deficient and ΔCP-mutant cardiomyocytes infected by coxsackievirus B3. Additionally, ERS-associated proteins (GRP78, p-PERK, p-eIF2α, ATF4 and CHOP) were up-regulated in coxsackievirus B3-infected CP-deficient and ΔCP-mutant cardiomyocytes compared to wild type control cells. These results suggested ER-initiated apoptosis was induced by coxsackievirus B3-infected cardiomyocytes and caused apoptosis through ER stress. CP can relieve ERS-initiated apoptosis in viral myocarditis.

Effects of UPR and ERAD pathway on the prolyl endopeptidase production in Pichia pastoris by controlling of nitrogen source

Prolyl endopeptidase (PEP) is very useful in various industries, while the high cost of enzyme production remains a major obstacle for its industrial applications. Pichia pastoris has been used for the PEP production; however, the fermentation process has not be investigated and little is known about the impact of excessive PEP production on the host cell physiology. Here, we optimized the nitrogen source to improve the PEP expression level and further evaluated the cellular response including UPR and ERAD. During methanol induction phase the PEP activity (1583 U/L) was increased by 1.48-fold under the optimized nitrogen concentration of NH4+ (300 mmol/L) and casamino acids [1.0% (w/v)] in a 3-L bioreactor. Evaluated by RT-PCR the UPR and ERAD pathways were confirmed to be activated. Furthermore, a strong decrease of ERAD-related gene transcription was observed with the addition of nitrogen source, which contributed to a higher PEP expression level.

Bioinformatic analysis reveals potential properties of human Claudin-6 regulation and functions

Claudin-6 (CLDN6) is an integral component of the tight junction proteins in polarized epithelial and endothelial cells and plays a crucial role in maintaining cell integrity. Deregulation of CLDN6 expression and distribution in tumor tissues have been widely documented and correlated with cancer progression and metastasis. However, a complete mechanistic understanding of CLDN6 regulation and function remains to be studied. Herein, we show new potential properties of CLDN6 regulation and functions from bioinformatics analysis. Using numerous algorithms to characterize the CLDN6 gene promoter elements and the CLDN6 protein structure, physio-chemical and localization properties, and its evolutionary relationships. CLDN6 is regulated by a diverse set of transcription factors (SP1, SPR, AML-1a, CdxA, CRE-BP and CREB) and associated with the levels of methylation of CpG islands in promoters. The structural properties of CLDN6 indicate that it promotes cancer cell behavior via the ASK1-p38/JNK MAPK secretory signaling pathway. In conclusion, this information from bioinformatics analysis will help future attempts to better understand CLDN6 regulation and functions.

Cyclopamine sensitizes TRAIL-resistant gastric cancer cells to TRAIL-induced apoptosis via endoplasmic reticulum stress-mediated increase of death receptor 5 and survivin degradation

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is one of the most effective cancer treatments owing to its ability to selectively kill cancer cells, without affecting normal cells. However, it has been reported that several gastric cancer cells show resistance to TRAIL because of a scarcity of death receptor 5 (DR5) expressed on the cell surface. In this study, we show that cyclopamine sensitizes gastric cancer cells to TRAIL-induced apoptosis by elevating the expression of DR5. Interestingly, survivin hampers the existence of DR5 protein under normal conditions and cyclopamine decreases the expression of survivin, thus acting as a TRAIL sensitizer. Mechanistically, cyclopamine induces endoplasmic reticulum (ER) stress via reactive oxygen species (ROS) and CHOP, the last protein of the ER stress pathway and it regulates the proteasome degradation of survivin. Taken together, our results indicate that cyclopamine can be used for combination therapy in TRAIL-resistant gastric cancer cells.

Systematic Optimization of Protein Secretory Pathways in Saccharomyces cerevisiae to Increase Expression of Hepatitis B Small Antigen

Hepatitis B is a major disease that chronically infects millions of people in the world, especially in developing countries. Currently, one of the effective vaccines to prevent Hepatitis B is the Hepatitis B Small Antigen (HBsAg), which is mainly produced by the recombinant yeast Saccharomyces cerevisiae. In order to bring down the price, which is still too high for people in developing countries to afford, it is important to understand key cellular processes that limit protein expression. In this study, we took advantage of yeast knockout collection (YKO) and screened 194 S. cerevisiae strains with single gene knocked out in four major steps of the protein secretory pathway, i.e., endoplasmic-reticulum (ER)-associated protein degradation, protein folding, unfolded protein response (UPR), and translocation and exocytosis. The screening showed that the single deletion of YPT32, SBH1, and HSP42 led to the most significant increase of HBsAg expression over the wild type while the deletion of IRE1 led to a profound decrease of HBsAg expression. The synergistic effects of gene knockout and gene overexpression were next tested. We found that simultaneously deleting YPT32 and overexpressing IRE1 led to a 2.12-fold increase in HBsAg expression over the wild type strain. The results of this study revealed novel genetic targets of protein secretory pathways that could potentially improve the manufacturing of broad scope vaccines in a cost-effective way using recombinant S. cerevisiae.

Lysosomal Quality Control in Prion Diseases

Prion diseases are transmissible, familial or sporadic. The prion protein (PrP), a normal cell surface glycoprotein, is ubiquitously expressed throughout the body. While loss of function of PrP does not elicit apparent phenotypes, generation of misfolded forms of the protein or its aberrant metabolic isoforms has been implicated in a number of neurodegenerative disorders such as scrapie, kuru, Creutzfeldt-Jakob disease, fatal familial insomnia, Gerstmann-Sträussler-Scheinker and bovine spongiform encephalopathy. These diseases are all phenotypically characterised by spongiform vacuolation of the adult brain, hence collectively termed as late-onset spongiform neurodegeneration. Misfolded form of PrP (PrP^Sc) and one of its abnormal metabolic isoforms (the transmembrane ^CtmPrP) are known to be disease-causing agents that lead to progressive loss of structure or function of neurons culminating in neuronal death. The aberrant forms of PrP utilise and manipulate the various intracellular quality control mechanisms during pathogenesis of these diseases. Amongst these, the lysosomal quality control machinery emerges as one of the primary targets exploited by the disease-causing isoforms of PrP. The autophagosomal-lysosomal degradation pathway is adversely affected in multiple ways in prion diseases and may hence be regarded as an important modulator of neurodegeneration. Some of the ESCRT pathway proteins have also been shown to be involved in the manifestation of disease phenotype. This review discusses the significance of the lysosomal quality control pathway in affecting transmissible and familial types of prion diseases.

Ibutilide treatment protects against ER stress induced apoptosis by regulating calumenin expression in tunicamycin treated cardiomyocytes

Background

Ibutilide, a class III antiarrhythmic agent has been shown to be cardioprotective in treating atrial fibrillation, promoting cardioconversion and recently this agent has been shown to protect against ER stress induced apoptosis in cardiomyocytes. In this study we begin to identify the mechanism by which ibutilide exerts its cardioprotection in tunicamycin treated cardiomyocytes. We examined ER stress markers including calumenin; a calcium binding ER chaperone protein that has recently been linked to ER stress in cardiomyocytes, in our treated cells.

Methods

To assess the effect of ibutilide we used the well characterized in vitro model of ER stress induced apoptosis in rat neonatal cardiomyocytes (RNC). RNC were treated with tunicamycin and the degree of ER stress was assessed by quantifying mRNA and protein levels of GRP78, GRP94 and calumenin, and examined the extent of apoptosis by assessing the protein levels of caspase-3/9/12, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of deoxynucleotidyl-transferase- mediated dUTP nick end labeling (TUNEL) positive cells.

Results

We demonstrate ibutilide attenuated the up-regulation of ER stress markers GRP78 and GRP94 and rescued the decline in calumenin mRNA and protein levels in tunicamycin treated cardiomyocytes. The up-regulation of apoptotic markers caspase-3, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of TUNEL positive cells were also attenuated after ibutilide treatment while the protein levels of Caspase-9 and Caspase-12 were unaffected.

Conclusions

This study suggests another cardioprotective effect of the antiarrhythmic agent ibutilide whereby pretreatment leads to the attenuation of ER stress induced apoptosis by regulating calumenin expression. This study provides further evidence for the role of calumenin in the cardiomyocyte ER stress response.

A critical role for adiponectin-mediated development of endometrial luminal epithelial cells during the peri-implantation period of pregnancy

Adiponectin is one of the adipokines in the collagen superfamily. It is secreted primarily by white adipocytes and influences reproductive processes including ovarian and uterine functions. Adiponectin regulates energy homeostasis, insulin sensitivity, and is anti-inflammatory in various tissues. Its receptors (ADIPOR1 and ADIPOR2) are widely expressed in mammalian tissues, including porcine conceptuses and endometrial during the estrous cycle and peri-implantation period of pregnancy. However, regulatory effects of adiponectin on endometrial epithelial cells are unknown. Therefore, we investigated the effects of parity on expression of ADIPOR1 and ADIPOR2 and the effects of adiponectin in the porcine endometrium during early pregnancy. Results of this study revealed robust expression of ADIPOR1 and ADIPOR2 in uterine luminal (LE) and glandular (GE) epithelia during early pregnancy and expression decreased as with increasing parity. For porcine luminal epithelial (pLE) cells, adiponectin enhanced proliferation, and increased phosphorylation of AKT, P70S6K, S6, ERK1/2, JNK, P38, and P90RSK in a time-dependent manner. Moreover, the abundance of adiponectin-activated signaling molecules were suppressed by pharmacological inhibitors including wortmannin, U0126, SP600125, and SB203580, respectively, in pLE cells. Furthermore, inhibition of each targeted signal transduction molecule influenced proliferation of adiponectin-stimulated pLE cells. In addition, adiponectin inhibited tunicamycin-induced endoplasmic reticulum (ER)-stress through effects on ER stress regulated proteins in pLE cells. Collectively, these results suggest that adiponectin affects development of porcine uterine epithelia and reproductive performance through modulation of PI3K/AKT and MAPK cell signaling pathways.

Structural basis of pH-dependent client binding by ERp44, a key regulator of protein secretion at the ER-Golgi interface

ERp44 retrieves some endoplasmic reticulum (ER)-resident enzymes and immature oligomers of secretory proteins from the Golgi. Association of ERp44 with its clients is regulated by pH-dependent mechanisms, but the molecular details are not fully understood. Here we report high-resolution crystal structures of human ERp44 at neutral and weakly acidic pH. These structures reveal key regions in the C-terminal tail (C tail) missing in the original crystal structure, including a regulatory histidine-rich region and a subsequent extended loop. The former region forms a short α-helix (α16), generating a histidine-clustered site (His cluster). At low pH, the three Trx-like domains of ERp44 ("a," "b," and "b'") undergo significant rearrangements, likely induced by protonation of His157 located at the interface between the a and b domains. The α16-helix is partially unwound and the extended loop is disordered in weakly acidic conditions, probably due to electrostatic repulsion between the protonated histidines in the His cluster. Molecular dynamics simulations indicated that helix unwinding enhances the flexibility of the C tail, disrupting its normal hydrogen-bonding pattern. The observed pH-dependent conformational changes significantly enlarge the positively charged regions around the client-binding site of ERp44 at low pH. Mutational analyses showed that ERp44 forms mixed disulfides with specific cysteines residing on negatively charged loop regions of Ero1α. We propose that the protonation states of the essential histidines regulate the ERp44-client interaction by altering the C-tail dynamics and surface electrostatic potential of ERp44.

RCN1 suppresses ER stress-induced apoptosis via calcium homeostasis and PERK-CHOP signaling

Endoplasmic reticulum (ER) stress is caused by the disturbance of ER homeostasis and leads to the activation of the unfolded protein response (UPR), which alleviates stress at an early stage and triggers apoptosis if homeostasis fails over a prolonged timeframe. Here, we report that reticulocalbin 1 (RCN1), a member of the CREC family, is transactivated by nuclear factor kappa B (NF-κB) during ER stress and inhibits ER stress-induced apoptosis. The depletion of RCN1 increases the UPR during drug-induced ER stress by activating PRKR-like ER kinase–CCAAT/enhancer-binding protein-homologous protein (PERK–CHOP) signaling, thus inducing apoptosis. Furthermore, we found that the first two EF-hand calcium-binding motifs of RCN1 specifically interact with inositol 1,4,5-trisphosphate (IP₃) receptor type 1 (IP₃R1) on loop 3 of its ER luminal domain and inhibit ER calcium release and apoptosis. Together, these data indicate that RCN1, a target of NF-κB, suppresses ER calcium release by binding to IP₃R1 and decreases the UPR, thereby inhibiting ER stress-induced apoptosis.

Deletion of an Endoplasmic Reticulum Stress Response Element in a ZmPP2C-A Gene Facilitates Drought Tolerance of Maize Seedlings

Drought is a major abiotic stress that causes the yearly yield loss of maize, a crop cultured worldwide. Breeding drought-tolerant maize cultivars is a priority requirement of world agriculture. Clade A PP2C phosphatases (PP2C-A), which are conserved in most plant species, play important roles in abscisic acid (ABA) signaling and plant drought response. However, natural variations of PP2C-A genes that are directly associated with drought tolerance remain to be elucidated. Here, we conducted a candidate gene association analysis of the ZmPP2C-A gene family in a maize panel consisting of 368 varieties collected worldwide, and identified a drought responsive gene ZmPP2C-A10 that is tightly associated with drought tolerance. We found that the degree of drought tolerance of maize cultivars negatively correlates with the expression levels of ZmPP2C-A10. ZmPP2C-A10, like its Arabidopsis orthologs, interacts with ZmPYL ABA receptors and ZmSnRK2 kinases, suggesting that ZmPP2C-A10 is involved in mediating ABA signaling in maize. Transgenic studies in maize and Arabidopsis confirmed that ZmPP2C-A10 functions as a negative regulator of drought tolerance. Further, a causal natural variation, deletion allele-338, which bears a deletion of ERSE (endoplasmic reticulum stress response element) in the 5'-UTR region of ZmPP2C-A10, was detected. This deletion causes the loss of endoplasmic reticulum (ER) stress-induced expression of ZmPP2C-A10, leading to increased plant drought tolerance. Our study provides direct evidence linking ER stress signaling with drought tolerance and genetic resources that can be used directly in breeding drought-tolerant maize cultivars.

Site-specific monitoring of N-Glycosylation profiles of a CTLA4-Fc-fusion protein from the secretory pathway to the extracellular environment

Glycosylation often plays a key role in the safety and efficacy of therapeutic proteins to patients, thus underlying the need for consistent control of this important post-translational modification during biologics production. In this study, we profiled the site-specific evolution of N-glycans on a CTLA4-Fc-fusion protein, from the intracellular secretory pathway to the conditioned medium (CM) in fed-batch cell culture. For this, we developed an approach that combined sub-cellular fractionation with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. The study revealed that there was a significant amount of heterogeneity in the glycans displayed amongst the three distinct N-glycosylation sites. Furthermore, 54-60% of the intracellular protein was characterized by Man8 and Man9 glycans on day 10, when the cell density peaks, indicative of a significant bottleneck between the endoplasmic reticulum (ER) and the cis-Golgi. At longer culture duration, the accumulation of intracellular protein with bi-antennary-fucosylated GlcNAc-terminated residues identified the formation of another bottleneck in the medial and trans-Golgi compartments, which subsequently led to a decrease in sialylated species in the secreted protein. Glucose deprivation caused a reduction in the Man8 and Man9 glycans in favor of Man5 glycans and bi-antennary-fucosylated GlcNAc-terminated residues in the organellar pool of the Fc-fusion protein. However, transient deprivation of glucose did not lead to major differences in the glycan profile of proteins secreted into the CM. The approach developed here allows us to probe the secretory pathway and sheds light on the site-specific intracellular processing of glycans during fed-batch cell culture, thus serving as an initial step towards their rational control. Biotechnol. Bioeng. 2017;114: 1550-1560. © 2017 Wiley Periodicals, Inc.

Roles of N-glycans in the polymerization-dependent aggregation of mutant Ig-μ chains in the early secretory pathway

The polymeric structure of secretory IgM allows efficient antigen binding and complement fixation. The available structural models place the N-glycans bound to asparagines 402 and 563 of Ig-μ chains within a densely packed core of native IgM. These glycans are found in the high mannose state also in secreted IgM, suggesting that polymerization hinders them to Golgi processing enzymes. Their absence alters polymerization. Here we investigate their role following the fate of aggregation-prone mutant μ chains lacking the Cμ1 domain (μ∆). Our data reveal that μ∆ lacking 563 glycans (μ∆5) form larger intracellular aggregates than μ∆ and are not secreted. Like μ∆, they sequester ERGIC-53, a lectin previously shown to promote polymerization. In contrast, μ∆ lacking 402 glycans (μ∆4) remain detergent soluble and accumulate in the ER, as does a double mutant devoid of both (μ∆4–5). These results suggest that the two C-terminal Ig-μ glycans shape the polymerization-dependent aggregation by engaging lectins and acting as spacers in the alignment of individual IgM subunits in native polymers.

Endoplasmic Reticulum Stress Response in Arabidopsis Roots

Roots are the frontier of plant body to perceive underground environmental change. Endoplasmic reticulum (ER) stress response represents circumvention of cellular stress caused by various environmental changes; however, a limited number of studies are available on the ER stress responses in roots. Here, we report the tunicamycin (TM) -induced ER stress response in Arabidopsis roots by monitoring expression patterns of immunoglobulin-binding protein 3 (BiP3), a representative marker for the response. Roots promptly responded to the TM-induced ER stress through the induction of similar sets of ER stress-responsive genes. However, not all cells responded uniformly to the TM-induced ER stress in roots, as BiP3 was highly expressed in root tips, an outer layer in elongation zone, and an inner layer in mature zone of roots. We suggest that ER stress response in roots has tissue specificity.

Trafficking and processing of bacterial proteins by mammalian cells: Insights from chondroitinase ABC

BACKGROUND

There is very little reported in the literature about the relationship between modifications of bacterial proteins and their secretion by mammalian cells that synthesize them. We previously reported that the secretion of the bacterial enzyme Chondroitinase ABC by mammalian cells requires the strategic removal of at least three N-glycosylation sites. The aim of this study was to determine if it is possible to enhance the efficacy of the enzyme as a treatment for spinal cord injury by increasing the quantity of enzyme secreted or by altering its cellular location.

METHODOLOGY/PRINCIPAL FINDINGS

To determine if the efficiency of enzyme secretion could be further increased, cells were transfected with constructs encoding the gene for chondroitinase ABC modified for expression by mammalian cells; these contained additional modifications of strategic N-glycosylation sites or alternative signal sequences to direct secretion of the enzyme from the cells. We show that while removal of certain specific N-glycosylation sites enhances enzyme secretion, N-glycosylation of at least two other sites, N-856 and N-773, is essential for both production and secretion of active enzyme. Furthermore, we find that the signal sequence directing secretion also influences the quantity of enzyme secreted, and that this varies widely amongst the cell types tested. Last, we find that replacing the 3'UTR on the cDNA encoding Chondroitinase ABC with that of β-actin is sufficient to target the enzyme to the neuronal growth cone when transfected into neurons. This also enhances neurite outgrowth on an inhibitory substrate.

CONCLUSION/SIGNIFICANCE

Some intracellular trafficking pathways are adversely affected by cryptic signals present in the bacterial gene sequence, whilst unexpectedly others are required for efficient secretion of the enzyme. Furthermore, targeting chondroitinase to the neuronal growth cone promotes its ability to increase neurite outgrowth on an inhibitory substrate. These findings are timely in view of the renewed prospects for gene therapy, and of direct relevance to strategies aimed at expressing foreign proteins in mammalian cells, in particular bacterial proteins.

BhbZIP60 from Resurrection Plant Boea hygrometrica Is an mRNA Splicing-Activated Endoplasmic Reticulum Stress Regulator Involved in Drought Tolerance

Adverse environmental conditions cause endoplasmic reticulum (ER) stress in plants. To mitigate ER stress damage, ER associated transcription factors and inositol-requiring enzyme-1 (IRE1)-mediated bZIP60 mRNA splicing are activated in plants. A drought-induced gene, encoding the ortholog of AtbZIP60, was identified in the resurrection plant Boea hygrometrica, termed BhbZIP60. In response to ER stress and dehydration, BhbZIP60 mRNA can be spliced to create a frame shift in the C terminus by the excision of 23b segment in a manner of its ortholog in other plants, thus translocating to the nucleus instead of the cytoplasm. The splicing-activated BhbZIP60 (BhbZIP60S) could function in the same way as its Arabidopsis ortholog by restoring the molecular phenotype of the mutant atbzip60. When overexpressed in Arabidopsis, BhbZIP60S provided transgenic plants with enhanced tolerance to drought, tunicamycin and mannitol stresses with upregulation of the expressions of ER quality control (QC) genes (BiP2, BiP3, CNX1, and sPDI) and abscisic acid (ABA) responsive genes (RD29A, RAB18, and RD17). Furthermore, in the yeast one-hybrid system, BhbZIP60S was capable of interacting with ER stress responsive elements (ERSE and ERSE-II) that exist in the promoters of known ER-QC genes, but not binding to ABA responsive cis-elements (ABREs). Our results demonstrated that drought-induced BhbZIP60 may have a function in drought tolerance via the splicing-activated BhbZIP60S to mediate ER-QC by direct binding to the promoters of ER-QC genes. This study evidently demonstrates the involvement of ER-QC in the drought tolerance of Arabidopsis and the desiccation tolerance of the resurrection plant B. hygrometrica.

Mechanistic Study of Tetrahydrofuran- acetogenins In Triggering Endoplasmic Reticulum Stress Response-apotoposis in Human Nasopharyngeal Carcinoma

For past three decades, numerous studies have elucidated the antiproliferative effects of acetogenins in hopes of developing a new class of clinical anticancer agents. However, clear and definitive action mechanisms of acetogenins were less clarified. In the present study, three tetrahydrofuran (THF)-containing acetogenins were found to have potent and selective antiproliferative activity against human nasopharyngeal carcinoma (NPC) cell lines and their methotrexate-resistant counterparts. The THF-containing acetogenins induced G₂/M phase arrest, mitochondrial damage and apoptosis, and increased cytosolic and mitochondrial Ca²⁺ in NPCs. Microarray analysis of NPC-TW01 cells treated with squamostatin A, a non-adjacent bis-THF acetogenin, demonstrated an increased endoplasmic reticulum (ER)-stress response (ESR). Enhanced ESR in squamostatin A-treated cells was confirmed by real-time PCR, Western blot and shRNA gene knockdown experiments. Although our results showed that squamostatin A-induced ESR was independent of extracellular Ca²⁺, the presence of extracellular Ca²⁺ enhanced the antiproliferative effect of acetogenins. In vivo analyses demonstrated that squamostatin A showed good pharmacokinetic properties and significantly retarded NPC tumor growth in the xenograft mouse model. Conclusively, our work demonstrates that acetogenins are effective and selective inducers of the ESR that can block NPC proliferation, and illustrate a previously unappreciated antitumor mechanism of acetogenins that is effective against nasopharyngeal malignancies.