Induced endoplasmic reticulum (ER) stress and binding of over-expressed ER specific chaperone GRP78/BiP with dimerized epidermal growth factor receptor in mammalian cells exposed to low concentration of N-methyl-N'-nitro-N-nitrosoguanidine

New role of endoplasmic reticulum chaperones in regulating metaplasia during tumorigenesis

Metaplasia is emerging as a key process in tumorigenesis. We discovered that 2 essential endoplasmic reticulum (ER) chaperones, 78-kilodalton glucose-regulated protein (GRP78) and 94-kilodalton glucose-regulated protein (GRP94) have a role in metaplasia. Grp78 haploinsufficiency in the mouse pancreas impairs acinar-to-ductal metaplasia, whereas in the uterus, Grp94 loss induces squamous cell metaplasia; both resulting in tumor suppression.

GRP78 haploinsufficiency suppresses acinar-to-ductal metaplasia, signaling, and mutant Kras-driven pancreatic tumorigenesis in mice

Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal disease in critical need of new therapeutic strategies. Here, we report that the stress-inducible 78-kDa glucose-regulated protein (GRP78/HSPA5), a key regulator of endoplasmic reticulum homeostasis and PI3K/AKT signaling, is overexpressed in the acini and PDAC of Pdx1-Cre;Kras^G12D/+;p53^f/+ (PKC) mice as early as 2 mo, suggesting that GRP78 could exert a protective effect on acinar cells under stress, as during PDAC development. The PKC pancreata bearing wild-type Grp78 showed detectable PDAC by 3 mo and rapid subsequent tumor growth. In contrast, the PKC pancreata bearing a Grp78^f/+ allele (PKC78^f/+ mice) expressing about 50% of GRP78 maintained normal sizes during the early months, with reduced proliferation and suppression of AKT, S6, ERK, and STAT3 activation. Acinar-to-ductal metaplasia (ADM) has been identified as a key tumor initiation mechanism of PDAC. Compared with PKC, the PKC78^f/+ pancreata showed substantial reduction of ADM as well as pancreatic intraepithelial neoplasia-1 (PanIN-1), PanIN-2, and PanIN-3 and delayed onset of PDAC. ADM in response to transforming growth factor α was also suppressed in ex vivo cultures of acinar cell clusters isolated from mouse pancreas bearing targeted heterozygous knockout of Grp78 (c78^f/+ ) and subjected to 3D culture in collagen. We further discovered that GRP78 haploinsufficiency in both the PKC78^f/+ and c78^f/+ pancreata leads to reduction of epidermal growth factor receptor, which is critical for ADM initiation. Collectively, our studies establish a role for GRP78 in ADM and PDAC development.

Synthesis and characterization of an antibacterial and non-toxic dimeric peptide derived from the C-terminal region of Bothropstoxin-I

Infectious diseases are among the leading global causes of death, increasing the search for novel antibacterial agents. Among these, biologically active peptides are an excellent research tool. Using solid-phase peptide synthesis (SPPS), this work aimed to synthesize the peptide derived from the C-terminal region of Bothropstoxin-I (BthTX-I) (p-BthTX-I, sequence: KKYRYHLKPFCKK), and its disulfide-linked dimeric form, obtained via air oxidation (p-BthTX-I)2. Two other peptides were synthesized to evaluate the dimerization effect on antimicrobial activity. In both sequences, the cysteine (Cys) residue was replaced by the serine (Ser) residue, differing, however, in their C-terminus position. The antimicrobial activity of the peptides against gram-negative (Escherichia (E.) coli) and gram-positive (Staphylococcus (S.) aureus) bacteria and yeast (Candida (C.) albicans) was evaluated. Interestingly, only peptides containing the Cys residue showed antimicrobial activity, suggesting the importance of Cys residue and its dimerization for the observed activity. Apparently, p-BthTX-I and (p-BthTX-I)2 did not promote lysis or form pores and were not able to interact with membranes. Furthermore, they neither showed antifungal activity against C. albicans nor toxicity against erythrocytes, epithelial cells, or macrophages, indicating a potential specificity against prokaryotic cells.

Endoplasmic reticulum stress in endometrial cancer

Endometrial cancer (EC) is a common gynecologic malignancy often diagnosed at early stage. In spite of a huge advance in our understanding of EC biology, therapeutic modalities do not have significantly changed over the past 40 years. A restricted number of genes have been reported to be mutated in EC, mediating cell proliferation and invasiveness. However, besides these alterations, few other groups and ourselves recently identified the activation of the unfolded protein response (UPR) and GRP78 increase following endoplasmic reticulum (ER) stress as mechanisms favoring growth and invasion of EC cells. Here, a concise update on currently available data in the field is presented, analyzing the crosstalk between the UPR and the main signaling pathways regulating EC cell proliferation and survival. It is evident that this is a rapidly expanding and promising issue. However, more data are very likely to yield a better understanding on the mechanisms through which EC cells can survive the low oxygen and glucose tumor microenvironment. In this perspective, the UPR and, particularly, GRP78 might constitute a novel target for the treatment of EC in combination with traditional adjuvant therapy.

A bispecific transmembrane antibody simultaneously targeting intra- and extracellular epitopes of the epidermal growth factor receptor inhibits receptor activation and tumor cell growth

Epidermal growth factor receptor (EGFR) plays an important role in essential cellular processes such as proliferation, survival and migration. Aberrant activation of EGFR is frequently found in human cancers of various origins and has been implicated in cancer pathogenesis. The therapeutic antibody cetuximab (Erbitux) inhibits tumor growth by binding to the extracellular domain of EGFR, thereby preventing ligand binding and receptor activation. This activity is shared by the single chain antibody fragment scFv(225) that contains the same antigen binding domain. The unrelated EGFR-specific antibody fragment scFv(30) binds to the intracellular domain of the receptor and retains antigen binding upon expression as an intrabody in the reducing environment of the cytosol. Here, we used scFv(225) and scFv(30) domains to generate a novel type of bispecific transmembrane antibody termed 225.TM.30, that simultaneously targets intra- and extracellular EGFR epitopes. Bispecific 225.TM.30 and related membrane-anchored monospecific 225.TM and TM.30 proteins carrying extracellular scFv(225) or intracellular scFv(30) antibody fragments linked to a transmembrane domain were expressed in EGFR-overexpressing tumor cells using a doxycycline-inducible retroviral system. Induced expression of 225.TM.30 and 225.TM, but not TM.30 reduced EGFR surface levels and ligand-induced EGFR activation, while all three molecules markedly inhibited tumor cell growth. Co-localization of 225.TM with EGFR was predominantly found on the cell surface, while interaction with 225.TM.30 and TM.30 proteins resulted in the redistribution of EGFR to perinuclear compartments. Our data demonstrate functionality of this novel type of membrane-anchored intrabodies in tumor cells and suggest distinct modes of action of mono- and bispecific variants.

Hp-β-CD-voriconazole in situ gelling system for ocular drug delivery: in vitro, stability, and antifungal activities assessment

The objective of the present study was to design ophthalmic delivery systems based on polymeric carriers that undergo sol-to-gel transition upon change in temperature or in the presence of cations so as to prolong the effect of HP- β -CD Voriconazole (VCZ) in situ gelling formulations. The in situ gelling formulations of Voriconazole were prepared by using pluronic F-127 (PF-127) or with combination of pluronic F-68 (PF-68) and sodium alginate by cold method technique. The prepared formulations were evaluated for their physical appearance, drug content, gelation temperature (T gel), in vitro permeation studies, rheological properties, mucoadhesion studies, antifungal studies, and stability studies. All batches of in situ formulations had satisfactory pH ranging from 6.8 to 7.4, drug content between 95% and 100%, showing uniform distribution of drug. As the concentration of each polymeric component was increased, that is, PF-68 and sodium alginate, there was a decrease in T gel with increase in viscosity and mucoadhesive strength. The in vitro drug release decreased with increase in polymeric concentrations. The stability data concluded that all formulations showed the low degradation and maximum shelf life of 2 years. The antifungal efficiency of the selected formulation against Candida albicans and Asperigillus fumigatus confirmed that designed formulation has prolonged effect and retained its properties against fungal infection.

A novel role for epidermal growth factor receptor tyrosine kinase and its downstream endoplasmic reticulum stress in cardiac damage and microvascular dysfunction in type 1 diabetes mellitus

Epidermal growth factor receptor tyrosine kinase (EGFRtk) and endoplasmic reticulum (ER) stress are important factors in cardiovascular complications. Understanding whether enhanced EGFRtk activity and ER stress induction are involved in cardiac damage, and microvascular dysfunction in type 1 diabetes mellitus is an important question that has remained unanswered. Cardiac fibrosis and microvascular function were determined in C57BL/6J mice injected with streptozotocin only or in combination with EGFRtk inhibitor (AG1478), ER stress inhibitor (Tudca), or insulin for 2 weeks. In diabetic mice, we observed an increase in EGFRtk phosphorylation and ER stress marker expression (CHOP, ATF4, ATF6, and phosphorylated-eIF2α) in heart and mesenteric resistance arteries, which were reduced with AG1478, Tudca, and insulin. Cardiac fibrosis, enhanced collagen type I, and plasminogen activator inhibitor 1 were decreased with AG1478, Tudca, and insulin treatments. The impaired endothelium-dependent relaxation and -independent relaxation responses were also restored after treatments. The inhibition of NO synthesis reduced endothelium-dependent relaxation in control and treated streptozotocin mice, whereas the inhibition of NADPH oxidase improved endothelium-dependent relaxation only in streptozotocin mice. Moreover, in mesenteric resistance arteries, the mRNA levels of Nox2 and Nox4 and the NADPH oxidase activity were augmented in streptozotocin mice and reduced with treatments. This study unveiled novel roles for enhanced EGFRtk phosphorylation and its downstream ER stress in cardiac fibrosis and microvascular endothelial dysfunction in type 1 diabetes mellitus.

Effect of microcystin-LR on protein phosphatase 2A and its function in human amniotic epithelial cells

Due to their toxicity, the increased distribution of microcystins (MCs) has become an important worldwide problem. MCs have been recognized as inhibitors of protein phosphatase 2A (PP2A) through their binding to the PP2A catalytic subunit. However, the exact mechanism of MC toxicity has not been elucidated, especially concerning the cellular response and its autoregulation. To further dissect the role of PP2A in MC-induced toxicity, the present study was undertaken to determine the response of PP2A in human amniotic epithelial (FL) cells treated with microcystin-LR (MCLR), one of the MC congeners. The results show that a low-dose treatment of MCLR in FL cells for 6 h induced an increase in PP2A activity, and a high-dose treatment of MCLR for 24 h decreased the activity of PP2A, as expected. The increased mRNA and protein levels of the PP2A C subunit may explain the increased activity of PP2A. Furthermore, MCLR altered microtubule post-translational modifications through PP2A. These results further clarify the underlying mechanism how MCLR affects PP2A and may be helpful for elucidating the complex toxicity of MCLR.

Interferon regulatory factor 1 transactivates expression of human DNA polymerase η in response to carcinogen N-methyl-N'-nitro-N-nitrosoguanidine

DNA polymerase η (Polη) implements translesion DNA synthesis but has low fidelity in replication. We have previously shown that Polη plays an important role in the genesis of nontargeted mutations at undamaged DNA sites in cells exposed to the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Here, we report that MNNG-induced Polη expression in an interferon regulatory factor 1 (IRF1)-dependent manner in human cells. Mutagenesis analysis showed that four critical residues (Arg-82, Cys-83, Asn-86, and Ser-87) located in the IRF family conserved DNA binding domain-helix α3 were involved in DNA binding and POLH transactivation by IRF1. Furthermore, Polη up-regulation induced by IRF1 was responsible for the increase of mutation frequency in a SupF shuttle plasmid replicated in the MNNG-exposed cells. Interestingly, IRF1 was acetylated by the histone acetyltransferase CBP in these cells. Lys → Arg substitution revealed that Lys-78 of helix α3 was the major acetylation site, and the IRF1-K78R mutation partially inhibited DNA binding and its transcriptional activity. Thus, we propose that IRF1 activation is responsible for MNNG-induced Polη up-regulation, which contributes to mutagenesis and ultimately carcinogenesis in cells.

Quantitative and subcellular localization analysis of the nuclear isoform dUTP pyrophosphatase in alkylating agent-induced cell responses

Our previous proteome analysis showed that the nuclear isoform of dUTP pyrophosphatase (DUT-N) was identified in the culture medium of human amnion FL cells after exposure to the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). These results suggest that DUT-N may be a potential early biomarker to assess the risk of alkylating agents exposure. DUT-N is one of the two isoforms of deoxyuridine triphosphate nucleotidohydrolase (dUTPase). Our current knowledge of DUT-N expression in human cells is very limited. In the current study, we first investigated the appearance of DUT-N in the culture medium of different human cell lines in response to a low concentration of MNNG exposure. We verified that the MNNG-induced appearance of DUT-N in the extracellular environment is cell-specific. Western blot analysis confirmed that the intracellular DUT-N changes responded to MNNG in a concentration-dependent and cell-specific manner. Furthermore, subcellular fraction experiments showed that 0.25μM MNNG treatment dramatically increased the DUT-N expression levels in the cytoplasmic extracts prepared from both FL and HepG2 cells, increased DUT-N levels in nuclear extracts prepared from HepG2 cells, and decreased DUT-N levels in nuclear extracts from FL cells. Morphological studies using immunofluorescence showed that a low concentration of MNNG could alter the distribution of DUT-N in FL and HepG2 cells in different ways. Taken together, these studies indicate a role of DUT-N in alkylating agent-induced cell responses.

Overexpression of the endoplasmic reticulum chaperone BiP3 regulates XA21-mediated innate immunity in rice

Recognition of pathogen-associated molecular patterns by pattern recognition receptors (PRRs) activates the innate immune response. Although PRR-mediated signaling events are critical to the survival of plants and animals, secretion and localization of PRRs have not yet been clearly elucidated. Here we report the in vivo interaction of the endoplasmic reticulum (ER) chaperone BiP3 with the rice XA21 PRR, which confers resistance to the Gram negative bacterium, Xanthomonas oryzae pv. oryzae (Xoo). We show that XA21 is glycosylated and is primarily localized to the ER and also to the plasma membrane (PM). In BiP3-overexpressing rice plants, XA21-mediated immunity is compromised, XA21 stability is significantly decreased, and XA21 proteolytic cleavage is inhibited. BiP3 overexpression does not affect the general rice defense response, cell death or brassinolide-induced responses. These results indicate that BiP3 regulates XA21 protein stability and processing and that this regulation is critical for resistance to Xoo.

The alternative TrkAIII splice variant targets the centrosome and promotes genetic instability

The hypoxia-regulated alternative TrkAIII splice variant expressed by human neuroblastomas exhibits oncogenic potential, driven by in-frame exon 6 and 7 alternative splicing, leading to omission of the receptor extracellular immunoglobulin C(1) domain and several N-glycosylation sites. Here, we show that the TrkAIII oncogene promotes genetic instability by interacting with and exhibiting catalytic activity at the centrosome. This function depends upon intracellular TrkAIII accumulation and spontaneous interphase-restricted activation, in cytoplasmic tyrosine kinase (tk) domain orientation, predominantly within structures that closely associate with the fully assembled endoplasmic reticulum intermediate compartment and Golgi network. This facilitates TrkAIII tk-mediated binding of gamma-tubulin, which is regulated by endogenous protein tyrosine phosphatases and geldanamycin-sensitive interaction with Hsp90, paving the way for TrkAIII recruitment to the centrosome. At the centrosome, TrkAIII differentially phosphorylates several centrosome-associated components, increases centrosome interaction with polo kinase 4, and decreases centrosome interaction with separase, the net results of which are centrosome amplification and increased genetic instability. The data characterize TrkAIII as a novel internal membrane-associated centrosome kinase, unveiling an important alternative mechanism to "classical" cell surface oncogenic receptor tk signaling through which stress-regulated alternative TrkAIII splicing influences the oncogenic process.

Alteration of proteins expression in apoptotic FL cells induced by MCLR

Microcystins (MCs) are a family of monocyclic heptapeptide hepatotoxins produced by freshwater species of cyanobacteria. Microcystin-LR (MCLR) is the most frequently studied and most toxic in over 80 MC congeners. Great deals of studies have demonstrated that MCLR can induce apoptosis in a wide variety of cell types. Although much evidence indicates that mitochondria play a pivotal role in MCLR-induced apoptosis, the complicated apoptosis mechanisms induced by MCLR have not been completely characterized. It is possible that there are other apoptotic pathways existing in MCLR-induced apoptosis. The present study was undertaken to determine the expression of PP2A, CHOP, Bax, Bcl-2, and p53 proteins in MCLR-induced apoptosis in FL cells. The results showed that MCLR could induce apoptosis in FL cells and the process was accompanied with the upregulation of PP2A, Bax, and p53 proteins and the downregulation of Bcl-2 proteins. In addition, the CHOP protein was upregulated at most treatment groups and decreased at the highest concentration group. These results, especially the alteration of PP2A and CHOP proteins might provide new insights into MCLR-induced apoptosis.

Proteomic analysis of different temporal expression patterns induced by N-methyl-N'-nitro-N-nitrosoguanidine treatment

We have previously shown that N-methyl- N'-nitro- N-nitrosoguanidine (MNNG), a well-known DNA alkylating agent and carcinogen, can induce multiple cellular responses with dynamic characteristics, including such responses as nontargeted mutations (NTM) at undamaged bases in DNA, up-regulation of low fidelity DNA polymerases, clustering of epidermal growth factor receptor (EGFR) and interference with its downstream signaling pathway. A dose-related analysis also revealed that different concentrations of MNNG can trigger diverse proteome changes associated with different cytotoxic effects. To further understand the dynamic cellular responses and hazardous effects caused by environmental carcinogen, a proteomic time-course study of whole cellular proteins from human amniotic epithelial cells after MNNG treatment was performed. Analysis at three different time points (3, 12 and 24 h after exposure) revealed that the major changes were taking place around 3 and 12 h after exposure. Using MALDI-TOF MS coupled with a micro solid-phase extraction (SPE) device, 90% ( n = 70) differentially expressed proteins were identified. Functional assignment revealed that many important pathways were affected, including the protein biosynthesis pathway and Ran GTPase system. We also carried out a network analysis of these proteins and the data suggest a central role for some key regulators in different pathways.