Myogenesis in C2C12 Cells Requires Phosphorylation of ATF6α by p38 MAPK

Activating transcription factor 6α (ATF6α) is an endoplasmic reticulum protein known to participate in unfolded protein response (UPR) during ER stress in mammals. Herein, we show that in mouse C2C12 myoblasts induced to differentiate, ATF6α is the only pathway of the UPR activated. ATF6α stimulation is p38 MAPK-dependent, as revealed by the use of the inhibitor SB203580, which halts myotube formation and, at the same time, impairs trafficking of ATF6α, which accumulates at the cis-Golgi without being processed in the p50 transcriptional active form. To further evaluate the role of ATF6α, we knocked out the ATF6α gene, thus inhibiting the C2C12 myoblast from undergoing myogenesis, and this occurred independently from p38 MAPK activity. The expression of exogenous ATF6α in knocked-out ATF6α cells recover myogenesis, whereas the expression of an ATF6α mutant in the p38 MAPK phosphorylation site (T166) was not able to regain myogenesis. Genetic ablation of ATF6α also prevents the exit from the cell cycle, which is essential for muscle differentiation. Furthermore, when we inhibited differentiation by the use of dexamethasone in C2C12 cells, we found inactivation of p38 MAPK and, consequently, loss of ATF6α activity. All these findings suggest that the p-p38 MAPK/ATF6α axis, in pathophysiological conditions, regulates myogenesis by promoting the exit from the cell cycle, an essential step to start myoblasts differentiation.

Down Syndrome Fetal Fibroblasts Display Alterations of Endosomal Trafficking Possibly due to SYNJ1 Overexpression

Endosomal trafficking is essential for cellular homeostasis. At the crossroads of distinct intracellular pathways, the endolysosomal system is crucial to maintain critical functions and adapt to the environment. Alterations of endosomal compartments were observed in cells from adult individuals with Down syndrome (DS), suggesting that the dysfunction of the endosomal pathway may contribute to the pathogenesis of DS. However, the nature and the degree of impairment, as well as the timing of onset, remain elusive. Here, by applying imaging and biochemical approaches, we demonstrate that the structure and dynamics of early endosomes are altered in DS cells. Furthermore, we found that recycling trafficking is markedly compromised in these cells. Remarkably, our results in 18–20 week-old human fetal fibroblasts indicate that alterations in the endolysosomal pathway are already present early in development. In addition, we show that overexpression of the polyphosphoinositide phosphatase synaptojanin 1 (Synj1) recapitulates the alterations observed in DS cells, suggesting a role for this lipid phosphatase in the pathogenesis of DS, likely already early in disease development. Overall, these data strengthen the link between the endolysosomal pathway and DS, highlighting a dangerous liaison among Synj1, endosomal trafficking and DS.

Structural and Functional Significance of the Endoplasmic Reticulum Unfolded Protein Response Transducers and Chaperones at the Mitochondria-ER Contacts: A Cancer Perspective

In the last decades, the endoplasmic reticulum (ER) has emerged as a key coordinator of cellular homeostasis, thanks to its physical interconnection to almost all intracellular organelles. In particular, an intense and mutual crosstalk between the ER and mitochondria occurs at the mitochondria–ER contacts (MERCs). MERCs ensure a fine-tuned regulation of fundamental cellular processes, involving cell fate decision, mitochondria dynamics, metabolism, and proteostasis, which plays a pivotal role in the tumorigenesis and therapeutic response of cancer cells. Intriguingly, recent studies have shown that different components of the unfolded protein response (UPR) machinery, including PERK, IRE1α, and ER chaperones, localize at MERCs. These proteins appear to exhibit multifaceted roles that expand beyond protein folding and UPR transduction and are often related to the control of calcium fluxes to the mitochondria, thus acquiring relevance to cell survival and death. In this review, we highlight the novel functions played by PERK, IRE1α, and ER chaperones at MERCs focusing on their impact on tumor development.

Bioactive Ent-Kaurane Diterpenes Oridonin and Irudonin Prevent Cancer Cells Migration by Interacting with the Actin Cytoskeleton Controller Ezrin

The ent-kaurane diterpene oridonin was reported to inhibit cell migration and invasion in several experimental models. However, the process by which this molecule exerts its anti-metastatic action has not been yet elucidated. In this article, we have investigated the anti-metastatic activity of Oridonin and of one homolog, Irudonin, with the aim to shed light on the molecular mechanisms underlying the biological activity of these ent-kaurane diterpenes. Cell-based experiments revealed that both compounds are able to affect differentiation and cytoskeleton organization in mouse differentiating myoblasts, but also to impair migration, invasion and colony formation ability of two different metastatic cell lines. Using a compound-centric proteomic approach, we identified some potential targets of the two bioactive compounds among cytoskeletal proteins. Among them, Ezrin, a protein involved in the actin cytoskeleton organization, was further investigated. Our results confirmed the pivotal role of Ezrin in regulating cell migration and invasion, and indicate this protein as a potential target for new anti-cancer therapeutic approaches. The interesting activity profile, the good selectivity towards cancer cells, and the lower toxicity with respect to Oridonin, all suggest that Irudonin is a very promising anti-metastatic agent.

Different mechanisms underlie IL-6 release in chemosensitive and chemoresistant ovarian carcinoma cells

Interleukin (IL)-6 has been detected in serum and ascites from patients affected by epithelial ovarian cancers, and also in some human ovarian cancer cell lines. To investigate the role of IL-6 in ovarian lesions, we first measured its levels in serum samples of 24 healthy donors and in 17 and 9 patients affected by ovarian carcinomas and ovarian benign cysts respectively. IL-6 levels were significantly higher than healthy donors in serum samples from ovarian cancer patients, but not in benign ovarian cysts. We then investigated the mechanism of IL-6 production in two cell lines obtained from the same patient with high grade serous ovarian carcinoma before (PEA1) and after (PEA2) development of cisplatinum resistance. The levels of intracellular IL-6, analysed by western blotting, did not relevantly differ in the two cell lines, and they did not change after the cell treatment with an AKT inhibitor. Although the interleukin was present in supernatants from both cell lines, its concentration in the supernatant of chemoresistant cells was significantly higher than chemosensitive cells. Interestingly, exposure to the AKT inhibitor resulted in a reduced IL-6 release in PEA1, but not in PEA2 cells. These results let infer different mechanisms of IL-6 release in chemoresistant and chemosensitive cell lines, and contribute new insights in ovarian cancer biology that suggest more in depth studies about the role of AKT in IL-6 release and in development of chemoresistance.

Binding of the Anti-FIV Peptide C8 to Differently Charged Membrane Models: From First Docking to Membrane Tubulation

Gp36 is the virus envelope glycoproteins catalyzing the fusion of the feline immunodeficiency virus with the host cells. The peptide C8 is a tryptophan-rich peptide corresponding to the fragment ⁷⁷⁰W-I⁷⁷⁷ of gp36 exerting antiviral activity by binding the membrane cell and inhibiting the virus entry. Several factors, including the membrane surface charge, regulate the binding of C8 to the lipid membrane. Based on the evidence that imperceptible variation of membrane charge may induce a dramatic effect in several critical biological events, in the present work we investigate the effect induced by systematic variation of charge in phospholipid bilayers on the aptitude of C8 to interact with lipid membranes, the tendency of C8 to assume specific conformational states and the re-organization of the lipid bilayer upon the interaction with C8. Accordingly, employing a bottom-up multiscale protocol, including CD, NMR, ESR spectroscopy, atomistic molecular dynamics simulations, and confocal microscopy, we studied C8 in six membrane models composed of different ratios of zwitterionic/negatively charged phospholipids. Our data show that charge content modulates C8-membrane binding with significant effects on the peptide conformations. C8 in micelle solution or in SUV formed by DPC or DOPC zwitterionic phospholipids assumes regular β-turn structures that are progressively destabilized as the concentration of negatively charged SDS or DOPG phospholipids exceed 40%. Interaction of C8 with zwitterionic membrane surface is mediated by Trp1 and Trp4 that are deepened in the membrane, forming H-bonds and cation-π interactions with the DOPC polar heads. Additional stabilizing salt bridge interactions involve Glu2 and Asp3. MD and ESR data show that the C8-membrane affinity increases as the concentration of zwitterionic phospholipid increases. In the lipid membrane characterized by an excess of zwitterionic phospholipids, C8 is adsorbed at the membrane interface, inducing a stiffening of the outer region of the DOPC bilayer. However, the bound of C8 significantly perturbs the whole organization of lipid bilayer resulting in membrane remodeling. These events, measurable as a variation of the bilayer thickness, are the onset mechanism of the membrane fusion and vesicle tubulation observed in confocal microscopy by imaging zwitterionic MLVs in the presence of C8 peptide.

The Mitochondria-Endoplasmic Reticulum Contacts and Their Critical Role in Aging and Age-Associated Diseases

The recent discovery of interconnections between the endoplasmic reticulum (ER) membrane and those of almost all the cell compartments is providing novel perspectives for the understanding of the molecular events underlying cellular mechanisms in both physiological and pathological conditions. In particular, growing evidence strongly supports the idea that the molecular interactions occurring between ER and mitochondrial membranes, referred as the mitochondria (MT)-ER contacts (MERCs), may play a crucial role in aging and in the development of age-associated diseases. As emerged in the last decade, MERCs behave as signaling hubs composed by structural components that act as critical players in different age-associated disorders, such as neurodegenerative diseases and motor disorders, cancer, metabolic syndrome, as well as cardiovascular diseases. Age-associated disorders often derive from mitochondrial or ER dysfunction as consequences of oxidative stress, mitochondrial DNA mutations, accumulation of misfolded proteins, and defective organelle turnover. In this review, we discuss the recent advances associating MERCs to aging in the context of ER-MT crosstalk regulating redox signaling, ER-to MT lipid transfer, mitochondrial dynamics, and autophagy.

PERK-Mediated Unfolded Protein Response Activation and Oxidative Stress in PARK20 Fibroblasts

PARK20, an early onset autosomal recessive parkinsonism is due to mutations in the phosphatidylinositol-phosphatase Synaptojanin 1 (Synj1). We have recently shown that the early endosomal compartments are profoundly altered in PARK20 fibroblasts as well as the endosomal trafficking. Here, we report that PARK20 fibroblasts also display a drastic alteration of the architecture and function of the early secretory compartments. Our results show that the exit machinery from the Endoplasmic Reticulum (ER) and the ER-to-Golgi trafficking are markedly compromised in patient cells. As a consequence, PARK20 fibroblasts accumulate large amounts of cargo proteins within the ER, leading to the induction of ER stress. Interestingly, this stressful state is coupled to the activation of the PERK/eIF2α/ATF4/CHOP pathway of the Unfolded Protein Response (UPR). In addition, PARK20 fibroblasts reveal upregulation of oxidative stress markers and total ROS production with concomitant alteration of the morphology of the mitochondrial network. Interestingly, treatment of PARK20 cells with GSK2606414 (GSK), a specific inhibitor of PERK activity, restores the level of ROS, signaling a direct correlation between ER stress and the induction of oxidative stress in the PARK20 cells. All together, these findings suggest that dysfunction of early secretory pathway might contribute to the pathogenesis of the disease.

The Impact of Aging on Cardio and Cerebrovascular Diseases

A growing number of evidences report that aging represents the major risk factor for the development of cardio and cerebrovascular diseases. Understanding Aging from a genetic, biochemical and physiological point of view could be helpful to design a better medical approach and to elaborate the best therapeutic strategy to adopt, without neglecting all the risk factors associated with advanced age. Of course, the better way should always be understanding risk-to-benefit ratio, maintenance of independence and reduction of symptoms. Although improvements in treatment of cardiovascular diseases in the elderly population have increased the survival rate, several studies are needed to understand the best management option to improve therapeutic outcomes. The aim of this review is to give a 360° panorama on what goes on in the fragile ecosystem of elderly, why it happens and what we can do, right now, with the tools at our disposal to slow down aging, until new discoveries on aging, cardio and cerebrovascular diseases are at hand.

N6-isopentenyladenosine dual targeting of AMPK and Rab7 prenylation inhibits melanoma growth through the impairment of autophagic flux

Targeting the autophagic process is considered a promising therapeutic strategy in cancer since a great number of tumors, including melanoma, show high basal levels of protective autophagy that contributes to tumor progression and chemoresistance. Here, exploiting both in vitro and in vivo approaches, we identified N6-isopentenyladenosine (iPA), an end product of the mevalonate pathway, as a novel autophagy inhibitor with an interesting anti-melanoma activity. iPA, after being phosphorylated by adenosine kinase into 5'-iPA-monophosphate, induces autophagosome accumulation through AMPK activation, measured by increased fluorescent GFP-LC3 puncta and enhanced conversion into the lipidated autophagosome-associated LC3-II. However, at a later stage iPA blocks the autophagic flux monitored by p62 accumulation, Luciferase reporter-based assay for LC3 turnover in living cells and fluorescence of a tandem RFP-GFP-LC3 construct. Impaired autophagic flux is due to the block of autophagosome-lysosome fusion through the defective localization and function of Rab7, whose prenylation is inhibited by iPA, resulting in a net inhibition of autophagy completion that finally leads to melanoma apoptotic cell death. AMPK silencing prevents apoptosis upon iPA treatment, whereas basal autophagosome turnover is still inhibited due to unprenylated Rab7. These results strongly support the advantage of targeting autophagy for therapeutic gain in melanoma and provide the preclinical rational to further investigate the antitumor action of iPA, able to coordinately induce autophagosome accumulation and inhibit the autophagic flux, independently targeting AMPK and Rab7 prenylation. This property may be particularly useful for the selective killing of tumors, like melanoma, that frequently develop chemotherapy resistance due to protective autophagy activation.

The anti-apoptotic BAG3 protein is involved in BRAF inhibitor resistance in melanoma cells

BAG3 protein, a member of BAG family of co-chaperones, has a pro-survival role in several tumour types. BAG3 anti-apoptotic properties rely on its characteristic to bind several intracellular partners, thereby modulating crucial events such as apoptosis, differentiation, cell motility, and autophagy. In human melanomas, BAG3 positivity is correlated with the aggressiveness of the tumour cells and can sustain IKK-γ levels, allowing a sustained activation of NF-κB. Furthermore, BAG3 is able to modulate BRAFV600E levels and activity in thyroid carcinomas. BRAFV600E is the most frequent mutation detected in malignant melanomas and is targeted by Vemurafenib, a specific inhibitor found to be effective in the treatment of advanced melanoma. However, patients with BRAF-mutated melanoma may result insensitive ab initio or, mostly, develop acquired resistance to the treatment with this molecule.

Here we show that BAG3 down-modulation interferes with BRAF levels in melanoma cells and sensitizes them to Vemurafenib treatment. Furthermore, the down-modulation of BAG3 protein in an in vitro model of acquired resistance to Vemurafenib can induce sensitization to the BRAFV600E specific inhibition by interfering with BRAF pathway through reduction of ERK phosphorylation, but also on parallel survival pathways.

Future studies on BAG3 molecular interactions with key proteins responsible of acquired BRAF inhibitor resistance may represent a promising field for novel multi-drugs treatment design.

The Endoplasmic Reticulum Unfolded Protein Response in Neurodegenerative Disorders and Its Potential Therapeutic Significance

In eukaryotic cells, the endoplasmic reticulum (ER) is the cell compartment involved in secretory protein translocation and quality control of secretory protein folding. Different conditions can alter ER function, resulting in the accumulation of unfolded or misfolded proteins within the ER lumen. Such a condition, known as ER stress, elicits an integrated adaptive response known as the unfolded protein response (UPR) that aims to restore proteostasis within the secretory pathway. Conversely, in prolonged cell stress or insufficient adaptive response, UPR signaling causes cell death. ER dysfunctions are involved and contribute to neuronal degeneration in several human diseases, including Alzheimer, Parkinson and Huntington disease and amyotrophic lateral sclerosis. The correlations between ER stress and its signal transduction pathway known as the UPR with neuropathological changes are well established. In addition, much evidence suggests that genetic or pharmacological modulation of UPR could represent an effective strategy for minimizing the progressive neuronal loss in neurodegenerative diseases. Here, we review recent results describing the main cellular mechanisms linking ER stress and UPR to neurodegeneration. Furthermore, we provide an up-to-date panoramic view of the currently pursued strategies for ameliorating the toxic effects of protein unfolding in disease by targeting the ER UPR pathway.

Identification of Cysteine Ubiquitylation Sites on the Sec23A Protein of the COPII Complex Required for Vesicle Formation from the ER

BACKGROUND

COPII is a multiprotein complex that surrounds carrier vesicles budding from the Endoplasmic Reticulum and allows the recruitment of secretory proteins. The Sec23a protein plays a crucial role in the regulation of the dynamics of COPII formation ensuring the proper function of the secretory pathway.

OBJECTIVE

Since few evidences suggest that ubiquitylation could have a role in the COPII regulation, the present study was aimed to establish whether the Sec23a component of the vesicular envelope COPII could be ubiquitylated.

METHOD

Sec23a ubiquitylation was revealed by co-immunoprecipitation experiments. Recombinant Sec23a was gel-purified and analyzed by mass spectrometry subjected to trypsin proteolysis. Signature peptides were identified by the presence of Gly-Gly remnants from the C-terminus of the ubiquitin attached to the amino acid residues of the substrate. Recombinant Sec23a proteins bearing mutations in the ubiquitylation sites were used to evaluate the effect of ubiquitylation in the formation of COPII.

RESULTS

We identified two cysteine ubiquitylation sites showed at position 432 and 449 of the Sec23a protein sequence. Interestingly, we revealed that the amino acid residues of Sec23a joined to ubiquitin were cysteine instead of the conventional lysine residues. This unconventional ubiquitylation consists of the addition of one single ubiquitin moiety that is not required for Sec23a degradation. Immunofluorescence results showed that Sec23a ubiquitylation might influence COPII formation by modulating Sec23a interaction with the ER membrane. Presumably, this regulation could occur throughout continual ubiquitylation/de-ubiquityliation cycles.

CONCLUSION

Our results suggest a novel regulatory mechanism for the Sec23a function that could be crucial in several pathophysiological events known to alter COPII recycling.

Pentraxin 3 Induces Vascular Endothelial Dysfunction Through a P-selectin/Matrix Metalloproteinase-1 Pathway

BACKGROUND

Pentraxin 3 (PTX3), the prototype of long pentraxins, has been described to be associated with endothelial dysfunction in different cardiovascular disorders. No study has yet evaluated the possible direct effect of PTX3 on vascular function.

METHODS AND RESULTS

Through in vitro experiments of vascular reactivity and ultrastructural analyses, we demonstrate that PTX3 induces dysfunction and morphological changes in the endothelial layer through a P-selectin/matrix metalloproteinase-1 pathway. The latter hampered the detachment of endothelial nitric oxide synthase from caveolin-1, leading to an impairment of nitric oxide signaling. In vivo studies showed that administering PTX3 to wild-type mice induced endothelial dysfunction and increased blood pressure, an effect absent in P-selectin-deficient mice. In isolated human umbilical vein endothelial cells, PTX3 significantly blunted nitric oxide production through the matrix metalloproteinase-1 pathway. Finally, using ELISA, we found that hypertensive patients (n=31) have higher plasma levels of PTX3 and its mediators P-selectin and matrix metalloproteinase-1 than normotensive subjects (n=21).

CONCLUSIONS

Our data show for the first time a direct role of PTX3 on vascular function and blood pressure homeostasis, identifying the molecular mechanisms involved. The findings in humans suggest that PTX3, P-selectin, and matrix metalloproteinase-1 may be novel biomarkers that predict the onset of vascular dysfunction in hypertensive patients.

Endoplasmic reticulum stress reduces COPII vesicle formation and modifies Sec23a cycling at ERESs

Exit from the Endoplasmic Reticulum (ER) of newly synthesized proteins is mediated by COPII vesicles that bud from the ER at the ER Exit Sites (ERESs). Disruption of ER homeostasis causes accumulation of unfolded and misfolded proteins in the ER. This condition is referred to as ER stress. Previously, we demonstrated that ER stress rapidly impairs the formation of COPII vesicles. Here, we show that membrane association of COPII components, and in particular of Sec23a, is impaired by ER stress-inducing agents suggesting the existence of a dynamic interplay between protein folding and COPII assembly at the ER.

In the Huh7 Hepatoma Cells Diclofenac and Indomethacin Activate Differently the Unfolded Protein Response and Induce ER Stress Apoptosis

Non-steroidal anti-inflammatory drugs (NSAIDs) are cyclooxygenases (COXs) inhibitors frequently used in the treatment of acute and chronic inflammation. Side effects of NSAIDs are often due to their ability to induce apoptosis. Located at the Endoplasmic Reticulum membranes a tripartite signalling pathway, collectively known as the Unfolded Protein Response (UPR), decides survival or death of cells exposed to cytotoxic agents. To shed light on the molecular events responsible for the cytotoxicity of NSAIDs, we analysed the ability of diclofenac and indomethacin to activate the UPR in the human hepatoma cell line Huh7. We report that both NSAIDs can induce differently the single arms of the UPR. We show that indomethacin turns on the PERK and, only in part, the ATF6 and IRE1 pathways. Instead, diclofenac reduces the expression of ATF6 and does not stimulate the IRE1 endonuclease, which drives the expression of the prosurvival factor XBP1. Diclofenac, as well as indomethacin, is able to activate efficiently only the PERK pathway of the UPR, which induces the expression of the proapoptotic GADD153/CHOP protein. Our results highlight the importance of the UPR in evaluating the potential of drugs to induce apoptosis.

The identification of a novel natural activator of p300 histone acetyltranferase provides new insights into the modulation mechanism of this enzyme

Many severe human pathologies are related to alterations of the fine balance between histone acetylation and deacetylation; because not all such diseases involve hypoacetylation, but also hyperacetylation, compounds able to enhance or repress the activities of histone acetyltransferases (HATs) could be promising therapeutic agents. We evaluated in vitro and in cell the ability of eleven natural polyisoprenylated benzophenone derivatives to modulate the HAT activity of p300/CBP, an enzyme that plays a pivotal role in a variety of cellular processes. Some of the tested compounds bound efficiently to the p300/CBP protein: in particular, guttiferone A, guttiferone E and clusianone inhibit its HAT activity, whereas nemorosone showed a surprising ability to activate the enzyme. The ability of nemorosone to penetrate cell membranes and modulate histone acetylation into the cell together with its high affinity for the p300/CBP enzyme made this compound a suitable lead for the design of optimized anticancer drugs. Besides, the studies performed at a cellular and molecular level on both the inhibitors and the activator provided new insights into the modulation mechanism of p300/CBP by small molecules.

Non-coding RNAs change their expression profile after Retinoid induced differentiation of the promyelocytic cell line NB4

Background

The importance of non-coding RNAs (ncRNAs) as fine regulators of eukaryotic gene expression has emerged by several studies focusing on microRNAs (miRNAs). miRNAs represent a newly discovered family of non coding-RNAs. They are thought to be crucial players of human hematopoiesis and related tumorigenesis and to represent a potential tool to detect the early stages of cancer. More recently, the expression regulation of numerous long ncRNAs has been linked to cell growth, differentiation and cancer although the molecular mechanism of their function is still unknown.

NB4 cells are promyelocytic cells that can be induced to differentiation upon retinoic acid (ATRA) treatment and represent a feasible model to study changes of non coding RNAs expression between cancer cells and their terminally differentiated counterpart.

Findings

we screened, by microarray analysis, the expression of 243 miRNAs and 492 human genes transcribing for putative long ncRNAs different from miRNAs in NB4 cells before and after ATRA induced differentiation. Our data show that 8 miRNAs, and 58 long ncRNAs were deregulated by ATRA induced NB4 differentiation.

Conclusion

our data suggest that ATRA-induced differentiation lead to deregulation of a large number of the ncRNAs that can play regulatory roles in both tumorigenesis and differentiation.

Regulation of ERGIC-53 gene transcription in response to endoplasmic reticulum stress

Accumulation of unfolded proteins within the endoplasmic reticulum (ER) activates the unfolded protein response, also known as the ER stress response. We previously demonstrated that ER stress induces transcription of the ER Golgi intermediate compartment protein ERGIC-53. To investigate the molecular events that regulate unfolded protein response-mediated induction of the gene, we have analyzed the transcriptional regulation of ERGIC-53. We found that the ERGIC-53 promoter contains a single cis-acting element that mediates induction of the gene by thapsigargin and other ER stress-causing agents. This ER stress response element proved to retain a novel structure and to be highly conserved in mammalian ERGIC-53 genes. The ER stress response element identified contains a 5'-end CCAAT sequence that constitutively binds NFY/CBF and, 9 nucleotides away, a 3'-end region (5'-CCCTGTTGGCCATC-3') that is equally important for ER stress-mediated induction of the gene. This sequence is the binding site for endogenous YY1 at the 5'-CCCTGTTGG-3' part and for undefined factors at the CCATC 3'-end. ATF6 alpha-YY1, but not XBP1, interacted with the ERGIC-53 regulatory region and activated ERGIC-53 ER stress response element-dependent transcription. A molecular model for the transcriptional regulation of the ERGIC-53 gene is proposed.

Nitric oxide-induced endoplasmic reticulum stress activates the expression of cargo receptor proteins and alters the glycoprotein transport to the Golgi complex

The endoplasmic reticulum Golgi intermediate compartment 53 protein recycles continuously between the endoplasmic reticulum and the Golgi complex and ensures the anterograde transport of specific glycoproteins with the assistance of the Multiple Clotting Factor Deficiency adaptor protein. Therefore, to analyze the effect of the endoplasmic reticulum stress on the secretory pathway beyond the endoplasmic reticulum, we analyzed the expression of both proteins in J774 macrophages incubated with the nitric oxide donor DETA NONOate or with thapsigargin. Both proteins accumulated progressively, by a transcriptional mechanism, in response to these inducers. Nitric oxide also induced a higher level of calreticulin and glucose regulated 78 protein, two endoplasmic reticulum proteins controlled by the unfolded protein response. Interestingly, nitric oxide induced the processing of the activating transcription factor 6alpha of the unfolded protein response, while thapsigargin also induced the activation of the transcription factor X-box Binding Protein 1. In addition, we showed that the accumulation of both transporters occurred simultaneously with the activation of endoplasmic reticulum-stress-dependent apoptosis, suggesting that these proteins may participate in the events that will eventually decide the fate of the cell. Induction of endoplasmic reticulum stress affected the rate of anterograde transport of a reporter glycoprotein, indicating that the endoplasmic reticulum to Golgi transport is remarkably impaired. Our results indicate that increased levels of cargo receptor proteins might have a function either in the quality control of protein folding in the endoplasmic reticulum or in the homeostasis of the intermediate compartment and Golgi complex during cell stress.

Heat Shock Induces Preferential Translation of ERGIC-53 and Affects Its Recycling Pathway

ERGIC-53 is a lectin-like transport receptor protein, which recirculates between the ER and the Golgi complex and is required for the intracellular transport of a restricted number of glycoproteins. We show in this article that ERGIC-53 accumulates during the heat shock response. However, at variance with the unfolded protein response, which results in enhanced transcription of ERGIC-53 mRNA, heat shock leads only to enhanced translation of ERGIC-53 mRNA. In addition, the half-life of the protein does not change during heat shock. Therefore, distinct signal pathways of the cell stress response modulate the ERGIC-53 protein level. Heat shock also affects the recycling pathway of ERGIC-53. The protein rapidly redistributes in a more peripheral area of the cell, in a vesicular compartment that has a lighter sedimentation density on sucrose gradient in comparison to the compartment that contains the majority of ERGIC-53 at 37 degrees C. This effect is specific, as no apparent reorganization of the endoplasmic reticulum, intermediate compartment and Golgi complex is morphologically detectable in the cells exposed to heat shock. Moreover, the anterograde transport of two unrelated reporter proteins is not affected. Interestingly, MCFD2, which interacts with ERGIC-53 to form a complex required for the ER-to-Golgi transport of specific proteins, is regulated similarly to ERGIC-53 in response to cell stress. These results support the view that ERGIC-53 alone, or in association with MCFD2, plays important functions during cellular response to stress conditions.

Zinc transport and metallothionein secretion in the intestinal human cell line Caco-2

Caco-2, a human cell line, displays several biochemical and morphological characteristics of differentiated enterocytes. Among these is the ability to transport zinc from the apical to the basal compartment. This process was enhanced following exposure by the apical compartment to increasing concentrations of the metal. High pressure liquid chromatography fractionation of the media obtained from cells labeled with radioactive zinc showed that metallothioneins (MTs), small metal-binding, cysteine-rich proteins), were present in the apical and basal media of controls as well as in cells grown in the presence of high concentrations of zinc. Following exposure to the metal, the levels of Zn-MTs in the apical medium increased, while in the basal compartment the greatest part of zinc appeared in a free form with minor changes in the levels of basal MTs. Metabolic labeling experiments with radioactive cysteine confirmed the apical secretion of MTs. A stable transfectant clone of Caco-2 cells (CL11) was selected for its ability to express constitutively high levels of the mouse metallothionein I protein. This cell line showed an enhanced transport of the metal following exposure to high concentrations of zinc and a constitutive secretion of the mouse metallothionein I protein in the apical compartment. Together, these findings strongly support the hypothesis of a functional role between the biosynthesis and secretion of MTs and the transport of zinc in intestinal cells.

Assembly of the CD8alpha/p56(lck) protein complex in stably expressing rat epithelial cells

We have previously characterized the biogenesis of the human CD8alpha protein expressed in rat epithelial cells. We now describe the biosynthesis, post-translational maturation and hetero-oligomeric assembly of the human CD8alpha/p56(lck) protein complex in stable transfectants obtained from the same cell line. There were no differences in the myristilation of p56(lck), or in the dimerization, O-glycosylation and transport to the plasma membrane of CD8alpha, between cells expressing either one or both proteins. In the doubly expressing cells, dimeric forms of CD8alpha established hetero-oligomeric complexes with p56(lck), as revealed by co-immunoprecipitation assays performed with anti-CD8alpha antibody. Moreover, p56(lck) bound in these hetero-oligomeric complexes was endowed with auto- and hetero-phosphorylating activity. The present study shows that: (1) the newly synthesized p56(lck) binds rapidly to CD8alpha and most of the p56(lck) is bound to CD8alpha at steady state; (2) CD8alpha/p56(lck) protein complexes are formed at internal membranes as well as at the plasma membrane; and (3) about 50% of complexed p56(lck) reaches the cell surface.

Sequence and expression of the monkey homologue of the ER-golgi intermediate compartment lectin, ERGIC-53

We obtained the cDNA sequence of the monkey homologue of the intermediate compartment protein ERGIC-53 by both cDNA library screening and RT-PCR amplification. The final sequence of 2422 nts of the monkey ERGIC-53 cDNA is 96.2% identical to the human ERGIC-53 cDNA and 87% and 67% identical to the rat and amphibian cDNA, respectively. The translated CV1 ERGIC-53 protein is 96.47% identical to the human ERGIC-53, 87% identical to the rat p58 and 66. 98% to the Xenopus laevis protein. Southern blot analysis of multiple genomic DNAs shows the presence of sequences similar to ERGIC-53 in different species. ERGIC-53 is expressed as a major transcript of about 5.5 kb in either monkey CV1 or in human CaCo2. A shorter transcript of 2.3 kb was detected in both cell lines and in mRNAs derived from human pancreas and placenta.

Regulation of ZiRF1 and basal SP1 transcription factor MRE-binding activity by transition metals

The metal-dependent activation of metallothionein (MT) genes requires the interaction of positive trans-activators (MRFs) with metal-regulatory (MRE) regions of MT promoters. In this report, we examined the role of transition metals in modulating the MRE-binding activities of two different MRE-binding proteins: the metal-regulated factor ZiRF1 and the basal factor SP1. We showed the ability of both proteins to interact with a similar sequence specificity with the cognate target site (MRE-S) of another known MRE-binding protein, mMTF1. We next evaluated the role of metal ions in modulating the MRE-binding activity of recombinant ZiRF1 and basal SP1 proteins by measuring the effect of different metal chelators on DNA interaction. We observed a dose-dependent inhibition of the GST-ZiRF1/MRE-binding activity using three different metal chelators: EDTA, 1,10 PHE and TPEN. Interestingly, EDTA treatment failed to inhibit the recombinant SP1 MRE-binding activity while the effect of 1,10 PHE was comparable to that obtained analyzing 1,10 PHE-treated GST-ZiRF1. The MRE-binding complexes detected in cell extracts showed a response to metal chelator treatment very similar to that displayed by the recombinant ZiRF1 and SP1 proteins. The hypothesis of mutual interactions of both basal and metal-regulated transcription factors with the same metal-regulatory regions is discussed.

Interactions of the zinc-regulated factor (ZiRF1) with the mouse metallothionein Ia promoter

A mouse cDNA clone, M96, encoding a metal-regulating-element (MRE)-binding protein, was analysed for its ability to act as a metal-regulated transcription factor. The metal depletion of a glutathione S-transferase (GST)-M96 fusion protein showed that Zn2+ ions modulate the MRE-binding activity, suggesting that the M96-encoded protein is a Zn2+-regulated factor (ZiRF1). The methylation interference assay showed the specific interactions of ZiRF1 with the MRE, MREd/c, present on the mouse metallothionein Ia promoter. Point mutations of the MREd/c nullified the metal-regulatory properties of this region. In mouse L-cell nuclear extracts, mobility-shift assays revealed a Zn2+-dependent MRE-binding complex (MBC) with DNA-recognition properties similar to those of ZiRF1. Antibodies raised against purified GST-ZiRF1 were able to specifically recognize MBC in Western-blot analyses. Competition analysis of MRE-binding proteins from mouse NIH3T3 cells with oligonucleotide matching the binding sites for SP1 and MTF1 confirmed that both the basal SP1 and the metal-regulated MBC/ZiRF1 interact with the MREd/c region. The significance of mutual interactions with the metal-responsive promoter regions of either metal-regulated or basal transcription factors is discussed.

Analysis of metal-regulated metallothionein and heat shock gene expression in HeLa-derived cadmium-resistant cells

The expression of metallothionein (MT) and heat shock protein gene families was investigated in normal and in HeLa-derived cadmium-resistant cells, named H454. In the absence of amplification of MT genes H454 cells accumulated elevated concentrations of cadmium ions and synthesized higher levels of MT proteins than unselected HeLa cells. Northern blot analyses revealed higher levels of MT mRNAs in the resistant cells than in wild-type cells after Cd2+ and Zn2+ exposure. Evaluation of the cytotoxic potential of the different metals confirmed the high resistance to cadmium of the H454 cells. Two proteins of the heat shock family, hsp70 and GRP78, were synthesized in Cd(2+)-exposed H454 cells at levels comparable to the ones present in Cd(2+)-treated normal cells. Northern blot analyses of the mRNA levels corresponding to these proteins revealed elevated expression of both hsp70 and GRP78 mRNAs in H454 cells upon exposure to cadmium ions and no response to zinc induction. These data suggest the existence in the H454 cells of a cadmium-specific pathway of regulation of MT and heat shock genes.

Isolation of a cDNA encoding a metal response element binding protein using a novel expression cloning procedure: the one hybrid system

A new method for isolation of cDNA clones encoding sequence-specific DNA-binding proteins is described. This method, the one-hybrid system, is based on the use of reporter genes whose transcription can be activated through synthetic cis elements recognized by the sought-after DNA-binding protein. These reporter genes are used for in vivo screening of a library of cDNAs fused to a DNA fragment encoding the GAL4 activation domain. cDNA clones expressing the appropriate fusion proteins lead to activation of these reporter genes in transformed yeast cells. We have used this approach to isolate a mammalian cDNA clone encoding a sequence-specific DNA-binding protein that recognizes the metal response elements (MREs) of the metallothionein (MT) genes. The protein encoded by this cDNA, M96, shows similarity to the trithorax proteins. Expression of a functional DNA-binding form of M96 requires Zn2+ ions. The recombinant protein binds to several different MREs but fails to recognize nonfunctional mutant MREs. M96 may be involved in the activation of MT genes in response to heavy-metal ions.

Interactions of nuclear proteins from uninduced, induced and superinduced HeLa cells with metal regulatory elements MRE3 and 4 of the human metallothionein IIa-encoding gene

Transcriptional activation of metallothionein (MT)-encoding genes(MT) is regulated during heavy metal induction by short non-identical repeats, termed 'metal regulatory elements' (MRE), present in multiple imperfect copies in MT promoter regions of eukaryotes. Using mobility shift assays, we have studied the interaction between the human MRE 3 and 4 regions (hMRE3/4) of the MTIIa promoter and nuclear proteins from uninduced and Cd(2+)-induced HeLa cells, and from Cd(2+)-superinduced H454 cells, a HeLa-derived Cd(2+)-resistant cell isolate which overexpresses hMTIIa after exposure to metal. A specific complex with a similar electrophoretic mobility was formed in all three extracts. Dialysis of the extracts using EDTA inhibited the formation of the complexes, which could be reconstituted only after the addition of Zn2+. UV cross-linking analyses of the specific complexes formed by the three nuclear extracts interacting with the hMRE3/4 region revealed that in all of them polypeptides were present having similar electrophoretic mobilities and different molecular masses. Mobility shift assays showed no major differences in the binding of nuclear proteins from induced or uninduced cells. Proposed models of activation of metal-induced MT transcription are discussed.

Serum beta 2-microglobulin levels and p24 antigen, lymphocyte depletion and disease progression in human immunodeficiency virus infection

Abnormally elevated serum beta 2-microglobulin levels have been associated with progression of human immunodeficiency virus disease. In this study we have analyzed the relationship between serum beta 2-microglobulin levels of patients at different stages of the disease and serological and immunological parameters commonly used for monitoring the infection. The investigation was performed on 150 patients and 30 controls during the period from March 1989 to March 1990. At that time, 30 patients had the acquired immunodeficiency syndrome or its related complex and 120 had persistent generalized lymphadenopathy or were asymptomatic. Thirty-nine antibody-negative subjects, belonging to a high-risk group for the acquired immunodeficiency syndrome, were used as controls. All patients had normal renal function. There was a significant relationship between increased serum beta 2-microglobulin levels and the presence of p24 antigen, a decrease in the total number of lymphocytes (less than or equal to 1500/mm3) and a decrease in CD4+ T lymphocytes (less than or equal to 200/mm3). No significant relationship between serum beta 2-microglobulin levels and CD3+ T lymphocytes was found.

A nuclear factor binds to the metal regulatory elements of the mouse gene encoding metallothionein-I

The ability of vertebrate metallothionein (MT) genes to be induced by heavy metals is controlled by metal regulatory elements (MREs) present in the promoter in multiple, non-identical copies. The binding specificity of the mouse L-cell nuclear factor(s) that interact with the element MREd of the mouse MT-I gene was analyzed by in vitro footprinting, protein blotting, and UV cross-linking assays. In vitro footprinting analyses revealed that synthetic oligodeoxynucleotides (oligomers) corresponding to the metal regulatory elements MREa, MREb, MREc, MREd and MREe of the mouse MT-I gene, as well as the MRE4 of the human MT-IIA gene and the MREa of the trout MT-B gene, all competed for the nuclear protein species binding to the MREd region of the mouse MT-I gene, the MREe oligomer being the weakest competitor. In addition, protein blotting experiments revealed that a nuclear protein of 108 kDa, termed metal element protein-1 (MEP-1), which specifically binds with high affinity to mouse MREd, binds with different affinities to the other mouse MRE elements, mimicking their relative transcriptional strength in vivo: MREd greater than or equal to MREa = MREc greater than MREb greater than MREe greater than MREf. Similarly, human MRE4 and trout MREa bind to MEP-1. A protein similar in size to MEP-1 was also detected in HeLa-cell nuclear extracts. In UV cross-linking experiments the major protein species, complexed with mouse MREd oligomers, migrated on a denaturating gel with an apparent Mr of 115,000 and was detected using each of the mouse MRE oligomers tested. These results show that a mouse nuclear factor can bind to multiple MREs in mouse, trout, and human MT genes.

In vitro activation of isophosphamide and trophosphamide to metabolites mutagenic for bacteria

The ability of S9 liver fractions from uninduced rats to activate isophosphamide (IP) and trophosphamide (TP) to metabolites mutagenic for bacteria was compared to that of S9 fractions prepared from rats pretreated in vivo with three inducers of hepatic monooxygenase. Pretreatment of rats with phenobarbital (PB) and Aroclor 1254 increased IP and TP mutagenic activation by S9 fractions as compared to control and 3-methylcholanthrene (3-MC)-induced rat liver S9. Furthermore, the effect of mixed-function oxidase inhibitors, such as alpha-naphthoflavone, metyrapone and SKF 525-A on S9-mediated mutagenic activation of IP and TP was investigated. The data obtained suggest the involvement of a PB-inducible form of cytochrome P-450 in the activation of IP and TP to mutagenic species.

[Hematologic characterization and analysis of genetic transmission in a case of double heterozygosity Hb Lepore/beta-thalassemia]

Double heterozygosis condition for hemoglobin variants induce clinical syndromes known as intermediate thalassemias. Their diagnosis is often of certain difficulty because of their low frequency and heterogeneity of clinical expressions. We report a case of a 4 year child admitted to our medical center with a story of hepatosplenomegaly. An appropriate hematological study on patient's family permitted a diagnosis of double heterozygosis for Hb Lepore and beta-thalassemia. Results of hematological investigation are reported.

[Toxic genetic effects of flunitrazepam]

The mutagenic activity of Flunitrazepam, the active ingredient of the drug Rohypnol, has been investigated by using the Salmonella/microsome mutagenicity test. A dose-related mutagenic effect was observed on Salmonella typhimurium strain TA 100 either in the absence or in the presence of a rat liver microsomal fraction (S9) as in vitro metabolic activation system. By adopting a modification of the Salmonella test, the mutagenicity of urines from rats or patients treated with the drug was evaluated. In these cases mutagenic activity was detected toward the Salmonella strains TA 98 and TA 100 both in presence and in absence of the metabolic activation system. The data indicate that Flunitrazepam and/or its urinary metabolites can induce both base-pair substitutions or frame-shift point mutations.