Major Vault Protein Promotes Hepatocellular Carcinoma Through Targeting Interferon Regulatory Factor 2 and Decreasing p53 Activity.

BACKGROUND AND AIMS: Major vault protein (MVP) is up-regulated during infections with hepatitis B virus (HBV) and hepatitis C virus (HCV). Here, we found that MVP deficiency inhibited hepatocellular carcinoma (HCC) development induced by diethylnitrosamine, hepatitis B X protein, and HCV core. APPROACH AND RESULTS: Forced MVP expression was sufficient to induce HCC in mice. Mechanistic studies demonstrate that the ubiquitin ligase human double minute 2 (HDM2) forms mutual exclusive complexes either with interferon regulatory factor 2 (IRF2) or with p53. In the presence of MVP, HDM2 is liberated from IRF2, leading to the ubiquitination of the tumor suppressor p53. Mouse xenograft models showed that HBV and HCV promote carcinogenesis through MVP induction, resulting in a loss of p53 mediated by HDM2. Analyses of clinical samples from chronic hepatitis B, liver cirrhosis, and HCC revealed that MVP up-regulation correlates with several hallmarks of malignancy and associates with poor overall survival. CONCLUSIONS: Taken together, through the sequestration of IRF2, MVP promotes an HDM2-dependent loss of p53 that promotes HCC development.

Major vault protein plays important roles in viral infection.

Viral replication and related protein expression inside the host cells, and host antiviral immune responses can lead to the occurrence of diverse diseases. With the outbreak of viral infection, a large number of newly diagnosed and died patients infected with various viruses are still reported every year. Viral infection has already been one of the major global public health issues and lead to huge economic and social burdens. Studying of viral pathogenesis is a very important way to find methods for prevention, diagnosis, and cure of viral infection; more evidence has confirmed that major vault protein (MVP) is closely associated with viral infection and pathogenesis, and this review is intended to provide a broad relationship between viruses and MVP to stimulate the interest of related researchers.

Immunoregulatory protein B7-H3 regulates cancer stem cell enrichment and drug resistance through MVP-mediated MEK activation.

B7-H3 is a tumor-promoting glycoprotein that is expressed at low levels in most normal tissues, but is overexpressed in various human cancers which is associated with disease progression and poor patient outcome. Although numerous publications have reported the correlation between B7-H3 and cancer progression in many types of cancers, mechanistic studies on how B7-H3 regulates cancer malignancy are rare, and the mechanisms underlying the role of B7-H3 in drug resistance are almost unknown. Here we report a novel finding that upregulation of B7-H3 increases the breast cancer stem cell population and promotes cancer development. Depletion of B7-H3 in breast cancer significantly inhibits the cancer stem cells. By immunoprecipitation and mass spectrometry, we found that B7-H3 is associated with the major vault protein (MVP) and activates MEK through MVP-enhancing B-RAF and MEK interaction. B7-H3 expression increases stem cell population by binding to MVP which regulates the activation of the MAPK kinase pathway. Depletion of MVP blocks the activation of MEK induced by B7-H3 and dramatically inhibits B7-H3 induced stem cells. This study reports novel functions of B7-H3 in regulating breast cancer stem cell enrichment. The novel mechanism for B7-H3-induced stem cell propagation by regulating MVP/MEK signaling axis independent of the classic Ras pathway may have important implications in the development of strategies for overcoming cancer cell resistance to chemotherapy.

The major vault protein mediates resistance to epidermal growth factor receptor inhibition in human hepatoma cells.

To better understand the response of HCC to EGFR inhibition, we analyzed factors connected to the resistance of HCC cells against gefitinib. Sensitive HCC3 cells co-expressed EGFR and ErbB3 but lacked kinase-domain mutations in EGFR. Interestingly, expression of MVP was restricted to resistant cell lines, whereas ABCB1 and ABCC1 showed no association with gefitinib resistance. Moreover, ectopic MVP expression in HCC3 cells decreased gefitinib sensitivity, increased AKT phosphorylation and reduced the expression of inflammatory pathway-associated genes, whereas silencing of MVP in Hep3B and HepG2 cells increased sensitivity. These findings suggest MVP as a novel player in resistance against EGFR inhibition.

Función dinámica de los músculos peroneus en apoyo unipodal / Dynamic function of fibular muscles during the unipodal support stage

Los autores hacen una descripción, adentrándose en la fisiología articular, del movimiento de las articulaciones del pie en general y del tobillo en particular. Analizan la acción de los dos músculos retromaleolares, peroneo lateral largo (PLL) y peroneo lateral corto (PLC) cuando el pie está apoyado en el suelo durante el movimiento lineal, marcha y carrera. Describen las ventajas mecánicas que propicia la ubicación, trayecto e inserción de ambos músculos para facilitar el movimiento, tanto en la fase de apoyo unipodal, como en la fase de impulso. Para concluir afirman que es la acción en carga del pie la que ha solicitado de todas las modificaciones mecánicas necesarias, en el complejo articular del tobillo, para economizar al máximo el gasto energético, utilizando como ejemplo la acción de los músculos PLL y PLC (AU)

The authors carry out a description of foot joints movement and more particularly of the ankle joint one, taking into account the joint physiology. They analyse the action of retromalleolar muscles, peroneus longus (PLL) and peroneus brevis (PLC), during the unipodal phase of linear movement (running and walking). The mechanical advantage in the movement as result of location, trajectory and insertion of muscles are described for both the unipodal support and impulse phases. In order to conclude, the writers argue that mechanical modifications of ankle joint during the human evolution process have been conditioned by the foot load force and energy consumption reduction principle. They use as example PLL and PLC muscles (AU)

Implications of anthracycline-resistant and taxane-resistant metastatic breast cancer and new therapeutic options.

Patients with advanced or metastatic breast cancer commonly develop disease resistant to chemotherapy (typically anthracyclines and taxanes), which presents a major obstacle to therapy and leaves few effective treatment options. Drug resistance can occur due to various mechanisms including modification of drug efflux membrane transporters such as P-glycoprotein, as well as alterations in beta-tubulin. The novel epothilone B analog, ixabepilone, which has low susceptibility to various drug-resistance mechanisms, has demonstrated preclinical activity in drug-resistant breast cancer. The clinical activity of ixabepilone was evaluated in metastatic breast cancer patients with highly pretreated and/or resistant/refractory disease. Results were reviewed from three phase II trials in which ixabepilone was administered as monotherapy and one phase III trial that evaluated ixabepilone in combination with capecitabine. As a single agent, ixabepilone demonstrated activity in women who were heavily pretreated and resistant to an anthracycline, a taxane, and/or capecitabine. The combination of ixabepilone and capecitabine was significantly more active than capecitabine alone in patients with prior treatment or resistance to anthracyclines and taxanes. Treatment-related adverse events were generally low grade except for grade 3/4 toxicities, including neutropenia (53-54%) and reversible peripheral sensory neuropathy (14-16%). Ixabepilone has significant activity in patients with heavily pretreated metastatic breast cancer who are disease resistant or refractory to anthracyclines and taxanes. Further clinical evaluation of this agent in patients with drug-resistant breast cancer and in specific patient subsets is warranted.

The non-coding RNA of the multidrug resistance-linked vault particle encodes multiple regulatory small RNAs.

Vault particles are conserved organelles implicated in multidrug resistance and intracellular transport. They contain three different proteins and non-coding vault RNAs (vRNAs). Here we show that human vRNAs produce several small RNAs (svRNAs) by mechanisms different from those in the canonical microRNA (miRNA) pathway. At least one of these svRNAs, svRNAb, associates with Argonaute proteins to guide sequence-specific cleavage and regulate gene expression similarly to miRNAs. We demonstrate that svRNAb downregulates CYP3A4, a key enzyme in drug metabolism. Our findings expand the repertoire of small regulatory RNAs and assign, for the first time, a function to vRNAs that may help explain the association between vault particles and drug resistance.

Targeting major vault protein in senescence-associated apoptosis resistance.

BACKGROUND: Recent studies have shown that major vault protein (MVP) is involved in intracellular signaling, cell survival, differentiation and innate immunity and that it is not directly responsible for nucleo-cytoplasmic drug transport in multi-drug-resistant cancer cell lines. Recently, we reported that MVP increases with age both in vitro and in vivo, and that age-related upregulation of MVP facilitates apoptosis resistance of senescent human diploid fibroblasts (HDFs) based on the interaction with c-Jun-mediated downregulation of bcl-2. OBJECTIVES: To discuss the role of MVP in cell survival and signaling in the development of resistance to apoptosis exhibited by senescent HDFs. CONCLUSIONS: MVP represents a versatile platform for regulation of cellular signaling and survival and is a potential therapeutic target for modulation of resistance to apoptosis, implicated in aging modulation and cancer treatment.

Imatinib is a substrate for various multidrug resistance proteins.

UNLABELLED: An increasing resistance to imatinib is an emerging problem in patients with chronic myeloid leukemia (CML). The aim of the study was to asses mechanisms related to cellular drug resistance in imatinib-resistant derivates of chronic myeloid leukemia K-562 cell line. A parental K-562 and its imatinib-resistant derivate cell lines were used. Cell lines were tested for cytotoxicity of imatinib, cytarabine, busulfan and etoposide by the MTT assay. The cytotoxicity was expressed as IC50, inhibitory concentration for 50% of cells. Multidrug resistance proteins expression, rhodamine retention and daunorubicin accumulation were measured for each cell line. Continuous exposition of K-562 cell line to 0.01-0.02 mM imatinib resulted in development of resistance, while exposition to 0.1 microM imatinib increased cell sensitivity to this drug. There was a high correlation between PGP, MRP1 and LRP expression and IC50 values for imatinib and etoposide. All tested cell lines were highly resistant to cytarabine. Rhodamine retention alone and in the presence of cyclosporine was the lowest in imatinib-resistant K-562R-0.1 cell line, what suggest high PGP activity in this cell line. The highest daunorubicin accumulation was observed in parental K-562 cell line, while it was lower in imatinib-resistant cell lines. These data suggest that imatinib is a substrate for multidrug resistance proteins, and an increased expression of PGP, MRP1 and LRP play a role in resistance to imatinib in CML. KEYWORDS: imatinib, multidrug resistance proteins, chronic myeloid leukemia, PGP, MRP1, LRP.

Vaults and the major vault protein: novel roles in signal pathway regulation and immunity.

The unique and evolutionary highly conserved major vault protein (MVP) is the main component of ubiquitous, large cellular ribonucleoparticles termed vaults. The 100 kDa MVP represents more than 70% of the vault mass which contains two additional proteins, the vault poly (ADP-ribose) polymerase (vPARP) and the telomerase-associated protein 1 (TEP1), as well as several short untranslated RNAs (vRNA). Vaults are almost ubiquitously expressed and, besides chemotherapy resistance, have been implicated in the regulation of several cellular processes including transport mechanisms, signal transmissions and immune responses. Despite a growing amount of data from diverse species and systems, the definition of precise vault functions is still highly complex and challenging. Here we review the current knowledge on MVP and vaults with focus on regulatory functions in intracellular signal transduction and immune defence.

Chemoresistance in gliomas.

Despite improved knowledge and advanced treatments of gliomas, the overall survival rate for glioma patients remains low. Gliomas comprise of significant cell heterogeneity that contains a large number of multidrug resistant (MDR) phenotypes and cancer stem cells (CSCs), a combination that may contribute to the resistance to treatment. This article reviews the MDR related genes, major-vault protein (MVP), anti-apoptotic protein (Bcl-2) and the molecular mechanisms that may contribute to chemoresistance, in addition to the upregulated MDR phenotypes present in CSCs that has recently been identified in gliomas. Moreover, future potential therapies that modulate MDR phenotypes and CSCs are also reviewed. An improved understanding of MDR may lead to a combined treatment, targeting both CSCs and their protective MDR phenotypes leading eventually to attractive strategies for the treatment of gliomas.

Host resistance to lung infection mediated by major vault protein in epithelial cells.

The airway epithelium plays an essential role in innate immunity to lung pathogens. Ribonucleoprotein particles primarily composed of major vault protein (MVP) are highly expressed in cells that encounter xenobiotics. However, a clear biologic function for MVP is not established. We report here that MVP is rapidly recruited to lipid rafts when human lung epithelial cells are infected with Pseudomonas aeruginosa, and maximal recruitment is dependent on bacterial binding to the cystic fibrosis transmembrane conductance regulator. MVP was also essential for optimal epithelial cell internalization and clearance of P. aeruginosa. These results suggest that MVP makes a substantial contribution to epithelial cell-mediated resistance to infection.

Role of chemotherapy resistance genes in outcome of neuroblastoma.

BACKGROUND: Neuroblastoma is a heterogeneous pediatric disease. Most patients with localized disease usually have a favorable prognosis, but patients with advanced disease have a poor prognosis despite combination chemotherapy. Treatment failure may be attributable to resistance to cytotoxic drugs. PROCEDURE: Using quantitative RT-PCR, we investigated the clinical significance of the level of mRNA expression of multidrug resistance genes (MDR1, MRP1, MRP5, LRP) in a series of 29 advanced neuroblastoma samples. RESULTS: At the end of induction chemotherapy, 48% of patients achieved a clinical complete response, 28% achieved a partial response or stable disease, and 24% presented progressive disease. MDR1 mRNA overexpression (i.e., mRNA level >2 copies of MDR1 gene) was observed in 74% of samples, and MRP1, MRP5, LRP overexpression was observed less frequently (30, 33, and 33% of samples, respectively). None of these parameters were predictive of response, relapse, or survival. However, clinical response to treatment was highly predictive of relapse-free survival and overall survival. CONCLUSIONS: High expression of these multidrug resistance genes in advanced neuroblastoma is not the main parameter of response to cytotoxic drugs; clinical response to treatment remains the most important parameter in predicting the prognosis of patients with advanced neuroblastoma, until other relevant laboratory parameters have been identified.

Movement of vault particles visualized by GFP-tagged major vault protein.

Vaults are abundant large ribonucleoprotein particles. They frequently colocalize with microtubules and accumulate in filamentous actin-rich lamellipodia. To examine the movement of vaults in living cells, a chimera between the green fluorescent protein and the major vault protein was created. This fusion protein assembled into vault particles as assayed by biochemical fractionation and direct observation of living or fixed cells. By fluorescence recovery after photobleaching, we analyzed the bulk transport of vault particles into neuritic tips of PC12 cells treated with nerve growth factor. Confocal laser scanning microscopy demonstrated co-localization of the major vault protein and microtubules. Video microscopy indicated that, whereas the majority of vault particles were stationary, some individual vault particles moved rapidly, consistent with the action of a microtubule-based or actin-based molecular motor.

Major vault protein, in concert with constitutively photomorphogenic 1, negatively regulates c-Jun-mediated activator protein 1 transcription in mammalian cells.

Constitutively photomorphogenic 1 (COP1), a RING finger ubiquitin ligase with substrates including c-Jun and p53, was recently found to be overexpressed in a number of breast and ovarian tumor samples. In addition to its E3 activity, COP1 was also shown to be able to inhibit activator protein 1 (AP-1) transcription. Through an affinity purification method, we have identified major vault protein (MVP) as a novel interacting partner for COP1 in mammalian cells. MVP, also known as lung resistance protein, is the main component of a ribonucleoprotein organelle called vault, and has been implicated in multiple drug resistance in many cancer cell lines and primary tumor samples. The interaction between COP1 and MVP is detectable at the endogenous level and occurs mostly in the cytoplasm. Similar to COP1, MVP inhibits c-Jun accumulation and AP-1 transcription activity. MVP knockout or knockdown cells contain elevated amount of c-Jun and increased AP-1 transcription activity. UV irradiation enhances MVP tyrosine phosphorylation, causes dissociation of COP1 from MVP, and alleviates the inhibitory activity of MVP on AP-1 transcription. Taken together, we propose that MVP, most likely through its interaction with COP1, suppresses c-Jun-mediated AP-1 transcription under unstressed conditions, thereby preventing cells from undergoing stress response.

Major vault protein does not play a role in chemoresistance or drug localization in a non-small cell lung cancer cell line.

The human major vault protein (MVP) is the primary component of the 13 MDa vault complex. MVP has been implicated in the development of non-P-glycoprotein-mediated drug resistance in cancer cells. Here we present several lines of evidence that dispute this assertion. siRNAs capable of specifically and efficiently knocking down expression of MVP do not alter the ability of resistant cells to remove doxorubicin from the nucleus and do not increase sensitivity to the drug. Conversely, upregulation of MVP in chemosensitive cells does not confer increased drug resistance. In multi-drug resistant (MDR) lung carcinoma cells, fluorescence microscopy reveals that doxorubicin enters the nucleus and is then removed, inconsistent with suggestions that vaults either act to prevent the drug from entering the nucleus or are involved as a nuclear efflux pump. These data suggest that vaults play no direct role in the MDR phenotype in non-small cell lung carcinoma cells and that their cellular function remains unknown. These results also have important implications concerning the value of MVP as a drug target and as a prognostic marker for chemotherapy failure. Our results suggest the need for further investigation into the link between upregulation of vaults and malignancy, the mechanism behind non-P-gp-mediated drug resistance, and the role of vaults in human cells.

SP-transcription factors are involved in basal MVP promoter activity and its stimulation by HDAC inhibitors.

The major vault protein (MVP) has been implicated in multidrug resistance, cellular transport, and malignant transformation. In this study we aimed to identify crucial MVP promoter elements that regulate MVP expression. By mutation as well as deletion analysis a conserved proximal GC-box element was demonstrated to be essential for basal human MVP promoter transactivation. Binding of Sp-family transcription factors but not AP2 to this element in vitro and in vivo was shown by EMSA and ChIP assays, respectively. Inhibition of GC-box binding by a dominant-negative Sp1-variant and by mithramycin A distinctly attenuated MVP promoter activity. In Sp-null Drosophila cells, the silent human MVP promoter was transactivated by several human Sp-family members. In human cells the MVP promoter was potently stimulated by the histone deacetylase (HDAC) inhibitors butyrate (NaB) and trichostatin A (TSA), resulting in enhanced MVP expression. This stimulation was substantially decreased by mutation of the single GC-box and by application of mithramycin A. Treatment with HDAC inhibitors led to a distinct decrease of Sp1 but increase of Sp3 binding in vivo to the respective promoter sequence as demonstrated by ChIP assays. Summarising, this study identifies variations in Sp-transcription factor binding to a single proximal GC-box element as critical for basal MVP promoter activation and its stimulation by HDAC inhibitors.

[Multidrug resistance mediated by membrane P-glycoprotein in acute myeloid leukemia].

A key issue in the treatment of acute leukemia is the development of resistance to chemotherapeutic drugs. Several mechanisms may account for this phenomenon, including failure of the cell to undergo apoptosis in response to chemotherapy, or failure of the drug to reach and/or affect its intracellular target. This review focuses on the latter mechanisms, and on intracellular drug transport resistance mechanisms in particular. Expression of the ATP-binding cassette (ABC) transporter P-glycoprotein (P-gp) has generally been reported to correlate with prognosis in acute myeloid leukemia (AML). Additionally, of more controversial, expression of the ABC transporter multidrug resistance protein (MRP) and the vault-transporter lung resistance protein (LRP) have been correlated with the outcome in AML.