Cloning and initial analysis of the human multidrug resistance-related MVP/LRP gene promoter

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Y-box binding protein 1 (YB-1) promotes gefitinib resistance in lung adenocarcinoma cells by activating AKT signaling and epithelial-mesenchymal transition through targeting major vault protein (MVP)

PURPOSE

Gefitinib is a first-line treatment option for epidermal growth factor receptor (EGFR)-mutated lung adenocarcinoma. However, most patients inevitably develop gefitinib resistance. The mechanism underlying this resistance is not fully understood. Y-box binding protein 1 (YB-1) has been reported to play a role in modulating drug sensitivity, but its role in gefitinib resistance is currently unknown. Here, we investigated the role of YB-1 in gefitinib resistance of lung adenocarcinoma.

METHODS

We determined the expression of YB-1, epithelial-mesenchymal transition (EMT) and AKT signaling markers, as well as the viability of lung adenocarcinoma cell lines bearing mutant (HCC827, PC-9) or wild-type (H1299) EGFR. We also evaluated PC-9 cell migration and invasion using transwell assays. The clinical importance of YB-1 and major vault protein (MVP) was evaluated using primary lung adenocarcinoma patient samples.

RESULTS

We found that YB-1 was significantly upregulated in gefitinib-resistant lung adenocarcinoma cells compared to gefitinib-sensitive cells. YB-1 augmented gefitinib resistance by activating the AKT pathway and promoting EMT. Decreased migration and invasion was observed upon MVP silencing in YB-1-overexpressing PC-9 cells, as well as restored gefitinib sensitivity. A retrospective analysis of 85 patients with lung adenocarcinoma revealed that YB-1 levels were significantly increased in tyrosine kinase inhibitor (TKI)-resistant patients compared to those in TKI-sensitive patients, indicating that YB-1 may serve as a biomarker to clinically predict acquired gefitinib resistance.

CONCLUSION

YB-1 activates AKT signaling and promotes EMT at least in part by directly activating MVP. Hence, targeting the YB-1/MVP axis may help to overcome gefitinib resistance in lung adenocarcinoma patients.

Major vault protein suppresses lung cancer cell proliferation by inhibiting STAT3 signaling pathway

Background

Major vault protein (MVP) is the major component of vault, a eukaryotic organelle involved in multiple cellular processes, and is important in multiple cellular processes and diseases including the drug resistance in cancer chemotherapies. However, the role of MVP in lung cancer remains unclear.

Methods

We examined MVP expression in 120 non-small cell lung cancer (NSCLC) tumors and matched normal tissues by immunohistochemistry. Its relationship with NSCLC prognosis was determined by investigating the patient cohort and analyzing the data from a published dataset consisting with more than 1900 lung cancer patients. We further performed shRNA-introduced knockdown of MVP in Lewis lung carcinoma (LLC) cells and examined its effects on the tumor formation in a xenograft mouse model and the tumor cell proliferation, apoptosis, and signal transduction in vitro.

Results

We found that MVP was up-regulated significantly in tumor tissues compared with the matched tumor-adjacent normal tissues. The increased expression of MVP in lung adenocarcinoma was associated with a better prognosis. Knockdown of MVP in LLC cells promoted xenografted lung cancer formation in mice, which was accompanied with accelerated tumor cell proliferation and suppressed cell apoptosis in vitro. Knockdown of MVP stimulated STAT3 phosphorylation, nuclear localization, and activation of JAK2 and RAF/MEK/ERK pathways in LLC cells. Administration of STAT3 inhibitor WP1066 could prevent MVP knockdown induced tumorigenesis.

Conclusions

Our findings demonstrate that MVP may act as a lung tumor suppressor via inhibiting STAT3 pathway. MVP would be a potential target for novel therapies of lung adenocarcinoma.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5665-6) contains supplementary material, which is available to authorized users.

Major vault protein suppresses obesity and atherosclerosis through inhibiting IKK-NF-κB signaling mediated inflammation

Macrophage-orchestrated, low-grade chronic inflammation plays a pivotal role in obesity and atherogenesis. However, the underlying regulatory mechanisms remain incompletely understood. Here, we identify major vault protein (MVP), the main component of unique cellular ribonucleoprotein particles, as a suppressor for NF-κB signaling in macrophages. Both global and myeloid-specific MVP gene knockout aggravates high-fat diet induced obesity, insulin resistance, hepatic steatosis and atherosclerosis in mice. The exacerbated metabolic disorders caused by MVP deficiency are accompanied with increased macrophage infiltration and heightened inflammatory responses in the microenvironments. In vitro studies reveal that MVP interacts with TRAF6 preventing its recruitment to IRAK1 and subsequent oligomerization and ubiquitination. Overexpression of MVP and its α-helical domain inhibits the activity of TRAF6 and suppresses macrophage inflammation. Our results demonstrate that macrophage MVP constitutes a key constraint of NF-κB signaling thereby suppressing metabolic diseases.

Metabolic diseases are associated with chronic, low-grade inflammation. Here the authors show that major vault protein (MVP) suppresses NF-κB signalling in macrophages via an IRAK1–TRAF6 axis and that loss of MVP in myeloid cells exacerbates the inflammatory response in mice fed a high fat diet.

Regulation of major vault protein expression by upstream stimulating factor 1 in SW620 human colon cancer cells

Major vault protein (MVP) is the main constituent of the vault ribonucleoprotein particle and is identical to lung resistance-related protein (LRP). Although MVP is also expressed in several types of normal tissues, little is known about its physiological role. In the present study, we identified the crucial MVP promoter elements that regulate MVP expression. An examination of tissue expression profiles revealed that MVP was expressed in the heart, placenta, lung, liver, kidney and pancreas. Elements of the MVP promoter contain binding sites for transcription factors, STAT, p53, Sp1, E-box, GATA, MyoD and Y-box. By deletion analysis, a conserved proximal E-box binding site was demonstrated to be important for human MVP promoter transactivation. Introduction of siRNA against upstream stimulating factor (USF) 1, which is known to bind the E-box binding site, decreased the expression of MVP in SW620 and ACHN cells. Using a chromatin immunoprecipitation (ChIP) assay, USF1 bound the MVP promoter in SW620 cells. These findings suggest that USF1 binding to an E-box element may be critical for basal MVP promoter activation. The results of the present study are useful in understanding the molecular mechanisms regulating MVP gene expression, and may aid in elucidating the physiological functions of MVP.

Molecular basis for the expression of major vault protein induced by hyperosmotic stress in SW620 human colon cancer cells

Major vault protein (MVP) is identical to lung resistance-related protein (LRP), which is the major component of vaults. Vaults are considered to play a protective role against xenobiotics and other types of stress. In a previous study, we reported that the expression levels of MVP in SW620 human colon cancer cells were increased in hypertonic culture medium with sucrose. However, the molecular mechanism behind the induction of MVP expression by osmotic stress has not yet been elucidated. Therefore, in the present study, we investigated the mechanism behind the induction of MVP expression by osmotic stress. Under hyperosmotic stress conditions, the ubiquitination of specificity protein 1 (Sp1) decreased, Sp1 protein levels increased, its binding to the MVP promoter was enhanced, and small interfering RNA (siRNA) for Sp1 suppressed the induction of MVP expression. The inhibition of c-jun N-terminal kinase (JNK) by SP600125, a specific JNK inhibitor, decreased the expression of MVP and Sp1 under hyperosmotic conditions. Our data indicate that the stabilization and upregulation of Sp1 protein expression by JNK participate in the inhibition of the ubiquitination and degradation of Sp1, and thus in the induction of MVP expression under hyperosmotic conditions.

Association of nuclear YB-1 localization with lung resistance-related protein and epidermal growth factor receptor expression in lung cancer

BACKGROUND

Y-box binding protein 1 (YB-1) is an oncogenic transcription factor that is activated in response to various genotoxic stresses. The purpose of this study was to elucidate whether YB-1 correlates with the expression of lung resistance-related protein (LRP) and epidermal growth factor receptor (EGFR) in primary lung cancer.

PATIENTS AND METHODS

One hundred and five non-small-cell lung cancer (NSCLC) specimens were analyzed by immunohistochemistry. Knockdown of YB-1 messenger RNA by small interfering RNA(siRNA) was tested for the lung cancer cell lines A549 and Calu-3.

RESULTS

Nuclear YB-1 expression significantly correlated with positive LRP and EGFR expression (P < .001). Nuclear YB-1 expression and positive LRP and EGFR expression were independent adverse prognostic factors in patients with NSCLC. Furthermore, patients with tumors positive for nuclear YB-1 and LRP had a significantly worse prognosis than those negative for nuclear YB-1 and LRP (P < .001). In addition, patients with tumors positive for nuclear YB-1 and EGFR had a significantly worse prognosis than those negative for nuclear YB-1 and EGFR (P < .001). In in vitro analyses that use the NSCLC cell lines A549 and Calu-3, the downregulation of YB-1 with siRNAs drastically decreased the expression of EGFR. However, downregulation of YB-1 remarkably decreased the expression of LRP in A549 cells; however, a slight decrease in LRP was induced by the downregulation of YB-1 in Calu-3 cells.

CONCLUSION

Our data demonstrate that nuclear YB-1 localization is associated with LRP and EGFR expression in NSCLC, and nuclear YB-1 localization and LRP and EGFR expression are of prognostic significance in NSCLC.

MVP and vaults: a role in the radiation response

Vaults are evolutionary highly conserved ribonucleoproteins particles with a hollow barrel-like structure. The main component of vaults represents the 110 kDa major vault protein (MVP), whereas two minor vaults proteins comprise the 193 kDa vault poly(ADP-ribose) polymerase (vPARP) and the 240 kDa telomerase-associated protein-1 (TEP-1). Additionally, at least one small and untranslated RNA is found as a constitutive component. MVP seems to play an important role in the development of multidrug resistance. This particle has also been implicated in the regulation of several cellular processes including transport mechanisms, signal transmission and immune responses. Vaults are considered a prognostic marker for different cancer types. The level of MVP expression predicts the clinical outcome after chemotherapy in different tumour types. Recently, new roles have been assigned to MVP and vaults including the association with the insulin-like growth factor-1, hypoxia-inducible factor-1alpha, and the two major DNA double-strand break repair machineries: non-homologous endjoining and homologous recombination. Furthermore, MVP has been proposed as a useful prognostic factor associated with radiotherapy resistance. Here, we review these novel actions of vaults and discuss a putative role of MVP and vaults in the response to radiotherapy.

Lung Resistance Protein and Multidrug Resistance Protein in Non-Small Cell Lung Cancer and Their Clinical Significance

This study examined lung resistance protein (LRP) and multidrug resistance protein (MRP) in lung tumour tissue from 92 patients with non-small cell lung cancer (NSCLC) and normal lung tissue from 20 patients with benign lung tumours. The rates for LRP- and MRP-positive tumours among the NSCLC cases were 54% and 59%, respectively, and their combined positive rate was 45%. These rates were significantly higher than in normal lung tissue. The rates of LRP- and MRP-positive tumours were significantly higher among cases of adenocarcinoma than in cases of squamous cell carcinoma, and in highly differentiated tumours compared with tumours of low or moderate differentiation. There was a significant association between LRP- and MRP-positive tumours and a decrease in overall survival. In conclusion, LRP and MRP play a role in multidrug resistance in NSCLC and are related to prognosis in patients with NSCLC.

Age associated high level of major vault protein is p53 dependent

Major vault protein (MVP) represents the main component of vaults and has been linked to multi-drug resistance (MDR) in cancer cells. We previously reported that MVP plays an important role in the resistance of senescent human diploid fibroblasts (HDFs) to apoptosis and also that MVP expression is markedly reduced in young HDFs but not in senescent HDFs. In this study, designed to elucidate the regulation of MVP in young and senescent HDFs, we examined the levels of transcriptional factors for the MVP gene, which revealed that among the putative transcriptional factors, p53 decreased only in young HDFs, but not in senescent HDFs in response to H(2)O(2) treatment in the same mode as the expression of MVP. Moreover, the phosphorylation status of p53 increased only in senescent HDFs but not in young HDFs in response to H(2)O(2) treatment. Therefore, we tested the possibility of MVP regulation by p53 status. MVP is upregulated in p53 over-expressing young HDFs, while MVP is downregulated in p53-specific small interfering RNA (siRNA)-transfected senescent HDFs, which suggests that the expression of MVP would be p53 dependent. Furthermore, using chromatin immunoprecipitation (ChIP) assay, we observed that p53 binds directly to the MVP promoter. Taken together, these results suggest that p53 would be a major transcriptional factor for MVP gene expression.

Severe hypoxia induces chemo-resistance in clinical cervical tumors through MVP over-expression

Oxygen molecule modulates tumour response to radiotherapy. Higher radiation doses are required under hypoxic conditions to induce cell death. Hypoxia may inhibit the non-homologous end-joining DNA repair through down regulating Ku70/80 expression. Hypoxia induces drug resistance in clinical tumours, although the mechanism is not clearly elucidated. Vaults are ribonucleoprotein particles with a hollow barrel-like structure composed of three proteins: major vault protein (MVP), vault poly(ADP-ribose) polymerase, and telomerase associated protein-1 and small untranslated RNA. Over-expression of MVP has been associated with chemotherapy resistance. Also, it has been related to poor outcome in patients treated with radiotherapy alone. The aim of the present study was to assess the relation of Major Vault Protein expression and tumor hypoxia in clinical cervical tumors. MVP, p53 and angiogenesis, together with tumor oxygenation, were determined in forty-three consecutive patients suffering from localized cervix carcinoma. High MVP expression was related to severe hypoxia compared to low MVP expressing tumors (p = 0.022). Tumors over-expressing MVP also showed increased angiogenesis (p = 0.003). Besides it, in this study we show for the first time that severe tumor hypoxia is associated with high MVP expression in clinical cervical tumors. Up-regulation of MVP by hypoxia is of critical relevance as chemotherapy is currently a standard treatment for those patients. From our results it could be suggested that hypoxia not only induces increased genetic instability, oncogenic properties and metastatization, but through the correlation observed with MVP expression, another pathway of chemo and radiation resistance could be developed.

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.

Hyperosmotic stress up-regulates the expression of major vault protein in SW620 human colon cancer cells

The major vault protein (MVP) is the major constituent of the vault particle, the largest ribonuclear protein complex described to date and is identical to lung resistance-related protein (LRP). Although MVP is also expressed in several normal tissues, little is known about its physiological role. MVP played a protective role against some xenobiotics and other stresses. We thus investigated the effect of osmotic stress on MVP expression by treating human colon cancer SW620 cells with sucrose or NaCl. The expression level of both MVP protein and MVP mRNA was increased by the osmostress. Sucrose or sodium chloride could also enhance MVP promoter activity. Inhibition of p38 MAPK in SW620 cells by SB203580 inhibited the expression of MVP under hyperosmotic stress. These findings suggested that osmotic stress up-regulated the MVP expression through p38 MAPK pathway. Down-regulation of MVP expression by MVP interfering RNA (RNAi) in SW620 cells increased the sensitivity of the cells to hyperosmotic stress and enhanced apoptosis. Furthermore, MVP RNAi prevented the osmotic stress-induced, time-dependent increase in phosphorylated Akt. These findings suggest that the PI3K/Akt pathway might be implicated in the cytoprotective effect of MVP. Our data demonstrate that exposure of cells to hyperosmotic stress induces MVP that might play an important role in the protection of the cells from the adverse effects of osmotic stress.

The major vault protein is responsive to and interferes with interferon-γ-mediated STAT1 signals

The major vault protein (MVP) is the main component of vaults, large ribonucleoprotein particles implicated in the regulation of cellular signaling cascades and multidrug resistance. Here, we identify MVP as an interferon γ (IFN-γ)-inducible protein. Treatment with IFN-γ resulted in a significant upregulation of MVP promoter activity as well as mRNA and protein levels. Activation of MVP expression by IFN-γ involved transcriptional upregulation through the JAK/STAT pathway based on an interaction of STAT1 with an interferon-γ-activated site (GAS) within the proximal MVP promoter. Mutation of this site distinctly reduced basal as well as IFN-γ-stimulated MVP transcription. IFN-γ also significantly enhanced the translation rate of MVP. Ectopic MVP overexpression in the MVP-negative lung cancer cell model H65 led to a downregulation of three known IFN-γ-regulated genes, namely ICAM-1, CD13 and CD36. Additionally, presence of MVP in H65 cells blocked both basal and IFN-γ-induced ICAM-1 expression whereas downmodulation of endogenous MVP levels by shRNA enhanced IFN-γ-induced ICAM-1 expression in U373 glioblastoma cells. MVP-mediated IFN-γ insensitivity was accompanied by significantly reduced STAT1 phosphorylation at Y701 and diminished translocation of STAT1 into the nucleus. Summarizing, we identify MVP as an IFN-γ-responsive gene interfering with IFN-γ-activated JAK/STAT signals. These data further substantiate that the vault particle functions as a general interaction platform for cellular signaling cascades.

Inhibiting gene expression at transcription start sites in chromosomal DNA with antigene RNAs

Transcription start sites are critical switches for converting recognition of chromosomal DNA into active synthesis of RNA. Their functional importance suggests that they may be ideal targets for regulating gene expression. Here, we report potent inhibition of gene expression by antigene RNAs (agRNAs) complementary to transcription start sites within human chromosomal DNA. Silencing does not require methylation of DNA and differs from all known mechanisms for inhibiting transcription. agRNAs overlap DNA sequences within the open complex formed by RNA polymerase, and silencing is acutely sensitive to single base shifts. agRNAs effectively silence both TATA-less and TATA-box-containing promoters. Transcription start sites occur within every gene, providing predictable targets for agRNAs. Potent inhibition of multiple genes suggests that agRNAs may represent a natural mechanism for controlling transcription, may complement siRNAs and miRNAs that target mRNA, and will be valuable agents for silencing gene expression.

YB-1 facilitates basal and 5-fluorouracil-inducible expression of the human major vault protein (MVP) gene

Vaults have been suggested to play a direct role in multidrug resistance (MDR) to anticancer drugs. The human major vault protein (MVP) also known as lung resistance-related protein (LRP) represents the predominant component of vaults that may be involved in the defense against xenobiotics. Here, we demonstrate that besides MDR-related cytostatics, also the non-MDR-related drug 5-fluorouracil (5-FU) was able to induce MVP mRNA and protein expression. Treatment with 5-FU amplified the binding activity and interaction of the transcription factor Y-box binding protein-1 (YB-1) with the Y-box of the human MVP gene promoter in a time-dependent manner. 5-FU also induced reporter expressions driven by a panel of newly generated MVP promoter deletion mutants. Interestingly, stably YB-1 overexpressing cell clones showed enhanced binding of YB-1 to the Y-box motif, associated with enhanced basal as well as 5-FU-inducible MVP promoter-driven reporter expressions. Moreover, transduction of YB-1 cDNA led to increased expression of endogenous MVP protein. Under physiological conditions, we observed a strong coexpression of MVP and YB-1 in human colon carcinoma specimen. In summary, our data demonstrate a direct involvement of YB-1 in controlling basal and 5-FU-induced MVP promoter activity. Therefore, YB-1 is directly linked to MVP-mediated drug resistance.

Identification of Porcine Oocyte Proteins That Are Associated with Somatic Cell Nuclei after Co-Incubation1

Relatively little is known with respect to the oocyte proteins that are involved in nuclear reprogramming of somatic cells in mammals. The aim of the present study was to use a cell-free incubation system between porcine oocyte proteins and somatic cell nuclei and to identify oocyte proteins that remain associated with these somatic cell nuclei. In two separate experiments, porcine oocytes were either labeled with biotin to label total proteins at the germinal vesicle stage or metaphase II stage or they were labeled with 0.1 mM (35)S-methionine either during the first 6 h or 22-28 h of in vitro maturation to characterize protein synthesis during two distinct phases. To determine which oocyte proteins associate with somatic nuclei, labeled proteins were incubated in a collecting buffer and energy-regenerating system with isolated ovarian epithelial-like cell nuclei. After incubation, the nuclei were subjected to a novel affinity-binding system to recover biotin-labeled oocyte proteins or two-dimensional SDS-PAGE for separation and visualization of radiolabeled proteins. Proteins of interest were sent for identification using either matrix-assisted laser desorption/ionization time of flight or liquid chromatography-tandem mass spectrometry. Of the proteins that remain associated with isolated nuclei after incubation, 4 were identified using the affinity-binding system and 24 were identified using mass spectrometry and the two-dimensional gel interface. This study has identified porcine oocyte proteins that associate with somatic cell nuclei in a cell-free system using proteomics techniques, providing a novel way to identify oocyte proteins potentially functionally involved in nuclear reprogramming.

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.

A genomic approach reveals a novel mitotic pathway in papillomavirus carcinogenesis

More than 90% of cervical carcinomas are associated with human papillomavirus (HPV) infection. The two viral oncogenes E6 and E7 play a major role in transforming the cells by disrupting p53- and pRb-dependent cell cycle checkpoints. A hallmark of HPV-associated cervical carcinoma is loss of the expression of the viral E2 protein, often by disruption of E2-encoding gene. We showed previously that reintroduction of E2 in HPV18-associated cervical carcinoma cells induces cell cycle arrest in G(1) because of the transcriptional repression of the viral oncogenes E6 and E7 and concomitant reactivation of the p53 and pRb pathways. Here we describe global gene profiling of HeLa cells expressing different HPV18 E2 mutants to study the effects of repression of the viral oncogenes. We identified 128 genes transcriptionally regulated by the viral oncogenes in cervical carcinoma. Surprisingly, E2 repressed a subset of E2F-regulated mitotic genes in an E6/E7-dependent pathway. This was corroborated by the observation that E2 delayed mitotic progression, suggesting the involvement of a mitotic pathway in HPV carcinogenesis. These mitotic genes constitute an as yet unrecognized set of genes, which were also found deregulated in other HPV-associated cervical carcinoma cell lines and therefore represent new targets for both diagnosis and therapeutic approaches in cervical cancer.

Analysis of MVP and VPARP promoters indicates a role for chromatin remodeling in the regulation of MVP

Multi-drug-resistant cancer cells frequently express elevated levels of ribonucleoprotein complexes termed vaults. The increased expression of vault proteins and their mRNAs has led to the suggestion that vaults may play a direct role in preventing drug toxicity. To further understand vault component up-regulation, the three proteins that comprise the vault, the major vault protein (MVP), vault poly(ADP-ribose) polymerase (VPARP), and telomerase-associated protein-1 (TEP1), were examined with respect to gene amplification and drug-induced chromatin remodeling. Gene amplification was not responsible for increased vault component levels in multi-drug-resistant cancer cell lines. The TATA-less murine MVP and human VPARP promoters were identified and functionally characterized. There was no significant activation of either the MVP or VPARP promoters in drug-resistant cell lines in comparison to their parental, drug-sensitive counterparts. Treatment of various cell lines with sodium butyrate, an inhibitor of histone deacetylase (HDAC), led to an increase in vault component protein levels. Furthermore, treatment with trichostatin A (TSA), a more specific inhibitor of HDAC, caused an increase in MVP protein, mRNA, and promoter activity. These results suggest that up-regulation of MVP in multi-drug resistance (MDR) may involve chromatin remodeling.

Vaults: a ribonucleoprotein particle involved in drug resistance?

Vaults are ribonucleoprotein particles found in the cytoplasm of eucaryotic cells. The 13 MDa particles are composed of multiple copies of three proteins: an M(r) 100 000 major vault protein (MVP) and two minor vault proteins of M(r) 193 000 (vault poly-(ADP-ribose) polymerase) and M(r) 240 000 (telomerase-associated protein 1), as well as small untranslated RNA molecules of approximately 100 bases. Although the existence of vaults was first reported in the mid-1980s no function has yet been attributed to this organelle. The notion that vaults might play a role in drug resistance was suggested by the molecular identification of the lung resistance-related (LRP) protein as the human MVP. MVP/LRP was found to be overexpressed in many chemoresistant cancer cell lines and primary tumor samples of different histogenetic origin. Several, but not all, clinico-pathological studies showed that MVP expression at diagnosis was an independent adverse prognostic factor for response to chemotherapy. The hollow barrel-shaped structure of the vault complex and its subcellular localization indicate a function in intracellular transport. It was therefore postulated that vaults contributed to drug resistance by transporting drugs away from their intracellular targets and/or the sequestration of drugs. Here, we review the current knowledge on the vault complex and critically discuss the evidence that links vaults to drug resistance.

The relevance of alternative RNA splicing to pharmacogenomics

The importance of alternative RNA splicing in the generation of genetic diversity is now widely accepted. This article highlights how alternative RNA splicing can have an impact on drug efficacy and safety, and demonstrates its potential pharmacogenomic value. The analysis of the repertoire of alternative RNA splicing events could potentially identify markers of pharmacogenomic relevance with high sensitivity and specificity and also provides a route through which genes can be selected for single nucleotide polymorphism (SNP) genotyping. Recent methodological advances, including microarray and splice-dedicated expression profiling, have made it possible to perform high-throughput alternative splicing analyses.

Expression of multidrug resistance genes MVP, MDR1, and MRP1 determined sequentially before, during, and after hyperthermic isolated limb perfusion of soft tissue sarcoma and melanoma patients

PURPOSE

Isolated, hyperthermic limb perfusion (ILP) with recombinant human tumor necrosis factor alpha and melphalan is a highly effective treatment for advanced soft tissue sarcoma (STS) and locoregional metastatic malignant melanoma. Multidrug resistance (MDR)-associated genes are known to be inducible by heat and drugs; expression levels of the major vault protein (MVP), MDR1, and MDR-associated protein 1 (MRP1) were determined sequentially before, during, and after ILP of patients.

PATIENTS AND METHODS

Twenty-one STS or malignant melanoma patients were treated by ILP. Tumor tissue temperatures were recorded continuously and ranged from 33.4 degrees C initially to peak values of 40.4 degrees C during ILP. Serial true-cut biopsy specimens from tumor tissues were routinely microdissected. Expression analyses for MDR genes were performed by real-time reverse transcriptase polymerase chain reaction and immunohistochemistry.

RESULTS

In 83% of the patients, MVP expression was induced during hyperthermic ILP. MVP-mRNA inductions often paralleled the increase in temperature during ILP. Increased MVP protein expressions either were observed simultaneously with the MVP-mRNA induction or were delayed until after the induction at the transcriptional level. Inductions of MDR1 and MRP1 were observed in only 13% and 27% of the specimens analyzed. Temperatures and drugs applied preferentially led to an induction of MVP and were not sufficient to induce MDR1 and MRP1 in the majority of tumors.

CONCLUSION

This study is the first to analyze the expression of MDR-associated genes sequentially during ILP of patients and demonstrates that treatment might lead to increased levels of MVP, whereas enhanced levels of MDR1 and MRP1 remain rare events.

The genomic sequence of the murine major vault protein and its promoter

Vaults are ribonucleoproteins of unknown function, consisting of three different proteins and multiple copies of small untranslated RNA molecules. One of the protein subunits has been identified as TEP1, a protein that is also associated with the telomerase complex. Another protein appears to contain a functional PARP domain and is hence called VPARP. The third protein, major vault protein (MVP), is believed to make up 70% of the total mass of the vault complex and to be responsible for the typical barrel-shaped structure of vaults. We have isolated the murine MVP cDNA and compared the amino acid sequence with MVP from other species. Over 90% of sequence identity was found between mouse, human and rat, and a considerable degree of identity between mouse and MVPs from lower eukaryotes. We also found that the genomic structure of the murine MVP gene closely resembles the organization of the human MVP gene, both consisting of 15 exons of which most have exactly the same size. Finally we have isolated a genomic region upstream (and partially overlapping) the first untranslated exon, that displayed promoter activity in a luciferase reporter assay. Furthermore, we showed that the sequences from the first exon together with the 5'-end of the first intron enhance the promoter activity, implying the presence of essential promoter elements in this region. Alignment of the murine promoter region with the homologous sequences of the human gene revealed an identity of 58%. The apparent presence of conserved promoter elements suggests a similar regulation of human and murine MVP expression.

Human T-cell lymphotropic virus type I Tax activates lung resistance-related protein expression in leukemic clones established from an adult T-cell leukemia patient

OBJECTIVE

We examined the significance of human T-cell lymphotropic virus type I (HTLV-I) Tax protein-induced resistance to anticancer drugs and the relationship between Tax and multidrug resistance proteins.

MATERIALS AND METHODS

S1T cell, a leukemic non-Tax-producing T-cell clone established from an adult T-cell leukemia (ATL) patient, S1TcTax05 and S1TcTax10 clones, transfected with Tax stably expressing cDNA, and S1Tneo, transfected with a neomycin-resistant gene, were examined for Tax-related anticancer drug resistance. Resistance of those cells to the anticancer drugs doxorubicin, etoposide, cisplatin, and vindesine was tested with the MTT method. Expression of multidrug resistance protein mRNAs (MDR1, MRP1, cMOAT/MRP2, and LRP) was analyzed with reverse transcriptase polymerase chain reaction (RT-PCR). Doxorubicin subcellular distribution in those cells was examined by fluorescence microscopy.

RESULTS

S1TcTax05 and S1TcTax10 showed resistance to doxorubicin, etoposide, and vindesine, but not to cisplatin as compared with S1T or S1Tneo. RT-PCR demonstrated that MRP1 mRNA was expressed, but MDR1, cMOAT, and LRP mRNAs were not in S1T or S1Tneo. Marked expression of LRP mRNA was detected, but no change of MDR1, MRP1, or cMOAT mRNA expression in Tax-expressing S1TcTax05 and S1TcTax10. Fluorescence microscopy demonstrated that doxorubicin was distributed mainly in the cytoplasm of S1TcTax05 and S1TcTax10, and in the nucleus of S1T and S1Tneo.

CONCLUSIONS

These findings suggest that Tax-related drug resistance of ATL cells is due to LRP and not MDR1, as reported previously. These findings in cells derived from an ATL patient suggest a novel mechanism for drug resistance in Tax-expressing ATL cells.

Cancer chemoresistance: the relationship between p53 and multidrug transporters

Extensive studies indicate that both p53 and multidrug transporters play important roles in chemoresistance. Since the initial reports a decade ago demonstrating a transcriptional dependence of the ABCB1 gene (MDR) promoter by p53, much data have been accumulated. However, despite being the subject of intense study, this p53-MDR relationship remains unclear in human cancers. The data are confounded by variable and contrasting results when considering the in vitro regulation and attempting to draw parallels in tissue specimens. The original model suggested that wild-type p53 downregulates the ABCB1 promoter, whereas mutant p53 increases expression of ABCB1. This review summarizes the data for and against this hypothesis. What emerges from these studies is a complex picture, where data have been obtained in support of this hypothesis, but there are also many circumstances where it is not supported. Taken together, these data suggest that the relationship between p53 and multidrug transporters is conditional. It is dependent on cellular environment, the drug used, and the nature of the p53 mutation.

Sp1 plays a critical role in the transcriptional activation of the human cyclin-dependent kinase inhibitor p21(WAF1/Cip1) gene by the p53 tumor suppressor protein

In the present study we present evidence for the critical role of Sp1 in the mechanism of transactivation of the human cell cycle inhibitor p21(WAF1/Cip1) (p21) gene promoter by the tumor suppressor p53 protein. We found that the distal p53-binding site of the p21 promoter acts as an enhancer on the homologous or heterologous promoters in hepatoma HepG2 cells. In transfection experiments, p53 transactivated the p21 promoter in HaCaT cells that express Sp1 but have a mutated p53 form. In contrast, p53 could not transactivate the p21 promoter in the Drosophila embryo-derived Schneider's SL2 cells that lack endogenous Sp1 or related factors. Cotransfection of SL2 cells with p53 and Sp1 resulted in a synergistic transactivation of the p21 promoter. Synergistic transactivation was greatly decreased in SL2 cells and HaCaT cells by mutations in either the p53-binding site or in the -82/-77 Sp1-binding site indicating functional cooperation between Sp1 and p53 in the transactivation of the p21 promoter. Synergistic transactivation was also decreased by mutations in the transactivation domain of p53. Physical interactions between Sp1 and p53 proteins were established by glutathione S-transferase pull-down and coimmunoprecipitation assays. By using deletion mutants we found that the DNA binding domain of Sp1 is required for its physical interaction with p53. In conclusion, Sp1 must play a critical role in regulating important biological processes controlled by p53 via p21 gene activation such as DNA repair, cell growth, differentiation, and apoptosis.

A small upstream open reading frame causes inhibition of human major vault protein expression from a ubiquitous mRNA splice variant

Overexpression of the major vault protein (MVP) has been linked to a multidrug resistance (MDR) phenotype. We describe a ubiquitously expressed MVP mRNA splice variant (long (L)-MVP) differing from the regular isoform (short (S)-MVP) within the 5'-leader. Only L-MVP mRNA contains a small upstream open reading frame which was proven to inhibit in vitro and in vivo MVP expression in cis. L-MVP represented an almost constant portion of total MVP mRNA in diverse normal tissues, but was more variable in malignant cell types. MDR sublines with altered MVP expression displayed changed S-MVP/L-MVP ratios as compared to their drug-sensitive counterparts. Our results suggest alternative splicing as one mechanism for regulation of MVP expression.