Increased expression of multidrug resistance related proteins Pgp, MRP1, and LRP/MVP occurs early in colorectal carcinogenesis

Major Vault Protein Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection in CRL2843CD163 Cell Lines and Primary Porcine Alveolar Macrophages

Porcine reproductive and respiratory syndrome (PRRS), a significant viral infectious disease that commonly occurs among farmed pigs, leads to considerable economic losses to the swine industry worldwide. Major vault protein (MVP) is a host factor that induces type Ⅰ interferon (IFN) production. In this study, we evaluated the effect of MVP on PRRSV infection in CRL2843^CD163 cell lines and porcine alveolar macrophages (PAMs). Our results showed that MVP expression was downregulated by PRRSV infection. Adenoviral overexpression of MVP inhibited PRRSV replication, whereas the siRNA knockdown of MVP promoted PRRSV replication. In addition, MVP knockdown has an adverse effect on the inhibitive role of MVP overexpression on PRRSV replication. Moreover, MVP could induce the expression of type Ⅰ IFNs and IFN-stimulated gene 15 (ISG15) in PRRSV-infected PAMs. Based on these results, MVP may be a potential molecular target of drugs for the effective prevention and treatment of PRRSV infection.

Chemotherapy Resistance Explained through Endoplasmic Reticulum Stress-Dependent Signaling

Cancers cells have the ability to develop chemotherapy resistance, which is a persistent problem during cancer treatment. Chemotherapy resistance develops through different molecular mechanisms, which lead to modification of the cancer cells signals needed for cellular proliferation or for stimulating an immune response. The endoplasmic reticulum (ER) is an important organelle involved in protein quality control, by promoting the correct folding of protein and ER-mediated degradation of unfolded or misfolded protein, namely, ER-associated degradation. Disturbances of the normal ER functions causes an accumulation of unfolded or misfolded proteins in the ER lumen, resulting in a condition called “ER stress (ERS).” ERS triggers the unfolded protein response (UPR)—also called the ERS response (ERSR)—to restore homeostasis or activate cell death. Although the ERSR is one emerging potential target for chemotherapeutics to treat cancer, it is also critical for chemotherapeutics resistance, as well. However, the detailed molecular mechanism of the relationship between the ERSR and tumor survival or drug resistance remains to be fully understood. In this review, we aim to describe the most vital molecular mechanism of the relationship between the ERSR and chemotherapy resistance. Moreover, the review also discusses the molecular mechanism of ER stress-mediated apoptosis on cancer treatments.

Multifaceted Interpretation of Colon Cancer Stem Cells

Colon cancer is one of the leading causes of cancer-related deaths worldwide, despite recent advances in clinical oncology. Accumulating evidence sheds light on the existence of cancer stem cells and their role in conferring therapeutic resistance. Cancer stem cells are a minor fraction of cancer cells, which enable tumor heterogeneity and initiate tumor formation. In addition, these cells are resistant to various cytotoxic factors. Therefore, elimination of cancer stem cells is difficult but essential to cure the malignant foci completely. Herein, we review the recent evidence for intestinal stem cells and colon cancer stem cells, methods to detect the tumor-initiating cells, and clinical significance of cancer stem cell markers. We also describe the emerging problems of cancer stem cell theory, including bidirectional conversion and intertumoral heterogeneity of stem cell phenotype.

Sphingolipid abnormalities in cancer multidrug resistance: Chicken or egg?

The cancer multidrug resistance (MDR) phenotype encompasses a myriad of molecular, genetic and cellular alterations resulting from progressive oncogenic transformation and selection. Drug efflux transporters, in particular the MDR P-glycoprotein ABCB1, play an important role in MDR but cannot confer the complete phenotype alone indicating parallel alterations are prerequisite. Sphingolipids are essential constituents of lipid raft domains and directly participate in functionalization of transmembrane proteins, including providing an optimal lipid microenvironment for multidrug transporters, and are also perturbed in cancer. Here we postulate that increased sphingomyelin content, developing early in some cancers, recruits and functionalizes plasma membrane ABCB1 conferring a state of partial MDR, which is completed by glycosphingolipid disturbance and the appearance of intracellular vesicular ABCB1. In this review, the independent and interdependent roles of sphingolipid alterations and ABCB1 upregulation during the transformation process and resultant conferment of partial and complete MDR phenotypes are discussed.

Mechanisms of drug resistance in colon cancer and its therapeutic strategies

Drug resistance develops in nearly all patients with colon cancer, leading to a decrease in the therapeutic efficacies of anticancer agents. This review provides an up-to-date summary on over-expression of ATP-binding cassette (ABC) transporters and evasion of apoptosis, two representatives of transport-based and non-transport-based mechanisms of drug resistance, as well as their therapeutic strategies. Different ABC transporters were found to be up-regulated in colon cancer, which can facilitate the efflux of anticancer drugs out of cancer cells and decrease their therapeutic effects. Inhibition of ABC transporters by suppressing their protein expressions or co-administration of modulators has been proven as an effective approach to sensitize drug-resistant cancer cells to anticancer drugs in vitro. On the other hand, evasion of apoptosis observed in drug-resistant cancers also results in drug resistance to anticancer agents, especially to apoptosis inducers. Restoration of apoptotic signals by BH3 mimetics or epidermal growth factor receptor inhibitors and inhibition of cancer cell growth by alternative cell death pathways, such as autophagy, are effective means to treat such resistant cancer types. Given that the drug resistance mechanisms are different among colon cancer patients and may change even in a single patient at different stages, personalized and specific combination therapy is proposed to be more effective and safer for the reversal of drug resistance in clinics.

The importance of G2677T/A and C3435T polymorphisms of the MDR1 gene in the aetiology of colorectal cancer

Introduction

Colorectal cancer (CRC) is the most common cancer among patients, and its aetiology is still not precisely known. It is believed that 15–30% of colorectal cancers are genetically determined. P-glycoprotein (P-gp) encoded by the MDR1 gene in normal conditions plays an important role in the action of colon epithelial cells. However, the MDR1 polymorphism influences the P-gp expression and can weaken its effect against xenobiotics (procarcinogens) and increase the frequency of CRC.

Aim

To evaluate the correlation between the MDR1 C3435T and G2677T/A polymorphisms and the risk of colorectal cancer.

Material and methods

The study group with colorectal cancer included 47 women and 60 men while the control group consisted of 110 healthy patients. The diagnosis in patients suffering from CRC was confirmed by histopathological report. Genetic analysis was performed using PCR-RFLP method.

Results

We showed only a correlation between the frequency of CT and TT genotypes of C3435T polymorphism and the risk of colorectal cancer in younger age. There was no correlation between the C3435T and G2677T/A polymorphisms of the MDR1 gene and other clinical parameters.

Conclusions

Our findings suggest that T allele carriers of C3435T polymorphism have an increased risk of CRC. However, further studies are needed on a much larger number of patients and genes associated with metabolism and transport of xenobiotics including procarcinogens.

Decreased functional activity of multidrug resistance protein in primary colorectal cancer

Background

The ATP-Binding Cassette (ABC)-transporter MultiDrug Resistance Protein 1 (MDR1) and Multidrug Resistance Related Protein 1 (MRP1) are expressed on the surface of enterocytes, which has led to the belief that these high capacity transporters are responsible for modulating chemosensitvity of colorectal cancer. Several immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR) studies have provided controversial results in regards to the expression levels of these two ABC-transporters in colorectal cancer. Our study was designed to determine the yet uninvestigated functional activity of MDR1 and MRP1 transporters in normal human enterocytes compared to colorectal cancer cells from surgical biopsies.

Methods

100 colorectal cancer and 28 adjacent healthy mucosa samples were obtained by intraoperative surgical sampling. Activity of MDR1 and MRP1 of viable epithelial and cancer cells were determined separately with the modified calcein-assay for multidrug resistance activity and sufficient data of 73 cancer and 11 healthy mucosa was analyzed statistically.

Results

Significantly decreased mean MDR1 activity was found in primary colorectal cancer samples compared to normal mucosa, while mean MRP1 activity showed no significant change. Functional activity was not affected by gender, age, stage or grade and localization of the tumor.

Conclusion

We found lower MDR activity in cancer cells versus adjacent, apparently, healthy control tissue, thus, contrary to general belief, MDR activity seems not to play a major role in primary drug resistance, but might rather explain preferential/selective activity of Irinotecan and/or Oxaliplatin. Still, this picture might be more complex since chemotherapy by itself might alter MDR activity, and furthermore, today limited data is available about MDR activity of cancer stem cells in colorectal cancers.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1675739129145824

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.

Expression profiles of vault components MVP, TEP1 and vPARP and their correlation to other multidrug resistance proteins in ovarian cancer

Vaults are cytoplasmic ribonucleoprotein particles composed of three proteins (MVP, TEP1, vPARP) and vault‑associated RNAs (vRNAs). Although the cellular functions of vaults remain unclear, vaults are strongly linked to the development of multidrug resistance (MDR), the major obstacle to the efficient treatment of cancers. Available published data suggest that vaults and their components are frequently upregulated in broad variety of multidrug-resistant cancer cell lines and tumors of different histological origin. Here, we provide detailed analysis of vault protein expression in post-surgery ovarian cancer samples from patients that were not exposed to chemotherapy. Our analysis suggests that vault proteins are expressed in the ovaries of healthy individuals but their expression in cancer patients is changed. Specifically, MVP, TEP1 and vPARP mRNA levels are significantly decreased in cancer samples with tendency of lower expression in higher-grade tumors. The pattern of vault protein mRNA expression is strongly correlated with the expression of other MDR-associated proteins such as MDR1, MRP1 and BCRP. Surprisingly, the protein levels of MVP, TEP1 and vPARP are actually increased in the higher‑grade tumors suggesting existence of post-transcriptional regulation of vault component production.

Tamoxifen magnifies therapeutic impact of ceramide in human colorectal cancer cells independent of p53

Poor prognosis in patients with later stage colorectal cancer (CRC) necessitates the search for new treatment strategies. Ceramide, because of its role in orchestrating death cascades in cancer cells, is a versatile alternative. Ceramide can be generated by exposure to chemotherapy or ionizing radiation, or it can be administered in the form of short-chain analogs (C6-ceramide). Because intracellular P-glycoprotein (P-gp) plays a role in catalyzing the conversion of ceramide to higher sphingolipids, we hypothesized that administration of P-gp antagonists with C6-ceramide would magnify cell death cascades. Human CRC cell lines were employed, HCT-15, HT-29, and LoVo. The addition of either tamoxifen, VX-710, verapamil, or cyclosporin A, antagonists of P-gp, enhanced C6-ceramide cytotoxicity in all cell lines. In depth studies with C6-ceramide and tamoxifen in LoVo cells showed the regimen induced PARP cleavage, caspase-dependent apoptosis, mitochondrial membrane permeabilization (MMP), and cell cycle arrest at G1 and G2. At the molecular level, the regimen, but not single agents, induced time-dependent upregulation of tumor suppressor protein p53; however, introduction of a p53 inhibitor staved neither MMP nor apoptosis. Nanoliposomal formulations of C6-ceramide and tamoxifen were also effective, yielding synergistic cell kill. We conclude that tamoxifen is a favorable adjuvant for enhancing C6-ceramide cytotoxicity in CRC, and demonstrates uniquely integrated effects. The high frequency of expression of P-gp in CRC presents an adventitious target for complementing ceramide-based therapies, a strategy that could hold promise for treatment of resistant disease.

Aberrant DNA methylation of drug metabolism and transport genes in nodular goiter

The genes encoding drug-metabolizing enzymes and transporters play an important role in maintaining the normal life processes of human body. Their disorder or defect will lead to the occurrence and development of various diseases. Currently, most of studies have focused on genetic variations in these genes, however, in the present study, we analyzed promoter methylation of 11 drug metabolism and transport genes in a cohort of nodular goiter and normal thyroid tissues using methylation-specific PCR (MSP). Our data first revealed a distinct methylation profiling in drug metabolism and transport genes between nodular goiter and normal thyroid tissues, particularly ABCB4, CYP1B1 and CYP24A1 and SLC1A2. Given these genes contribute to the development and progression of various diseases, such as multidrug resistance and tumorigenesis, these epigenetic events may thus play a critical role in the pathogenesis of nodular goiter.

Expression of mutant p53 and of the multidrug resistant proteins P-glycoprotein and glutathione S-transferase-pi correlated in colorectal adenocarcinoma

OBJECTIVE

Accumulating studies suggest that multidrug resistance is related to expression of p53, P-glycoprotein (Pgp) and Glutathione S-Transferase-pi (GST-pi). This study was to estimate mutant p53 expression and its correlation with drug resistance related proteins Pgp and GST-pi expression in colorectal adenocarcinoma patients.

MATERIAL AND METHODS

Immunohistochemical ABC technique was used to detect the expression of mutant p53 protein, Pgp and GST-pi in 404 cases with colorectal adenocarcinoma.

RESULTS

A low frequency of mutant p53 accumulation was observed, consistent with findings in colorectal cancers (CRCs) from other Asian populations. Accumulation of mutant p53 was related to AJCC staging (p < 0.05). Pgp expression was significantly correlated with tumor location (p = 0.039) and gender (p = 0.043). The positive percentage of Pgp and GST-pi expression was all significantly higher in mutant p53 protein positive group than mutant p53 protein negative cases (r = 0.634, p < 0.001 and r = 0.680, p < 0.001, respectively).

CONCLUSIONS

These findings demonstrate association of three biomarkers with clinicopathologic parameters of colorectal carcinoma, and overexpression of Pgp and GST-pi was closely correlated with mutant p53.

Adrenaline induces chemoresistance in HT-29 colon adenocarcinoma cells

Psychological distress and its ensuing chronic elevation of plasma catecholamines (adrenaline and noradrenaline) lead to poor response of tumors to chemotherapy, and constitute a poor prognostic factor for survival. Colorectal cancer patients suffer from various forms of psychological stress reflected in elevated plasma catecholamines, and their cancer cells express adrenergic receptors. Our objective was to investigate whether adrenergic activation contributes to the chemoresistance of colon cancers, and to explore the signal transduction pathway involved in the activation. The mRNA expression of the ABCB1 gene (previously MDR1) in human colon carcinoma HT-29 cell line was measured after treatment with an adrenergic receptor agonist (adrenaline) and various antagonists (propranolol, prazosin, and yohimbine). The function of P-glycoprotein, the protein product of the ABCB1 gene, was assessed by rhodamine 123 (Rh123)-retention assay, and chemosensitivity was determined by evaluating the cytotoxicity of 5-fluorouracil (5-FU) on the tumor cells. Increased ABCB1 mRNA expression and P-glycoprotein function levels in HT-29 cells by adrenaline was dose-dependent. This was accompanied by promotion of Rh123 efflux, and resistance to the growth-inhibiting effect of 5-FU in the tumor cells. The alpha2-adrenergic receptor antagonist yohimbine completely abolished the induction of ABCB1 mRNA, the stimulatory effect of adrenaline on Rh123 efflux, and the growth-inhibiting effect of 5-FU. The alpha1-adrenergic receptor and beta-adrenergic receptor antagonists did not inhibit the induction of ABCB1. The stimulating effects were coupled with extracellular receptor kinase 1/2 (Erk1/2) phosphorylation, but were not associated with protein kinase A activity. We conclude that adrenaline induces multidrug resistance in colon cancer cells by upregulating ABCB1 gene expression via alpha2-adrenergic receptors, and such effects were associated with the mitogen activated protein kinase (MAPK) pathway.

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.

Immunolocalization and Cell Expression of Lung Resistance-related Protein (LRP) in Normal and Tumoral Human Respiratory Cells

Lung resistance-related protein (LRP) is an integral part of the multidrug resistance (MDR) phenotype involved in cell resistance toward xenobiotics or chemotherapy. The aim of this study was to compare the intracellular localization and cell expression of LRP in normal bronchial cells and their tumoral counterparts from non-small cell lung cancer (NSCLC). LRP expression was also investigated concurrently with DNA ploidy and chromosome 16 ( lrp gene locus) aberrations. Confocal microscopy showed that LRP localization was exclusively intracytoplasmic regardless of the cell type and was never observed in the nuclear pore complex. Flow cytometry demonstrated a similar level of LRP expression in normal bronchial cells and in cancer cells from NSCLC samples. FISH analysis, performed to evaluate the number of chromosome 16 and lrp loci, demonstrated a significant gain of chromosome 16 in DNA aneuploid tumors. Furthermore, we did not find any link between LRP expression and DNA ploidy status or chromosome 16 number. These results suggest that LRP expression observed in NSCLC, maintained through the carcinogenesis process of respiratory cells, is not altered by the increased number of copies of chromosome 16 and probably controlled by mechanisms different from those of MRP1 expression, whereas both proteins are associated with the MDR phenotype. (J Histochem Cytochem 55: 773–782, 2007)

Prognostic significance of multidrug-resistance protein (MDR-1) in renal clear cell carcinomas: a five year follow-up analysis

Background

A large number of renal cancer patients shows poor or partial response to chemotherapy and the mechanisms have not been still understood. Multi-drug resistance is the principal mechanism by which many cancers develop resistance to chemotherapic drugs. The role of the multi-drug resistant transporter (MDR-1/P-glycoprotein), the gene product of MDR-1, and that one of the so-called multi-drug resistance associated protein (MRP), two energy-dependent efflux pumps, are commonly known to confer drug resistance.

We studied MDR-1 expression in selected cases of renal cell carcinoma (RCC), clear cell type, with long-term follow-up, in order to establish its prognostic role and its possible contribution in the choice of post-surgical therapy.

Methods

MDR-1 has been studied by standard LSAB-HRP immunohistochemical technique, in paraffin embedded RCC samples. Protein expression has been compared to clinical and histopathological data and to disease specific survival of RCC patients, by Kaplan-Meier curve and Cox multivariate regression analyses.

Results

Two groups of RCCs were obtained by esteeming MDR-1 expression and disease specific survival (obtained with Kaplan-Meier curve and Cox multivariate regression analyses): the first one presents low or absent MDR-1 expression and good survival; the second one is characterized by high MDR-1 expression and significant poor outcome (p < 0.05). Afterwards, we have found disease specific survival, adjusted for stages and independent of therapy: this difference of survival rates was statistically significant (p < 0.05). Stage adjusted disease specific survival rate, according to MDR-1 expression and therapy in patients affected by RCC in early stage (stage I), has revealed that the group of patients with high MDR-1 expression and without adjuvant therapy showed poor survival (p < 0.05). Cox multivariate regression analysis has confirmed that, in our cohort of RCC (clear cell type) patients, the strong association between MDR-1 and worse outcome is independent not only of the adjuvant therapy, but also of the other prognostic parameters (p < 0.05).

Conclusion

In our opinion, the results of this study well prove the relationship between MDR-1 expression and worse clinical prognosis in RCC, because MDR-1 over-expressing RCCs can be considered a group of tumours with a more aggressive behavior. This finding outlines a possible role of MDR-1 as prognostic factor, dependent and independent of multidrug resistance. These results could be useful to predict cancer evolution and to choose the appropriate treatment: this is another step that can stimulate further promising and interesting investigations on broader study population.

Correlations of Cyclins expression types with multi-drug resistance-1 and TNM staging in gastrointestinal cancer

AIM: To investigate the expression of four Cyclins in gastrointestinal cancers, and to explore their correlations with multi-drug resistance-1 (MDR1) and TNM staging.

METHODS: Sixty-two fresh samples (gastric cancer 32, colorectal cancer 30) from patients underwent operation were collected, and the expression of Cyclin (D1, E, A, B1) and MDR1 were detected by flow cytometry. In addition, pathological reports were analyzed for TNM staging.

RESULTS: According to the expression of four Cyclins, four cell cycle types were divided in the gastrointestinal cancers. These four cell cycle types were in accordance with TNM staging (κ = 0.599, P < 0.01) and marked correlation with the level of MDR1 expression (r_s = 0.495, P < 0.01).

CONCLUSION: Cell cycle typing based on Cyclins expression has the same significance as TNM staging. MDR1 expression is correlated with the cell cycle typing, so it is possible to reverse MDR through interfering in cell cycle.

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.

Carcinogenesis, cancer therapy and chemoprevention

Carcinogenesis and cancer therapy are two sides of the same coin, such that the same cytotoxic agent can cause cancer and be used to treat cancer. This review links carcinogenesis, chemoprevention and cancer therapy in one process driven by cytotoxic agents (carcinoagents) that select either for or against cells with oncogenic alterations. By unifying therapy and cancer promotion and by distinguishing nononcogenic and oncogenic mechanisms of resistance, I discuss anticancer- and chemopreventive agent-induced carcinogenesis and tumor progression and, vice versa, carcinogens as anticancer drugs, anticancer drugs as chemopreventive agents and exploiting oncogene-addiction and drug resistance for chemoprevention and cancer therapy.

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.

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.

The major vault protein is a novel substrate for the tyrosine phosphatase SHP-2 and scaffold protein in epidermal growth factor signaling

The catalytic activity of the Src homology 2 (SH2) domain-containing tyrosine phosphatase, SHP-2, is required for virtually all of its signaling effects. Elucidating the molecular mechanisms of SHP-2 signaling, therefore, rests upon the identification of its target substrates. In this report, we have used SHP-2 substrate-trapping mutants to identify the major vault protein (MVP) as a putative SHP-2 substrate. MVP is the predominant component of vaults that are cytoplasmic ribonucleoprotein complexes of unknown function. We show that MVP is dephosphorylated by SHP-2 in vitro and it forms an enzyme-substrate complex with SHP-2 in vivo. In response to epidermal growth factor (EGF), SHP-2 associates via its SH2 domains with tyrosyl-phosphorylated MVP. MVP also interacts with the activated form of the extracellular-regulated kinases (Erks) in response to EGF and a constitutive complex between tyrosyl-phosphorylated MVP, SHP-2, and the Erks was detected in MCF-7 breast cancer cells. Using MVP-deficient fibroblasts, we demonstrate that MVP cooperates with Ras for optimal EGF-induced Elk-1 activation and is required for cell survival. We propose that MVP functions as a novel scaffold protein for both SHP-2 and Erk. The regulation of MVP tyrosyl phosphorylation by SHP-2 may play an important role in cell survival signaling.

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.

Multidrug resistance proteins and topoisomerase IIalpha expression in colon cancer: association with metastatic potential

AIMS

To investigate the role of multidrug resistance proteins and topoisomerase IIalpha in colon cancer.

METHODS

Tissue sections from 89 Dukes' stage B-D colon cancer patients were selected. The expression of multidrug resistance proteins and topoisomerase IIalpha in primary tumour cells was assessed by standard immunohistochemistry. The extent of their expression was measured by image analysis and was correlated with clinicopathological features of the patients.

RESULTS

P-glycoprotein was associated with the presence of lymph node metastasis (P=0.005), vessel invasion (P=0.0001) and perineural invasion (P=0.020).

CONCLUSIONS

P-glycoprotein is probably involved in the processes of local invasion and metastatic dissemination.

Relationship between expression of P-glycoprotein and efficacy of chemotherapy in gastric cancer

AIM: To investigate the significance of the expression of P-glycoprotein and the relationship between its expression and the efficacy of chemotherapy in patients with gastric cancer.

METHODS: P-glycoprotein was examined by immunohistochemical staining in 101 specimens of paraffin embedded gastric cancer tissues.

RESULTS: The expression rates of P-glycoprotein in normal gastric mucosa, paracancerous tissues and gastric cancer tissues were 13%, 22% and 43%, respectively (P < 0.05). The expression rates of P-glycoprotein in the highly and moderately differentiated tumors (58% and 80%, respectively) were significantly higher than those in the lowly and poorly differentiated tumors (36% and 25%, respectively) (P < 0.01). The postoperative cumulative survival rate of the patients receiving chemotherapy was significantly higher than that of the patients without chemotherapy in P-glycoprotein-negative patients with gastric cancer (P < 0.01).

CONCLUSION: The expression of P-glycoprotein was correlated with the degree of tumor differentiation and influenced the efficacy of postoperative chemotherapy.

MDR1 genotype-related pharmacokinetics and pharmacodynamics

The multidrug resistant transporter MDR1/P-glycoprotein, the gene product of MDR1, is a glycosylated membrane protein of 170 kDa, belonging to the ATP-binding cassette superfamily of membrane transporters. MDR1 acts as an energy-dependent efflux pump that exports its substrates out of cells. MDR1 was originally isolated from resistant tumor cells as part of the mechanism of multidrug resistance, but over the last decade, it has been elucidated that human MDR1 is also expressed throughout the body to confer intrinsic resistance to the tissues by exporting unnecessary or toxic exogeneous substances or metabolites. A number of structurally unrelated drugs are substrates for MDR1, and MDR1 and other transporters are recognized as an important class of proteins for regulating pharmacokinetics and pharmacodynamics. In 2000, Hoffmeyer et al. performed a systemic screening for MDR1 polymorphisms and detected 15 single nucleotide polymorphisms (SNPs). They also indicated that a polymorphism in exon 26 at position 3435 (C3435T), a silent mutation, affected the expression level of MDR1 protein in duodenum, and thereby the intestinal absorption of digoxin. To date, the genotype frequencies of C3435T have been investigated extensively using a larger population and interethnic difference has been elucidated, and a total of 28 SNPs have been found at 27 positions on the MDR1 gene. Clinical studies on MDR1 genotype-related MDR1 expression and pharmacokinetics have also been performed around the world; however, results were not always consistent with Hoffmeyer's report. In this review, published reports are summarized for the future individualization of pharmacotherapy based on MDR1 genotyping. In addition, recent investigations have raised the possibility that MDR1 and related transporters play a fundamental role in regulating apoptosis and immunology, and in fact, there are reports of MDR1-related susceptibility to inflammatory bowel disease, HIV infection and renal cell carcinoma. Herein, these issues are also summarized, and the current status of the knowledge in the area of pharmacogenomics of other transporters is briefly introduced.

Oncogenic resistance to growth-limiting conditions

Many carcinogens are mutagens, indicating that mutagenesis is the driving force of carcinogenesis. But what if we turn this prevailing view on its head? I will argue here that carcinogens are cytostatic and/or cytotoxic, and it is not mutation per se, but clonal selection for resistance to these antiproliferative conditions, that leads to cancer. But why aren't all cytotoxins carcinogenic?

Methylation of the hMLH1, p16, and MDR1 genes in colorectal carcinoma: associations with clinicopathological features

The methylation status of seven cancer-related genes was investigated in a series of 58 colorectal cancers, 18 of which showed the microsatellite instability (MSI+) phenotype. Methylation of the hMLH1, p16 and MDR1 genes was found in 23, 29 and 28% of tumors, respectively. None of the tumors showed methylation of the TS, ATM, PARP or p21 genes. Methylation of the hMLH1, p16 and MDR1 genes was more frequent and more concordant in MSI+ compared to MSI- tumors (P<0.001) and was also strongly associated with poor histological differentiation (P<0.001). There were trends for associations between methylation at one or more of these loci and proximal tumor location, advanced Dukes' stage and the presence of wild-type p53 (P=0.06 for each).

Hyperthermia-induced nuclear translocation of transcription factor YB-1 leads to enhanced expression of multidrug resistance-related ABC transporters

Genotoxic stress leads to nuclear translocation of the Y-box transcription factor YB-1 and enhanced expression of the multidrug resistance gene MDR1. Because hyperthermia is used for the treatment of colon cancer in combination with chemoradiotherapy, we investigated the influence of hyperthermia on YB-1 activity and the expression of multidrug resistance-related genes. Here we report that hyperthermia causes YB-1 translocation from the cytoplasm into the nucleus of human colon carcinoma cells HCT15 and HCT116. Nuclear translocation of YB-1 was associated with increased MDR1 and MRP1 gene activity, which is reflected in strong efflux pump activity. However, a combination of hyperthermia and drug treatment effectively reduced cell survival of the HCT15 and HCT116 cells. These results demonstrate that activation of MDR1 and MRP1 gene expression and increased efflux pump activity after hyperthermia were insufficient to cause an increase in drug resistance in colon cancer cell lines. The ability of hyperthermia to abrogate drug resistance in the presence of an increase in functional MDR proteins may provide an explanation for the efficacious results seen in the clinic in colon cancer patients treated with a combination of hyperthermia and chemotherapy.

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.

Lung resistance-related protein/major vault protein and vaults in multidrug-resistant cancer

Tumor cells that are insensitive to anticancer drugs frequently have a multidrug-resistant (MDR) phenotype. Proteins that can be involved in this phenomenon are transport-associated proteins such as P-glycoprotein, multidrug-resistance protein 1, breast cancer resistance protein, and lung resistance-related protein (LRP). LRP was identified as the major vault protein (MVP), the main component of multimeric vault particles. With the recent identification of the two minor vault proteins as telomerase-associated protein (TEP1) and vault-poly (ADP-ribose) polymerase (VPARP), and with high-resolution three-dimensional imaging, the composition of vaults is almost unraveled. Although the first direct evidence for a causal relationship between LRP/MVP expression and drug resistance has been obtained, many functional aspects of vaults in normal physiology and in MDR still need to be clarified. The current clinical data on LRP/MVP detection indicate that LRP/MVP expression can be of high clinical value to predict the response to chemotherapy of several tumor types.

Detection of MRP1 mRNA in human tumors and tumor cell lines by in situ RT-PCR

The detection of the multridrug resistance-associated proteins is becoming increasingly important in assessing tumor sensitivity to treatment. In this work we describe a new, rapid, sensitive, and robust method for the detection of MRP1 expression based on direct RT-in situ-PCR technology and fluorochrome-modified (dCTP(Cy3)) nucleotides. MRP1 expression was found in both placenta (BeWo) and liver (Hep G2)-derived tumor cell line as well as in small cell lung carcinoma. In liver-derived cells, MRP1 expression was detected by RT-in situ-PCR but not by in situ hybridization, suggesting a higher sensitivity of in situ amplification for the low level of expression in Hep G2 cells. RT solution PCR confirmed the presence of MRP1 in BeWo and Hep G2 cells, although the level of the gene expression was lower in liver cells. This method represents a viable alternative to conventional immunohistochemistry, and may be useful in the evaluation of MRP1 expression in different tissue or cell lines.