Direct involvement of the Y-box binding protein YB-1 in genotoxic stress-induced activation of the human multidrug resistance 1 gene

Protein kinase C epsilon mediates the induction of P-glycoprotein in LNCaP prostate carcinoma cells

P-glycoprotein (P-gp) mediates drug resistance. Protein kinase C (PKC) expression correlates with drug resistance in several types of cancer. We determined whether PKC signals the induction of P-gp in LNCaP human prostate cancer cells, and identified a specific isozyme involved, in a model of aspirin-induced P-glycoprotein expression. An inhibitor of PKC activity, and a specific peptide inhibitor of PKC epsilon translocation, suppressed the induction of P-gp. The PKC activator ingenol, but not OAG, induced P-gp expression in a dose-dependent manner. Based on our results, we conclude that PKC epsilon mediates the induction of P-gp. Accordingly, PKC epsilon is activated and translocates from the membrane fraction to the cytoskeleton fraction in aspirin-treated cells. The findings of this study point to PKC epsilon as a signalling molecule for the induction of P-gp in LNCaP prostate cancer cells.

The major messenger ribonucleoprotein particle protein p50 (YB-1) promotes nucleic acid strand annealing

p50, a member of the Y-box binding transcription factor family, is tightly associated with eukaryotic mRNAs and is responsible for general translational regulation. Here we show that p50, in addition to its previously described ability to melt mRNA secondary structure, is capable of promoting rapid annealing of complementary nucleic acid strands. p50 accelerates annealing of RNA and DNA duplexes up to 1500-fold within a wide range of salt concentrations and temperatures. Phosphorylation of p50 selectively inhibits DNA annealing. Moreover, p50 catalyzes strand exchange between double-stranded and single-stranded RNAs yielding a product bearing a more extended double-stranded structure. Strikingly, p50 displays both RNA-melting and -annealing activities in a dose-dependent manner; a relatively low amount of p50 promotes formation of RNA duplexes, whereas an excess of p50 causes unwinding of double-stranded forms. Our results suggest that the alteration of nucleic acid conformation is a basic mechanism of the p50-dependent regulation of gene expression.

Hammerhead ribozyme against gamma-glutamylcysteine synthetase sensitizes human colonic cancer cells to cisplatin by down-regulating both the glutathione synthesis and the expression of multidrug resistance proteins

Multidrug resistance in cancer cells is often associated with an elevation in the concentration of glutathione (GSH) and the expression of gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme for GSH. We constructed a hammerhead ribozyme against a gamma-GCS heavy subunit (gamma-GCSh) mRNA transcript and transfected it to human colonic cancer cells (HCT8DDP) resistant to cisplatin (CDDP). The effect of the ribozyme transfection on the drug resistance of cancer cells was studied. (a) Transfection of the ribozyme decreased the GSH level and the efflux of CDDP-GSH adduct, resulting in higher sensitivity of the cells to CDDP. (b) The transfection suppressed the expression of ATP-binding cassette (ABC) family of transporters such as MRP1, MRP2, and MDR1, and stimulated the expression of mutant p53. (c) An electrophoretic mobility shift assay showed that mutant p53 suppresses the SP1-DNA binding activity, suggesting that this mutant p53 is functional and it, in turn, suppresses the expression of ABC transporters. Collectively, transfection of anti-gamma-GCSh ribozyme reduced the synthesis of GSH and the expression of ABC transporters, which causes an increase in the sensitivity of cancer cells to anticancer drugs. Suppression of the SP1-DNA binding activity by p53 may be a factor of down-regulation of ABC transporters.

Cathepsin B-like cysteine proteases and Caenorhabditis elegans homologues dominate gene products expressed in adult Haemonchus contortus intestine

Proteins expressed by nematode intestinal cells are potential targets for parasite control by immune or chemical based strategies. To expand our knowledge on nematode intestinal proteins, expressed sequence tags were generated for 131 cDNA clones from the intestine of adult female Haemonchus contortus. An estimated 55 distinct protein genes or gene families were identified. Predicted proteins represented diverse functions. Several predicted polypeptides were related to H. contortus proteins implicated in inducing protective immunity against challenge infections of this parasite. The dominant intestinal transcripts were represented by cathepsin B-like cysteine protease genes (cbl) (17% of protein coding expressed sequence tags (ESTs) analyzed). An estimated 11 previously undescribed cbl genes were identified, doubling the recognized members of this gene family. Multiple C-type lectin sequences were identified. Other notable sequences included a predicted Y-box binding protein, serine/threonine kinases and a cyclin E-like sequence. Predicted protein homologues were found in Caenorhabditis elegans for all but one H. contortus sequence (99%), while fewer homologues from other parasitic nematodes were found. Many of the proteases, lipase and C-type lectin homologues in C. elegans had apparent signal peptides, suggesting that they are secreted. Several gene products had no obvious similarity outside the phylum Nematoda. The ESTs identified intestinal genes with potential application to immune control, understanding of basic intestinal regulatory processes and refinement of nematode genomic resources.

Recognition of cisplatin adducts by cellular proteins

Cisplatin is a widely used chemotherapeutic agent. It reacts with nucleophilic bases in DNA and forms 1,2-d(ApG), 1,2-d(GpG) and 1,3-d(GpTpG) intrastrand crosslinks, interstrand crosslinks and monofunctional adducts. The presence of these adducts in DNA is through to be responsible for the therapeutic efficacy of cisplatin. The exact signal transduction pathway that leads to cell cycle arrest and cell death following treatment with the drug is not known but cell death is believed to be mediated by the recognition of the adducts by cellular proteins. Here we describe the structural information available for cisplatin and related platinum adducts, the interactions of the adducts with cellular proteins and the implications of these interactions for cell survival.

Stimulation of human endonuclease III by Y box-binding protein 1 (DNA-binding protein B). Interaction between a base excision repair enzyme and a transcription factor

Human endonuclease III (hNth1) is a DNA glycosylase/apurinic/apyrimidinic (AP) lyase that initiates base excision repair of pyrimidines modified by reactive oxygen species, ionizing, and ultraviolet radiation. Using duplex 2'-deoxyribose oligonucleotides containing an abasic (AP) site, a thymine glycol, or a 5-hydroxyuracil residue as substrates, we found the AP lyase activity of hNth1 was 7 times slower than its DNA glycosylase activity, similar to results reported for murine and human 8-oxoguanine-DNA glycosylase, which are also members of the endonuclease III family. This difference in rates contrasts with the equality of rates found in Escherichia coli and Saccharomyces cerevisiae endonuclease III homologs. A yeast two-hybrid screen for potential modulators of hNth1 activity revealed interaction with the damage-inducible transcription factor Y box-binding protein 1 (YB-1), also identified as DNA-binding protein B (DbpB). The in vitro addition of His(6)YB-1 to hNth1 increased the rate of DNA glycosylase and AP lyase activity. Analysis revealed that YB-1 affects the steady state equilibrium between the covalent hNth1-AP site Schiff base ES intermediate and the noncovalent ES intermediate containing the AP aldehydic sugar and the epsilon-amino group of the hNth1 active site lysine. This equilibrium may be a checkpoint in modulating hNth1 activity.

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.

Retrovirus insertion and transcriptional activation of the multidrug-resistance gene in leukemias treated by a chemotherapeutic agent in vivo

To understand the molecular basis for multidrug-resistant (MDR) cancer cells in vivo, this study analyzed molecular changes of the mdr1a gene region in leukemia cells in mice during continuous treatment with vincristine. An inverse insertion of murine leukemia retrovirus (MuLV) into the 5'-flanking region of the mdr1a gene was found. This insertion was concomitantly accompanied by up-regulation of the mdr1a gene and the loss of chemosensitivity. Deletion of long-terminal repeat (LTR) sequences dramatically decreased the mdr1a promoter-driven reporter activity. The MuLV LTR insertion appears to exert its enhancer activity on mdr1a transcription during the appearance of MDR leukemia cells. Two mechanisms were postulated to explain the mdr1a gene activation by retrovirus insertion during in vivo chemotreatment: de novo insertion of MuLV induced by vincristine treatment and selection of a small fraction of pre-existing cells carrying MuLV insertion during vincristine treatment. No rearranged sequence was detected by polymerase chain reaction in parental cells. This result argued for the first mechanism. The randomly altered distribution of MuLV during repetitive chemotreatment might also be consistent with this hypothesis. On the other hand, the retrovirus insertion was detected at the same site of the mdr1a promoter region in 2 independent experiments, which suggests the second mechanism. It should be noted that in vivo chemotreatment using vincristine could generate the mdr1a-overexpressing cells through retrovirus insertion and the enhancer effect of the LTR.

Function and regulation of ATP-binding cassette transport proteins involved in hepatobiliary transport

Hepatobiliary transport of endogenous and exogenous compounds is mediated by the coordinated action of multiple transport systems present at the sinusoidal (basolateral) and canalicular (apical) membrane domains of hepatocytes. During the last few years many of these transporters have been cloned and functionally characterized. In addition, the molecular bases of several forms of cholestatic liver disease have been defined. Combined, this has greatly expanded our understanding of the normal physiology of bile formation, the pathophysiology of intrahepatic cholestasis, as well as of drug elimination and disposition processes. In this review recent advances, with respect to function and regulation of ATP binding cassette transport proteins expressed in liver, are summarized and discussed.

Gene trapping identifies transiently induced survival genes during programmed cell death

BACKGROUND

The existence of a constitutively expressed machinery for death in individual cells has led to the notion that survival factors repress this machinery and, if such factors are unavailable, cells die by default. In many cells, however, mRNA and protein synthesis inhibitors induce apoptosis, suggesting that in some cases transcriptional activity might actually impede cell death. To identify transcriptional mechanisms that interfere with cell death and survival, we combined gene trap mutagenesis with site-specific recombination (Cre/loxP system) to isolate genes from cells undergoing apoptosis by growth factor deprivation.

RESULTS

From an integration library consisting of approximately 2 x 106 unique proviral integrations obtained by infecting the interleukin-3 (IL-3)-dependent hematopoietic cell line - FLOXIL3 - with U3Cre gene trap virus, we have isolated 125 individual clones that converted to factor independence upon IL-3 withdrawal. Of 102 cellular sequences adjacent to U3Cre integration sites, 17% belonged to known genes, 11% matched single expressed sequence tags (ESTs) or full cDNAs with unknown function and 72% had no match within the public databases. Most of the known genes recovered in this analysis encoded proteins with survival functions.

CONCLUSIONS

We have shown that hematopoietic cells undergoing apoptosis after withdrawal of IL-3 activate survival genes that impede cell death. This results in reduced apoptosis and improved survival of cells treated with a transient apoptotic stimulus. Thus, apoptosis in hematopoietic cells is the end result of a conflict between death and survival signals, rather than a simple death by default.

Direct interaction of p53 with the Y-box binding protein, YB-1: a mechanism for regulation of human gene expression

The Y-box binding protein, YB-1, belongs to a family of multifunctional proteins which regulate gene expression on both transcriptional and translational levels. The tumor suppressor gene p53 displays growth suppressive properties by regulating gene expression through transcriptional regulation. We now demonstrate that YB-1 directly interacts with p53 using an in vitro pull-down assay. Using immunochemical co-precipitation methods, we also found that the two proteins are bound in vivo. Deletion analysis showed that three independent domains of YB-1, one at the N-terminal and two at the C-terminal, interact with p53. Conversely, a 14 amino acid sequence at the C-terminal of p53 was required for its interaction with YB-1. Gel mobility shift assays showed that the interaction of YB-1 with p53 stimulated the sequence-specific DNA binding of p53 to its consensus sequence. By contrast, this interaction inhibited the binding of YB-1. Using a p53-responsive p21 promoter linked to a reporter gene, it can be shown that antisense expression of YB-1 inhibits the induction of this promoter by p53 in transient transfection assays. These findings delineate a straightforward mechanism for gene expression through p53-YB-1 interaction.

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

The lung resistance-related protein (LRP) was identified as the human major vault protein (MVP), and is overexpressed in various multidrug-resistant cancer cell lines and clinical samples. We characterized DNA sequences upstream to the transcription initiation site of the MVP gene in the human non-small cell lung cancer cell line SW-1573. A 1.9-kb and a shortened 0.7-kb fragment of the 5'-upstream genomic region show strong promoter activity in chloramphenicol acetyltransferase (CAT) reporter assays. The promoter is TATA-less and contains an inverted CCAAT-box and a Sp1 site located near to a p53 binding motif. An alternative 3'-splice site of intron 1 results in a splicing variant within the 5'-untranslated region of MVP mRNA.

Function and regulation of ATP-binding cassette transport proteins involved in hepatobiliary transport

Hepatobiliary transport of endogenous and exogenous compounds is mediated by the coordinated action of multiple transport systems present at the sinusoidal (basolateral) and canalicular (apical) membrane domains of hepatocytes. During the last few years many of these transporters have been cloned and functionally characterized. In addition, the molecular bases of several forms of cholestatic liver disease have been defined. Combined, this has greatly expanded our understanding of the normal physiology of bile formation, the pathophysiology of intrahepatic cholestasis, as well as of drug elimination and disposition processes. In this review recent advances, with respect to function and regulation of ATP binding cassette transport proteins expressed in liver, are summarized and discussed.

Acquisition of double-stranded DNA-binding ability in a hybrid protein between Escherichia coli CspA and the cold shock domain of human YB-1

Escherichia coli CspA, a major cold shock protein, is dramatically induced upon temperature downshift. As it binds co-operatively to single-stranded DNA (ssDNA) and RNA without apparent sequence specificity, it has been proposed that CspA acts as an RNA chaperone to facilitate transcription and translation at low temperature. CspA consists of a five-stranded beta-barrel structure containing two RNA-binding motifs, RNP1 and RNP2. Eukaryotic Y-box proteins, such as human YB-1, are a family of nucleic acid-binding proteins that share a region of high homology with CspA (43% identity), termed the cold shock domain (CSD). Their cellular functions are very diverse and are associated with growth-related processes. Here, we replaced the six-residue loop region of CspA between the beta3 and beta4 strands with the corresponding region of the CSD of human YB-1 protein. The resulting hybrid protein became capable of binding to double-stranded DNA (dsDNA) in addition to ssDNA and RNA. The dsDNA-binding ability of an RNP1 point mutant (F20L) of the hybrid was almost unchanged. On the other hand, the dsDNA-binding ability of the hybrid protein was abolished in high salt concentrations in contrast to its ssDNA-binding ability. These results indicate that the loop region between the beta3 and beta4 strands of Y-box proteins, which is a little longer and more basic than that of CspA, plays an important role in their binding to dsDNA.

Thrombin activates a Y box-binding protein (DNA-binding protein B) in endothelial cells

Thrombin stimulates the expression of multiple genes in endothelial cells (ECs), but the trans-acting factors responsible for this induction remain undefined. We have previously described a thrombin-inducible nuclear factor (TINF), which binds to an element in the PDGF B promoter and is responsible for the thrombin inducibility of this gene. Inactive cytoplasmic TINF is rapidly activated and translocated to nuclei of ECs upon stimulation with thrombin. We have now purified TINF from thrombin-treated ECs. Amino acid sequencing revealed it to be a member of the Y-box protein family, and the sole Y-box protein-encoding cDNA we detected in human or bovine ECs corresponded to DNA-binding protein B (dbpB). DbpB translocated to the nucleus after thrombin stimulation of ECs as shown by FACS analysis of nuclei from ECs expressing GFP-dbpB fusion proteins. During thrombin activation, dbpB was found to be cleaved, yielding a 30-kDa NH(2)-terminal fragment that recognized the thrombin-response element sequence, but not the Y-box consensus sequence. Preincubation of ECs with protein tyrosine phosphatase inhibitors completely blocked dbpB activation by thrombin and blocked induction of endogenous PDGF B-chain mRNA and promoter activation by thrombin. Y-box proteins are known to act constitutively to regulate the expression of several genes. Activation of this class of transcription factors in response to thrombin or any other agonist represents a novel signaling pathway.

Regulation of multidrug resistance 1 (MDR1)/P-glycoprotein gene expression and activity by heat-shock transcription factor 1 (HSF1)

Infection of HeLa cells with adenovirus-carrying HSF1(+) cDNA, which encodes a mutated form of HSF1 with constitutive transactivation capacity, increased multidrug resistance 1 (MDR1) mRNA level and P-glycoprotein (P-gp) cell surface content and stimulated rhodamine 123 accumulation and vinblastine efflux activity. On the other hand, infection with adenovirus-carrying HSP70 and HSP27 cDNAs did not increase MDR1/P-gp expression. HSF1 regulates MDR1/P-gp expression at the transcriptional level, since HSF1(+) bound the heat-shock consensus elements (HSEs) in the MDR1 gene promoter and also activated the expression of an MDR1 promoter-driven reporter plasmid (pMDR1(-1202)). In addition, heat-shock increased pMDR1(-1202) promoter activity but not the activity of a similar reporter plasmid with point mutations at specific HSEs, and the heat-induced increase was totally inhibited by co-transfection with an expression plasmid carrying HSF1(-), a dominant negative mutant of HSF1. The stress inducers arsenite, butyrate, and etoposide also increased pMDR1(-1202) promoter activity, but the increase was not inhibited (in the case of butyrate) or was only partially inhibited (in the case of arsenite and etoposide) by HSF1(-). These results demonstrate that HSF1 regulates MDR1 expression, and that the HSEs present in the -315 to -285 region mediate the heat-induced activation of the MDR1 promoter. However, other factors may also participate in MDR1 induction by stressing agents.

Regulation of the human fas promoter by YB-1, Puralpha and AP-1 transcription factors

Fas (CD95/Apo-1) gene expression is dysregulated in a number of diseased states. Towards understanding the regulation of fas gene expression, we previously identified activator and repressor elements within the human fas promoter. Using a combination of expression screening and reporter gene assays, we have identified transcription factors which bind to these elements and thereby regulate transcription of the fas promoter. These are three single-stranded DNA binding proteins, YB-1, Puralpha and Purbeta and two components of the AP-1 complex, c-Fos and c-Jun. c-Jun is a potent transcriptional activator of fas and stimulated expression levels up to 184-fold in reporter gene assays. Co-expression with c-Fos abrogated c-Jun-mediated activation. YB-1 and Puralpha are transcriptional repressors of fas and decreased basal transcription by 60-fold in reporter gene assays. Purbeta was predominantly an antagonist of YB-1/Puralpha-mediated repression. Overexpression of YB-1 and Puralpha in Jurkat cells was shown to reduce the level of cell surface Fas staining, providing further evidence that these proteins regulate the fas promoter. It has been suggested that YB-1 plays a role in cell proliferation as an activator of growth-associated gene expression. We have shown that YB-1 is a repressor of a cell death-associated gene fas. These results suggest that YB-1 may play an important role in controlling cell survival by co-ordinately regulating the expression of cell growth-associated and death-associated genes.

Alu-associated interstitial deletions and chromosomal re-arrangement in 2 human multidrug-resistant cell lines

Previous studies have shown that gene re-arrangements play a significant role in tumorigenesis. Gene re-arrangements involving the human multidrug resistance-1 (MDR1) gene have been identified as a mechanism for MDR1 over-expression in human malignant cells. In 2 multidrug-resistant human cancer sublines with high levels of MDR1 and P-glycoprotein (MCF7/TX400 and S48-3s/Adr10), hybrid mRNAs containing sequences from MDR1 and an unrelated gene have previously been identified. To characterize and determine the site of the re-arrangements resulting in generation of hybrid mRNAs, we first constructed a lambda phage library extending over a contiguous genomic region of 100 kb and containing the region upstream of MDR1. In MCF7/TX400 cells, homologous recombination was observed involving an Alu repeat 80 kb upstream of the MDR1 gene, with a 79 bp intra-Alu deletion flanked by chi-like sequences at the re-arrangement junction. By contrast, non-homologous recombination was observed in S48-3s/Adr10 cells with Alu repeats near the junction sequence. While the specific features of the breakpoints appear to be different, Alu repeats might be involved in both gene re-arrangements. The gene re-arrangements at or near the Alu sequence should be regarded as potentially involved in the transcriptional activation of human MDR1.

The tight junction protein ZO-1 and an interacting transcription factor regulate ErbB-2 expression

Epithelial tight junctions regulate paracellular diffusion and restrict the intermixing of apical and basolateral plasma membrane components. We now identify a Y-box transcription factor, ZONAB (ZO-1-associated nucleic acid-binding protein), that binds to the SH3 domain of ZO-1, a submembrane protein of tight junctions. ZONAB localizes to the nucleus and at tight junctions, and binds to sequences of specific promoters containing an inverted CCAAT box. In reporter assays, ZONAB and ZO-1 functionally interact in the regulation of the ErbB-2 promoter in a cell density-dependent manner. In stably transfected overexpressing cells, ZO-1 and ZONAB control expression of endogenous ErbB-2 and function in the regulation of paracellular permeability. These data indicate that tight junctions directly participate in the control of gene expression and suggest that they function in the regulation of epithelial cell differentiation.

Enhancement of mdr1 gene expression in normal tissue adjacent to advanced breast cancer

In the present study, mdr1 gene expression was investigated by a sensitive reverse transcriptase-PCR assay in advanced breast cancer and in corresponding adjacent normal tissues obtained before and after treatment with primary chemotherapy. Comparatively to normal tissues, a significant induction of mdr1 expression was observed in untreated tumors (p = 0.0222). Similarly, a significant induction of mdr1 expression was revealed when treated samples were compared to untreated counterparts (p = 0.0222), but no differences were detected between tumor and normal samples (p = 0.3199). Noteworthy, a significant induction of mdr1 gene expression occurred in treated normal samples comparatively to untreated ones (p = 0.0037), and this induction was even more important in normal than in tumoral tissue (p = 0.0627). However, neither the basal expression nor the induction of mdr1 were correlated with subsequent response to chemotherapy or with survival. Thus, in agreement with previous reports, our data show that chemotherapy induce mdr1 gene expression in breast cancer cells, but they also indicate that a similar phenomenon occurs in adjacent normal tissues. Therefore, our results strongly suggest that mdr1 gene overexpression is not a characteristic of breast malignant cells, but rather constitutes a general phenomenon occurring both in normal and tumor cells which could explain at least in part the absence of relationship between mdr1 expression and the clinical outcome of breast cancer patients.

Regulation of MDR1 gene expression: emerging concepts

Drug resistance genes, such as MDR1, involved in drug efflux, and their regulation have been the subject of intense research efforts in the past 10 years. Many factors and cellular signalling pathways play a role in the regulation of MDR1 gene expression. Commonly used chemotherapeutic agents activate in vitro and in vivo general stress response pathways, potential targets of which include MDR1 and other drug resistance genes. The contribution of these agents to the emergence of drug-resistant tumour cells is of concern. Recent evidence points to a role for the epigenetic regulation of MDR1 gene expression. The identification of key components in the DNA methylation/chromatin system of gene regulation may in time lead to more informed and targeted approaches to treating drug-resistant tumours. Copyright 2000 Harcourt Publishers Ltd.

Transcriptional activation of the MDR1 gene by UV irradiation. Role of NF-Y and Sp1

The MDR1 promoter is subject to control by various internal and external stimuli. We have previously shown that the CCAAT box-binding protein, NF-Y, mediates MDR1 activation by the histone deacetylase inhibitors, trichostatin A and sodium butyrate, through the recruitment of the co-activator, P/CAF. We have now extended our investigation to the activation of MDR1 by genotoxic stress. We show that activation of the MDR1 promoter by UV irradiation is also dependent on the CCAAT box (-82 to -73) as well as on a proximal GC element (-56 to -42). Gel shift and supershift analyses with nuclear extracts prepared from human KB-3-1 cells identified NF-Y as the transcription factor interacting with the CCAAT box, while Sp1 was the predominant factor binding to the GC element. Mutations that abrogated binding of either of these factors reduced or abolished activation by ultraviolet irradiation; moreover, co-expression of a dominant-negative NF-Y protein (NF-YA29) reduced UV-activated transcription. Interestingly, YB-1, a transcription factor that also recognizes the CCAAT motif and had been reported to mediate induction of the MDR1 promoter by ultraviolet light, was incapable of interacting with the double-stranded MDR1 CCAAT box oligonucleotide in nuclear extracts, although it did interact with a single-stranded oligonucleotide. Furthermore, a mutation that abolished activation of MDR1 by UV-irradiation had no effect on YB-1 binding and co-transfection of a YB-1 expression plasmid had a repressive effect on UV-inducible transcription. Taken together, these results indicate a role for both NF-Y and Sp1 in the transcriptional activation of the MDR1 gene by genotoxic stress, and indicate that YB-1, if involved, is not sufficient to mediate this activation.

Identification and characterization of the MDR1 promoter-enhancing factor 1 (MEF1) in the multidrug resistant HL60/VCR human acute myeloid leukemia cell line

In this report, the molecular mechanisms involved in the overexpression of MDR1 mRNA in the multidrug resistant variant of the HL60 human acute myeloid leukemia cell line, HL60/VCR, were investigated. RT-PCR and nuclear run-on assays revealed that the expression of MDR1 mRNA is regulated by increased transcriptional initiation in HL60/VCR cells. Transient transfections with a 241 bp MDR1 promoter (spanning the -198 to +43 region) DNA fragment/pGL3-basic plasmid construct resulted in about 6-fold increased luciferase activity in HL60/VCR but not in HL60 cells. Moreover, ds CAAT-oligomer from the MDR1 promoter cloned upstream of the SV-40 promoter in the pGL3-promoter plasmid caused about a 7-fold increase in luciferase activity compared with plasmid constructs containing CAAT-deleted, GC-box, and nonspecific oligomers in HL60/VCR transfectants. These results were confirmed by transfecting HL60/VCR cells with the pGL3-basic plasmid containing a 237 bp mutated MDR1 proximal promoter lacking the CAAT sequence in which no change in luciferase activity was observed. However, a 5-6-fold increase in luciferase activity was measured in these cells when transfected with the wt MDR1 promoter DNA/pGL3-basic plasmid constructs. These results show that the CAAT-region is involved in upregulating the MDR1 promoter in HL60/VCR cells. A nuclear factor binding to the CAAT-region of the MDR1 promoter specifically was detected in electrophoretic mobility shift assays (EMSAs) in HL60/VCR but not in HL60 extracts. Two MDR1 promoter-associated polypeptides with molecular masses of about 130 and 162 kDa were identified in HL60/VCR cells by electroelution, specific DNA-affinity chromatography, and silver staining. Interestingly, cross-linking and Southwestern analysis indicate that only the 130 kDa protein, which we refer to as MDR1-promoter enhancing factor 1 (MEF1), has a strong DNA-binding ability, interacting with the 5'-GTCAATCC-3' element of the MDR1 promoter, as determined by DNase I protection assay. These data reveal that MEF1 upregulates the MDR1 promoter activity.

Enhanced coexpression of YB-1 and DNA topoisomerase II alpha genes in human colorectal carcinomas

The transcription factor YB-1 is expressed in a wide range of cell types and has been implicated in the regulation of various genes involved in cell proliferation. Nuclear expression of YB-1 is correlated with MDR-1 gene expression in breast cancer and osteosarcoma. In this study, we asked whether YB-1 expression is enhanced in human colorectral carcinoma and if it is associated with the expression of target genes such as MDR-1, DNA topoisomerase II alpha and PCNA. YB-1, DNA topoisomerase II alpha, PCNA and MDR-1 expression were assessed by Western blotting, Northern blotting and immunohistochemistry in 26 human colorectal carcinomas. The involvement of YB-1 in DNA topoisomerase II alpha gene expression was examined by transient DNA transfection assays. YB-1 was overexpressed in almost all cancerous lesions in comparison with normal mucosa in surgically resected colorectal carcinomas of 26 patients. YB-1 expression correlated well with both DNA topoisomerase II alpha and PCNA expression. In contrast, no correlation was observed between YB-1 and MDR-1 expression. We also found that a transient co-transfection with a DNA topoisomerase II alpha promoter-luciferase plasmid and an antisense YB-1 expression construct resulted in a significant reduction of the promoter activity in KM12C human colon cancer cells. YB-1 may be an excellent proliferation-associated marker and may be a transcription factor regulating DNA topoisomerase II alpha gene expression in human colorectal carcinoma.

Enhanced coexpression of YB-1 and DNA topoisomerase II alpha genes in human colorectal carcinomas

The transcription factor YB-1 is expressed in a wide range of cell types and has been implicated in the regulation of various genes involved in cell proliferation. Nuclear expression of YB-1 is correlated with MDR-1 gene expression in breast cancer and osteosarcoma. In this study, we asked whether YB-1 expression is enhanced in human colorectral carcinoma and if it is associated with the expression of target genes such as MDR-1, DNA topoisomerase II alpha and PCNA. YB-1, DNA topoisomerase II alpha, PCNA and MDR-1 expression were assessed by Western blotting, Northern blotting and immunohistochemistry in 26 human colorectal carcinomas. The involvement of YB-1 in DNA topoisomerase II alpha gene expression was examined by transient DNA transfection assays. YB-1 was overexpressed in almost all cancerous lesions in comparison with normal mucosa in surgically resected colorectal carcinomas of 26 patients. YB-1 expression correlated well with both DNA topoisomerase II alpha and PCNA expression. In contrast, no correlation was observed between YB-1 and MDR-1 expression. We also found that a transient co-transfection with a DNA topoisomerase II alpha promoter-luciferase plasmid and an antisense YB-1 expression construct resulted in a significant reduction of the promoter activity in KM12C human colon cancer cells. YB-1 may be an excellent proliferation-associated marker and may be a transcription factor regulating DNA topoisomerase II alpha gene expression in human colorectal carcinoma.

Cisplatin induces renal expression of P-glycoprotein and canalicular multispecific organic anion transporter

The expression of two members of the ATP-binding cassette family of transport proteins, P-glycoprotein (P-gp) and the canalicular multispecific organic anion transporter (cMOAT or Mrp2), was evaluated in renal brush-border membranes (BBM) and various rat tissues after cisplatin treatment. One administration of cisplatin (5 mg/kg) increased P-gp expression by >200-300% in renal BBM and in crude membranes from liver and intestine. The increase in P-gp expression in the kidney was also detected in photolabeling experiments, suggesting the induction of functional P-gp. cMOAT expression was increased by >10-fold in renal BBM after cisplatin administration, although it had no effect on liver cMOAT expression. The increase in the levels of both proteins was maximal at 2 days after cisplatin treatment and lasted for at least 8 days. These results indicate that a single administration of cisplatin induces overexpression of P-gp and cMOAT in specific tissues. This may be of significant relevance to the design of clinical trials using cisplatin as a single chemotherapeutic agent or in combination with other drugs.

Structural characterization of the human interleukin-13 receptor alpha1 gene promoter

Human cancer cells have been found to express a large number of IL-13 receptors. We have previously shown that mRNA encoding one of these receptors, IL-13Ralpha1, is increased in cisplatin-resistant cells and is upregulated in tumor cells cultured with cisplatin. To understand the molecular mechanism of IL-13Ralpha1 gene expression, we cloned approximately 52 kbp of the IL-13Ralpha1 gene and sequenced the first exon and about 1 kbp of the upstream DNA. The first exon is 211 bp and contains 88 bp of coding sequence, while the first intron is about 13 kbp in length. The promoter region, which is GC rich, was found to lack both TATA and CCAAT boxes. Transient expression assays revealed that transcription of the IL-13Ralpha1 gene was significantly higher in cisplatin-resistant cells than in parental, cisplatin-sensitive cells. Deletion analysis of the IL-13Ralpha1 promoter identified a 70-bp core promoter region upstream of the transcription initiation site. Electrophoretic gel mobility shift assays showed that a synthetic IL-13Ralpha1 oligonucleotide (nt -40 to nt -15) bound a nuclear factor from cisplatin-resistant cells to a significantly greater degree than the equivalent factor from parental cells. This oligonucleotide was found to contain a palindromic sequence with a BstEII recognition site at its center. This palindromic sequence functions to mediate upregulation of IL-13Ralpha1 promoter in cisplatin-resistant cells and deletion or disruption of this sequence also resulted in severe reduction of the promoter activity. These findings suggest that IL-13Ralpha1 expression is upregulated at the transcriptional level in cisplatin-resistant cells. The characterization of both the IL-13Ralpha1 promoter and the transcription factors binding to it may contribute to our understanding of IL-13Ralpha1 regulation in cancer cells.

Altered Multidrug Resistance Phenotype Caused by Anthracycline Analogues and Cytosine Arabinoside in Myeloid Leukemia

The expression of P-glycoprotein (Pgp) is often increased in acute myeloid leukemia (AML). However, little is known of the regulation of Pgp expression by cytotoxics in AML. We examined whether Pgp expression and function in leukemic blasts was altered after a short exposure to cytotoxics. Blasts were isolated from 19 patients with AML (15 patients) or chronic myeloid leukemia in blastic transformation (BT-CML, 4 patients). Pgp expression and function were analyzed by flow cytometric analysis of MRK 16 binding and Rhodamine 123 retention, respectively. At equitoxic concentrations, ex vivo exposure for 16 hours to the anthracyclines epirubicin (EPI), daunomycin (DAU), idarubicin (IDA), or MX2 or the nucleoside analogue cytosine arabinoside (AraC) differentially upregulated MDR1/Pgp expression in Pgp-negative and Pgp-positive blast cells. In Pgp-negative blasts, all four anthracyclines and AraC significantly increased Pgp expression (P = .01) and Pgp function (P = .03). In contrast, MX2, DAU, and AraC were the most potent in inducing Pgp expression and function in Pgp positive blasts (P < .05). A good correlation between increased Pgp expression and function was observed in Pgp-negative (r = .90, P = .0001) and Pgp-positive blasts (r = .77,P = .0002). This increase in Pgp expression and function was inhibited by the addition of 1 μmol/L PSC 833 to blast cells at the time of their exposure to these cytotoxics. In 1 patient with AML, an increase in Pgp levels was observed in vivo at 4 and 16 hours after the administration of standard chemotherapy with DAU/AraC. Upregulation of Pgp expression was also demonstrated ex vivo in blasts harvested from this patient before the commencement of treatment. In 3 other cases (1 patient with AML and 2 with BT-CML) in which blasts were Pgp negative at the time of initial clinical presentation, serial samples at 1 to 5 months after chemotherapy showed the presence of Pgp-positive blasts. All 3 patients had refractory disease. Interestingly, in all 3 cases, upregulation of Pgp by cytotoxics was demonstrated ex vivo in blasts harvested at the time of presentation. These data suggest that upregulation of the MDR1 gene may represent a normal response of leukemic cells to cytotoxic stress and may contribute to clinical drug resistance.

Altered Multidrug Resistance Phenotype Caused by Anthracycline Analogues and Cytosine Arabinoside in Myeloid Leukemia

The expression of P-glycoprotein (Pgp) is often increased in acute myeloid leukemia (AML). However, little is known of the regulation of Pgp expression by cytotoxics in AML. We examined whether Pgp expression and function in leukemic blasts was altered after a short exposure to cytotoxics. Blasts were isolated from 19 patients with AML (15 patients) or chronic myeloid leukemia in blastic transformation (BT-CML, 4 patients). Pgp expression and function were analyzed by flow cytometric analysis of MRK 16 binding and Rhodamine 123 retention, respectively. At equitoxic concentrations, ex vivo exposure for 16 hours to the anthracyclines epirubicin (EPI), daunomycin (DAU), idarubicin (IDA), or MX2 or the nucleoside analogue cytosine arabinoside (AraC) differentially upregulated MDR1/Pgp expression in Pgp-negative and Pgp-positive blast cells. In Pgp-negative blasts, all four anthracyclines and AraC significantly increased Pgp expression (P = .01) and Pgp function (P = .03). In contrast, MX2, DAU, and AraC were the most potent in inducing Pgp expression and function in Pgp positive blasts (P &lt; .05). A good correlation between increased Pgp expression and function was observed in Pgp-negative (r = .90, P = .0001) and Pgp-positive blasts (r = .77,P = .0002). This increase in Pgp expression and function was inhibited by the addition of 1 μmol/L PSC 833 to blast cells at the time of their exposure to these cytotoxics. In 1 patient with AML, an increase in Pgp levels was observed in vivo at 4 and 16 hours after the administration of standard chemotherapy with DAU/AraC. Upregulation of Pgp expression was also demonstrated ex vivo in blasts harvested from this patient before the commencement of treatment. In 3 other cases (1 patient with AML and 2 with BT-CML) in which blasts were Pgp negative at the time of initial clinical presentation, serial samples at 1 to 5 months after chemotherapy showed the presence of Pgp-positive blasts. All 3 patients had refractory disease. Interestingly, in all 3 cases, upregulation of Pgp by cytotoxics was demonstrated ex vivo in blasts harvested at the time of presentation. These data suggest that upregulation of the MDR1 gene may represent a normal response of leukemic cells to cytotoxic stress and may contribute to clinical drug resistance.

Association of 5' CpG demethylation and altered chromatin structure in the promoter region with transcriptional activation of the multidrug resistance 1 gene in human cancer cells

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. However, the precise mechanism underlying such transcriptional activation of MDR1 remains unclear. The relation between methylation status of CpG sites in the MDR1 promoter region and transcriptional activation of MDR1 has now been investigated. The P-glycoprotein-overexpressing, multidrug-resistant KB/VJ300 and KB-C1 cells, which were established from human cancer KB3-1 cells, were examined; MDR1 is transcriptionally activated but not amplified in KB/VJ300 cells, whereas it is amplified in KB-C1 cells. Determination of the methylation status revealed that the MDR1 promoter region was hypomethylated in KB/VJ300 and KB-C1 cells, but hypermethylated in KB3-1 cells. Prior treatment of KB3-1 cells with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine resulted in a 90-fold increase in the frequency of vincristine-resistance. Of three lines, KB/CdR-1, KB/CdR-2, and KB/CdR-3, established from KB3-1 cells after exposure to 5-aza-2'-deoxycytidine, MspI/HpaII sites in the MDR1 promoter region were hypomethylated in KB/CdR-1 and KB/CdR-2 cells, but not in KB/CdR-3 cells. MDR1 mRNA expression was detected in KB/CdR-1 and KB/CdR-2 cells, but not in KB/CdR-3 cells. The binding of YB-1 and Sp1, transcription factors implicated in MDR1 expression, in the MDR1 promoter was not affected by the methylation status of a neighboring CpG sites. The MDR1 promoter region in KB/VJ300 cells showed an increased sensitivity to DNase I compared with that in KB3-1 cells, suggesting an altered chromatin structure. The methylation status of the promoter region may plays an important role in MDR1 overexpression and in acquisition of the P-glycoprotein-mediated multidrug resistance phenotype.

Is nuclear expression of Y box-binding protein-1 a new prognostic factor in ovarian serous adenocarcinoma?

BACKGROUND

Nuclear expression of Y box-binding protein (YB-1), a member of the DNA binding protein family, has been reported to be much more highly concentrated in cisplatin-resistant cell lines than in their parental counterparts, suggesting an ability to limit cisplatin sensitivity. Moreover, YB-1 plays a key role in P-glycoprotein expression. Because ovarian carcinoma traditionally has been treated with cisplatin-based chemotherapy, the sensitivity of the tumors to chemotherapy could reflect a particular prognosis in patients with ovarian carcinoma. The aim of the current study was to determine whether YB-1 expression correlated with prognosis in ovarian serous adenocarcinoma patients.

METHODS

The expression of YB-1 in the nucleus was examined immunohistochemically in 42 paraffin embedded primary Stage III (International Federation of Gynecology and Obstetrics) serous ovarian carcinoma tumors extirpated by primary surgery at Kyushu University Hospital between 1985-1995.

RESULTS

Of the 40 primary ovarian tumors examined, 12 (30%) were positive for YB-1 expression in the nucleus. There was no significant difference in intraperitoneal stage, histologic grade, or residual tumor size after primary surgery between patients with tumors with positive and those with negative nuclear expression of YB-1 protein. The disease free survival curve for patients whose tumors were positive for nuclear expression of YB-1 protein was significantly worse than that for patients whose tumors were negative (P = 0.0025). P-glycoprotein was overexpressed in 4 of 12 tumors with nuclear YB-1 expression (33%) but there was no statistical significance between the expression of nuclear YB-1 and P-glycoprotein.

CONCLUSIONS

The expression of YB- 1 protein in the nucleus may be considered a useful prognostic marker and also may reflect the sensitivity of ovarian serous adenocarcinoma to chemotherapy.

Negative regulation of MDR1 promoter activity in MCF-7, but not in multidrug resistant MCF-7/Adr, cells by cross-coupled NF-kappa B/p65 and c-Fos transcription factors and their interaction with the CAAT region

In this study, the possible involvement of repressor protein(s) in suppressing MDR1 promoter activity in the sensitive MCF-7 human breast cancer cell line and its drug resistant variant MCF-7/Adr was investigated. RT-PCR revealed that MDR1 mRNA is under detectable levels in MCF-7, while it is highly expressed in MCF-7/Adr cells. After treatment of MCF-7 cells with cycloheximide (CHX), MDR1 mRNA reached detectable levels, suggesting that MDR1 mRNA expression might be controlled by a labile negative regulatory protein(s) in MCF-7 cells. In electrophoretic mobility shift assays (EMSA) using a 5'-end-labeled 241 bp MDR1 promoter DNA fragment (residues -198 to +43) as a probe, one protein complex that specifically binds to the CAAT region of the MDR1 promoter was detected in MCF-7, but not MCF-7/Adr. In addition, following transient transfections of MCF-7 and MCF-7/Adr cells with a pGL3-Basic plasmid construct containing a CAAT-deleted MDR1 promoter DNA fragment, a significant increase in luciferase activity was observed compared to the 241 bp MDR1 promoter in MCF-7 but not MCF-7/Adr cells. Moreover, a ds CAAT oligomer, cloned upstream of the SV-40 promoter in the pGL3-Promoter vector, resulted in a 70-80% decrease in luciferase activity in MCF-7 cells. To identify the CAAT binding protein complex, EMSA and SDS-PAGE were performed. Two proteins with molecular masses of about 65 and 60 kDa were detected by silver staining. Western blot analysis revealed that this complex consists of NF-kappa B/p65 and c-Fos transcription factors. Moreover, incubating MCF-7 nuclear extracts with antibodies specific for NF-kappa B/p65 or c-Fos in EMSAs almost completely inhibited formation of the complex, supporting the association of NF-kappa B/p65 and c-Fos. Therefore, this study provides evidence that molecular interplay between the NF-kappa B/p65 and c-Fos transcription factors exhibits a negative regulatory function on MDR1 promoter by interacting with the CAAT region in MCF-7.

Hypomethylation Status of CpG Sites at the Promoter Region and Overexpression of the Human MDR1 Gene in Acute Myeloid Leukemias

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. Moreover, overexpression of the MDR1 gene has been shown to be associated closely with clinical outcome in various hematological malignancies, including acute myeloid leukemia (AML). However, the precise mechanism underlying overexpression of the MDR1 gene during acquisition of drug resistance remains unclear. We recently described an inverse correlation between the methylation status of CpG sites at the promoter region and expression of the MDR1 gene in malignant cell lines. In this study, we expanded this analysis to 42 clinical AML samples. We adapted a quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for gene expression and a quantitative PCR after digestion by Hpa II for methylation status of the MDR1gene. We observed a statistically significant inverse correlation between methylation and MDR1 expression in clinical samples. The hypomethylation status of the MDR1 promoter region might be a necessary condition for MDR1 gene overexpression and establishment of P-glycoprotein–mediated multidrug resistance in AML patients.

Hypomethylation Status of CpG Sites at the Promoter Region and Overexpression of the Human MDR1 Gene in Acute Myeloid Leukemias

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. Moreover, overexpression of the MDR1 gene has been shown to be associated closely with clinical outcome in various hematological malignancies, including acute myeloid leukemia (AML). However, the precise mechanism underlying overexpression of the MDR1 gene during acquisition of drug resistance remains unclear. We recently described an inverse correlation between the methylation status of CpG sites at the promoter region and expression of the MDR1 gene in malignant cell lines. In this study, we expanded this analysis to 42 clinical AML samples. We adapted a quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for gene expression and a quantitative PCR after digestion by Hpa II for methylation status of the MDR1gene. We observed a statistically significant inverse correlation between methylation and MDR1 expression in clinical samples. The hypomethylation status of the MDR1 promoter region might be a necessary condition for MDR1 gene overexpression and establishment of P-glycoprotein–mediated multidrug resistance in AML patients.

Transcriptional regulation of MDR genes

The emergence of resistance in a tumor population is most often associated with a disregulation of gene expression, usually at the level of transcription. A major goal in the field of cancer chemotherapy is to define the mechanisms underlying transcriptional regulation of drug resistance genes in an effort to identify targets for therapeutic intervention. Recently, considerable progress has been made in identifying the molecular mechanisms involved in the transcriptional regulation of the P-glycoprotein (Pgp) gene. When overexpressed in tumor cells, Pgp confers resistance to a variety of chemotherapeutic agents; this resistance has been termed MDR (multidrug resistance). Moreover, Pgp is a normal component of a variety of highly differentiated cell types and, as such, is regulated by both internal and external environmental stimuli. In this review, we will discuss the current knowledge regarding the DNA elements and protein factors involved in both constitutive and inducible regulation of Pgp transcription in normal and tumor cells.

Cellular resistance to adriamycin conferred by enhanced Rb expression is associated with increased MDR1 expression

In order to investigate if the enhanced expression of Rb confers increased cellular resistance to adriamycin, we made Rb stable transfectants from colon carcinoma cells, SW620. Rb stable transfectants exhibited 5- to 10-fold more resistance to adriamycin than the control cells. To study the correlation between enhanced Rb expression and MDR1 expression, products of the Rb gene and the MDR1 gene in Rb stable transfectants were measured by Western blot analysis. These Rb transfectants showed increased MDR1 expression. Transient transfection of the MDR1 promoter-CAT reporter gene and the Rb gene demonstrated that Rb up-regulated MDR1 promoter activity in SW620 cells. Rb may, at least partly, contribute to a role in protecting cells from carcinogen exposure by up-regulating the MDR1 gene.