Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 14 de 14
Filtrar
1.
J Natl Cancer Inst ; 90(22): 1735-41, 1998 Nov 18.
Artículo en Inglés | MEDLINE | ID: mdl-9827529

RESUMEN

BACKGROUND: Multidrug resistance-associated protein (MRP) and canalicular multispecific organic anion transporter (cMOAT) are transporter proteins that pump organic anions across cellular membranes and have been linked to resistance to cytotoxic drugs. We previously identified MOAT-B, an MRP/cMOAT-related transporter, by use of a polymerase chain reaction approach. However, analysis of expressed sequence tag (EST) databases indicated that there might be additional MRP/cMOAT-related transporters. To further define the MRP/cMOAT subfamily of transporters, we used EST probes to isolate complementary DNAs for two related transporter proteins, MOAT-C and MOAT-D. METHODS: MOAT-C and MOAT-D expression patterns in human tissues were determined by RNA blot analysis, and chromosomal localization of the genes was determined by fluorescence in situ hybridization. RESULTS: MOAT-C is predicted to encode a 1437-amino-acid protein that, among eukaryotic transporters, is most closely related to MRP, cMOAT, and MOAT-B (about 36% identity). However, MOAT-C is less related to MRP and cMOAT than MRP and cMOAT are to each other (about 48% identity). Like MOAT-B, MOAT-C lacks an N-terminal membrane-spanning domain, indicating that the topology of this protein is similarly distinct from that of MRP and cMOAT. MOAT-D is predicted to encode a 1527-amino-acid protein that is the closest known relative of MRP (about 58% identity). MOAT-D is also highly related to cMOAT (about 47% identity). The presence of an N-terminal membrane-spanning domain indicates that the topology of MOAT-D is quite similar to that of MRP and cMOAT. MOAT-C transcripts are widely expressed in human tissues; however, MOAT-D transcript expression is more restricted. The MOAT-C and MOAT-D genes are located at chromosomes 3q27 and 17q21.3, respectively. CONCLUSIONS: On the basis of amino acid identity and protein topology, the MRP/cMOAT transporter subfamily falls into two groups; the first group consists of MRP, cMOAT, and MOAT-D, and the second group consists of MOAT-B and MOAT-C.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/química , Proteínas Portadoras/química , ADN de Neoplasias/análisis , Leucemia/genética , Proteínas de Neoplasias/química , Neoplasias Ováricas/genética , Transportadoras de Casetes de Unión a ATP/genética , Secuencia de Aminoácidos , Proteínas de Transporte de Anión , Proteínas Portadoras/genética , Cromosomas Humanos Par 17/genética , Cromosomas Humanos Par 3/genética , ADN de Neoplasias/aislamiento & purificación , Femenino , Regulación Neoplásica de la Expresión Génica , Humanos , Datos de Secuencia Molecular , Proteínas Asociadas a Resistencia a Múltiples Medicamentos , Proteínas de Neoplasias/genética , Análisis de Secuencia de ADN
2.
Cancer Res ; 59(23): 5964-7, 1999 Dec 01.
Artículo en Inglés | MEDLINE | ID: mdl-10606242

RESUMEN

Multidrug resistance-associated protein (MRP)1 and canalicular multispecific organic anion transporter (cMOAT)/MRP2 are ATP-binding cassette (ABC) transporters that confer resistance to natural product cytotoxic drugs. We recently described the complete coding sequences of four human MRP/cMOAT subfamily members and found that, among these proteins, MRP3/MOAT-D is most closely related to MRP1 (58% identity; M. G. Belinsky and G. D. Kruh, Br. J. Cancer, 80: 1342-1349, 1999). In the present study, we sought to determine whether MRP3 is capable of conferring resistance to cytotoxic drugs. To address this question, human embryonic kidney 293 cells were transfected with an MRP3 expression vector, and the drug resistance phenotype of the transfected cells was analyzed. The MRP3-transfected cells displayed approximately 4-fold resistance to etoposide and approximately 2-fold resistance to vincristine, compared with control transfected cells. In addition, approximately 1.7-fold resistance was observed for the antimetabolite methotrexate. Increased resistance was not observed for several other natural product agents, including anthracyclines and Taxol. The MRP-transfected cells exhibited reduced accumulation of radiolabeled etoposide, consistent with the operation of a plasma membrane efflux pump. These results indicate that MRP3 confers resistance to some anticancer agents but that its resistance pattern is distinct from the resistance patterns of other ABC transporters involved in resistance to natural product chemotherapeutic agents.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/fisiología , Antineoplásicos/toxicidad , Resistencia a Múltiples Medicamentos , Etopósido/farmacocinética , Etopósido/toxicidad , Proteínas Asociadas a Resistencia a Múltiples Medicamentos , Vincristina/toxicidad , Transportadoras de Casetes de Unión a ATP/genética , Línea Celular , Supervivencia Celular/efectos de los fármacos , Embrión de Mamíferos , Humanos , Riñón , Proteínas Recombinantes/metabolismo , Transfección
3.
Cancer Res ; 58(13): 2741-7, 1998 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-9661885

RESUMEN

Multidrug resistance-associated protein (MRP) and canalicular multispecific organic anion transporter (cMOAT) are closely related mammalian ATP-binding cassette transporters that export organic anions from cells. Transfection studies have established that MRP confers resistance to natural product cytotoxic agents, and recent evidence suggests the possibility that cMOAT may contribute to cytotoxic drug resistance as well. Based upon the potential importance of these transporters in clinical drug resistance and their important physiological roles in the export of the amphiphilic products of phase I and phase II metabolism, we sought to identify other MRP-related transporters. Using a degenerate PCR approach, we isolated a cDNA that encodes a novel ATP-binding cassette transporter, which we designated MOAT-B. The MOAT-B gene was mapped using fluorescence in situ hybridization to chromosome band 13q32. Comparison of the MOAT-B predicted protein with other transporters revealed that it is most closely related to MRP, cMOAT, and the yeast organic anion transporter YCF1. Although MOAT-B is closely related to these transporters, it is distinguished by the absence of a approximately 200 amino acid NH2-terminal hydrophobic extension that is present in MRP and cMOAT and which is predicted to encode several transmembrane spanning segments. In addition, the MOAT-B tissue distribution is distinct from MRP and cMOAT. In contrast to MRP, which is widely expressed in tissues, including liver, and cMOAT, the expression of which is largely restricted to liver, the MOAT-B transcript is widely expressed, with particularly high levels in prostate, but is barely detectable in liver. These data indicate that MOAT-B is a ubiquitously expressed transporter that is closely related to MRP and cMOAT and raise the possibility that it may be an organic anion pump relevant to cellular detoxification.


Asunto(s)
Proteínas Portadoras/química , Cromosomas Humanos Par 13 , Resistencia a Múltiples Medicamentos , Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/química , Secuencia de Aminoácidos , Proteínas de Transporte de Anión , Secuencia de Bases , Proteínas Portadoras/genética , Mapeo Cromosómico , Cromosomas Humanos Par 13/genética , Resistencia a Múltiples Medicamentos/genética , Humanos , Datos de Secuencia Molecular
4.
Cancer Res ; 61(19): 7225-32, 2001 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-11585759

RESUMEN

We have recently determined that human multidrug resistance protein (MRP) 3, which confers resistance to certain natural product agents and methotrexate (MTX), is competent in the MgATP-energized transport of MTX and the monoanionic bile constituent glycocholate as well as several glutathione and glucuronate conjugates. Of these capabilities, the facility of MRP3 in conferring resistance to and mediating the transport of MTX is of particular interest because it raises the possibility that this pump is a component of the previously described cellular efflux system for this antimetabolite. However, if this is to be the case, a critical property of cellular MTX efflux that must be addressed is its ability to mediate the export of MTX but not that of its intracellular polyglutamylated derivatives. Here we examine the role of MRP3 in these and related processes by determining the selectivity of this transporter for MTX, MTX polyglutamates, and physiological folates. In so doing, we show that MRP3 is not only active in the transport of MTX but is also active in the transport the physiological folates folic acid (FA) and N(5)-formyltetrahydrofolic acid (leucovorin) and that polyglutamylation of MTX abolishes transport. Both FA and leucovorin are subject to high-capacity (V(max(FA)), 1.71 +/- 0.05 nmol/mg/min; V(max(leucovorin)), 3.63 +/- 1.20 nmol/mg/min), low-affinity (K(m(FA)), 1.96 +/- 0.13 mM; K(m(leucovorin)), 1.74 +/- 0.65 mM) transport by MRP3. Addition of a single glutamyl residue to MTX is sufficient to diminish transport by >95%. We also show that polyglutamylation similarly affects the capacity of MRP1 to transport MTX and that physiological folates are also subject to MgATP-stimulated transport by MRP1. On the basis of the capacity to transport MTX but not MTX-Glu(2), it is concluded that MRP3 and MRP1 represent components of the previously described cellular efflux system for MTX. The capacity of MRP3 to transport folates indicates that it may reduce intracellular levels of these compounds and thereby indirectly influence antifolate cytotoxicity, and it also implies that this pump may play a role in the response to chemotherapeutic regimens in which leucovorin is a component.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Resistencia a Múltiples Medicamentos , Ácido Fólico/farmacocinética , Leucovorina/farmacocinética , Metotrexato/farmacocinética , Ácido Poliglutámico/farmacocinética , Células 3T3 , Transportadoras de Casetes de Unión a ATP/antagonistas & inhibidores , Animales , Transporte Biológico/efectos de los fármacos , Humanos , Metotrexato/análogos & derivados , Metotrexato/metabolismo , Ratones , Proteínas Asociadas a Resistencia a Múltiples Medicamentos , Concentración Osmolar , Ácido Poliglutámico/análogos & derivados , Ácido Poliglutámico/metabolismo , Tritio
5.
Cancer Res ; 58(7): 1332-7, 1998 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-9537224

RESUMEN

An estramustine-resistant human ovarian carcinoma cell line, SKEM, was generated to explore resistance mechanisms associated with this agent. Cytogenetic analysis revealed that SKEM cells have a homogeneously staining region (hsr) at chromosome 9q34. Microdissection of the hsr, followed by fluorescence in situ hybridization to SKEM and normal metaphase spreads, confirmed that the amplified region was derived from sequences from 9q34. In situ hybridization with a probe specific for ABC2, a gene located at 9q34 that encodes an ATP-binding cassette 2 (ABC2) transporter, indicated that this gene is amplified approximately 6-fold in the estramustine-resistant cells. Southern analysis confirmed that ABC2 was amplified in SKEM, and Northern analysis indicated that the ABC2 transcript was overexpressed approximately 5-fold. The ABC1 gene located at 9q22-31 was not amplified in the resistant cells, and mRNA levels of several other ABC transporter genes were unaltered. Consistent with the concept that increased ABC2 expression contributes to the resistant phenotype, we observed that the rate of efflux of dansylated estramustine was increased in SKEM compared with control cells. In addition, antisense treatment directed toward ABC2 mRNA sensitized the resistant cells to estramustine. Together, these results suggest that amplification and overexpression of ABC2 contributes to estramustine resistance and provides the first indication of a potential cellular function for this product.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/fisiología , Antineoplásicos Hormonales/farmacocinética , Carcinoma/genética , Carcinoma/metabolismo , Estramustina/farmacocinética , Neoplasias Ováricas/genética , Neoplasias Ováricas/metabolismo , Transportadoras de Casetes de Unión a ATP/biosíntesis , Antineoplásicos Hormonales/farmacología , Carcinoma/patología , Cromosomas Humanos Par 9 , Regulación hacia Abajo , Resistencia a Antineoplásicos , Estramustina/farmacología , Femenino , Amplificación de Genes , Regulación Neoplásica de la Expresión Génica , Humanos , Hibridación Fluorescente in Situ , Oligonucleótidos Antisentido/farmacología , Neoplasias Ováricas/patología , Reacción en Cadena de la Polimerasa , ARN Mensajero/genética , ARN Mensajero/metabolismo , Transcripción Genética , Células Tumorales Cultivadas
6.
Cancer Res ; 61(8): 3339-47, 2001 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-11309290

RESUMEN

We have isolated the full-length cDNA for human ATP-binding cassette, sub-family A, member 2 transporter (ABCA2). The ORF of this cDNA encodes a protein consisting of 2436 amino acids with apparent molecular weight of M(r) 270,000. Accordingly, ABCA2 is the largest known mammalian ABC transporter described thus far. Analysis of mRNA expression levels indicated that ABCA2 is highest in human brain and has a broad expression pattern in a panel of tumor cell lines. Using specific antibodies to ABCA2 and various organelle marker proteins, ABCA2 was found to colocalize with the lysosomal/endosomal marker LAMP1, forming discrete, punctate intracellular vesicles. In ABCA2-transfected cells, the transporter also colocalized with a fluorescently labeled steroid analogue, estramustine. The sequestration of the steroid into the lysosomal/endosomal compartment indicates a potential substrate specificity for ABCA2. Furthermore, the presence of a lipocalin signature motif in the ABCA2 sequence suggests a possible broad role for this protein in the transport of steroids, lipids, and related molecules.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/biosíntesis , Transportadoras de Casetes de Unión a ATP/metabolismo , Secuencia de Aminoácidos , Animales , Northern Blotting , Clonación Molecular , ADN Complementario/genética , ADN Complementario/aislamiento & purificación , Estramustina/farmacocinética , Perfilación de la Expresión Génica , Humanos , Ratones , Microscopía Confocal , Datos de Secuencia Molecular , Conformación Proteica , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Fracciones Subcelulares/metabolismo , Especificidad por Sustrato , Distribución Tisular , Células Tumorales Cultivadas
7.
Cancer Lett ; 162(2): 181-91, 2001 Jan 26.
Artículo en Inglés | MEDLINE | ID: mdl-11146224

RESUMEN

The MRP subfamily of ABC transporters currently consists of at least six members, several of which have been demonstrated to transport amphipathic anions and to confer in vitro resistance to chemotherapeutic agents. In searching the data bases we identified the product of a cDNA sequencing project that bears significant similarity to MRP subfamily transporters. In this report the predicted coding sequence, protein product and expression pattern of this cDNA, termed MRP7, are analyzed. The MRP7 cDNA sequence encodes a 1492 amino acid ABC transporter whose structural architecture resembles that of MRP1, MRP2, MRP3, and MRP6, in that its transmembrane helices are arranged in three membrane spanning domains. However, in contrast to the latter transporters, a conserved N-linked glycosylation site is not found at the N-terminus of MRP7. Comparisons of the MRP7 amino acid sequence indicated that while it is most closely related to other MRP subfamily members, its degree of relatedness is the lowest of any of the known MRP-related transporters. The integrity of the predicted MRP7 coding sequence was confirmed by the synthesis of an approximately 158 kDa protein in reticulocyte lysates programmed with the MRP7 cDNA. While MRP7 transcript was detected in a variety of tissues by RT/PCR, it was not readily detectable by RNA blot analysis, suggesting that it is expressed at low levels in these tissues. Fluorescence in situ hybridization indicated that MRP7 maps to chromosome 6p12-21, in proximity to several genes associated with glutathione conjugation and synthesis. On the basis of these findings and evolutionary cluster analysis, we conclude that MRP7 is a member of the MRP subfamily of amphipathic anion transporters.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/genética , Transportadoras de Casetes de Unión a ATP/biosíntesis , Transportadoras de Casetes de Unión a ATP/química , Secuencia de Aminoácidos , Análisis por Conglomerados , ADN Complementario/genética , ADN Complementario/metabolismo , Perfilación de la Expresión Génica , Humanos , Hibridación Fluorescente in Situ , Datos de Secuencia Molecular , Proteínas Asociadas a Resistencia a Múltiples Medicamentos , Estructura Terciaria de Proteína , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido
9.
Nucleic Acids Res ; 19(3): 559-64, 1991 Feb 11.
Artículo en Inglés | MEDLINE | ID: mdl-2011528

RESUMEN

Analysis of the self-cleavage of ribozymes derived from the genomic RNA of Hepatitis delta virus (HDV) has revealed that certain co-transcribed vector sequences significantly affect the activity of the ribozyme. Specifically, the t1/2 of self-cleavage for a 135 nucleotide HDV RNA varied, at 42 degrees C, from 5 min to 88 min, depending on the vector-derived sequences flanking the 5' end of the ribozyme. Further analysis suggested that this phenomenon was most likely due to the interaction of vector-derived sequences with a 16 nucleotide region found at the 3' end of the ribozyme. These findings have implications for studies of ribozymes transcribed from cDNA templates, and may provide information regarding the catalytic structure of the HDV ribozyme.


Asunto(s)
Virus de la Hepatitis Delta/metabolismo , ARN Catalítico/metabolismo , ARN Viral/metabolismo , Secuencia de Bases , Clonación Molecular , Análisis Mutacional de ADN , Vectores Genéticos , Enlace de Hidrógeno , Datos de Secuencia Molecular , Estructura Molecular , Conformación de Ácido Nucleico , Relación Estructura-Actividad , Temperatura
10.
Br J Cancer ; 80(9): 1342-9, 1999 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-10424734

RESUMEN

Multidrug resistance-associated protein (MRP) and the canalicular multispecific organic anion transporter (cMOAT) are organic anion pumps that have been linked to cytotoxic drug resistance. We previously reported the isolation of three human MRP/cMOAT-related transporters, MOAT-B (MRP4), MOAT-C (MRP5) and MOAT-D (MRP3). In the present study we describe the fourth MRP/cMOAT-related transporter. We analysed ARA, a human cDNA reported to encode a 453 residue MRP-related transporter, and found that it represents a fused transcript composed of MRP sequences and partial sequences of a novel transporter. The complete coding sequence of this novel transporter, which we designated MOAT-E, was isolated. MOAT-E encodes a 1503 residue transporter that is most closely related to MRP (45%), MOAT-D (44%) and cMOAT (39%), both in terms of amino acid identity and sharing a common topology in which approximately 17 transmembrane spanning helices are distributed within three membrane spanning domains. RNA blot analysis indicated that MOAT-E expression is restricted to kidney and liver. These observations suggest that MOAT-E may function as an organic anion transporter involved in cellular detoxification and possibly in the hepatobiliary and renal excretion of xenobiotics and/or endogenous metabolites. Isolation of MOAT-E helps to define the MRP/cMOAT subfamily of transporters.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/análisis , Proteínas Portadoras/análisis , Riñón/química , Hígado/química , Transportadoras de Casetes de Unión a ATP/química , Transportadoras de Casetes de Unión a ATP/genética , Secuencia de Aminoácidos , Proteínas de Transporte de Anión , Proteínas Portadoras/química , Proteínas Portadoras/genética , ADN Complementario/aislamiento & purificación , Humanos , Datos de Secuencia Molecular , Proteínas Asociadas a Resistencia a Múltiples Medicamentos
11.
FASEB J ; 7(1): 130-6, 1993 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-8422959

RESUMEN

A chemical modification-interference assay was used to evaluate the sequence requirements for self-cleavage of a 73-nucleotide self-cleaving RNA from the genomic hepatitis delta virus (HDV). Twenty-two nucleotides were categorized as individually essential for self-cleavage, shown by loss of activity when modified. All of these required nucleotides fell within 38 nucleotides downstream of the cleavage site, suggesting an essential structural or functional role for this region. Lesser effects were seen for nucleotides further 3' of the cleavage site, and a small number of nucleotides had a negligible effect on the extent of self-cleavage when modified. Several modifications increased the extent of self-cleavage, suggesting these nucleotides may act to inhibit the reaction when unmodified. The functional requirements for certain nucleotides are discussed in the light of structural probing data and conventional mutational analysis available for other HDV RNAs.


Asunto(s)
Virus de la Hepatitis Delta/metabolismo , ARN Catalítico/metabolismo , ARN Viral/metabolismo , Secuencia de Bases , Dietil Pirocarbonato/farmacología , Genoma Viral , Virus de la Hepatitis Delta/genética , Hidrazinas/farmacología , Datos de Secuencia Molecular , Mutagénesis , Conformación de Ácido Nucleico , ARN Catalítico/química , ARN Catalítico/genética , ARN Viral/química , ARN Viral/genética , Relación Estructura-Actividad , Transcripción Genética
12.
Biochemistry ; 35(42): 13647-55, 1996 Oct 22.
Artículo en Inglés | MEDLINE | ID: mdl-8885844

RESUMEN

MRP is a recently described ATP-binding cassette transporter that confers cellular resistance to natural product cytotoxic drugs. To examine the biochemical activity and cellular physiology of this transporter, we isolated the murine MRP homologue and analyzed its in vitro substrate specificity. Murine MRP transcript is widely expressed in tissues and encodes a protein of 1528 amino acids that is 88% identical to its human homologue. Hydropathy analysis indicated that murine and human MRP, the yeast cadmium resistance transporter and the sulfonylurea receptor share a conserved topology distinguished from P-glycoprotein and the cystic fibrosis conductance regulator by an N-terminal hydrophobic region that contains several potential transmembrane domains. Drug uptake assays performed with membrane vesicles prepared from NIH3T3 cells transfected with a murine MRP expression vector revealed ATP-dependent transport for the natural product cytotoxic drugs daunorubicin and vincristine, as well as for the glutathione S-conjugates leukotriene C4 and azidophenacyl-S-glutathione. Drug transport was osmotically sensitive and saturable with regard to drug and ATP concentrations, with K(m) values of 19 microM, 19 microM, 26 nM, 17 microM, and 77 microM for daunorubicin, vincristine, leukotriene C4, APA-SG, and ATP, respectively. Consistent with broad substrate specificity, the drug glutathione conjugate APA-SG, oxidized glutathione, the LTD4 antagonist MK571, arsenate, and genistein were competitive inhibitors of daunorubicin transport, with Ki values of 32 microM, 25 microM, 1.9 microM, 108 microM, and 23 microM, respectively. This study demonstrates that the substrate specificity of murine MRP is quite broad and includes both the neutral or mildly cationic natural product cytotoxic drugs and the anionic products of glutathione conjugation. The widespread expression pattern of murine MRP in tissues, combined with its ability to transport both lipophilic xenobiotics and the products of phase II detoxification, indicates that it represents a widespread and versatile cellular defense mechanism.


Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Antineoplásicos/metabolismo , Azidas/metabolismo , Daunorrubicina/metabolismo , Glutatión/análogos & derivados , Leucotrieno C4/metabolismo , Células 3T3 , Transportadoras de Casetes de Unión a ATP/química , Adenosina Trifosfato/farmacología , Secuencia de Aminoácidos , Animales , Transporte Biológico/efectos de los fármacos , Membrana Celular/metabolismo , Clonación Molecular , Resistencia a Múltiples Medicamentos , Genisteína , Glutatión/metabolismo , Humanos , Isoflavonas/farmacología , Cinética , Ratones , Datos de Secuencia Molecular , Proteínas Asociadas a Resistencia a Múltiples Medicamentos , Concentración Osmolar , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Especificidad por Sustrato , Vincristina/metabolismo
13.
J Bioenerg Biomembr ; 33(6): 493-501, 2001 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11804191

RESUMEN

The MRP subfamily of ABC transporters from mammals consists of at least seven members, six of which have been implicated in the transport of amphipathic anions. MRP1, MRP2, and MRP3 bear a close structural resemblance, confer resistance to a variety of natural products as well as methotrexate, and have the facility for transporting glutathione and glucuronate conjugates. MRP1 is a ubiquitously expressed efflux pump for the products of phase II of xenobiotic detoxification, while MRP2, whose hereditary deficiency results in Dubin-Johnson syndrome, functions to extrude organic anions into the bile. MRP3 is distinguished by its capacity to transport the monoanionic bile constituent glycocholate, and may function as a basolateral back-up system for the detoxification of hepatocytes when the usual canalicular route is impaired by cholestatic conditions. MRP4 and MRP5 resemble each other more closely than they resemble MRPs 1-3 and confer resistance to purine and nucleotide analogs which are either inherently anionic, as in the case of the anti-AIDS drug PMEA, or are phosphorylated and converted to anionic amphiphiles in the cell, as in the case of 6-MP. Given their capacity for transporting cyclic nucleotides, MRP4 and MRP5 have also been implicated in a broad range of cellular signaling processes. The drug resistance activity and physiological substrates of MRP6 are unknown. However, its hereditary deficiency results in pseudoxanthoma elasticum, a multisystem disorder affecting skin, eyes, and blood vessels. It is hoped that elucidation of the resistance profiles and physiological functions of the different members of the MRP subfamily will provide new insights into the molecular basis of clinical drug resistance and spawn new strategies for combating this phenomenon.


Asunto(s)
Resistencia a Antineoplásicos/fisiología , Proteínas Asociadas a Resistencia a Múltiples Medicamentos/fisiología , Aminoácidos/química , Animales , Humanos , Fenotipo
14.
Int J Cancer ; 93(1): 107-13, 2001 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-11391629

RESUMEN

We previously isolated agosterol A (AG-A) from a marine Spongia sp. and found that it completely reversed colchicine resistance in P-glycoprotein (Pgp)-over-expressing KB-C2 cells and vincristine resistance in multidrug-resistance protein (MRP)1-over-expressing CV60 cells. However, a tri-deacetylated derivative of AG-A (IAG-A) showed almost no activity in reversing Pgp- or MRP1-mediated drug resistance. In this study, we examined the mechanisms by which AG-A reverses MRP1-mediated drug resistance by investigating the interaction between agosterols and MRP1 in MRP1-over-expressing human KB carcinoma (KB/MRP) cells. [3H]-Leukotriene C4 (LTC4), [3H]-2,4-dinitrophenyl-S-glutathione uptake into membrane vesicles prepared from KB/MRP cells and intracellular [3H]-vincristine accumulation and efflux in KB/MRP cells were measured with or without AG-A and/or inactive IAG-A. AG-A reduced MRP1-mediated [3H]-LTC4 transport in a dose-dependent manner, but IAG-A did not. Inhibition by AG-A was competitive, with a K(i) value of 31 microM. AG-A at 10 microM enhanced the accumulation of [3H]-vincristine in KB/MRP cells to the level of that in control cells in the absence of the agent. Likewise, ATP-dependent efflux of [3H]-vincristine from KB/MRP cells was enhanced compared with KB-3-1 cells and inhibited by AG-A. In addition, AG-A reduced intracellular levels of glutathione, a compound required for MRP1-mediated transport of some anti-cancer drugs. These findings suggest that AG-A reverses MRP1-mediated drug resistance by directly inhibiting the capacity of MRP1 to transport drugs. In addition, the capacity of AG-A to reduce cellular glutathione levels may contribute to the modulating activity of MRP1.


Asunto(s)
Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/efectos de los fármacos , Antineoplásicos/toxicidad , Colchicina/farmacología , Resistencia a Múltiples Medicamentos , Toxinas Marinas/toxicidad , Esteroles/toxicidad , Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/genética , Miembro 1 de la Subfamilia B de Casetes de Unión a ATP/metabolismo , Adenosina Trifosfato/metabolismo , Transporte Biológico/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Supervivencia Celular/efectos de los fármacos , Doxorrubicina/toxicidad , Etopósido/toxicidad , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Células KB , Proteínas Recombinantes/efectos de los fármacos , Proteínas Recombinantes/metabolismo , Vincristina/farmacocinética , Vincristina/toxicidad
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA