Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the present paper it is shown that the marine sponges Geodia cydonium and Verongia aerophoba contain the gene coding for P-glycoprotein P170, also known as a multidrug-resistance gene. Western blot studies revealed that polyclonal antibodies raised against hamster P170 cross-react with the sponge polypeptide of Mr 125,000. After endoglycosidase F treatment, the sponge P125 is converted to a polypeptide of Mr 105,000. Northern blot studies, using the human P170 cDNA probe, revealed a size of 4.2 kb for the sponge P125 transcript. The level of this transcript does not change in response to incubation with the aggregation factor. Confocal laser scanning microscopy showed that P125 is a cell membrane bound protein. In addition, sponge membrane vesicles possess a potential to bind in vitro 2-acetylamino-fluorene, vincristine and daunomycin. This process is Verapamil-sensitive, a characteristic known also for the mammalian vesicle associated P170. The data reported demonstrate that the classical multidrug resistance mechanism, described in drug-resistant tumor cell lines, functions also in sponges and may explain the relative resistance of these animals to pollution.
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PMID:Expression of P-glycoprotein gene in marine sponges. Identification and characterization of the 125 kDa drug-binding glycoprotein. 134 72

The brush border membrane of the proximal tubule contains two efflux pathways for organic cations from the cell to the tubular fluid: a P-glycoprotein and an organic cation/H+ exchanger. There is evidence that they transport many of the same substrates. Their structural relatedness is unknown and is the subject of this report. The experimental approach was to identify the exchanger with photoaffinity labeling reagents. The rationale was that if the P-glycoprotein and the organic cation/H+ exchanger transport many of the same substrates, then they might be photoaffinity labeled by the same reagents. [125I]Iodoarylazidoprazosin and [3H]azidopine are two reagents, which have been used, to photoaffinity label the P-glycoprotein. We found that several polypeptides were photolabeled in a time- and concentration-dependent manner. The photoincorporation into only two of these polypeptides (41 and 28 kDa) was blocked extensively by the presence of known substrates for the exchanger. The photoaffinity labeling of only the 41-kDa polypeptide was affected by treatment with the chemical reagents, N-ethylmaleimide and dithiothreitol, which are known to affect the exchanger reaction. The findings are consistent with the interpretation that a 41-kDa polypeptide is, or is a component of, the exchanger.
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PMID:Photoaffinity labeling of the organic cation/H+ exchanger in renal brush border membrane vesicles. 135 95

Retinal vascular endothelia form one aspect of the blood-retinal barrier and, like the blood-brain barrier, control the passage of molecules and cells into the parenchyma. To facilitate comparative in vitro studies, rat retinal endothelial cells have been cultured and characterised. Using immunocytochemical techniques, retinal endothelium was positive for von Willebrand's factor, tight junction-associated polypeptide (ZO-1) and the transferrin receptor. The cells also expressed high-affinity uptake of acetylated low-density lipoprotein. Using the monoclonal antibodies JSB-1 and C219, the product of the multidrug resistance gene, P-glycoprotein, was found to be expressed on primary cultures of both brain and retinal endothelium.
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PMID:Characterization of a rat retinal endothelial cell culture and the expression of P-glycoprotein in brain and retinal endothelium in vitro. 135 11

In the present study we have analyzed the involvement of phosphorylation in the function of P-glycoprotein and have also examined sites of phosphorylation along the P-glycoprotein polypeptide chain. The results show that in HL60 cells isolated for resistance to vincristine the protein kinase inhibitor staurosporine induces a major inhibition in the phosphorylation of P-glycoprotein. Further studies show that under the same conditions in which staurosporine inhibits P-glycoprotein phosphorylation there is a concomitant increase in cellular drug accumulation and a major inhibition in drug efflux. Additional studies using pulse-chase experiments show that the P-glycoprotein phosphate groups are metabolically active and that the protein undergoes rapid cycles of phosphorylation and dephosphorylation in the cell. Structural analyses demonstrate that cleavage of 32P-labeled P-glycoprotein at Asp-Pro linkages with formic acid results in the formation of a major phosphorylated peptide of 35 kDa and a minor peptide of 42 kDa. Western blot analysis using site-specific anti-sera against P-glycoprotein suggests that P35 represents a phosphorylated fragment containing P-glycoprotein amino acids 446-744. Analysis of tryptic peptides using site-specific antisera identifies a second major phosphorylated region of P-glycoprotein which contains amino acids 745-1088. These studies thus suggest that phosphorylation plays an important role in the biological activity of P-glycoprotein. The results also indicate that two adjacent internal regions are highly phosphorylated in the P-glycoprotein molecule.
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PMID:Analysis of P-glycoprotein phosphorylation in HL60 cells isolated for resistance to vincristine. 167 14

We have transfected a eukaryotic expression vector containing a mdr1 complementary DNA isolated from normal human liver into human BRO melanoma cells to study the drug-resistant phenotype produced by the exclusive overexpression of normal human mdr1 P-glycoprotein. The drug resistance pattern of mdr1-transfected clones includes relatively high resistance to gramicidin D (about 300-fold), vincristine (about 100-fold), and actinomycin D (about 100-fold) and a lower degree of resistance to doxorubicin (about 10-fold), VP16-213 (about 10-fold), and colchicine (about 6-fold). The transfectants did not exhibit resistance to trimetrexate, cis-platinum, mitomycin C, 1-beta-D-arabinofuranosylcytosine, bleomycin, G418, or magainin-2-amide; they were slightly more sensitive to verapamil (2-fold) but not to Triton X-100. As in other multidrug-resistant cell lines, resistance to vincristine could be reversed by verapamil and, more effectively, by cyclosporin A. Chloroquine only marginally increased drug sensitivity in mdr1-transfected cells. Gramicidin D resistance was also reversed by verapamil, suggesting that the mechanism of resistance to this polypeptide antibiotic is similar to that of other drugs transported by P-glycoprotein. Thus, expression of the wild-type mdr1 complementary DNA induces a drug-resistant phenotype similar to that induced by mdr1 complementary DNAs isolated from drug-resistant cell lines with relatively low colchicine resistance. As other cell lines may display a different pattern of drug resistance, it is clear that other resistance mechanisms or cell type-specific factors may modulate the resistance. mdr1-transfected cell lines provide a convenient tool for the identification of P-glycoprotein-mediated phenomena.
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PMID:Multidrug resistance phenotype of human BRO melanoma cells transfected with a wild-type human mdr1 complementary DNA. 196 59

The complete nucleotide sequence of comA, a gene required for induction of competence for genetic transformation in Streptococcus pneumoniae, was determined by using plasmid DNA templates and synthetic oligonucleotide primers. The sequence contained a single large open reading frame, ORF1, of 2,151 bp. ORF1 was included within the comAB locus previously mapped genetically and accounted for 50% of its extent. The predicted molecular weight of the largest polypeptide encoded within ORF1, 80,290, coincided with that measured previously (77,000) for the product of in vitro transcription-translation of the cloned comA locus. A Shine-Dalgarno sequence (AAAGGAG, delta G = -14 kcal) lay immediately upstream of ORF1. A sequence (TTtAat-17 bp-TAaAAT) similar to the Escherichia coli sigma 70 promoter consensus was located 410 bp upstream of ORF1. The deduced protein sequence of ComA showed a very strong similarity to the E. coli hemolysin secretion protein, HlyB, and strong similarities to other members of the family of ATP-dependent transport proteins, including the mammalian multidrug resistance P-glycoprotein. These similarities suggest that ComA functions in the transport of some molecule, possibly pneumococcal competence factor itself.
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PMID:Genetic transformation in Streptococcus pneumoniae: nucleotide sequence analysis shows comA, a gene required for competence induction, to be a member of the bacterial ATP-dependent transport protein family. 198 29

One reason for the failure of chemotherapy in the treatment of advanced cancers may be the outgrowth of multidrug-resistant tumour cells. Multidrug resistance has been modelled in numerous mammalian cell lines in which the phenotype is characterized by a pleiotropic cross-resistance to unrelated drugs. In the study reported here, we have produced monoclonal antibodies whose binding to plasma membranes of different multidrug-resistant mammalian cells correlates with the degree of drug resistance. All these antibodies are specific for P-glycoprotein, a cell surface component of relative molecular mass (Mr) 170,000 (170K) that has been described previously, and are directed against three spatially distinct epitopes which define a conserved cytoplasmic domain in the C-terminal region of the P-glycoprotein polypeptide. The conserved nature of P-glycoprotein and its low-level expression is drug-sensitive cells suggest that it has an important function at the cell surface. The monoclonal antibodies against P-glycoprotein described here might serve as diagnostic reagents for clinically unresponsive tumours.
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PMID:Detection of P-glycoprotein in multidrug-resistant cell lines by monoclonal antibodies. 241 30

The predicted cytoplasmic orientation and two-domain structure of the multidrug efflux pump P-glycoprotein were demonstrated with sequence-specific antibodies. We synthesized peptides corresponding to amino acid residues, Glu393-Lys408 (anti-P) and Leu1206-Thr1226 (anti-C) in P-glycoprotein from human mdr1 cDNA and used these peptides to produce polyclonal antibodies. From the primary structure of P-glycoprotein, and anti-C antibody is expected to recognize another position, Leu561-Thr581, in the duplicate structure of P-glycoprotein, but anti-P recognizes only one site. These antibodies bind to multidrug-resistant cells (KB-C2) with permeabilized plasma membrane but do not bind to nonpermeabilized KB-C2 cells or parental KB cells, supporting the predicted cytoplasmic orientation of these sequences. With immunoblotting of the membrane fractions from KB-C2 cells, a major 140-kDa polypeptide of the P-glycoprotein was detected with both anti-P and anti-C. Two minor polypeptides with molecular mass of 95 and 55 kDa were also detected. When membrane vesicles were digested mildly with trypsin, the amount of these two polypeptides increased. Anti-P detected only the 95-kDa polypeptide, and anti-C detected both 95- and 55-kDa polypeptides. Achromobacter lyticus protease I (lysyl endopeptidase) and Staphylococcus aureus V8 protease also produced two polypeptides with similar molecular weights. Absorption into lectin-agarose beads and labeling with [3H]glucosamine indicated that the 95-kDa polypeptide was glycosylated but that the 55-kDa polypeptide was not. These two polypeptides as well as P-glycoprotein were photoaffinity-labeled with a calcium channel blocker, [3H]azidopine, but most of the label was found in the 55-kDa polypeptide. The yield of labeled fragments from membrane vesicles photolabeled after digestion with trypsin was similar to that from membrane vesicles digested with trypsin after photolabeling. These data indicate 1) that the 95-kDa polypeptide is the fragment corresponding to the amino-terminal half of P-glycoprotein containing sugar chains; 2) that the 55-kDa polypeptide is the carboxyl-terminal half which was mainly labeled with [3H]azidopine; and 3) that P-glycoprotein has a relatively rigid structure with a small number of protease-sensitive sites and its global structure is not destroyed by tryptic cleavage.
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PMID:Cytoplasmic orientation and two-domain structure of the multidrug transporter, P-glycoprotein, demonstrated with sequence-specific antibodies. 247 41

A monoclonal antibody (C219) that recognizes the P-glycoprotein (Mr = 170,000) in plasma membranes of multidrug-resistant Chinese hamster ovary (CHO) cell lines was used to assay renal brush border membrane (BBM) and basolateral membrane (BLM) fractions for the presence of a cross-reactive polypeptide. The C219 antibody bound to a 155,000 dalton protein in immunoblots of rat BBM but not BLM proteins resolved by sodium dodecyl sulfate gel electrophoresis. The corresponding human kidney BBM and dog kidney BBM proteins had molecular weights of 170,000 and 160,000 respectively. The glycoprotein nature of the renal protein was shown by its sensitivity to N-glycanase treatment which reduced the apparent molecular weight of the dog protein to 120,000. In addition, dog P-glycoprotein could be bound to and eluted from immobilized wheat germ agglutinin. The molecular weight, antibody crossreactivity, glycosidase sensitivity and lectin binding show that this protein is a normal kidney analogue of the P-glycoprotein induced in multidrug resistant cell lines.
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PMID:Identification of P-glycoprotein in renal brush border membranes. 256 33

Two photoactive radiolabeled analogs of colchicine, N-(p-azido[3,5-[3H]benzoyl)aminohexanoyldeacetylcolchicine ([3H]NABC]) and N-(p-azido-[3-125I]salicyl)aminohexanoyldeacetylcolchicine ([125I]NASC) were synthesized and used to identify colchicine-specific acceptor(s) in membrane vesicles from multidrug resistant (MDR) variant DC-3F/VCRd-5L Chinese hamster lung cells. Both [3H]NABC and [125I]NASC specifically photolabeled a prominent 150-180 kDa polypeptide in membrane vesicles from DC-3F/VCRd-5L cells. The photolabeled polypeptide was immunoprecipitated by monoclonal antibody C219 specific for the MDR-related P-glycoprotein (P-gp) indicating the identity of this protein with P-gp. Colchicine at 1000 microM reduced [3H]NABC photolabeling of P-gp by 72%. Furthermore, 100 microM of colchicine, vincristine, vinblastine, doxorubicin and actinomycin D inhibited [125I]NASC photolabeling by 45, 88.8, 91.1, 61.5, and 51% respectively. However, methotrexate did not affect the [125I]NASC photolabeling of P-gp, indicating the multidrug specificity of the P-gp colchicine acceptor for drugs to which these cells are resistant.
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PMID:Photoaffinity labeling of P-glycoprotein in multidrug resistant cells with photoactive analogs of colchicine. 256 69


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