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At least 361 records · Page 20Linked to original sources
PubMed1989

Altered expression of epidermal growth factor receptor gene in a classical multidrug-resistant variant of a human cancer cell line, KB.

A variant clone resistant to high doses of colchicine (KB-C1) derived from human cancer KB cell line is resistant to various anticancer agents. The KB-C1 cells were much more resistant to epidermal growth factor and a chimeric toxin, EGF-Pseudomonas exotoxin (PE), than the parental KB cells. KB-C1 cells have decreased numbers of EGF-receptors, though the affinity of the receptors is similar to that in the parental KB cells. A drug-sensitive revertant (C1-R2) partially recovered its EGF-receptor activity. Northern blot analysis showed a decreased level of EGF-receptor mRNA in KB-C1 cells, while the multidrug-resistance gene, mdr-1, was expressed at very high levels in KB-C1 cells, but not in KB or C1-R2 cells. The drug-resistant cells were less tumorigenic than the parental cells when injected into nude mice. A decreased expression of EGF-receptor in these cells may be one of the pleiotropic properties of multidrug-resistant cells and may perhaps represent the basis for their reduced tumorigenicity.

Animals↗
PubMed2002

Downregulation of PGY1/MDR1 mRNA level in human KB cells by antisense oligonucleotide conjugates. RNA accessibility in vitro and intracellular antisense activity.

Inhibition of PGY1/MDR1 (multidrug resistance gene 1) mRNA expression in multidrug resistant KB-8-5 cells by 5'-bis-pyrenyl-3'-aminohexyl oligodeoxyribonucleotide conjugates targeted to four sites of this mRNA has been investigated. Three of the tested oligonucleotide conjugates specifically inhibited the expression of PGY1/MDR1 mRNA as monitored by the RT-PCR assay. The oligonucleotide conjugate targeted to the region (+178; +194) of the PGY1/MDR1 mRNA decreased level of this mRNA to 10% compared to the control. Nuclease-resistant analogs of oligonucleotide, complementary to this MDR1 mRNA region therefore, might be considered as a prototype compounds for development of gene-targeted therapeutic agents for overcoming the MDR phenotype caused by the overexpression of the PGY1/MDR1 gene.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Overexpression of CXC-chemokines and CXC-chemokine receptor type II constitute an autocrine growth mechanism in the epidermoid carcinoma cells KB and A431.

The CXC-chemokines Groalpha and interleukin-8 (IL-8) are well characterized growth factors for melanoma cells. Here the constitutive expression of Groalpha, IL-8 and their receptors (CXCR1 and CXCR2) as well as their functional involvement in the proliferation response were analyzed in normal keratinocytes and epidermoid carcinoma cell lines A431 and KB. Flow cytometric measurements, ELISA and semi-quantitative RT-PCR revealed low constitutive protein secretion and mRNA expression of both CXC-chemokines as well as CXCR1 and 2 in normal keratinocytes, whereas significant higher levels of CXC-chemokines and CXCR2 were deteced in epidermoid carcinoma cells. Proliferation of epidermoid carcinoma cells could be induced by CXC-chemokines and constitutive proliferation could be inhibited by neutralizing antibodies against CXC-chemokines and CXCR2. These studies indicate that constitutive Groalpha, IL-8 and CXCR2 protein expression enable an autocrine growth mechanism in epidermoid carcinoma cells.

Antigens, CD↗
PubMed2005

[An anti-P-gp/anti-CD3 bispecific antibody cytotoxic to human multidrug resistant KB cells].

OBJECTIVE: To study the specific cytotoxicity mediated by anti-P-gp/anti-CD(3) diabodies in multidrug resistant solid tumor using P-gp as target. METHODS: The anti-P-gp/anti-CD(3) diabodies were secreted from E. coli strain 16C9 containing the expression plasmid PAYZDCP, grown at 30 degrees C in a shaker flask; the diabodies were purified by affinity chromatography and identified by SDS-PAGE; the effect of the anti-P-gp/anti-CD(3) diabody mediated lysis of P-gp-expressing tumor cells was assayed by (51)Cr release assay in vitro, and by human KB nude mouse xenograft models in vivo. RESULTS: The diabodies were generated by bacteria as a soluble functional form and purified by one-step affinity chromatography with a yield > 4 mg/L culture medium. In (51)Cr release assay, the diabodies targeted human activated T cells to lyse P-gp(+)-KB/MDR cells in a dose-dependent manner. It suggested that the diabody was able to induce an efficient lysis of the target cells by human T cells in vitro. When combined with activated human T cells, the diabody significantly inhibited the growth of KB/MDR, but had no effect on KB xenografts. CONCLUSION: The anti-P-gp/anti-CD(3) bispecific antibody is a potent agent for targeting human T lymphocytes to lyse solid tumor cells overexpressing P-gp in vitro and in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1986

5-Fluorouracil augmentation of dihydrofolate reductase gene transcripts containing intervening sequences in methotrexate-resistant KB cells.

Several fragments of the human dihydrofolate reductase gene (tetrahydrofolate dehydrogenase, 5,6,7,8-tetrahydrofolate NADP+ oxidoreductase, EC 1.5.1.3) were isolated from gene-amplified KB7B cells and characterized. Recombinant plasmids containing intron sequences were constructed. Probes prepared from these plasmids were tested for dihydrofolate reductase precursor mRNA specificity via solution hybridization studies and Northern blot analysis. One probe, p0.69EH, was shown to be specific for dihydrofolate reductase RNA by its greatly enhanced level of hybridization with total RNA from dihydrofolate reductase gene-amplified versus non-amplified cells. In addition, solution hybridization studies with various classes of RNA and Northern blot analysis revealed that p0.69EH hybridizes predominantly with polyadenylated, high molecular weight, nuclear RNA species. Subsequent solution hybridization studies revealed a disproportionate 5-fluorouracil-induced increase in dihydrofolate reductase intron-containing RNA over dihydrofolate reductase mRNA. These results suggest that 5-fluorouracil incorporation into RNA may inhibit the conversion of precursor mRNA to mature mRNA.

Fluorouracil↗
PubMed1984

DNA primase from KB cells. Evidence for a novel model of primase catalysis by a highly purified primase/polymerase-alpha complex.

The oligonucleotide primers synthesized by a highly purified KB fraction containing DNA primase and DNA polymerase-alpha activities display reproducible alterations of structure and composition in response to dNTPs. These observations are sufficiently explained by a novel model of primase catalysis that defines the primase as a complex enzyme with distinct catalytic properties that are regulated by mechanisms exquisitely sensitive to dNTP concentration. The enzyme performs the template-directed, de novo synthesis of 1 unit of oligoribonucleotide (canonical priming reaction) and then elongates that moiety to a limited extent by several cycles of addition of short tracts of homogeneous oligoribonucleotide or oligodeoxynucleotide. The oligomeric units have modal lengths of approximately 11- to 14- nucleotides that are postulated to reflect the inherent processivity of the catalytic mechanisms. Elongation is accomplished by two catalytic centers, or conformers of a single center, that are synchronously coupled, mutually exclusive, and extremely stringent for respective rNTP and dNTP substrates. Transitions between these two catalytic modes are regulated by dNTPs and demonstrable at dNTP:rNTP concentrations of less than or equal to 10(-4). In the absence of dNTPs, the primase produces a family of oligoribonucleotides, approximately 24- to 36- nucleotides long; at dNTP levels between 0.08 and 0.80 micron, the primase synthesizes mixed oligomers composed of strictly alternating tandem arrays of oligoribo- and oligodeoxynucleotide units; and at dNTP levels greater than or equal to 4.8 micron, the primase becomes stabilized in the deoxy mode after the initial oligoribo leads to oligodeoxy transition and products contain only a single 5' -terminal unit of oligoribonucleotide. The model predicts that the physiologically significant primer for DNA polymerase-alpha is a mixed 5' -oligoribo-3' -oligodeoxynucleotide and the signal which governs the switch from RNA leads to DNA synthesis is intrinsic in the primase mechanism and is generated by ambient dNTPs.

Carcinoma↗
PubMed2006

Induction of cancer cell-specific apoptosis by folate-labeled cationic liposomes.

We have previously reported that cationic liposomes themselves can induce apoptosis in macrophages and lymphocytes. In this paper, we attempted the cancer cell-specific delivery of cationic liposomes and the induction of apoptosis utilizing this characteristic. Cationic liposomes composed of stearylamine (SA-liposomes) induced apoptosis in human nasopharyngeal epidermoid carcinoma cells (KB cells) overexpressing the folate receptor and human fibroblasts (WI-38 cells) with no folate receptor, without showing selectivity. To recruit liposomes to cancer cells and induce apoptosis, we focused on the folate receptor and prepared folic acid-labeled liposomes using polyethyleneglycol (PEG) (folate-PEG-liposomes). Folate-PEG-liposomes showed selectivity and induced apoptosis in KB cells, but not WI-38 cells. The apoptosis occurred in a dose-dependent manner. Furthermore, folate-PEG-liposomes appear to associate with KB cells via the folate receptor, whereas SA-liposomes may associate with cells through electrostatic interactions. To confirm the contribution of the folate receptor to apoptosis of KB cells induced by folate-PEG-liposomes, the effect of folic acid on the apoptosis was examined. The addition of free folic acid drastically suppressed the apoptosis of KB cells and the percentage of cells with hypodiploid nuclei returned to the control level. Taken together, cationic liposomes labeled with folate bound to KB cells via folate receptors and, interestingly, the cationic liposomes themselves could cause apoptosis in cancer cells.

Amines↗
PubMed1994

Site-directed mutagenesis of tryptophan residues to conserved hydrophobic residues inhibits the processing of human KB cell folate receptor.

We are interested in identifying the ligand binding site of the human folate receptor (hFR). Previous reports have suggested a role of tryptophan(W) residues in ligand binding. We used site-directed mutagenesis to change the conserved W residues in positions 86, 116, 142, 143, 156, 160, and 193 of the hFR to either leucine(L) or phenylalanine(F) to examine the role of these W residues in hFR function. Although all W to L changes except W86L produced unstable proteins, W to F changes were tolerated. Based on total folate binding and transport studies, Chinese hamster ovary (CHO) cells transfected with W86L, W116F, and W143F expressed high levels of functional hFR, equivalent to cells transfected with wt hFR. CHO cells transfected with W142F, W156F, W160F, and W193F expressed low or undetectable levels of functional hFR although mRNA was present. Of these four mutants, only W142F expressed easily detectable immunoprecipitable protein but it was not fully glycosylated. Since glycosylation may affect the ability of hFR to bind folate, we expressed W142F in Xenopus oocytes which glycosylate the mutant and wild type proteins to the same apparent extent. In oocytes, the stoichiometry of folate binding was identical between the fully processed mutant protein and the wild type hFR. These results indicate that in CHO cells three of the seven W mutations (W86L, W116F, and W143F) function normally, whereas four of the seven W mutations (W142F, W156F, W160F, and W193F) produce unstable or abnormally processed protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗