Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “KB Cells”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed1995

Activation of the MAP kinase homologue RK requires the phosphorylation of Thr-180 and Tyr-182 and both residues are phosphorylated in chemically stressed KB cells.

A MAP kinase homologue, termed the reactivating kinase (RK), lies in a signalling pathway which mediates cellular responses to stress. Here we demonstrate that the stress-induced activation of the RK in human KB cells is accompanied by the phosphorylation of Thr-180 and Tyr-182, and that the phosphorylation of both residues is required for the activation of this enzyme.

Amino Acid Sequence↗
PubMed1982

Excision-repair patch size in DNA from human KB cells treated with UV-light, or methyl methanesulfonate.

We have used the method of combined bromodeoxyuridine density label and radioactive label to measure the size of the repair patches appearing in the DNA of KB cells following treatment with UV-light or MMS. The repair patch size distribution was found to be the same for both agents, corresponding to the insertion of 34-40 nucleotides. These results, confirm recent results obtained by the bromodeoxyuridine-photolysis technique, that simple alkylating agents induce 'long patch' repair in human cells.

Bromodeoxyuridine↗
PubMed1974

Antibody to the type 5 adenovirus hexon polypeptide: detection of nascent polypeptides in the cytoplasm of infected KB cells.

Antibody to type 5 adenovirus hexon polypeptides reacted with the isolated hexon polypeptide chanis (monomers) but not with the native multimeric hexon capsomers (trimers). Indirect immunofluorescence detected hexon polypeptides mainly in the cytoplasm of KB cells infected with types 2 and 5 adenoviruses. Cells infected with adenovirus mutants H5ts116 or H5ts115, which are defective in the production of immunologically detectable hexons, synthesized immunologically detectable hexon polypeptides at the nonpermissive temperature.

Adenoviridae↗
PubMed1984

The kinetics of synthesis of early viral proteins in KB cells infected with wild-type and transformation-defective host-range mutants of human adenovirus type 5.

We have studied the kinetics of early adenovirus type 5 (Ad5) protein synthesis during lytic infection of KB cells by wild-type (wt) and transformation-defective host-range (hr) mutants. Proteins encoded within four early regions were studied: early region 1A (E1A: 1.5 to 4.5 map units, mu), E1B (4.5 to 11.2 mu), E2A (61.6 to 74.9 mu), and E4 (91.4 to 99.1 mu). Synthesis of E1A products, the first to appear during wt lytic infection, was detectable within 2 h after injection, reached a peak within the next hour, then declined to very low levels by 7 h post-infection. Synthesis of E2 and E4 proteins began at about 3 h post-infection, was maximal by 6 h and thereafter declined sharply. The E1B 19K and 58K proteins were first detected around 3 h post-infection and, after reaching maximal levels of expression by 8 h, declined to lower levels by 12 h post-infection. Infections with the E1A mutant hr3 were characterized by greatly depressed levels of early expression of E1B, E2 and E4 polypeptides but protein synthesis from these regions appeared to recover at late times. The pattern of expression exhibited by the E1B mutant hr6 revealed delayed and reduced levels of expression of E1B, E2 and E4 protein synthesis but increased levels of E1A protein synthesis. These results are consistent with the reported role of E1A gene products in the activation of early gene expression and, in addition, suggest that a function encoded in E1B may also influence the expression of Ad5 early genes at early and late times.

Adenoviruses, Human↗
PubMed1975

Adenovirus deoxyribonucleic acid replication. II. Synthesis of viral deoxyribonucleic acid in vitro by a nuclear membrane fraction from infected KB cells.

A cell-free system for the study of viral DNA replications was developed by the isolation of a nuclear membrane fraction "DNA replication complex" from adenovirus 2-infected human KB cells late after infection. This complex which possesses both DNA polymerase activity and a virus-specific endonuclease synthesizes exclusively virus-specific DNA sequences in vitro by a semiconservative mechanism. Analysis by rate zonal sedimentation in alkaline sucrose gradients showed that the products of the reaction are small DNA chains approximately 6 to 9 S, presumably "Okazaki intermediates," that are not sealed under our in vitro conditions. Analysis by rate zonal sedimentation in neutral sucrose gradients showed that labeled viral DNA fragments are hydrogen bonded to viral 18 S DNA segments, 0.25 the size of the linear, viral 31 S DNA genome. The 18 S DNA is probably a specific cleavage product of the viral endonuclease found in the replication complex and could represent intermediates in viral DNA replication or degradation products.

Adenosine Triphosphate↗
PubMedDate not supplied

KB cell culture I. Role in discovery of antitumor agents from higher plants.

KB (Eagle) cell culture has played a powerful role in discovery of antitumor agents from higher plants. Had KB alone been used as a preliminary screen, with in vivo screening limited to KB-active extracts, fractions, or compounds, KB activity of crude products would have led to discovery of vinblastine, vincristine, podophyllotoxin (from which the semisynthetics VM-26 and VP-16 were derived), and all but one of the antitumor agents now under development toward or in clinical evaluation, including bouvardin, bruceantin, camptothecin, ellipticine, homoharringtonine, maytansine, taxol, thalicarpine, and tripdiolide. Indicine N-oxide is the only important antitumor agent which would have been discovered only by in vivo screening of crude plant products. A substantial number of compounds effective against lymphoid leukemia L1210 and B16 melanoma were isolated from plants, extracts of which were active against KB.

Antineoplastic Agents, Phytogenic↗
PubMed1993

Altered folate-binding protein mRNA stability in KB cells grown in folate-deficient medium.

Folate-binding protein (FBP), a high-affinity folate receptor, is responsible for cellular accumulation of folate and folate analogs such as methotrexate in human KB (nasopharyngeal carcinoma) cells. Both FBP and FBP mRNA increase 3- to 5-fold when KB cells are grown in folate-deficient (less than 10 nM folate) medium (KB-FD), compared with growth in standard folate-replete medium containing at least 2 microM folate (KB-FR). The possible mechanisms of enhanced FBP gene expression in KB-FD were examined in this study. Southern blot analysis revealed no significant change in the FBP gene organization or copy number in the KB-FD DNA. While hypomethylation of the FBP gene was observed in KB-FD DNA, relative to KB-FR DNA, exposure of KB-FR to the DNA methylation inhibitors did not result in elevated FBP mRNA levels. The transcriptional rate of the FBP gene was the same in KB-FR and KB-FD. RNA half-life studies indicated that the half-life of FBP mRNA in KB-FD was increased approximately 2.5-fold, compared with KB-FR. Thus, the increase in the steady-state levels of FBP mRNA in KB-FD can be attributed partly to increased FBP mRNA stability.

Carrier Proteins↗
PubMed1976

Antiviral activity of arabinosyladenine and arabinosylhypoxanthine in herpes simplex virus-infected KB cells: selective inhibition of viral deoxyribonucleic acid synthesis in synchronized suspension cultures.

The drug 9-beta-d-arabinofuranosyladenine (ara-A) significantly suppressed the formation of herpes simplex virus type 1-induced syncytia in BHK-21/4 cells at concentrations as low as 0.1 mug/ml. Optimal activity was noted when the drug was added before initiation of viral deoxyribonucleic acid (DNA) synthesis (3.5 h postinfection). The deaminated derivative of ara-A, 9-beta-d-arabinofuranosylhypoxanthine (ara-H), was at least 10 times less effective in suppressing the development of herpes simplex virus-induced syncytia. The replication of herpes simplex virus was measured by assaying fluids and cells from infected drug-treated cultures by using a plaque production technique. Ara-A at drug levels of >10 < 32 mug/ml completely blocked the replication of infectious virus particles. Ara-H was less effective than ara-A in reducing the replication of virions. Rates of host and viral DNA synthesis were monitored by pulse labeling herpes simplex virus-infected synchronized KB cells with [(3)H]thymidine and subsequently separating viral from cellular DNA in CsCl density gradients. During synthetic (S) phase, ara-A or ara-H at concentrations ranging from 3.2 to 32 mug/ml selectively inhibited viral DNA synthesis. At 3.2 mug of ara-A per ml, viral DNA synthesis was reduced 74% although total cellular DNA synthesis was unaffected. Increasing concentrations of ara-A produced increasing temporal delays in the maximal rate of host DNA synthesis. This time shift was not observed in cells treated with ara-H.

Antiviral Agents↗
PubMed1996

Expression, subcellular distribution and response to phorbol esters of protein kinase C (PKC) isozymes in drug-sensitive and multidrug-resistant KB cells evidence for altered regulation of PKC-alpha.

Protein kinase C (PKC) comprises a family of related phospholipid-dependent serine/threonine protein kinases. PKC has been implicated in the induction and maintenance of the multidrug-resistance (MDR) phenotype but the role of different isozymes is not well understood. We compared the expression and subcellular distribution, and membrane association and down-regulation induced by phorbol esters, of individual PKC isozymes in drug-sensitive KB-3 and multidrug-resistant KB-V1 human carcinoma cell lines. Immunoblotting with isozyme-specific antibodies indicated the presence of PKC alpha (cytosol only). PKC beta (membrane only). PKC epsilon (mainly membrane associated) and PKC zeta (both fractions). PKC delta and PKC gamma were not detected. The expression levels of PKC beta. PKC epsilon and PKC zeta were unchanged in KB-V1 cells; PKC alpha was modestly increased ( approximately 65%) in the resistant cells as further determined by enzyme assay. The cytosolic nature and increased expression of PKC alpha were confirmed by immunofluorescent localization studies. Revertant cells, obtained by culturing KB-V1 cells in a drug-free medium, regained drug sensitivity with a loss of P-glycoprotein and a concomitant decrease in expression of PKC alpha, KB-V1 cells were found to differ markedly from KB-3 cells with respect to the translocation and down-regulation specifically of PKC alpha upon exposure to 12-O-tetradecanoyl-1-phorbol-13-acetate (TPA). Treatment with 30 nM TPA for 24 h completely depleted KB-3 cells of PKC alpha whereas 1 microM TPA was required to deplete KB-V1 cells of PKC alpha. Similar results were obtained when phorbol-12, 13-dibutyrate was used instead of TPA. Defective TPA-mediated down-regulation of PKC alpha was also observed in another PKC alpha-overexpressing MDR cell line. KB-A1. Importantly, cellular uptake of radiolabeled phorbol ester was similar for both drug-sensitive and MDR cells. Sensitive and resistant cells exhibited similar expression levels of RACK1, a PKC-binding protein important in activation-induced translocation. These findings further highlight the importance of PKC alpha in the MDR phenotype, and suggest that this isozyme may be expressed in a modified form or be subject to an altered regulation in MDR cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1967

Nucleotide sequence of KB cell 5S RNA.

The nucleotide sequence of 5S RNA derived from KB carcinoma cell ribosomes has been determined. The molecule has a length of either 120 or 121 nucleotides with uridine at its 3'-terminus and guanylic acid at its 5'-terminus. If, in addition to Watson-Crick base-pairing, one accepts occasional base-pairing of guanylic acid to uridylic acid, long sequences of complementary nucleotides can be identified within the molecule. Two regions of the molecule contain sequences complementary to four or five bases in the pentanucleotide sequence guanylic acid, ribothymidylic acid, pseudouridylic acid, cytidylic acid, guanylic acid, which is common to most transfer RNA molecules. This is the first time the sequence of an animal-cell RNA has been determined.

Autoradiography↗
PubMed1981

Ordered sequential mechanism of substrate recognition and binding by KB cell DNA polymerase alpha.

We have used a steady-state kinetic approach in conjunction with direct velocity gradient sedimentation binding studies to examine the detailed steps that are involved in the recognition of DNA primer-template and dNTPs by near-homogeneous human DNA polymerase alpha. We demonstrate that the interaction of the polymerase with its substrates obeys a rigidly ordered sequential terreactant mechanism, with template as the first substrate, followed by primer as the second substrate and dNTP as the third. Although the binding of primer is prerequisite to the kinetically significant binding of dNTP, specification of which of the four dNTPs can then add to the enzyme is absolutely determined by base sequence of the template (the first substrate). The critical element in the proof of the ordered mechanism is the demonstration of the phenomenon of induced substrate inhibition; the presence of a dideoxy-terminated primer (dead-end inhibitor) induces substrate inhibition by dNTP which is absolutely restricted to the dNTP complementary to the template to which the blocked primer is annealed. This inhibition is kinetically com the demonstration of the phenomenon of induced substrate inhibition; the presence of a dideoxy-terminated primer (dead-end inhibitor) induces substrate inhibition by dNTP which is absolutely restricted to the dNTP complementary to the template to which the blocked primer is annealed. This inhibition is kinetically com the demonstration of the phenomenon of induced substrate inhibition; the presence of a dideoxy-terminated primer (dead-end inhibitor) induces substrate inhibition by dNTP which is absolutely restricted to the dNTP complementary to the template to which the blocked primer is annealed. This inhibition is kinetically competitive with 3' -hydroxyl-terminated (unblocked) primer and approaches 100% at saturating levels of the complementary dNTP. Direct binding studies document the specific and exclusive ability of complementary dNTPs to drive the polymerase into a stable dead-end complex with the proposed structure, enzyme.template.dideoxy primer.dNTP, thus corroborating the kinetic observations. Attempts to elucidate the order of product release from the enzyme by product inhibition studies have shown the polymerization reaction to be essentially irreversible and have thus been unsuccessful. On the basis the known processivity of KB cell DNA polymerase alpha, a preliminary model involving initial release of pyrophosphate is reasonable; however, the relationship between product release and the process of polymerase translocation remains obscure. All of the kinetic and sedimentation binding studies were performed on a variety of homopolymeric and natural heteropolymeric DNA substrates, and the consistency of the results establishes absolutely the qualitative identity of the general mechanism by which human DNA polymerase alpha recognizes and replicated polydeoxynucleotide primer-templates, regardless of their precise physicochemical nature.

Binding Sites↗
PubMed1996

Cellular uptake of trivalent arsenite and pentavalent arsenate in KB cells cultured in phosphate-free medium.

Trivalent arsenite (As(III)) and pentavalent arsenate (As(V)) have been shown to have differential uptake mechanisms. In regular RPMI 1640 medium, As(III) was about 40-fold more toxic to KB oral epidermoid carcinoma cells. However, the cytotoxicity and intracellular accumulation of As(V) were dramatically enhanced, equalling those of As(III) when cells were grown in phosphate-free RPMI medium, As(V) uptake was dose-dependently inhibited by phosphate, mersalyl acid (a membrane sulfhydryl agent), and energy poisons, such as sodium azide and potassium cyanide. These results suggest that As(V) and phosphate share a common transport system. In contrast, As(III) uptake was not affected by the above agents. However, the initial uptake rates of As(III) were linearly correlated with its extracellular concentrations, suggesting that As(III) uptake is probably accomplished through simple diffusion. Our results also show that As(III) and As(V) are excreted from KB cells at a comparable rate, and at least half of As(V) is reduced to the more toxic As(III) prior to excretion into the medium. Therefore, the toxicity of As(V) may in part result from its reduction to As(III).

Arsenates↗
PubMed1994

Active efflux system for cisplatin in cisplatin-resistant human KB cells.

Mutants, KCP-4 and PC-5, resistant to an anticancer agent, cisplatin, were selected in multiple steps from human epidermoid KB carcinoma cells and human prostate PC-3 carcinoma cells, respectively. KCP-4 and PC-5 were 63 and 10 fold more resistant to cisplatin than the parental cells, respectively. KCP-4 cells exhibited increased resistance to cisplatin analogues and were also slightly cross-resistant to melphalan, cyclophosphamide, mitomycin C and methotrexate. KCP-4 cells were not cross-resistant to doxorubicin, daunorubicin, vincristine or CdSO4. The accumulations of cisplatin in KCP-4 cells and PC-5 in medium containing 50 microM cisplatin were approximately 20% of those in the parental cells. Revertant analysis suggested that a defect in cisplatin accumulation may be related to cisplatin resistance in PC-5 cells. The uncoupling agent of oxidative phosphorylation, 2,4-dinitrophenol, increased the accumulation of cisplatin in KCP-4 and cisplatin-resistant human prostate carcinoma PC-5 cells to nearly the same level as in their parental KB-3-1 and human prostate carcinoma PC-3 cells without 2,4-dinitrophenol, but did not increase accumulation in KB-3-1 and PC-3 cells. Addition of glucose in the medium inhibited the enhancement of cisplatin accumulation in KCP-4 cells by 2,4-dinitrophenol. Enhanced active efflux of cisplatin from KCP-4 cells was observed. A cell-cell hybridization test showed that the cisplatin resistance and the accumulation defect behaved as codominant traits. These data suggest that an active efflux system for cisplatin exists in cisplatin-resistant KCP-4 cells.

Biological Transport, Active↗