Proteomic investigation of taxol and taxotere resistance and invasiveness in a squamous lung carcinoma cell line

Pulse selections on a chemotherapy naive squamous lung carcinoma cell line, SKMES-1, with clinically relevant concentrations of taxanes (taxol or taxotere) resulted in the development of a stable taxotere-resistant variant, SKMES-1-Taxotere and an unstable taxol-resistant variant, SKMES-1-Taxol. Both variants exhibited increased invasiveness in vitro. The unstable nature of SKMES-1-Taxol facilitated looking at factors involved in loss of taxol resistance and increased invasion. The taxotere and taxol-resistant cell lines were 5.9-fold and 12.5-fold resistant to taxotere and taxol respectively. Alterations in expression of/or point mutations in tubulin, the main target of taxanes, is a major mechanism or resistance. However, alterations in expression of beta tubulin were not consistent in the taxane-selected variants. Cross-resistance to adriamycin, vincristine and etoposide (VP-16) was consistent with overexpression of P-glycoprotein (P-gp). However, P-gp alone is not sufficient to confer the complete multiple drug resistance phenotype as all cell lines exhibited cross-resistance to 5-Fluorouracil (5-FU) and more than one mechanism has been linked to taxane resistance. There was no correlation between the fall of taxol resistance in SKMES-1-Taxol and P-gp expression indicating the loss in resistance to be independent of P-gp expression. Furthermore, resistance to the other drugs was not unstable in SKMES-1-Taxol suggesting some parallel mechanisms of resistance. Two-dimensional electrophoresis coupled with matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry was used to identify alterations in expression of specific proteins associated with taxane resistance. A large number of differentially regulated proteins were identified in the resistant and invasive variants affecting cellular processes including stress response, protein turnover and cytoskeleton proteins.     

A mutant beta-tubulin confers resistance to the action of benzimidazole-carbamate microtubule inhibitors both in vivo and in vitro

The mutant BEN210 of Physarum polycephalum is highly resistant to a number of benzimidazole carbamate agents, including methylbenzimidazole-2-yl-carbamate and parbendazole. The resistance is conferred by the benD210 mutation in a structural gene for beta-tubulin. This mutant allele encodes a beta-tubulin with novel electrophoretic mobility. We have used this strain to determine whether the mutant beta-tubulin is used in microtubules and whether this usage permits microtubule polymerisation in the presence of drugs both in vivo and in vitro. In vitro assembly studies of tubulin purified from the mutant strain have shown that microtubules are formed both in the absence of drugs and in all drug concentrations tested (up to 50 microM parbendazole). In contrast, the assembly of microtubules from wild-type tubulin in vitro is totally inhibited by 2-5 microM parbendazole. Thus the resistance of BEN210 to parbendazole observed in vivo has been reproduced in vitro using tubulin purified from the mutant strain. Electrophoretic analysis of the microtubules formed in vitro has shown that both the wild-type and the mutant beta-tubulin are incorporated into the microtubules and that the proportion of mutant to wild-type beta-tubulin appears to remain constant with increasing drug concentration. This is the first demonstration of a single mutation in a tubulin structural gene causing an altered function of the gene product in vitro.     

Tubulin Beta3 Serves as a Target of HDAC3 and Mediates Resistance to Microtubule-Targeting Drugs

We investigated the role of HDAC3 in anti-cancer drug-resistance. The expression of HDAC3 was decreased in cancer cell lines resistant to anti-cancer drugs such as celastrol and taxol. HDAC3 conferred sensitivity to these anti-cancer drugs. HDAC3 activity was necessary for conferring sensitivity to these anti-cancer drugs. The down-regulation of HDAC3 increased the expression of MDR1 and conferred resistance to anti-cancer drugs. The expression of tubulin β3 was increased in drug-resistant cancer cell lines. ChIP assays showed the binding of HDAC3 to the promoter sequences of tubulin β3 and HDAC6. HDAC6 showed an interaction with tubulin β3. HDAC3 had a negative regulatory role in the expression of tubulin β3 and HDAC6. The down-regulation of HDAC6 decreased the expression of MDR1 and tubulin β3, but did not affect HDAC3 expression. The down-regulation of HDAC6 conferred sensitivity to taxol. The down-regulation of tubulin β3 did not affect the expression of HDAC6 or MDR1. The down-regulation of tubulin β3 conferred sensitivity to anti-cancer drugs. Our results showed that tubulin β3 serves as a downstream target of HDAC3 and mediates resistance to microtubule-targeting drugs. Thus, the HDAC3-HDAC6-Tubulin β axis can be employed for the development of anti-cancer drugs.     

Study of multi-drug resistant mechanisms in a taxol-resistant hepatocellular carcinoma QGY-TR 50 cell line

Cancer chemotherapy with taxol often fails due to acquired resistance of cancer cells, which is frequently associated with an overexpression of P-gp and alterations of beta-tubulin. A taxol-resistant cell line, QGY-TR50, derived from a human hepatocellular carcinoma (HCC) QGY-7703 cell line was used to investigate the mechanisms of taxol-resistance. QGY-TR50 cells showed more than 250-fold resistance to taxol and exhibited cross-resistance to other drugs including actinomycin D, doxorubicin, vinblastine, and vincristine. P-gp was highly expressed in QGY-TR50 cells. Expression levels of five human beta-tubulin isotypes (betaI-, betaII-,betaIII-, betaIva, and betaIvb-tubulin) were examined by real-time semi-quantitative PCR. Comparing with QGY-7703 cells, QGY-TR50 cells did not show any significant change in the expression levels of betaI-, betaIva, and betaIvb-tubulin. While a 1.2-fold increased in betaII-tubulin and a 0.5-fold decreased in betaIII-tubulin levels were observed. All results suggest that the P-glycoprotein could be one key factor involved in enhancing drug resistance in QGY-TR50 cells.     

Altered expression, polymerisation and cellular distribution of alpha-/beta-tubulins and apoptosis-like cell death in arsenite resistant Leishmania donovani promastigotes

Studies in mammalian systems have shown specific affinity of arsenite for tubulin proteins. The sodium m-arsenite (NaAsO2) resistant Leishmania donovani used in this study is resistant to 20 microM NaAsO2, which is a 13-fold increase in resistance compared to the wild type. Data presented in this study shows decreased expression of alpha- and beta-tubulin in wild type L. donovani promastigotes on exposure to NaAsO2 from 0.0016 to 5.0 microM (IC50 in the wild type strain) in a dose-dependent manner. alpha- and beta-tubulins in the resistant strain show decreased expression levels only at 65.0 microM NaAsO2 (IC50 in the resistant strain). Treatment with respective IC50 concentrations of NaAsO2 caused alterations in tubulin polymerisation dynamics and deregulated the cellular distribution of the microtubules in wild type and resistant strains. The NaAsO2-induced cell death exhibited characteristics of apoptosis-like DNA laddering and fragmentation in both the affected wild type and resistant cells. However, poly(ADP-ribose)polymerase cleavage was evident in the wild type strain but not in the resistant strain.     

Alterations in microtubule assembly caused by the microtubule-active drug LY195448

LY195448 is an experimental drug that blocks cells at metaphase (Boder et al.: Microtubules and Microtubule Inhibitors 1985: 353-361, 1985). A 4 hour exposure of NRK cells to a drug concentration of 46 microM (15 micrograms/ml) increased the number of mitotic cells in the population from 4.9% to 18.5%. Examination of treated cells by immunofluorescence showed increased numbers of cells blocked at prometaphase, with short microtubules extending from the spindle pole to the kinetochores. The cytoskeleton of interphase cells remained intact at these concentrations. However, the number of microtubules appeared to be reduced, and those that remained appeared kinkier and curled, particularly toward the periphery of the cells. When cytoskeletal microtubules of NRK cells were depolymerized with nocodazole, they reassembled within minutes of transfer to drug-free media. However, nocodazole-treated cells transferred to fresh media containing 15 micrograms/ml of LY195448 required 2-3 times longer to reassemble cytoplasmic microtubules. Previously isolated Chinese hamster ovary cell microtubule mutants resistant to either taxol or Colcemid were tested for cross-resistance to this drug. Cell lines resistant to the depolymerizing drug Colcemid exhibited increased resistance to LY195448 compared to wild-type cells, whereas taxol resistant cell lines were more sensitive. Of eleven newly isolated mutant CHO cell lines selected for increased resistance to LY195448, seven exhibited an altered beta-tubulin protein by two-dimensional polyacrylamide gel electrophoresis. These 11 cell lines also showed a heterogenous pattern of resistance to several microtubule-active drugs. These data demonstrate that LY195448 is cytotoxic to mammalian cells because it inhibits microtubule assembly, most likely through a direct interaction with tubulin.     

Differential partitioning of Gαi1 with the cellular microtubules: a possible mechanism of development of Taxol resistance in human ovarian carcinoma cells

Background

Taxol binds to the cellular microtubules and suppresses their dynamic instability. Development of tumor cell resistance to taxol is typically associated with increased expression of the drug efflux pump P-glycoprotein and/or alterations in the microtubules. Recently, changes in the dynamic instability of the microtubules have also been associated with development of taxol resistance in a lung cancer cell line. We have established a 250-fold taxol-resistant human ovarian carcinoma subline (2008/13/4) that does not display the typical alterations associated with development of drug resistance.

Results

Utilizing the mRNA differential display technique, we observed increased expression of an alpha subunit of the guanine nucleotide-binding protein, Gαi1, in the taxol-resistant human ovarian carcinoma cell lines compared to the parental 2008 cells. Several isoforms of the α-subunit of the G protein have been identified and the Gαi (inhibitory) are so named because they inhibit the activity of adenylate cyclase leading to inactivation of the cAMP-dependent protein kinase A (PKA) pathway. In addition, Gαi1 is also known to bind to microtubules and activates their GTPase activity and thus induces depolymerization of the microtubules. In the present study we demonstrate that the intracellular level of cAMP and the PKA activity were higher in the taxol-resistant 2008/13/4 and the 2008/17/4 cells despite the increased expression of Gαi1 in these cells. Moreover, Gαi1 was found to be localized not on the cell membrane, but in intracellular compartments in both the taxol-sensitive and -resistant human ovarian carcinoma cells. Interestingly, increased association of the Gαi1 protein and the microtubules in the taxol-resistant cells compared to the parental 2008 cells was observed, both prior to and after treatment of these cells with taxol.

Conclusion

Based on the opposing effects of taxol and the Gαi1 protein on the microtubule dynamic instability (taxol suppresses microtubule dynamic instability whilst the Gαi1 protein inhibits the suppression) our results indicate the operation of a novel pathway that would enable the cells to escape the cytotoxic effects of taxol.     

Transfer and amplification of a mutant beta-tubulin gene results in colcemid dependence: use of the transformant to demonstrate regulation of beta-tubulin subunit levels by protein degradation.

Total genomic DNA from a temperature-sensitive, colcemid-resistant Chinese hamster ovary (CHO) cell mutant expressing an electrophoretic variant beta-tubulin was used to transform wild-type CHO cells to colcemid-resistant cells at 37 degrees C. Southern blot analysis of the transformant demonstrated the three- to fivefold amplification of one of many beta-tubulin sequences compared with that of the wild type or mutant, thereby identifying a functional tubulin gene in CHO cells. This amplification of one tubulin-coding sequence resulted in a threefold increase in two beta-tubulin mRNA species, suggesting that both species may be encoded by a single gene. Pulse-chase experiments showed that in the transformant, total beta-tubulin was synthesized and degraded faster than in the revertant or wild-type cells, so that the steady-state levels of beta-tubulin and alpha-tubulin were unchanged in the transformant compared with those of wild-type, mutant, or revertant cells. Increased ratios of mutant to wild-type beta-tubulin made the transformant dependent on microtubule-depolymerizing drugs for growth at 37 but not 34 degrees C and supersensitive to the microtubule-stabilizing drug taxol at 34 degrees C.     

Taxol binds to polymerized tubulin in vitro

Taxol, a natural plant product that enhances the rate and extent of microtubule assembly in vitro and stabilizes microtubules in vitro and in cells, was labeled with tritium by catalytic exchange with (3)H(2)O. The binding of [(3)H]taxol to microtubule protein was studied by a sedimentation assay. Microtubules assembled in the presence of [(3)H]taxol bind drug specifically with an apparent binding constant, K(app), of 8.7 x 19(-7) M and binding saturates with a calculated maximal binding ration, B(max), of 0.6 mol taxol bound/mol tubulin dimer. [(3)H]Taxol also binds and assembles phosphocellulose-purified tubulin, and we suggest that taxol stabilizes interactions between dimers that lead to microtubule polymer formation. With both microtubule protein and phosphocellulose- purified tubulin, binding saturation occurs at approximate stoichiometry with the tubulin dimmer concentration. Under assembly conditions, podophyllotoxin and vinblastine inhibit the binding of [(3)H]taxol to microtubule protein in a complex manner which we believe reflects a competition between these drugs, not for a single binding site, but for different forms (dimer and polymer) of tubulin. Steady-state microtubules assembled with GTP or with 5’-guanylyl-α,β-methylene diphosphonate (GPCPP), a GTP analog reported to inhibit microtubule treadmilling (I.V. Sandoval and K. Weber. 1980. J. Biol. Chem. 255:6966-6974), bind [(3)H]taxol with approximately the same stoichiometry as microtubules assembled in the presence of [(3)H]taxol. Such data indicate that a taxol binding site exists on the intact microtubule. Unlabeled taxol competitively displaces [(3)H]taxol from microtubules, while podophyllotoxin, vinblastine, and CaCl(2) do not. Podophyllotoxin and vinblastine, however, reduce the mass of sedimented taxol-stabilized microtubules, but the specific activity of bound [(3)H]taxol in the pellet remains constant. We conclude that taxol binds specifically and reversibly to a polymerized form of tubulin with a stoichiometry approaching unity.     

The nature of the modification at position 37 of tRNAPhe correlates with acquired taxol resistance

Acquired drug resistance is a major obstacle in cancer therapy. Recent studies revealed that reprogramming of tRNA modifications modulates cancer survival in response to chemotherapy. However, dynamic changes in tRNA modification were not elucidated. In this study, comparative analysis of the human cancer cell lines and their taxol resistant strains based on tRNA mapping was performed by using UHPLC–MS/MS. It was observed for the first time in all three cell lines that 4-demethylwyosine (imG-14) substitutes for hydroxywybutosine (OHyW) due to tRNA-wybutosine synthesizing enzyme-2 (TYW2) downregulation and becomes the predominant modification at the 37^th position of tRNA^phe in the taxol-resistant strains. Further analysis indicated that the increase in imG-14 levels is caused by downregulation of TYW2. The time courses of the increase in imG-14 and downregulation of TYW2 are consistent with each other as well as consistent with the time course of the development of taxol-resistance. Knockdown of TYW2 in HeLa cells caused both an accumulation of imG-14 and reduction in taxol potency. Taken together, low expression of TYW2 enzyme promotes the cancer survival and resistance to taxol therapy, implying a novel mechanism for taxol resistance. Reduction of imG-14 deposition offers an underlying rationale to overcome taxol resistance in cancer chemotherapy.     

Effect of benzimidazole drugs on tubulin in benzimidazole resistant and susceptible strains of Caenorhabditis elegans

An in vitro assay was used to determine efficacy and if side resistance was present to benzimidazole anthelmintics tested against Caenorhabditis elegans after selection with albendazole. Side resistance was present to all the benzimidazoles tested, except for oxibendazole and parbendazole. At a concentration of 1 mM, all of the drugs, except thiabendazole, were effective in killing 100% of the albendazole susceptible worms. Tubulin from albendazole resistant and susceptible C. elegans was isolated and run on polyacrylamide gels. Western blots with anti-tubulin antibody showed that the albendazole resistant strain had an altered tubulin. Electron microscopy of albendazole-treated drug resistant worms showed microtubules throughout the intestinal cells. Microtubules were not observed in albendazole-treated drug susceptible worms.     

Resistance to antimitotic drugs in Chinese hamster ovary cells correlates with changes in the level of polymerized tubulin.

A sensitive and reproducible method to measure relative levels of polymerized and soluble tubulin in cells has been developed. This method involves metabolically labeling cells with radioactive amino acids followed by lysis in a microtubule-stabilizing buffer, centrifugation to separate soluble from polymerized tubulin, resolution of the proteins in each fraction by two-dimensional gel electrophoresis, and quantitation of the tubulin by liquid scintillation counting of spots excised from the gel. Several buffers were evaluated for their reproducibility and efficacy in preserving the state of in vivo microtubule assembly at the time of cell lysis, and the ability of the technique to measure drug-induced changes in tubulin polymerization was determined. Results using this method indicate that Chinese hamster ovary cells maintain approximately 40% of the cellular tubulin in an assembled form. Dose-dependent decreases in tubulin polymerization could be measured in Colcemid-treated cells, while dose-dependent increases in assembly were measured in taxol-treated cells. The results with taxol indicate that, following the increase in microtubule polymerization, there is a time-dependent bundling of microtubules that occurs without further increases in the extent of tubulin assembly. Examination of drug-resistant Chinese hamster ovary cells reveals that Colcemid-resistant mutants maintain more tubulin in the polymerized state (approximately 50%), while taxol-resistant mutants maintain less assembled tubulin (about 28%). Similar changes occur regardless of whether the mutant cells have an alteration in alpha- or in beta-tubulin. A model to explain these results is discussed.     

Resistance to the mitotic inhibitor NY 3170 in Chinese hamster ovary cells

Mutant CHO cells have been isolated which are resistant to NY 3170, a member of the metahalone group of antimitotic drugs. One NY 3170 resistant mutant is hypersensitive to the microtubule-stabilising drug, taxol, but there is not a reciprocal relationship between levels of resistance to these drugs in CHO cells, since it was found that sixteen other mutants isolated on the basis of taxol resistance had wild type levels of NY 3170 resistance. Our NY 3170 resistant mutants are cross-resistant to vincristine and other mutants, selected on the basis of vincristine resistance, are cross-resistant to NY 3170.     

High expression of class III β-tubulin has no impact on functional cancer cell growth inhibition of a series of key vinblastine analogs

Clinical association studies have implicated high expression of class III β-tubulin as a predictive factor for lower response rates and reduced overall survival in patients receiving tubulin binding drugs, most notably the taxanes. Because of the implications, we examined a series of key vinblastine analogs that emerged from our studies in functional cell growth inhibition assays for their sensitivity to high expression of class III β-tubulin (human non-small cell lung cancer cell line A549 vs taxol-resistant A549-T24). Unlike taxol, vinblastine and a set of key analogs 3–10 did not exhibit any loss in sensitivity toward A549-T24. The results suggest that vinblastine and related analogs are not likely prone to resistance derived from high expression of class III β-tubulin unlike the taxanes. Most significant are the results with 4–6, a subset of 20′ amide vinblastine analogs. They match or exceed the potency of vinblastine and they display more potent activity against taxol-resistant A549-T24 than even wild type A549 cells (1.2–2-fold), complementing our prior observations that they also display no sensitivity to overexpression of Pgp (HCT116/VM46 vs HCT116) and are not subject to resistance derived from Pgp efflux.     

Taxol from Tubercularia sp. strain TF5, an endophytic fungus of Taxus mairei

The diterpenoid taxol is an important anticancer agent used widely in the clinic. The purpose of this work was to identify a taxol-producing endophytic fungus (strain TF5) isolated from Taxus mairei and study its anticancer activities. Strain TF5 was identified as a Tubercularia sp. according to the morphology of the fungal culture, the mechanism of spore production and the characteristics of the spores. Strain TF5 produced taxol, when grown in potato dextrose liquid medium and analyzed by thin layer chromatography, high performance liquid chromatography, ultraviolet and mass spectrometry. The fungal taxol, which was isolated from the organic extract of the TF5 culture, had strong cytotoxic activity towards KB and P388 cancer cells in vitro, tested by the MTT assay. Observed with immunofluorescence and electron microscopy, the fungal taxol enhanced microtubule stability and bundling in culture cells and induced tubulin polymerization in vitro similar to the authentic taxol.     

In vivo and in vitro studies on the role of HMW-MAPs in taxol-induced microtubule bundling

The involvement of high molecular weight microtubule-associated proteins (HMW-MAPs) in the process of taxol-induced microtubule bundling has been studied using immunofluorescence and electron microscopy. Immunofluorescence microscopy shows that HMW-MAPs are released from microtubules in granulosa cells which have been extracted in a Triton X-100 microtubule-stabilizing buffer (T-MTSB), unless the cells are pretreated with taxol. 1.0 microM taxol treatment for 48 h results in microtubule bundle formation and the retention of HMW-MAPs in these cells upon extraction with T-MTSB. Electron microscopy demonstrates that microtubules in control cytoskeletons are devoid of surface structures whereas the microtubules in taxol-treated cytoskeletons are decorated by globular particles of a mean diameter of 19.5 nm. The assembly of 3 X cycled whole microtubule protein (tubulin plus associated proteins) in vitro in the presence of 1.0 microM taxol, results in the formation of closely packed microtubules decorated with irregularly spaced globular particles, similar in size to those observed in cytoskeletons of taxol-treated granulosa cells. Microtubules assembled in vitro in the absence of taxol display prominent filamentous extensions from the microtubule surface and center-to-center spacings greater than that observed for microtubules assembled in the presence of taxol. Brain microtubule protein was purified into 6 s and HMW-MAP-enriched fractions, and the effects of taxol on the assembly and morphology of these fractions, separately or in combination, were examined. Microtubules assembled from 6 s tubulin alone or 6 s tubulin plus taxol (without HMW-MAPs) were short, free structures whereas those formed in the presence of taxol from 6 s tubulin and a HMW-MAP-enriched fraction were extensively crosslinked into aggregates. These data suggest that taxol induces microtubule bundling by stabilizing the association of HMW-MAPs with the microtubule surface which promotes lateral aggregation.     

Taxol-dependent mutants of Chinese hamster ovary cells with alterations in alpha- and beta-tubulin

Chinese hamster ovary cell mutants resistant to the microtubule stabilizing drug taxol were isolated in a single step. Of these 139 drug-resistant mutants, 59 exhibit an absolute requirement for taxol for normal growth and division, 13 have a partial requirement, and 69 grow normally without the drug. Two-dimensional gel analysis of whole cell proteins reveal "extra" spots representing altered tubulins in 13 of the mutants. Six of these have an altered alpha-tubulin and seven have an altered beta-tubulin. Cells with an absolute dependence on taxol become large and multinucleated when deprived of the drug. In contrast, partially dependent cells exhibit some multinucleation, but most cells appear normal. In one mutant that has an absolute dependence on taxol, the cells appear to die more quickly and their nuclei do not increase in size or number. As previously found for another taxol-dependent mutant (Cabral, F., 1983, J. Cell. Biol., 97:22-29), the taxol dependence of the mutants described in this paper behaves recessively in somatic cell hybrids, and the cells are more susceptible to being killed by colcemid than are the wild-type parental cells. When compared with wild-type cells, taxol-dependent mutants have normal arrays of cytoplasmic microtubules but form much smaller mitotic spindles in the presence of taxol. When deprived of the drug, however, these mutants cannot complete assembly of the mitotic spindle apparatus, as judged by tubulin immunofluorescence. Thus, the defects leading to taxol dependence in these mutants with defined alterations in alpha- and beta-tubulin appear to result from the cell's inability to form a functional mitotic spindle. Reversion analysis indicates that the properties of at least one alpha-tubulin mutant are conferred by the altered tubulin seen on two-dimensional gels.     

TRAG-3, a novel gene, isolated from a taxol-resistant ovarian carcinoma cell line

The mechanisms responsible for the development of the taxol resistance phenotype are unclear, and are likely explained by multiple mechanisms. To understand the molecular changes associated with drug resistance more fully, a taxol-resistant subline, derived from the human ovarian cancer cell line SKOV-3, was established through selection by culture in incrementally increasing taxol concentrations. Comparison of SKOV-3 to SKOV-3TR by differential display identifies a new gene, TRAG-3 (Taxol Resistance Associated Gene- 3). In comparison to the parental line, SKOV-3, TRAG-3 mRNA is overexpressed in the taxol-resistant cell line SKOV-3TR. The nucleotide sequence of the TRAG-3 cDNA contains an open reading frame of 333bp that predicts for a protein product of 110 amino acids. A GenBank search identifies a cosmid clone containing a genomic sequence corresponding to that of TRAG-3. DNA and protein analysis reveals that TRAG-3 has no homology to any known cDNAs or proteins. Northern analysis demonstrates that TRAG-3 is overexpressed in the taxol-resistant breast cancer cell line MDA 435TR as well as the doxorubicin-resistant multiple myeloma cell lines 8226/DOX40 and 8226/MDR10V. A survey of normal tissue shows minimal or absent TRAG-3 mRNA expression. Screening of a wide variety of cancer cell lines demonstrates TRAG-3 expression in many cell lines derived from different tissue types. In summary, TRAG-3 is a novel gene whose expression is associated with the chemotherapy-resistant and neoplastic phenotype.     

Identification of a novel taxol-sensitive kinase activity associated with the cytoskeleton

The microtubule-targeted drug, taxol, enhances assembly of alphabeta tubulin dimers into microtubules. Recent work has established that taxol also elicits diverse effects on intracellular signaling. In-gel kinase assays with myelin basic protein as substrate revealed that taxol treatment significantly (P 相似文献