Biomedical subjects

X Cheng

Publications and source records attributed to X Cheng.

At least 163 records · Page 9Linked to original sources

PubMed1998

Gamma-glutamyl cysteine synthetase up-regulates glutathione and multidrug resistance-associated protein in patients with chemoresistant epithelial ovarian cancer.

Cellular detoxification, such as that mediated by the glutathione (GSH) system, is involved in the metabolism of various cytotoxic agents. Little is known, however, about the clinical relevance of cellular detoxification in chemoresistance. To elucidate the relevance of the GSH system to the resistance to chemotherapy observed in patients with ovarian cancer, we assayed the expression of mRNA encoded by the multidrug resistance-associated protein (MRP) and gamma-glutamyl cysteine synthetase (gamma-GCS) genes, as well as the level of GSH protein in 32 patients with epithelial ovarian cancer after chemotherapy. Tumors of 14 of the 32 patients responded to chemotherapy, whereas 18 did not. The levels of MRP and gamma-GCS transcripts in tumors from nonresponders were each about 2-fold higher than in responders. In contrast, the level of GSH did not differ between the two groups. We observed coordinated expression of gamma-GCS mRNA and GSH protein levels, and between gamma-GCS and MRP in nonresponders, but not in responders. Expression of MRP-encoded mRNA did not correlate to GSH level, however, in either group. These results suggest that gamma-GCS may up-regulate GSH and MRP expression in tumors unresponsive to chemotherapeutic agents, and that the GSH system may be involved in the mechanism of chemoresistance in ovarian cancer.

ATP-Binding Cassette Transporters↗

PubMed1997

Selection of peptides that functionally replace a zinc finger in the Sp1 transcription factor by using a yeast combinatorial library.

We have developed a strategy for the identification of peptides able to functionally replace a zinc finger domain in a transcription factor. This strategy could have important ramifications for basic research on gene regulation and for the development of therapeutic agents. In this study in yeast, we expressed chimeric proteins that included a random peptide combinatorial library in association with two zinc finger domains and a transactivating domain. The library was screened for chimeric proteins capable of activating transcription from a target sequence in the upstream regulatory regions of selectable or reporter genes. In a screen of approximately 1.5 x 10(7) transformants we identified 30 chimeric proteins that exhibited transcriptional activation, some of which were able to discriminate between wild-type and mutant DNA targets. Chimeric library proteins expressed as glutathione S-transferase fusions bound to double-stranded oligonucleotides containing the target sequence, suggesting that the chimeras bind directly to DNA. Surprisingly, none of the peptides identified resembled a zinc finger or other well-known transcription factor DNA binding domain.

Amino Acid Sequence↗

PubMed1997

The use of exfoliative cell samples to map clonal genetic alterations in the oral epithelium of high-risk patients.

Although it is widely accepted that clonal genetic alterations are an essential component of tumor progression, little is known of the distribution of such changes in high-risk lesions or how such clones are altered over time. We explored the feasibility of using exfoliative cells collected by scraping the mucosal surface to detect allelic loss in oral lesions of 22 patients (14 squamous cell carcinomas, 2 carcinomas in situ, and 6 dysplasias). The data show that the patterns of allelic loss observed in these samples closely represent those observed in biopsies of the same region. Furthermore, early indications are that this approach can be used to detect recurrent outgrowth of clones of altered cells in patients after therapy.

Adult↗

PubMed1997

Essential role of the first intron in the transcription of hsp90beta gene.

The human HSP90 gene family contains introns. There are two typical heat shock elements (HSE) in the first intron of human hsp90beta gene. As detected by chloramphenicol acetyl transferase (CAT) reporter activity assays, the HSE-containing intron is essential in maintaining high constitutive expression and is critical for heat shock inducibility of the human hsp90beta gene. Cellular heat shock factor 1 (HSF 1) shows much higher binding affinity toward the intronic HSEs in comparison to an atypical HSE in the 5' flanking sequence. Novel initiation sites found in the first intron probably also contribute to constitutive and heat-inducible expression of the hsp90beta gene in Jurkat cells.

Chloramphenicol O-Acetyltransferase↗

PubMed1997

Expression, purification, mass spectrometry, crystallization and multiwavelength anomalous diffraction of selenomethionyl PvuII DNA methyltransferase (cytosine-N4-specific).

The type II DNA-methyltransferase (cytosine N4-specific) M.PvuII was overexpressed in Escherichia coli, starting from the internal translation initiator at Met14. Selenomethionine was efficiently incorporated into this short form of M.PvuII by a strain prototrophic for methionine. Both native and selenomethionyl M.PvuII were purified to apparent homogeneity by a two-column chromatography procedure. The yield of purified protein was approximately 1.8 mg/g bacterial paste. Mass spectrometry analysis of selenomethionyl M.PvuII revealed three major forms that probably differ in the degree of selenomethionine incorporation and the extent of selenomethionine oxidation. Amino acid sequencing and mass spectrometry analysis of selenomethionine-containing peptides suggests that Met30, Met51, and Met261 were only partially replaced by selenomethionine. Furthermore, amino acid 261 may be preferentially oxidized in both native and selenomethionyl form. Selenomethionyl and native M.PvuII were crystallized separately as binary complexes of the methyl donor S-adenosyl-L-methionine in the monoclinic space group P2(1). Two complexes were present per asymmetric unit. Six out of nine selenium positions (per molecule), including the three that were found to be partially substituted, were identified crystallographically.

Amino Acid Sequence↗

PubMed1997

Structure of pvu II DNA-(cytosine N4) methyltransferase, an example of domain permutation and protein fold assignment.

We have determined the structure of Pvu II methyltransferase (M. Pvu II) complexed with S -adenosyl-L-methionine (AdoMet) by multiwavelength anomalous diffraction, using a crystal of the selenomethionine-substituted protein. M. Pvu II catalyzes transfer of the methyl group from AdoMet to the exocyclic amino (N4) nitrogen of the central cytosine in its recognition sequence 5'-CAGCTG-3'. The protein is dominated by an open alpha/beta-sheet structure with a prominent V-shaped cleft: AdoMet and catalytic amino acids are located at the bottom of this cleft. The size and the basic nature of the cleft are consistent with duplex DNA binding. The target (methylatable) cytosine, if flipped out of the double helical DNA as seen for DNA methyltransferases that generate 5-methylcytosine, would fit into the concave active site next to the AdoMet. This M. Pvu IIalpha/beta-sheet structure is very similar to those of M. Hha I (a cytosine C5 methyltransferase) and M. Taq I (an adenine N6 methyltransferase), consistent with a model predicting that DNA methyltransferases share a common structural fold while having the major functional regions permuted into three distinct linear orders. The main feature of the common fold is a seven-stranded beta-sheet (6 7 5 4 1 2 3) formed by five parallel beta-strands and an antiparallel beta-hairpin. The beta-sheet is flanked by six parallel alpha-helices, three on each side. The AdoMet binding site is located at the C-terminal ends of strands beta1 and beta2 and the active site is at the C-terminal ends of strands beta4 and beta5 and the N-terminal end of strand beta7. The AdoMet-protein interactions are almost identical among M. Pvu II, M. Hha I and M. Taq I, as well as in an RNA methyltransferase and at least one small molecule methyltransferase. The structural similarity among the active sites of M. Pvu II, M. Taq I and M. Hha I reveals that catalytic amino acids essential for cytosine N4 and adenine N6 methylation coincide spatially with those for cytosine C5 methylation, suggesting a mechanism for amino methylation.

Amino Acid Sequence↗

PubMed1997

DNA containing 4'-thio-2'-deoxycytidine inhibits methylation by HhaI methyltransferase.

4'-Thio-2'-deoxycytidine was synthesized as a 5'- protected phosphoramidite compatible with solid phase DNA synthesis. When incorporated as the target cytosine (C*) in the GC*GC recognition sequence for the DNA methyltransferase M. HhaI, methyl transfer was strongly inhibited. In contrast, these same oligonucleotides were normal substrates for the cognate restriction endonuclease R. HhaI and its isoschizomer R. Hin P1I. M. HhaI was able to bind both 4'-thio-modified DNA and unmodified DNA to equivalent extents under equilibrium conditions. However, the presence of 4'-thio-2'-deoxycytidine decreased the half-life of the complex by >10-fold. The crystal structure of a ternary complex of M. HhaI, AdoMet and DNA containing 4'-thio-2'-deoxycytidine was solved at 2.05 A resolution with a crystallographic R-factor of 0.186 and R-free of 0.231. The structure is not grossly different from previously solved ternary complexes containing M. HhaI, DNA and AdoHcy. The difference electron density suggests partial methylation at C5 of the flipped target 4'-thio-2'-deoxycytidine. The inhibitory effect of the 4'sulfur atom on enzymatic activity may be traced to perturbation of a step in the methylation reaction after DNA binding but prior to methyl transfer. This inhibitory effect can be partially overcome after a considerably long time in the crystal environment where the packing prevents complex dissociation and the target is accurately positioned within the active site.

DNA↗

PubMed1997

Crystal structure of human UP1, the domain of hnRNP A1 that contains two RNA-recognition motifs.

BACKGROUND: Heterogeneous nuclear ribonucleoprotein (hnRNP) A1 is one of the most abundant core proteins of hnRNP complexes in metazoan nuclei. It behaves as a global regulator of alternative pre-mRNA splicing by antagonizing the activities of several serine/arginine-rich splicing factors (SR proteins), resulting in the activation of distal alternative 5' splice sites and skipping of optional exons. Purified hnRNP A1 has nucleic acid annealing activity. The protein also shuttles continuously between the nucleus and the cytoplasm, a process mediated by signals within its C-terminal glycine-rich domain. The N-terminal region of human hnRNP A1, termed unwinding protein 1 (UP1), contains two RNA-recognition motifs (RRMs), RRM1 and RRM2. Understanding the structural elements by which hnRNP A1 interacts with RNA will have broad implications for studies of RNA processing. RESULTS: The crystal structure of UP1 has been determined to 1.9 A resolution. Each RRM independently adopts the characteristic RRM fold, consisting of a four-stranded antiparallel beta-pleated sheet and two alpha helices packed on one side of the beta sheet. The two RRMs are antiparallel and held in close contact, mainly by two Arg-Asp ion pairs. As a result, the two four-stranded beta sheets are brought together to form an extended RNA-binding surface. A segment of the linker connecting the two RRMs is flexible in the absence of bound RNA, but the general location of the linker suggests that it can make direct contacts with RNA. Comparison with other RRM structures indicates that a short 310 helix, found immediately N-terminal to the first beta strand in RRM1, may interact with RNA directly. CONCLUSIONS: The RRM is one of the most common and best characterized RNA-binding motifs. In certain cases, one RRM is sufficient for sequence-specific and high affinity RNA binding; but in other cases, synergy between several RRMs within a single protein is required. This study shows how two RRMs are organized in a single polypeptide. The two independently folded RRMs in UP1 are held together in a fixed geometry, enabling the two RRMs to function as a single entity in binding RNA, and so explaining the synergy between the RRMs. The UP1 structure also suggests that residues which lie outside of the RRMs can make potentially important interactions with RNA.

Amino Acid Sequence↗

PubMed1997

Crystal structure of the DNA-binding domain of Mbp1, a transcription factor important in cell-cycle control of DNA synthesis.

BACKGROUND: During the cell cycle, cells progress through four distinct phases, G1, S, G2 and M; transcriptional controls play an important role at the transition between these phases. MCB-binding factor (MBF), a transcription factor from budding yeast, binds to the so-called MCB (MluI cell-cycle box) elements found in the promoters of many DNA synthesis genes, and activates the transcription of those at the G1-->S phase transition. MBF is comprised of two proteins, Mbp1 and Swi6. RESULTS: The three-dimensional structure of the N-terminal DNA-binding domain of Mbp1 has been determined by multiwavelength anomalous diffraction from crystals of the selenomethionyl variant of the protein. The structure is composed of a six-stranded beta sheet interspersed with two pairs of alpha helices. The most conserved core region among Mbp1-related transcription factors folds into a central helix-turn-helix motif with a short N-terminal beta strand and a C-terminal beta hairpin. CONCLUSIONS: Despite little sequence similarity, the structure within the core region of the Mbp1 N-terminal domain exhibits a similar fold to that of the DNA-binding domains of other proteins, such as hepatocyte nuclear factor-3gamma and histone H5 from eukaryotes, and the prokaryotic catabolite gene activator. However, the structure outside the core region defines Mbp1 as a larger entity with substructures that stabilize and display the helix-turn-helix motif.

Amino Acid Sequence↗

PubMed1997

Glutathione S-transferase-pi expression and glutathione concentration in ovarian carcinoma before and after chemotherapy.

BACKGROUND: To clarify the role of glutathione (GSH) in the chemotherapy resistance of ovarian carcinoma, the authors examined the expression of glutathione S-transferase-pi (GST-pi) and the concentration of glutathione in tumors before and after chemotherapy in the same patients. METHODS: The cohort for this study comprised 20 patients with ovarian carcinoma who had residual disease after primary surgery. These patients received two to three courses of postoperative chemotherapy, then underwent surgery for a second time. Chemotherapy consisted of 50 mg/m2 cisplatin, 40 mg/m2 doxorubicin, and 400 mg/m2 cyclophosphamide. The expression of GST-pi in tumors was determined by immunohistochemical staining and Western blot analysis. GSH concentration was measured by an enzymatic assay. RESULTS: Of the 20 patients, 10 responded to chemotherapy and 10 did not. Immunohistochemical staining for GST-pi was positive in 3 tumors among the 10 responders and in 7 tumors among the 10 nonresponders, but Western blot analysis detected GST-pi expression in all tumors. Among the responders, GST-pi after chemotherapy increased in one patient, was unchanged in two patients, and decreased in seven patients. Among nonresponders, GST-pi increased in six patients, was unchanged in one patient, and decreased in three patients. The ratio of GST-pi density in tumors after chemotherapy to GST-pi density before chemotherapy was significantly higher in nonresponders than in responders (2.0 +/- 1.1 vs. 0.6 +/- 0.4). The concentration of GSH in tumors was widely distributed, but it was found that the ratio of GSH concentration in each tumor after chemotherapy to GSH concentration before chemotherapy was significantly higher for nonresponders than for responders (3.0 +/- 1.3 vs. 0.6 +/- 0.3). CONCLUSIONS: Increased levels of GST-pi expression after chemotherapy are linked to drug resistance in patients with ovarian carcinoma.

Aged↗

PubMed1997

Down-regulation of IL-12, not a shift from a T helper-1 to a T helper-2 phenotype, is responsible for impaired IFN-gamma production in mammary tumor-bearing mice.

Altered cytokine production has been implicated in the down-regulation of cell-mediated immunity in mice bearing large mammary tumors. In several diseases, an imbalance between helper T lymphocytes Th1 and Th2 and their cytokines has been suggested as a contributing factor. In this study, although IFN-gamma from splenic T cells of D1-DMBA-3 mammary tumor-bearing mice was greatly diminished, other cytokine levels remained unchanged, indicating no clear shift between the Th1, Th2, or Th3 phenotypes. The IFN-gamma levels can be restored in vitro by addition of rIL-12 to cultured splenocytes from tumor bearers. Furthermore, IL-12 production is greatly down-regulated in macrophages from tumor-bearing mice as detected by ELISA, and this correlates with diminished expression of IL-12 p40 chain RNA. The mammary tumor used in our studies produces several factors, including granulocyte macrophage-CSF, PGE2, and phosphatidyl serine, that can affect the immune system. Addition of these tumor-derived factors in vitro to macrophages from normal mice resulted in decreased levels of IL-12 protein in cultures treated with PGE2 or phosphatidyl serine. These results indicate that the down-regulation of T cell-produced IFN-gamma in this tumor model is the result of decreased IL-12 production caused by tumor-derived factors and not a shift from the Th1 to the Th2 phenotype.

Animals↗

PubMed1997

Mechanistic link between DNA methyltransferases and DNA repair enzymes by base flipping.

Rotation of a DNA nucleotide out of the double helix and into a protein binding pocket ("base flipping") was first observed in the structure of a DNA methyltransferase. There is now evidence that a variety of proteins, particularly DNA repair enzymes, use base flipping in their interactions with DNA. Though the mechanisms for base movement into extrahelical positions are still unclear, the focus of this review is how base recognition is modulated by the stringency of binding to the extrahelical base(s) or sugar moiety.

Base Composition↗

PubMed1997

Development of a sensitive nested PCR method for the specific detection of Mycoplasma mycoides subsp. mycoides SC.

A specific and sensitive test for the detection of Mycoplasma mycoides subsp. mycoides small colony type (SC), the aetiological agent of contagious bovine pleuropneumonia (CBPP) was developed using two nested PCR reactions. The PCR reactions are based on the nucleotide sequence of lipoprotein P72 of M. mycoides subsp. mycoides SC. The two specific oligonucleotide primer pairs were chosen to match those sequence segments of the P72 gene which differ most from the gene of the closely related lipoprotein P67 of Mycoplasma sp. bovine group 7 (strain PG50). The nested PCR reacted with all of the 34 different strains of M. mycoides subsp. mycoides SC analysed, and gave no amplification product with any of the closely related mycoplasmas tested, showing its high specificity. In bronchial lavage fluid experimentally contaminated with M. mycoides subsp. mycoides SC, the assay was able to detect as few as two viable cells per ml using a simple lysis procedure prior to the amplification step. With clinical samples, the sensitivity of the nested PCR was about 10(4)-10(5) higher than that of single PCR amplifications performed under the same conditions. The assay was also successfully used to detect M. mycoides subsp. mycoides SC in bronchial lavage fluid of experimentally infected cattle and proved to be more sensitive than classical culture methods.

Animals↗

PubMed1997

Biological activation of N(G)-nitro-D-arginine by kidney homogenate .

N(G)-nitro-L-arginine (L-NNA) and D-NNA have been shown to inhibit endothelium-dependent relaxation. This study examined if the inhibitory effect of L-NNA or D-NNA on relaxation is increased following incubation of the drug with the supernatant of tissue homogenates. Acetylcholine (ACh) caused concentration-dependent relaxation of pre-constricted rat aortic rings with maximum relaxation of 95%. Maximum relaxations to ACh were reduced to 71 and 37% in the presence of D-NNA (40 microM) and L-NNA (1 microM), respectively. Relaxation to ACh was further reduced to 18% in the presence of D-NNA that was incubated for 1 h with the supernatant of kidney homogenate, but unaffected by D-NNA incubated with the supernatant of trichloroacetic acid-denatured kidney homogenate. Incubation of L-NNA (1 microM) with either kidney supernatant or denatured kidney supernatant for 1 h did not affect its inhibitory effect on ACh-induced relaxation. Neither 1 h's incubation with plasma, or supernatants of liver, lungs or aorta homogenates affected the inhibitory action of D-NNA (40 or 120 microM) on ACh-induced relaxation. After D-NNA was incubated in kidney supernatant, its inhibitory effect on ACh-induced relaxation of the aorta was abolished by pretreatment of the aorta with L-arginine (L-Arg) but not D-Arg suggesting involvement of the L-Arg pathway. The results suggest that D-NNA is converted by the kidney to a compound that acts similar to L-NNA. There appears to be little conversion of L-NNA to D-NNA.

Acetylcholine↗

PubMed1997

Age-associated decline in human femoral neck cortical and trabecular content of insulin-like growth factor I: potential implications for age-related (type II) osteoporotic fracture occurrence.

Recent evidence suggests that regulatory peptides such as insulin-like growth factor-I (IGF-I) are released locally from bone during resorption, and may then act in a sequential manner to regulate the cellular events required for the coupling of bone formation to resorption. Among other factors, a decrease in bone-associated IGF-I levels could therefore result in remodeling imbalance and contribute to the gradual loss of bone that occurs with age. As the femoral neck region is of primary concern for the clinical manifestations of osteoporosis, the current study was intended to assess the IGF-I contents in femoral neck cortical and trabecular bone from aging individuals. Bone samples from the neck region were obtained at postmortem from 39 females and 35 males, aged 23-92 years. Concentrations of IGF-I and osteocalcin were measured by radioimmunoassay in the supernatants obtained after EDTA and guanidine hydrochloride extraction. The total amount of protein present in the extracts was determined by spectrophotometry. IGF-I levels were significantly lower in trabecular compared with cortical bone. Though femoral neck total protein did not vary with donor age, both IGF-I and osteocalcin were found to decline markedly. Between the ages of 23 and 92 years, average yearly rates of loss of 0.30 and 0.21 ng IGF-I/mg protein were observed in cortical and trabecular bone, respectively, corresponding with net losses of nearly 35% of the cortical skeletal content of IGF-I and 41% of the trabecular skeletal content of IGF-I. These changes in bone-associated IGF-I paralleled those of osteocalcin, consistent with an overall decrease in osteoblast function with aging. In women, the rate of decline was significantly faster for trabecular than for cortical IGF-I, however in men, age-dependent changes in cortical and trabecular IGF-I were similar. These findings support the hypothesis that changes in the local IGF regulatory system over time could be a pathophysiologic component of the age-related (type II) femoral neck osteoporotic syndrome.

Adult↗

PubMed1997

Antitumor effects of internal iliac arterial infusion of platinum compounds in a rabbit cervical cancer model.

OBJECTIVE: To compare three platinum compounds for their antitumor effects on cervical cancer after systemic and intra-arterial infusion. METHODS: Adult female rabbits with squamous cell carcinoma of the uterine cervix received infusions of 1.7 mg/kg cisplatin, 10 mg/kg carboplatin, or 6 mg/kg cis-diammine (glycolato)platinum (254-S) via the internal iliac artery or ear vein. Platinum concentrations in the tumor and tumor size were measured after internal iliac arterial or intravenous (i.v.) infusion with these platinum compounds. RESULTS: The platinum concentration in the tumor after intra-arterial infusion was significantly higher than that after i.v. infusion for cisplatin. However, the tumor concentrations of platinum for carboplatin and 254-S did not differ between the infusion methods. The platinum concentration 20 minutes after i.v. infusion was significantly higher for 254-S than for cisplatin or carboplatin. The platinum concentration 7 days after intra-arterial infusion was significantly higher with cisplatin than with carboplatin or 254-S. Tumor size 7 days after intra-arterial infusion was significantly smaller than that after i.v. infusion for cisplatin (1.85 +/- 0.54 versus 5.60 +/- 2.60 cm2; P < .05). Tumor size was significantly smaller with 254-S than with cisplatin or carboplatin using the i.v. infusion method (2.40 +/- 0.21 cm2 for 254-S, 5.60 +/- 2.60 cm2 for cisplatin, and 5.13 +/- 1.59 cm2 for carboplatin, P < .05. CONCLUSIONS: Intra-arterial infusion seems to be a suitable route of administration for cisplatin, whereas i.v. infusion appears to have an advantage for 254-S in the treatment of cervical cancer.

Animals↗

PubMed1997

The accuracy of peripheral skeletal assessment at the radius in estimating femoral bone density as measured by dual-energy X-ray absorptiometry: a comparative study of single-photon absorptiometry and computed tomography.

OBJECTIVES: One of the latest developments in bone densitometry is peripheral quantitative computed tomography (pQCT), a method which allows the separate determination of cortical and trabecular bone mineral density (BMD) in the peripheral skeleton. This study was designed to compare the relative abilities of single-photon absorptiometry (SPA) and pQCT to reflect BMD of the proximal femur as measured by dual-energy X-ray absorptiometry (DXA), an established predictor of osteoporotic hip fracture risk. DESIGN: Cross-sectional study. SUBJECTS: A well-defined community-based sample of 129 skeletally healthy women aged 70-87 years. MEASUREMENTS: Radial BMD by SPA and pQCT and femoral BMD by DXA. Univariate and multivariate regression analyses were performed relating the DXA measurements at the femoral neck and the trochanteric region with the values of SPA and pQCT. RESULTS: Approximately 38% of the variance in femoral neck BMD could be explained by BMD of the midradius assessed by SPA, in contrast to only 18-27% by pQCT. At the trochanter, 32% of BMD could be predicted by SPA as compared to 19-26% by pQCT. Moreover, according to multiple regression, prediction of femoral BMD by SPA was not enhanced by performing pQCT. CONCLUSIONS: Radial pQCT has little value as a screening tool to identify elderly women with low femoral BMD. Additional research is needed to determine whether or not pQCT will enhance fracture prediction beyond that obtainable from a density measurement by SPA.

Absorptiometry, Photon↗

PubMed1997

Enhanced topoisomerase I activity and increased topoisomerase II alpha content in cisplatin-resistant cancer cell lines.

Although the combined effects of cisplatin (CDDP) and DNA topoisomerase (Topo) inhibitors have been described in recent literature, little is known about the combined effects and their biological basis in CDDP-resistant cells. The aim of the present study was to elucidate the combined effect of CDDP and Topo inhibitors on CDDP-resistant cells as well as to investigate the biological factors involved in the sensitivity to these anti-cancer agents. We found synergistic actions between CDDP and SN-38 (a Topo I inhibitor) or VP-16 (a Topo II inhibitor) in KFr cells, a CDDP-resistant subline of the KF epithelial ovarian carcinoma cell line, but not in the parent KF cells. We subsequently assayed Topo protein levels and enzymatic activities in two sets of CDDP-sensitive and -resistant cell lines: KF and KFr, and HeLa and HeLa/CDDP. The levels of Topo I protein in the CDDP-resistant cells did not differ from those of their parent cell lines and were unaffected by exposure to CDDP. Topo I enzymatic activity, however, was 2- to 4-fold higher in the CDDP-resistant cell lines than in their respective parent cell lines. In contrast, higher levels of Topo II alpha protein were observed both before and after CDDP exposure in the CDDP-resistant cells than in their controls. However, no difference in Topo II catalytic activity was observed between the CDDP-resistant and -sensitive cells.

Antigens, Neoplasm↗