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Biomedical subjects

B P Kopnin

Publications and source records attributed to B P Kopnin.

At least 19 recordsLinked to original sources
PubMed2004

Restoration of p53 tumor-suppressor activity in human tumor cells in vitro and in their xenografts in vivo by recombinant avian adenovirus CELO-p53.

Human adenovirus (Ad) vectors are extensively used as gene transfer vehicles. However, a serious obstacle for the use of these vectors in clinical applications is due to pre-existing immunity to human Ads affecting the efficacy of gene transfer. One of the approaches to circumvent host immune response could be the development of vectors based on non-human Ads that are able to transduce genes into human cells. In this study, we explored the possibility of using avian Ad CELO vectors as gene-transfer vehicles. For this purpose, we constructed a set of recombinant CELO viruses and demonstrated that they are able to deliver transgenes into various organs on the background of pre-existing immunity to human Ad5. The created CELO-p53 vector restored the function of the p53 tumor suppressor both in cultured human tumor cells in vitro and in their xenografts in nude mice in vivo. The latter effect was accompanied by inhibition of tumor growth. Noteworthily, the delivery of CELO-p53 led to activation of p53 target genes in cells showing inactivation of endogenous p53 by three different mechanisms, that is, in the human epidermoid carcinoma A431, lung adenocarcinoma H1299, and cervical carcinoma HeLa.

Animals↗
PubMed2001

p53 activation in response to microtubule disruption is mediated by integrin-Erk signaling.

The p53 tumor suppressor is activated in response to various stresses driving the cells into growth arrest or apoptosis. We have addressed the question of how disintegration of microtubule system induces activation of p53. Depolymerization of microtubules by colcemid in rat and human quiescent fibroblasts resulted in accumulation of transcriptionally active p53 that caused cell-cycle arrest at the G1/S boundary. The p53 activation correlated with prominent activation of Erk1/2 MAP kinases that resulted from colcemid-stimulated development of focal adhesions. Inhibition of focal contacts development by plating of cells onto poly-L-lysine abrogated both Erk1/2 and p53 activations in colcemid-treated cells, while plating of cells onto fibronectin caused transient up-regulation of p53 even in the absence of colcemid. Pre-treatment of cells with the specific MEK1 inhibitor PD098059 also attenuated colcemid-induced p53 activation and G1 cell cycle arrest. Cell types which either failed to develop focal adhesions in response to colcemid treatment (human MCF-7 epithelial cells), or lacked colcemid-induced sustained Erk activation (primary mouse embryo fibroblasts and 12(1) cells) showed virtually no p53 up-regulation in response to disruption of microtubules during G0/G1. Our results indicate that p53 activation is not triggered by disintegration of microtubule system by itself, but rather originates from some of the consequences of such disintegration, in particular, from the development of focal adhesions leading to activation of Erk signaling pathway.

Animals↗
PubMed2000

Targets of oncogenes and tumor suppressors: key for understanding basic mechanisms of carcinogenesis.

Changes in expression of protooncogenes and tumor suppressor genes play a key role in oncogenesis. Dysfunction of their protein products leads to abnormal regulation of signaling pathways, which control the cell cycle, apoptosis, genetic stability, cell differentiation, and morphogenetic reactions. Changes in these important physiological processes are obviously responsible both for initial steps of neoplastic cell transformation and for determination of subsequent tumor progression resulting in the development of malignant tumors.

Apoptosis↗
PubMed2000

[Effect of inactivating the p33ING1 tumor suppressor on the function of cell cycle "checkpoints" and genome stability].

Novel candidate tumor suppressor p33ING1 is known to regulate activity of the p53 protein. The effect of p33ING1 inactivation on the functioning of the cell cycle "checkpoints" and the frequency of chromosomal aberrations was examined. Transduction of the p33-GSEas genetic suppressor element, known to reduce the p53 activity, into p53-positive rat and human cells resulted in: (1) partial abolishment of ethylmetansulphonate- or colcemid-induced arrest of the G1-to-S transition in the G0-synchronized cultures; (2) abolishment of the block in the S phase by the DNA synthesis inhibitor, N-phosphonacetil-L-aspartate (PALA); (3) an increase of the number of spontaneous chromosomal breaks and sister-chromatid exchanges; (4) increased frequency of colchicine-induced polyploidy. Similar effects were observed upon transduction of the p53-GSE22 genetic suppressor element, known to reduce p53 transcriptional activity. Presumably, the effect of p33ING1 inactivation on the cell cycle checkpoints and genetic stability is associated with a decrease in p53 activity.

Animals↗
PubMed1999

P53-dependent effects of RAS oncogene on chromosome stability and cell cycle checkpoints.

Mutations activating the function of ras proto-oncogenes are often observed in human tumors. Their oncogenic potential is mainly due to permanent stimulation of cellular proliferation and dramatic changes in morphogenic reactions of the cell. To learn more on the role of ras activation in cancerogenesis we studied its effects on chromosome stability and cell cycle checkpoints. Since the ability of ras oncogenes to cause cell transformation may be dependent on activity of the p53 tumor-suppressor the cells with different p53 state were analysed. Ectopic expression of N-ras(asp12) caused in p53-deficient MDAH041 cell line an augmentation in the number of chromosome breaks in mitogenic cells, significant increase in the frequency of metaphases showing chromosome endoreduplication and accumulation of polyploid cells. Similar effects were induced by different exogenous ras genes (N-ras(asp12), H-ras(leu12), N-ras proto-oncogene) in Rat1 and Rat2 cells which have a defect in p53-upstream pathways. In contrast, in REF52 and human LIM1215 cells showing ras-induced p53 up-regulation, ras expression caused only slight increase in the number of chromosome breaks and did not enhance the frequency of endoreduplication and polyploidy. Inactivation in these cells of p53 function by transduction of dominant-negative C-terminal p53 fragment (genetic suppressor element #22, GSE22) or mutant p53s significantly increased the frequency of both spontaneous and ras-induced karyotypic changes. In concordance with these observations we have found that expression of ras oncogene caused in p53-defective cells further mitigation of ethyl-metansulphonate-induced G1 and G2 cell cycle arrest, but did not abrogate G1 and G2 cell cycle checkpoints in cells with normal p53 function. These data indicate that along with stimulation of cell proliferation and morphological transformation ras activation can contribute to cancerogenesis by increasing genetic instability.

Animals↗
PubMed1999

p53 does not control the spindle assembly cell cycle checkpoint but mediates G1 arrest in response to disruption of microtubule system.

p53 plays a critical role as a tumour-suppressor in restricting the proliferation of damaged cells, thus preventing formation of genetically altered cell clones. Its inactivation leads, in particular, to accumulation of polyploid and aneuploid cells. To elucidate the role of p53 in control of chromosome number, we analysed its participation in the cell cycle checkpoints controlling: (1) spindle assembly; and (2) G1-to-S transitions in cells with disintegrated microtubule cytoskeleton. Treatment with 8-10 ng/ml of colcemid causing no visible destruction of the spindle leads to arrest of metaphase-to-anaphase transition in both p53-positive and p53-negative murine fibroblasts, as well as in p53-positive REF52 cells and their counterparts (where the p53 function was inactivated by transduction of dominant-negative p53 fragment). Furthermore, p53-positive and p53-defective rodent and human cells showed no significant difference in kinetics of metaphase-to-interphase transitions in cultures treated with high colcemid doses preventing spindle formation. These data argue against the hypothesis that p53 is a key component of the spindle-assembly checkpoint. However, p53 mediates activation of the G1 checkpoint in response to depolymerization of microtubules in interphase cells. Treatment of synchronized G0/G1 cells with colcemid causes arrest of G1-to-S transition. Inactivation of the p53 function by transduction of dominant-negative p53 fragment abolishes the G1 checkpoint that prevents entry into S phase of cells with disrupted microtubules. Transduction of kinase-defective dominant-negative c- raf mutant or application of PD 098059, a specific inhibitor of MEK1, also abrogates the G1 cell cycle arrest in cells with disintegrated microtubule system. It seems that Raf-MAP-kinase signalling pathways are responsible for p53 activation induced by depolymerization of microtubules.

Animals↗
PubMed1999

[Priorities in research of hemoblastosis].

Evidence is provided for that it is urgent to elaborate a problem of hemoblastosis and hemopoietic depressions within the framework of a special federal research and technological programme. Priorities of research lines in this areas, trends of their development till 2005 are presented.

Hematologic Neoplasms↗
PubMed1999

[Effect of inactivating various components of the signal pathways of the tumor suppressor p53 on genomic stability].

To evaluate the role of different p53-regulated signaling pathways in the control of genomic integrity, we studied the frequency of changes in chromosome number and structure of cells of the sublines of mouse primary embryonic fibroblasts with the "knocked-out" genes for proteins p53, p21WAF, pRb, and p19ARF. Protein p21WAF is transactivated by p53 and is responsible for the cell block in the G1 phase of the damaged cells; protein pRb is a target for p21WAF which controls the G1-S-phase transition; and p19ARF protein is responsible for p53 activation in cells with certain anomalies. Inactivation of either of the studied genes proved to increase significantly the frequency of changes in the karyotype. However, the resultant chromosome instability differed: the frequency of the chromosome breaks, both spontaneous and induced with ethylmethane sulfonate (EMS), was in cells with inactivated p53 and lowest in cells with inactivated pRb. These distinctions were not caused by a different effect of various gene inactivation on the cell cycle progression: in all sublines, the cell block in G1 was abolished and the checkpoint function in G2 remained normal. However, the induction of apoptosis in EMS-treated cells differed in the studied sublines. The lowest number of apoptotic nuclei were determined in p53-/- cultures, whereas the highest were in the Rb-/- cultures. It is apparent that the degree of genetic instability is determined by a combined effect of apoptosis and abnormal regulation of the cell-cycle checkpoints.

Animals↗
PubMed1998

Disruption of actin microfilaments by cytochalasin D leads to activation of p53.

Activation of p53 plays a central role in the cell's response to various stress signals. We investigated whether p53 is activated upon disruption of actin microfilaments, caused by cytochalasin D (CD). We show that treatment with CD leads to accumulation of p53 in the cells and activation of p53-dependent transcription. Treatment with CD led to arrest of G1-to-S transition in cells retaining wild-type p53, while cells with inactivated p53 showed partial rescue from it. CD also induces apoptosis in p53+/+, but not in p53-/- cells. The obtained data suggest that disruption of the actin microfilaments activates p53-dependent pathways.

Actin Cytoskeleton↗
PubMed1998

Activation of p53-mediated cell cycle checkpoint in response to micronuclei formation.

Inactivation of p53 tumor-suppressor leads to genetic instability and, in particular, to accumulation of cells with abnormal numbers of chromosomes. In order to better define the role of p53 function in maintaining genome integrity we investigated the involvement of p53 in the control of proliferation of micronucleated cells resulting from abnormal chromosome segregation. Using cell lines expressing temperature-sensitive (ts) p53 or containing p53 genetic suppressor element (p53-GSE) we showed that inhibition of p53 function increases the frequency of cells with micronuclei. Immunofluorescence study revealed that in REF52 cell cultures with both spontaneous and colcemid-induced micronuclei the proportion of p53-positive cells is considerably higher among micronucleated variants as compared with their mononuclear counterparts. Analysis of 12(1)ConA cells expressing the beta-galactosidase reporter gene under the control of a p53-responsive promoter showed activation of p53-regulated transcription in the cells with micronuclei. Importantly, the percentage of cells manifesting specific p53 activity in colcemid-treated cultures increased with an augmentation of the number of micronuclei in the cell. Activation of p53 in micronucleated cells was accompanied by a decrease in their ability to enter S-phase as was determined by comparative analysis of 5-bromodeoxyuridine (5-BrdU) incorporation by the cells with micronuclei and their mononuclear counterparts. Inhibition of p53 function in the cells with tetracycline-regulated p53 gene expression, as well as in the cells expressing ts-p53 or p53-GSE, abolished cell cycle arrest in micronucleated cells. These results along with the data showing no increase in the frequency of chromosome breaks in REF52 cells after colcemid treatment suggest the existence of p53-mediated cell cycle checkpoint(s) preventing proliferation of micronucleated cells derived as a result of abnormal chromosome segregation during mitosis.

Animals↗
PubMed1997

Distinct effects of various p53 mutants on differentiation and viability of human K562 leukemia cells.

Mutations of the p53 tumor suppressor are often observed in various human tumors, including blast crisis of chronic myelogenous leukemia (CML). The pattern of p53 mutations in CML shows some peculiarities compared with majority of other malignancies. In particular, the substitutions at codon 273, one of the most common p53 alterations in various tumors, are not characteristic of CML. To test whether the distinctions in the pattern of p53 mutations are connected with some peculiarities of the biological effects of different mutant proteins in leukemic cells, we obtained and analyzed a panel of human K562 cell sublines expressing various exogenous p53; human Pro156, His175, His194, Trp248, and His273, or murine temperature-sensitive (ts) Val135 that has properties of mutant protein at 37 degrees C, but shows activities of the wild-type (wt) p53 at 32 degrees C. We have found that expression of wt-p53 enhanced the dependence of cells on growth/survival factors. Incubation of sparse (< 10(5) cells per/ml) K562/Val135 cultures at 32 degrees C caused apoptosis. In media conditioned by cells of different origin (K562, colorectal carcinoma LIM1215, Rat1 fibroblasts) the p53-dependent apoptosis was inhibited. Under such conditions the expression of ts-wt-p53 was accompanied by dramatic increase in the number of cells producing specific markers of erythroid differentiation-GlycPhA and Ag-Eb. Unlike to the wt-p53, the majority of tumor-derived mutant p53 (Pro156, His175, His194) increased cell survival in low serum and decreased the number of cells expressing Glyc-PhA, CD9, CD15, and CD71 differentiation antigens. On the other hand, expression of His273-p53 caused significant augmentation in the number of CD9-positive cells and enhanced the dependence on growth/survival factors that are present in serum or conditioned media. The data obtained allow to suggest that an unusual pattern of p53 mutations in CML reflects some peculiarities of biological effects of certain mutant proteins on differentiation and viability of leukemic cells.

Animals↗
PubMed1996

Chromosome changes caused by alterations of p53 expression.

It has been proposed that p53 tumor-suppressor plays a key role in maintaining genome integrity in mammalian cells. We analyzed karyotype alterations in human and murine cell sublines expressing various exogenous human mutant (His175, Trp248, His273) or wild-type (wt) p53 cDNAs. In human pseudodiploid LIM1215 cells that contain two endogenous wt-p53 gene alleles, p53 mutants caused both an increase in the frequency of chromosome breaks and an emergence of hyperdiploid cells. Murine T12-/- and 10(1) fibroblasts lacking endogenous p53 expression have very unstable karyotypes and show a strong tendency to increase their ploidy levels during growth in culture. Transduction of a wt-p53 construct into p53-deficient cells inhibited an accumulation of highly polyploid cell variants. Transduction of mutant p53 did not show such an effect. Modification of endogenous and exogenous p53 expression by caffeine, which interferes with normal induction of p53 in response to DNA damage, showed no correlation between the induction of chromosome breaks and heteroploidy. We conclude that the caffeine- or mutant p53-induced increase in the frequency of chromosomal breaks in dividing LIM1215 cells is assonated with inactivation of wt-p53 function(s) responsible for control of G1 checkpoint and/or DNA repair, while numerical chromosome changes in these cells may be a result of elimination or modification of a separate p53 function, or due to gain-of-function activities of p53 mutants. p53 modifications may therefore cause chromosome instability by different pathways: (1) through changes in the system(s) preventing proliferation of cells with genomic alterations; and (2) by increasing the probability of events, such as chromosome non-disjunction and/or endoreduplication that can lead to chromosome gains.

Animals↗
PubMed1996

[The effect of the tumor suppressor p53 and its mutant forms on the differentiation and viability of K562 leukemic cells].

Mutations of the p53 tumor suppressor are often observed in various human malignancies including blast crisis of chronic myelogenous leukaemia (CML). The pattern of p53 mutation in CML shows some peculiarities as compared with the majority of other neoplasias. In particular, the substitutions at codon 273, one of the most common p53 alteration in various tumors, are not characteristic of CML. To test whether distinction in the pattern of p53 mutation are associated with certain peculiarities of biological effects of different mutant proteins in myeloid cells, we obtained and analysed a panel of human K562 cell sublines expressing various exogenous p53: human Pro156, His175, His194, Trp248 and His 273, or murine temperature-sensitive (ts) Val135 that has properties of mutant protein at 37 degrees C, but shows activities of wild-type (wt) p53 at 32 degrees C. We have found that expression of wt-p53 enhanced the dependence of cells on growth/survival factors, incubation of sparse (< 10(5) cells per/ml) K562/Val135 cultures at 32 degrees C caused apoptosis. In media conditioned by cells of different origin (K562, colorectal carcinoma LIM 1215, Rat1 fibroblast) the p53-dependent apoptosis was inhibited. In conditions that do not lead to apoptosis, the expression of ts-wt-p53 was accompanied by dramatic increase in the number of cells containing glycophorin A (GlycPhA) and "antigen of erythroblasts"--specific markers of erythroid differentiation. Unlike the wt-p53, the majority of tumor-derived mutant p53 (Pro156, His175, His194, Trp248) increased cells survival in media with low serum content and decreased the number of cell expressing GlycPhA, CD9, CD15 and CD71 differentiation antigens. On the other hand, expression of His273-p53 caused a significant augmentation in the number of CD9-positive cells and enhanced the dependence on growth/survival factors that are present in serum or conditioned media. The data obtained are consistent with the idea that unusual pattern of p53 mutations in CML can reflect the peculiarities of the effects of some mutant proteins on differentiation and/or viability of leukemic cells.

Cell Division↗
PubMed1995

Cell-specific effects of RAS oncogene and protein kinase C agonist TPA on P-glycoprotein function.

We compared the influence of exogenous N-ras oncogene and treatment with PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA) on P-glycoprotein (Pgp) function in various human, rat and dog cell lines. Two approaches were used: (a) flow cytometry analysis of Rhodamine 123 (Rh123) exclusion; and (b) sensitivity to cytotoxic action of colchicine. We have found that in Rat1 fibroblasts, rat IAR2 epithelial cells and rat McA RH 7777 (hepatoma), ras activates Pgp function, while in MDCK (dog kidney), K562 (human chronic myelogenous leukaemia) and LIM1215 (human colon carcinoma) cells it either has no effect or even acts in opposite direction. TPA-induced Pgp function shows dissimilar pattern of cell specificity. It is assumed that PKC and ras oncogene regulate mdr1 gene expression through at least partially distinct signalling pathways.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

[p53 with a mutation in codon 273 increases the probability of amplifying the dhfr gene in Rat-1 and LIM1215 cells].

The effect of the expression of the exogenous human mutant p53 (Arg-->His in codon 273) on the amplification rate of the gene dhfr in permissive Rat-1 and LIM1215 cells was studied. It was shown that injection of a retroviral construction with p53His273 resulted in the accumulation of methotrexate-resistant variants with an increased number of dhfr copies in populations of recipient cells. Luria-Delbruck fluctuation analysis revealed a four- to six-fold increase in the rate of appearance of new methotrexate-resistant cells. Chromosomal analysis demonstrated an extrachromosomal location of amplified DNA in cells containing p53His273, as was the case for control sublines. The data obtained indicate that modifications of p53 may induce gene amplification not only via removing the proliferation block of cells with amplified genes in selective medium, but also via some other mechanisms, that seem to increase the chromosomal recombination rate.

Animals↗
PubMed1995

Decreased sensitivity of multidrug-resistant tumor cells to cisplatin is correlated with sorcin gene co-amplification.

A set of multidrug resistant (MDR) murine leukemia P388 sublines processing 30-50-fold mdr1 gene amplification was obtained as a result of experimental chemotherapy with rubomycin, ruboxyl, vinblastine, vincristine, or combination of rubomycin and vincristine. Significant differences of developed MDR sublines in response to treatment with cisplatin, tiophosphamide, sarcolysin, and dopad were found. Strong correlation between drug sensitivity and a copy number of gene coding for 19-22 kDa calcium-binding sorcin gene co-amplification were hypersensitive to cisplatin and alkylating agents, the cell sublines showing amplification of sorcin DNA sequences did not possess such collateral sensitivity and even acquired cross-resistance. The dependence of sensitivity to cisplatin on sorcin gene co-amplification was confirmed by analysis of Djungarian hamster DM15 cell sublines that selected for MDR in vitro by colchicine.

Alkylating Agents↗