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S Benchimol

Publications and source records attributed to S Benchimol.

At least 55 records · Page 3Linked to original sources
PubMed1992

Friend virus induced murine erythroleukaemia: the p53 locus.

The development of Friend virus induced murine erythroleukaemia is associated with specific genetic events. One of these events is loss of wild type p53 expression, which can occur by internal deletion or proviral insertion in the p53 gene and by single point mutations in the coding sequence. In all cases, the corresponding wild type allele is absent. The high frequency of observed p53 mutations strongly suggests that inactivation of p53 may be an obligatory step in the development of Friend disease. Further evidence that abrogation of normal p53 expression contributes to the development of malignant clones was provided by in vitro reconstitution experiments in Friend cell lines: whereas exogenous mutant p53 was stably expressed in p53 negative FCLs, long term wild type p53 expression was not detected. Friend erythroleukaemia arises as a late consequence of infection of susceptible mice with Friend virus. In addition to p53 gene mutations, proviral insertions occur frequently adjacent to one of two cellular genes, Spi-1/PU.1 or Fli-1. Aberrant expression of these genes may therefore be involved in virus induced erythroleukaemia. Interaction of SFFV env gp55 with the EPO-R also appears to be important in providing a mitogenic signal to infected cells. The order in which these events occur and whether the order is relevant to the progression of the disease are not known. Investigation of the stepwise appearance of these events could provide information on the possible interactions of the gene products involved. Abrogation of normal p53 expression is not restricted to Friend erythroleukaemia: the observation of p53 mutations and allele loss in human breast, lung, colon and hepatocellular carcinomas and in leukaemia suggests that mutation of p53 may be the most common genetic abnormality detected in human cancer (reviewed in this issue). Studies of p53 expression in FCLs provided an early indication that p53 was a tumour suppressor gene. Further studies of the mechanisms by which wild type and mutant p53 affect the growth of p53 negative FCLs may reveal important biochemical properties of p53 in relation to cell cycle control and differentiation of erythroid cells.

Alleles↗
PubMed1991

Mutation of the p53 gene in human acute myelogenous leukemia.

Heterogeneity of p53 protein expression is seen in blast cells of patients with acute myelogenous leukemia (AML). p53 protein is detected in the blasts of certain AML patients but not in others. We have identified p53 protein variants with abnormal mobility on gel electrophoresis and/or prolonged half-life (t 1/2). We have sequenced the p53 coding sequence from primary blast cells of five AML patients and from the AML cell line (OCIM2). In OCIM2, a point mutation in codon 274 was identified that changes a valine residue to aspartic acid. A wild type p53 allele was not detected in these cells. Two point mutations (codon 135, cysteine to serine; codon 246, methionine to valine) were identified in cDNA from blasts of one AML patient. Both mutations were present in blast colonies grown from single blast progenitor cells, indicating that individual leukemia cells had sustained mutation of both p53 alleles. The cDNAs sequenced from blast samples of four other patients, including one with prolonged p53 protein t 1/2 and one with no detectable p53 protein, were fully wild type. Thus, the heterogeneity of p53 expression cannot be explained in all cases by genetic change in the p53 coding sequence. The prolonged t 1/2 of p53 protein seen in some AML blasts may therefore reflect changes not inherent to p53. A model is proposed in which mutational inactivation of p53, although not required for the evolution of neoplasia, would confer a selective advantage, favoring clonal outgrowth during disease progression.

Base Sequence↗
PubMed1991

Transforming activity of mutant human p53 alleles.

Mutant forms of the p53 gene have been shown to cooperate with an activated ras gene in transforming primary cells in culture. The aberrant proteins encoded by p53 mutants are thought to act in a dominant negative manner in these assays. In vivo data, however, reveal that where p53 has undergone genetic change in tumors, both alleles have been affected. We previously identified a case of human acute myelogenous leukemia (AML) in which both alleles of the p53 gene had undergone independent missense mutations (at codons 135 cys to ser and 246 met to val). In these blasts, p53 mutations appear to be acting recessively. We have assayed the transforming potential of these p53 mutations, as well as that of another mutation at codon 273, also identified in a human neoplasm. Both mutations from the AML blasts (codon 135 and codon 246) confer transforming ability on the mutant protein. While transformation assays may define functionally different subsets of p53 mutations, the overexpression phenotype of mutants in this assay may not accurately reflect the pathological effects of p53 mutations in vivo.

Alleles↗
PubMed1991

Expression of wild-type p53 is not compatible with continued growth of p53-negative tumor cells.

Inactivation of the cellular p53 gene is a common feature of Friend virus-induced murine erythroleukemia cell lines and may represent a necessary step in the progression of this disease. As well, frequent loss or mutation of p53 alleles in diverse human tumors is consistent with the view of p53 as a tumor suppressor gene. To examine the significance of p53 gene inactivation in tumorigenesis, we have attempted to express transfected wild-type p53 in three p53-negative tumor cell lines: murine DP16-1 Friend erythroleukemia cells, human K562 cells, and SKOV-3 cells. We found that aberrant p53 proteins, which differ from wild-type p53 by a single amino acid substitution, were expressed stably in these cells, whereas wild-type p53 expression was not tolerated. The inability of p53-negative tumor cell lines to support long-term expression of wild-type p53 protein is consistent with the view that p53 is a tumor suppressor gene.

Animals↗
PubMed1990

Inactivation of the cellular p53 gene is a common feature of Friend virus-induced erythroleukemia: relationship of inactivation to dominant transforming alleles.

The Friend erythroleukemia virus complex contains no cell-derived oncogene. Transformation by this virus may therefore involve mutations affecting cellular gene expression. We provide evidence that inactivating mutations of the cellular p53 gene are a common feature in Friend virus-induced malignancy, consistent with an antioncogene role for p53 in this disease. We have shown that frequent rearrangements of the p53 gene cause loss of expression or synthesis of truncated proteins, whereas overexpression of p53 protein is seen in other Friend cell lines. We now demonstrate that p53 expression in the latter cells is also abnormal, as a result of missense mutations in regions encoding highly conserved amino acids. Three of these aberrant alleles obtained from cells from different mice were cloned and found to function as dominant oncogenes in gene transfer assays, supporting the view that certain naturally occurring missense mutations in p53 confer a dominant negative phenotype on the encoded protein.

Alleles↗
PubMed1990

Synergism between pairs of immortalizing genes in transformation assays of rat embryo fibroblasts.

A number of cellular and viral genes encode proteins that play a role in the establishment of normal cells in culture. In addition, these genes cooperate with activated ras genes to induce cellular transformation. We show that ras-dependent transformation of rat embryo fibroblasts is more efficient when two establishment genes are used together compared with one alone. Both quantitative and qualitative differences in the efficiency of transformation were detected. The number of transformed foci generated was greater than the sum of the foci obtained with ras and each of the establishment genes used separately. In addition, the foci had a distinct morphology. Synergism was seen between the HPV-16 E7 gene and certain mutant alleles of the cellular p53 gene as well as between E7 and c-myc.

Alleles↗
PubMed1989

Carcinoembryonic antigen, a human tumor marker, functions as an intercellular adhesion molecule.

Carcinoembryonic antigen (CEA) is a member of a family of cell surface glycoproteins that are produced in excess in essentially all human colon carcinomas and in a high proportion of carcinomas at many other sites. The function of this widely used tumor marker and its relevance to malignant transformation is therefore of considerable interest. We demonstrate here that CEA mediates Ca2+-independent, homotypic aggregation of cultured human colon adenocarcinoma cells (LS-180) and rodent cells transfected with functional CEA cDNA. Furthermore, CEA can effect the homotypic sorting of cells in heterogeneous populations of aggregating cells. CEA can thus be considered a new addition to the family of intercellular adhesion molecules. We also show that, whereas CEA is localized mainly to epithelial cell membranes facing the lumen in normal adult intestine, it is found on adjacent cell membranes in both embryonic intestine and colonic tumors. A model for the role of CEA in the tissue architecture of adult, embryonic, and aberrant tumor intestinal epithelium is presented.

Biomarkers, Tumor↗
PubMed1989

Alterations in the p53 gene and the clonal evolution of the blast crisis of chronic myelocytic leukemia.

Molecular mechanisms responsible for the clinical progression of chronic myelocytic leukemia to its accelerated phase or to blast crisis have not been defined. We found alterations of the p53 gene (p53 is a 53-kDa nuclear protein) including deletions and rearrangements in 8 of 34 patients in blast crisis and 1 of 4 patients in the accelerated phase, but in only 1 of 38 patients in the chronic phase of chronic myelocytic leukemia. Only two other examples of p53 gene alterations were found among 203 patients with hematologic malignancies and solid tumors. Transcripts of the p53 gene were uniformly found in chronic-phase cells, but gene expression was variable in blast crisis, and transcripts were reduced or undetectable in 10 of 16 patients. Heterogeneous alterations in the structure and expression of the p53 gene appear to be relatively frequent in blast crisis and may be involved in the evolution of disease.

Blast Crisis↗
PubMed1988

Transcription of genes of the carcinoembryonic antigen family in malignant and nonmalignant human tissues.

Normal and diseased human tissues were analyzed for the transcription of genes of the carcinoembryonic (CEA) family. Epithelial tissues of colonic origin, whether malignant or normal, all express two closely related mRNA species of 3.0- and 3.5-kilobase mRNA which code for CEA. Only tissues of colonic origin were found to express these CEA-specific transcripts. Colon carcinomas consistently express a 2.6-kilobase mRNA species as well which codes for nonspecific cross-reacting antigen. Nonneoplastic colon mucosas, on the other hand, express lower or nondetectable levels of this transcript. Most breast carcinomas produce only the nonspecific cross-reacting antigen mRNA, whereas leukocytes of chronic myelogeneous leukemia express both nonspecific cross-reacting antigen mRNA and a 2.3-kilobase mRNA corresponding to a yet undefined gene of the CEA family. Thus the multiple CEA-like products reported to be produced by these tissues correspond to only four different mRNA species coding for three different peptides. These data suggest a less complex organization of the CEA family than was previously suspected and point to posttranscriptional modifications, such as variable patterns of glycosylation, as the likely reason for much of the observed complexity in CEA-like glycoproteins.

Carcinoembryonic Antigen↗
PubMed1988

Expression of the cellular p53 protein in cells transformed by adenovirus 12 and viral DNA fragments.

Expression of the p53 cellular phosphoprotein was examined in rat cells transformed by adenovirus 12 (Ad12) virions and by fragments of Ad12 DNA. p53 was detected in all the cell lines examined. Steady-state levels of p53 were highest in cells transformed by the entire E1 region rather than by E1A alone. Physical association between p53 and the Ad12 E1B 55K protein was not detected. The Ad12 E1B-encoded 55K protein, but not the Ad12 E1B 17K and 19K proteins, appears to participate in regulating p53 protein levels.

Adenovirus Early Proteins↗
PubMed1988

Introduction of new genetic material into human myeloid leukemic blast stem cells by retroviral infection.

An amphotropic retroviral vector containing the bacterial neomycin phosphotransferase gene (neo) was used to infect blast cells from patients with acute myeloblastic leukemia. The infected cells acquired a G418-resistant phenotype that was stable as measured in a clonogenic assay and in long-term suspension culture. Thus, gene transfer into stem cells was accomplished by this procedure. This approach for manipulating gene expression in blast stem cells provides a means to assess the roles of a variety of genes in self-renewal, differentiation, and leukemogenesis.

Blast Crisis↗
PubMed1988

Inactivation of the p53 oncogene by internal deletion or retroviral integration in erythroleukemic cell lines induced by Friend leukemia virus.

The p53 gene is rearranged in a high proportion of erythroleukemic cell lines derived from the spleens of mice infected with Friend leukemia virus. These rearrangements result in either the synthesis of a truncated protein or the inactivation of the p53 gene. Here we have molecularly characterized the rearrangements in two murine erythroleukemic cell lines induced by Friend leukemia virus, DP20-1 and CB3, that contain a rearranged p53 gene and fail to express p53 protein. The rearrangement in the DP20-1 cell line is due to the insertion of Friend spleen focus-forming provirus (SFFV) in the 3' end of the p53 gene in intron sequences between exons 9 and 10. Transfection of molecular clones of this SFFV provirus into NIH3T3 cells results in the generation of infectious virus as determined by its ability, in the presence of helper virus, to induce rapid splenomegaly and polycythemia when injected into adult DBA/2J mice. Insertion of SFFV in DP20-1 cells resulted in the expression of an aberrant 2.9 kb RNA species. Analysis of a molecular clone of the rearranged p53 gene in a second cell line, CB3, revealed that the p53 gene in this clone has sustained a large deletion within the p53 gene resulting in the loss of coding sequences between exons 4 and 8. The 5' end of the deletion originates within exon 4 and extends 3' to within the eighth intron. The significance of these findings with regard to the multi-stage nature of Friend virus induced erythroleukemia is discussed.

Animals↗
PubMed1988

Immortalization of rat embryo fibroblasts by the cellular p53 oncogene.

Intact and rearranged p53 genes from Friend virus-induced erythroleukemic cell lines which code for proteins of 53- (p53) and 44-kDa (p44), respectively, were cloned into pUC18 and tested for their ability to immortalize rat embryo fibroblasts. The functional p53 gene from normal Balb/c mouse liver was also tested for immortalizing activity. Immortal cells were obtained with the three genes although the efficiency of immortalization by p44 was lower than that by p53. Expression of murine p53 and p44 in the established rat cell lines was confirmed by metabolic labeling and Western Blotting. Our results demonstrate that elevated expression of the mouse p53 gene, driven by its natural promoter and in the absence of strong heterologous promoters and/or enhancers, can efficiently immortalize early-passage rat embryo fibroblasts. p53-immortalized cells but not p44-immortalized cells could be morphologically transformed by secondary transfection with activated Ha-ras. Thus 5'-coding sequences of the p53 gene appear necessary for ras complementation but not for immortalization.

Animals↗
PubMed1988

Loss of a highly conserved domain on p53 as a result of gene deletion during Friend virus-induced erythroleukemia.

We have investigated a mutation in the p53 gene leading to expression of a truncated 46,000-dalton protein in a Friend virus-induced erythroleukemia cell line. cDNA sequence analysis revealed a deletion of nucleotide sequences in exon 7 and part of exon 8; 17 additional nucleotides, derived from intron 6, were present in the cDNA and served to maintain the reading frame of the encoded protein. Comparison with p53 protein from other species indicated that the region of the molecule missing in p46 included a highly conserved region. In addition, p46 failed to bind SV40 large T antigen in vitro under conditions which promoted binding of p53 to large T. It seems likely, therefore, that an important functional property of p53 may be affected by the mutation.

Amino Acid Sequence↗
PubMed1987

Comparative analysis of the involvement of p53, c-myc and c-fos in epidermal growth factor-mediated signal transduction.

p53, a transformation-related protein located in the nucleus, shares several properties with the product of the nuclear proto-oncogene c-myc. The latter is transiently induced after different membrane-originating stimuli. A similar observation has been made with c-fos, a gene that also belongs to the 'nuclear' class of oncogenes. Here we show that p53, unlike the products of the c-myc and c-fos genes, is not induced by the signal generated by the interaction between epidermal growth factor (EGF) and its receptor. Hence, p53 does not appear to be involved in EGF signal transduction. In order to draw this conclusion we have used an EGF receptor gene-amplified human breast tumor cell line that is growth-inhibited by EGF, and exponentially growing normal human fibroblasts.

Cell Line↗
PubMed1987

Multistage Friend erythroleukemia: independent origin of tumor clones with normal or rearranged p53 cellular oncogenes.

The erythroleukemia induced by Friend virus complex in adult mice is a multistage malignancy characterized by the emergence, late in the disease, of tumorigenic cell clones. We have previously shown that a significant proportion of these clones have unique rearrangements in their cellular p53 oncogene. The clonal relationships among Friend tumor cells isolated in the late stages of Friend erythroleukemia were analyzed by examining the unique integration site of Friend murine leukemia virus and the unique rearrangement in their cellular p53 oncogene. The majority of clones isolated from individual mice infected with Friend virus were clonally related as judged by the site of Friend murine leukemia virus integration. However, Southern gel analysis of DNA from individual Friend cell clones indicated that all of the clones with a normal p53 gene from the same mice were clonally related, but were unrelated to the Friend cell lines with a rearranged p53 gene. These results suggest that Friend tumor cells with rearrangements in their p53 gene arise as the result of a unique transformation event, rather than by progression from already existing tumor cells with a normal p53 gene. They also suggest that such rearrangements in the p53 gene confer a strong selective advantage to these cells in vivo.

Animals↗