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Biomedical subjects

I Magrath

Publications and source records attributed to I Magrath.

At least 55 records · Page 3Linked to original sources
PubMed1994

Mutations in the coding region of c-myc occur frequently in acquired immunodeficiency syndrome-associated lymphomas.

We have analyzed 30 cases of high- and intermediate-grade acquired immunodeficiency syndrome-associated non-Hodgkin's lymphoma (AIDS-NHL) for mutations in the c-myc coding region. In addition, in these same tumors, we have sought the presence of mutations in a regulatory region within the first c-myc intron defined by the binding to a factor that inhibits c-myc transcription (MYC intron factor, or mif). Mutations in the c-myc coding region were present in 10 of 16 small noncleaved cell lymphoma (SNCL), but in only 3 of 14 other histologic subtypes tested (0/3 large non-cleaved cell, 2/8 immunoblastic, and 1/3 anaplastic large cell lymphomas). Nineteen of the AIDS-NHLs analyzed contained a c-myc rearrangement and in 10 of these the c-myc gene was mutated in its coding region. In contrast, we could detect a mutation in the coding region in only 2 of 8 AIDS-NHL without a c-myc rearrangement. Mutations in the mif region were detected in 5 of 16 SNCL. Among AIDS-NHL carrying mutations in the c-myc coding region, only 4 carried mutations in the regulatory region. These results suggest that the mutations in the coding region of the c-myc protein may either be a consequence of the translocations involving c-myc, or may be necessary only in tumors where c-myc is deregulated as a result of a c-myc/lg translocation.

Base Sequence↗
PubMed1993

Role of the p53 tumor suppressor gene in cell cycle arrest and radiosensitivity of Burkitt's lymphoma cell lines.

We have assessed the role of the p53 tumor suppressor gene in cell cycle arrest and cytotoxicity of ionizing radiation in 17 Burkitt's lymphoma and lymphoblastoid cell lines. Cell cycle arrest was assessed by flow cytometry of cells 16 h following irradiation. In addition to the usual G2 arrest, the cell lines exhibited three types of responses in G1: Class I, strong arrest in G1 following radiation; Class II, minimal arrest; and Class III, an intermediate response. All Class I cells contained normal p53 genes. Of the ten lines that showed minimal G1 arrest, eight had mutant p53 alleles, and two lines were heterozygous for p53 mutations. Both of the lines showing an intermediate response contained wild-type p53. Our results are consistent with the view that mutations abrogate the ability of p53 to induce G1 arrest following radiation. Studies with the heterozygotes showed that the mutant protein can have a dominant negative influence upon wild-type p53, and the reduced ability of two normal p53 lines to arrest in G1 indicated that p53 function can be impaired by other mechanisms. The radiosensitivity of most of the lines appeared to depend on the ability of p53 to induce a G1 arrest. The mean radiation dose that inhibited proliferation of the Class I lines by 50% was 0.98 Gy. Of the eight p53 mutant cell lines tested, five lines required approximately 2.9 Gy to cause a 50% inhibition of cell proliferation. The two heterozygotes were also more resistant to radiation than the Class I cells (50% inhibitory dose, 2.1 and 2.9 Gy). Our results suggest that radioresistance is afforded by a loss of function of wild-type p53, which would normally induce a G1 arrest and promote cell death in the presence of DNA damage.

Burkitt Lymphoma↗
PubMed1993

Cancer in developing countries: opportunity and challenge.

Epidemiologic observations indicate that environment and lifestyle are the major determinants of the geographical patterns of cancer. The developing countries, which account for 75% of the world's population, have lower incidence rates of cancer compared with the industrialized nations but bear more than half the global cancer burden. Demographic trends resulting from economic progress (decreasing incidence of infectious diseases, population growth, aging, and urbanization), coupled with increased tobacco consumption and dietary changes, indicate that developing countries will bear a continually increasing proportion of the world's cancer burden and its accompanying demand for the provision of costly treatment programs. Yet the developing countries command only 5% of the world's economic resources, and health care programs are already fully extended and frequently inadequate. Thus, cancer control in the developing countries, including preemptive prevention of the anticipated increases in cancers presently more common in the industrialized nations (e.g., lung, breast, and colon), should include much greater emphasis on cancer prevention than is presently the case. But there is another perspective. The developing countries, with their dramatic contrasts in lifestyles and environments and equally diverse patterns of cancer, provide an unparalleled, and often neglected, opportunity for studies directed toward understanding the mechanisms of environmental carcinogenesis. Such an understanding should eventually lead to the development of novel intervention approaches. Unfortunately, cancer research is much more difficult to conduct in the developing countries because of the lack of population-based registries, poor communication and transportation systems, and deficiencies in infrastructure, financial support, and the training of health professionals. These difficulties could be overcome, to the benefit of all, if the extent of collaboration in cancer research between the developing and industrialized nations were to be greatly expanded.

Developing Countries↗
PubMed1993

Replicative viral DNA in Epstein-Barr virus associated Burkitt's lymphoma biopsies.

Epstein-Barr virus (EBV) is linked to a spectrum of human diseases including epithelial and lymphoid malignancies in which it exists predominantly in a latent state. EBV is capable of establishing replicative infection at oropharyngeal and genital sites. Replicative EBV infection also occurs in oral hairy leukoplakia, in EBV associated lymphoproliferative disorders, and to a minor degree in nasopharyngeal carcinomas. Recent evidence also suggests that EBV replication, also, may be associated with AIDS related lymphomas and Hodgkin's disease. However it is widely believed that virus in circulating B-lymphocytes and in B-cell malignancies is stringently latent. We now show that by Southern blot analysis we can detect replicative forms of virion DNA in 14.5% (8 of 55) of EBV-positive Burkitt's lymphoma biopsies. This may be the explanation for the elevation of the titres of lytic cycle EBV antigens that is associated with presentation and relapse of EBV associated Burkitt's lymphoma.

Biopsy↗
PubMed1993

Point mutations in the c-Myc transactivation domain are common in Burkitt's lymphoma and mouse plasmacytomas.

We have screened the entire coding region of c-myc in a panel of Burkitt's lymphomas (BLs) and mouse plasmacytomas (PCTs). Contrary to the belief that c-myc is wild type in these tumours, we found that 65% of 57 BLs and 30% of 10 PCTs tested exhibit at least one amino acid (aa) substitution. These mutations were apparently homozygous in all BL cell lines tested and two tumour biopsies, implying that the mutations often occur before Myc/Ig translocation in BL. In PCTs, only the mutant c-myc allele was expressed indicating a functional homozygosity, but occurrence of mutations after the translocation. Many of the observed mutations are clustered in regions associated with transcriptional activation and apoptosis, and in BLs, they frequently occur at sites of phosphorylation, suggesting that the mutations have a pathogenetic role.

Alleles↗
PubMed1993

Hemi- or homozygosity: a requirement for some but not other p53 mutant proteins to accumulate and exert a pathogenetic effect.

Activating mutations within the p53 gene cause stabilization and therefore increased steady-state levels of the p53 protein; some, but not all, also result in the generation of an epitope recognized by the antibody pAB240. We have shown here that in 70% of Burkitt lymphoma cell lines, but not in normal EBV transformed B cell lines, p53 protein is readily detectable by Western blot analysis using either an antibody directed against the 240 epitope or an antibody against wild-type p53. Genomic analysis of these BL cell lines demonstrated the presence of mutations within the p53 gene in all cell lines with detectable p53 protein. We have also shown that in the cell lines ST486, Raji, and TE 110, which are heterozygous for a neutral sequence codon polymorphism (Arg/Pro) that causes altered migration of an otherwise normal protein and also contain a heterozygous mutation, only the protein derived from the mutated allele is stabilized. Thus the dominant effect of the mutations present in these cell lines apparently does not result from sequestering of the normal protein by the abnormal protein, and therefore presumably is a consequence of a gain-of-function resulting from the mutation. Although all cell lines with stabilized p53 also contained p53 mutations, three lymphoid tumors (two cell lines and one fresh B-CLL) with a heterozygous mutation at codon 248 did not express elevated levels of p53. In contrast, p53 was readily detectable in Western blot analysis from cell lines KK124, Namalwa, and CA46, which had homo- or hemizygous mutations at codon 248, and from PP1084, a cell line with a codon 273 mutation and a carboxyl-terminal truncation in the other allele. These results suggest that mutations at codon 248, unlike those in cell lines ST486 and TE110, are stabilizing only in the absence of the wild-type p53. Heterozygous mutations at codons 248 have been described in the germline of individuals belonging to cancer-prone families described by Li and Fraumeni (see ref 18), but tumors detected in such individuals are homozygous, i.e., contain only mutated p53. This is consistent with the possibility that such mutations exert a pathogenetic effect only in the absence of the wild-type protein, and are coupled to our findings that stabilization of p53 is a necessary component of the oncogenic pathways relevant to p53. However, whereas some mutations are stabilizing in the presence of the normal p53 protein, others are stabilizing only in the homozygous state.

Alleles↗
PubMed1992

Molecular basis of lymphomagenesis.

Lymphoid neoplasms, like all malignant tumors, arise as a consequence of the accumulation, in a single cell, of a set of genetic lesions that result in altered proliferation or increased clonal life span. The most frequently observed genetic abnormalities among the malignant non-Hodgkin's lymphomas are translocations, which appear to be lineage and, to a large extent, lymphoma specific. Recombinases that normally mediate the process of antigen receptor gene rearrangement appear to have an important (but not exclusive) role in the mediation of these translocations and of other types of gene fusion (e.g., deletion of intervening DNA). Frequently, such fusions result in the increased or inappropriate expression of crucially important proteins, many of which are transcription factors that regulate the expression of other genes. These abnormalities, however, do not appear to be sufficient to induce lymphoma, and it is likely that the additional genetic lesions required differ from one tumor to another. The likelihood of any given clone of cells accumulating a sufficient number of relevant genetic lesions to give rise to a lymphoma is probably a function of its life span. Prolonged survival of a cell clone may be mediated by viral genomes (e.g., Epstein-Barr virus and human T-cell leukemia/lymphoma virus type 1), by the abnormal expression of cellular genes that inhibit apoptosis (e.g., bcl-2), or by the mutation or deletion of cellular genes that are necessary for apoptosis, e.g., p53. The background rate at which genetic lesions occur is amplified by the interaction of inherited and environmental factors, the latter appearing to be the major determinant of incidence rates. However, inherited factors that influence lymphomagenesis, including variability in the ability to repair DNA damage or in the fidelity of antigen receptor recombinases for their signal sequences, may be crucial determinants of which particular individuals in a given environmental setting develop lymphoma.

Humans↗
PubMed1992

Epstein-Barr virus and Burkitt's lymphoma.

Recent investigations indicate that Burkitt's lymphoma consists of several subtypes, defined by their clinical and molecular features. Each geographical region so far studied appears to consist of a different mixture of subtypes. Interestingly, there appear to be geographic 'gradients' with respect to the fraction of tumors associated with EBV and the type of 8;14 chromosomal translocation. The rate of EBV association is highest in Equatorial Africa, lowest in North America and intermediate in South America. The fraction of tumors with breakpoints far upstream of the c-myc gene follows a similar pattern. These findings strongly suggest that the subtypes of Burkitt's lymphoma are environmentally determined, and we propose that the pattern of infection (e.g. malaria) to which the young child is exposed influences the tumor subtype distribution by altering the relative and absolute numbers of various B cell precursors at sites of B cell ontogeny (the bone marrow, and possibly mesentery). These B cell precursors are the cells which are susceptible to the specific chromosomal translocations associated with Burkitt's lymphoma. We further propose that immunoglobulin enhancers (recognized and unrecognized) both influence the likelihood of the translocation occurring, and in at least a fraction of cases, contribute to the deregulation of a c-myc. EBV, via EBNA-1, the only invariably expressed latent-gene in Burkitt's lymphoma, probably influences c-myc expression in Burkitt's lymphoma by increasing immunoglobulin enhancer function. Thus, in effect, EBV collaborates with the translocations associated with Burkitt's lymphoma in causing c-myc deregulation. This collaboration is independent of the breakpoint location. While other molecular abnormalities must be able to contribute to myc deregulation in the same way, EBV association in Burkitt's lymphoma is probably determined by the age at which EBV infection occurs (being more likely when infection occurs in very young children) and perhaps also by other infectious diseases that numerically influence the fraction, and predominant stage of differentiation (and hence translocation breakpoint sites) of immature B cells infected by EBV. The presence of EBV in many such cells greatly increases the incidence rate of Burkitt's lymphoma, since one of the genetic lesions needed to deregulate c-myc is already present.

Burkitt Lymphoma↗
PubMed1991

Relationship between DNA cross-links, cell cycle, and apoptosis in Burkitt's lymphoma cell lines differing in sensitivity to nitrogen mustard.

We surveyed 11 Burkitt's lymphoma cell lines for chemosensitivity to nitrogen mustard (HN2) in order to determine whether any simple correlates to cytotoxic response might be revealed. The lines tested varied over a 5-fold range in concentration of HN2 required to inhibit tumor cell growth by 50%. Drug sensitivity correlated neither with continental origin of tumor, growth fraction, presence of Epstein-Barr virus, nor with the precise locations of (8;14) translocation breakpoints. Furthermore, contrary to experience with other cell lines, no simple correlation was found between the HN2 sensitivity of the four most divergent lines (low sensitivity, CA46 and MC116 cells; high sensitivity, Namalwa and JLP119 cells) and exposure to DNA cross-links (area under the DNA cross-linking-versus-time curve). In addition, we found similar extents of gene-specific HN2-induced damage in the native and translocated c-myc alleles of CA46 and JLP119 cells. At equimolar HN2 treatment, CA46 cells exhibited a profound arrest in G2M phase, while JLP119 cells exhibited prolonged S-phase delay. This suggested that despite similar DNA cross-link exposure, JLP119 cells were less able to complete DNA replication while repair was in progress. As cell cycle distribution returned to near normal, JLP119 cells exhibited DNA degradation characterized by oligonucleosome-sized DNA fragments prior to cell membrane disintegration. Our findings indicate that HN2-sensitive Burkitt's lymphoma cells may be more susceptible to delay in S phase for a given frequency of DNA cross-links and that prolongation of S phase correlated with apoptotic cell death.

Alkylation↗
PubMed1991

Patterns of chromosomal breakpoint locations in Burkitt's lymphoma: relevance to geography and Epstein-Barr virus association.

We have examined, by Southern blotting, the patterns of chromosomal breakpoint locations in 55 cases of Burkitt's lymphoma (BL) with respect to geography and Epstein-Barr virus (EBV) association. We have confirmed the association between chromosome 8 breakpoint and geography: 74% of endemic (eBL) but only 9% of sporadic BL (sBL) had breakpoints outside the HindIII fragment encompassing the c-myc gene (P2 less than .00001). Conversely, not only did 91% of sBL manifest a rearranged HindIII fragment, but at least 56% of these cases, in contrast to 17% of eBL cases, had a breakpoint within the first exon or intron of c-myc (P2 less than .004). Breakpoints outside the switch mu (S mu) region (ie, the HindIII fragment encompassing S mu) on chromosome 14 were twice as common overall (73%) as those within S mu (27%), but in the 15 tumors with S mu breakpoints, 13 (87%) had a rearranged c-myc gene. Breakpoints outside the HindIII fragment encompassing c-myc on chromosome 8 were predominantly associated with non-S mu breakpoints on chromosome 14 (85%) and this was the combination most frequently associated with eBL (65%; 6% of sBL, P2 less than .00001). In sBL, the most frequent breakpoint combination was a rearranged c-myc gene with a non-S mu breakpoint (63%; 13% of eBL). Twenty-eight percent of sBL and 13% of eBL had breakpoints both within c-myc and within S mu. EBV DNA was present in 19 of 20 tumors with breakpoints outside c-myc, in none of 7 with a breakpoint in the immediate 5' region of c-myc, in 4 of 5 tumors with breakpoints in the first exon, and in 7 of 12 tumors with breakpoints in the first intron. These data suggest that the pathogeneses of eBL and sBL differ with regard to the mechanism of c-myc deregulation, and probably also with regard to the state of differentiation of the target cell for malignant transformation. We have formulated a testable hypothesis regarding the potential role of EBV in pathogenesis: that it is required to contribute to the deregulation of c-myc in the presence of some, but not all, types of c-myc damage arising from the chromosomal translocations.

Blotting, Southern↗
PubMed1991

A randomized pilot study of high-dose epirubicin as neoadjuvant chemotherapy in the treatment of cancer of the bilharzial bladder.

Seventy-one patients with T2 and T3 bladder cancer were randomized to receive either two courses of epirubicin 120 mg/m2 i.v. push every 21 days pre-operatively, and four additional courses post-operatively (group I = 34 patients), or radical surgery (group II = 37 patients). At a median follow-up of 24 months (range 22 months to 38 months) 25 patients from group I and 14 patients from group II are still alive and disease-free. The estimated two-year disease-free survival percentages were 73.5 and 37.9%, respectively (P = 0.05). After initial chemotherapy, resected specimens were subjected to histopathological study of chemotherapeutic effects. Necrosis was detected in 95% of cases with squamous cell carcinoma and in 57.3% of cases with transitional cell carcinoma. We conclude that the benefit which was obtained by pre-operative and post-operative chemotherapy with epirubicin is promising and may represent a significant improvement in the treatment of patients with carcinoma of the bilharzial bladder.

Adult↗
PubMed1991

Mouse bcl-3: cDNA structure, mapping and stage-dependent expression in B lymphocytes.

Human B-cell chronic lymphocytic leukemias (CLLs) are malignancies of mature B lymphocytes. A subset of these tumors is associated with a non-random t(14; 19) translocation (Ueshima et al., 1985). Recently a gene (bcl-3) has been identified in the region adjacent to the chromosome 19 breakpoint in this translocation (McKeithan et al., 1987; Ohno et al., 1990). We now report the isolation of cDNA clones of mouse bcl-3. The mouse bcl-3-coding region is 1746 bp long and exhibits 80% identity with human bcl-3 at both the nucleotide and amino acid level. The bcl-3 locus maps to the proximal end of mouse chromosome 7, which is syntenic to human chromosome 19. The bcl-3 probe readily detects particularly abundant amounts of a 1.8 kb mRNA in mouse tumors consisting of follicular center mature B cells and large pre-B cells, but not in small pre-B cells. The bcl-3 pattern of expression is distinctive in the spectrum of B-cell maturation in that bcl-3 transcripts are particularly abundant in B-cell lines immortalized just prior to Ig switch. The bcl-3 pattern of expression also bears close resemblance to that of bcl-2 (Gurfinkel et al., 1987), which is frequently associated with human B follicular lymphomas [t(14; 18)] and some chronic lymphocytic leukemias (Adachi et al., 1989; 1990; Adachi & Tsujimoto, 1989).

Amino Acid Sequence↗
PubMed1990

Localization of breakpoints by polymerase chain reactions in Burkitt's lymphoma with 8;14 translocations.

Translocations involving chromosomes 8 and 14 in Burkitt's lymphoma (BL) often involve the switch mu (Smu) region on chromosome 14, which contains multiple repeats. This has enabled us to use the polymerase chain reaction (PCR) to detect breakpoints that involve this region on chromosome 14 and the c-myc gene on chromosome 8. Using pairs of flanking primers, each pair including one annealing to repeat sequences within the switch region and one of three primers from the c-myc region (first intron, 3', or 5' flanking sequence of the first exon of c-myc), we have been able to amplify DNA fragments containing the corresponding breakpoint regions from chromosome 14 in both cell lines and biopsied tumor samples. The definitive demonstration of sequences from both chromosomes in these fragments permitted the confirmation of the presence of a translocation. Because of the sensitivity of PCR, we were able to localize breakpoints in samples containing as few as 1 neoplastic cell in 10(8) cells. PCR provides a valuable tool for the detection of 8;14 chromosomal translocations, which should prove to be of value in diagnosis and molecular epidemiologic studies, as well as providing a means of detecting minimal disease.

Burkitt Lymphoma↗
PubMed1990

[Molecular analysis in Argentinian patients with Burkitt's lymphoma].

Burkitt's lymphoma (BL) is a B-cell neoplasm that occurs in children throughout the world. Two distinct entities of this disease have been recognized: endemic BL (eBL), described in equatorial Africa, and sporadic BL (sBL), described in the USA and Europe. There are striking differences in the incidence, epidemiology, clinical presentation and molecular characteristics of the tumour cells between the two forms, although all BL carry identical specific chromosomal translocations. We have examined the position of the chromosomal breakpoints in the t (8;14) translocation, characteristic of this tumour, relative to the c-myc oncogene in chromosome 8, and the immunoglobulin heavy chain (IGH) locus in chromosome 14 in samples obtained from four Argentine patients using the Southern blot technique. DNA from the tumours was digested with specific enzymes and hybridized with DNA probes from the c-myc (first and third exons) and IGH locus (C mu, S mu and JH). Our analysis shows that all tumours carried the t (8;14) as shown by clonal rearrangements of c-myc in DNA treated with the enzymes Hind III and Eco RI. Moreover, all 4 tumours had chromosome 8 breakpoints within the Hind III restriction fragment that spans the gene. In case 1 it was between the Hind III and Pst I sites 5' to the first exon, in cases 2 and 4 between the Pvu II and Sma I sites 5' to the first exon and in case 3 within the first exon (Sma I-Pvu II segment).(ABSTRACT TRUNCATED AT 250 WORDS)

Argentina↗
PubMed1989

Immunoglobulin delta expression in Burkitt's lymphoma cell lines.

Eighteen Burkitt's lymphoma (BL) cell lines were analyzed for rearrangement and expression of the delta gene. None had rearrangement of the delta gene locus within the 9.0-kb BamHI restriction fragment. Cell lines that expressed the delta gene contained both mu alleles, with at least one productively rearranged. Thirteen of 18 cell lines had detectable transcripts hybridizing with the delta probe. In 10 of the 13 cell lines with delta transcripts, cytoplasmic delta chains were detected, but only two of these expressed delta chains strongly on the surface. All 13 lines made cytoplasmic mu chains, and all except one made cytoplasmic light chains. Surface IgM was detected in all except two of the 13 cell lines. Although BL has generally been considered not to express IgD, except in occasional cases, previous studies have been confined to examination of the cell surface. Many of the cell lines that we examined express delta mRNA transcripts as well as produce cytoplasmic delta chains but no detectable surface IgD. This suggests that delta chains are detectable in the cytoplasm prior to being apparent on the surface. Our findings argue against an origin of BL from germinal center cells since IgD is almost totally lacking in normal B cells present in germinal centers.

Africa↗
PubMed1989

Childhood non-Hodgkin's lymphoma in Egypt: preliminary results of treatment with a new ifosfamide-containing regimen.

Pediatric non-Hodgkin's lymphoma (NHL) constitutes 16% of pediatric malignancies reported to the National Cancer Institute (NCI) in Cairo. Since July 1985, we have treated 39 previously untreated pediatric NHL cases younger than 16 years of age (mean, 7.6 years) with a new protocol consisting of alternating cycles: regimen A comprised cyclophosphamide, high-dose ara-C, Adriamycin and vincristine; regimen B consisted of ifosfamide, methotrexate and VP16, with intrathecal methotrexate. Diagnoses included 20 abdominal masses, 16 peripheral lymphadenopathies and 6 bony lesions. Histopathology according to the working formulation revealed 21 cases of small non-cleaved lymphoma, 6 lymphoblastic, 5 large-cell and 7 unclassified diffuse lymphomas. Responses were complete in 31 cases (82%) and partial in 4 cases (10%), and no response was obtained in 4 cases (8%). Overall survival was 82% in limited disease and 60% in extensive disease at 28+ months. This short-term ifosfamide-containing regimen proved its efficacy, with results matching those of other regimens used in the United States and Europe.

Adolescent↗