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D Siwarski

Publications and source records attributed to D Siwarski.

33 records · Page 2Linked to original sources
PubMed1993

Co-amplification of c-myc/pvt-1 in immortalized mouse B-lymphocytic cell lines results in a novel pvt-1/AJ-1 transcript.

In a series of mouse pvt-1 cDNA clones prepared from an immortalized B-cell line that contains an amplified c-myc/pvt-1 region, we have identified a unique cDNA, AJ-I, which contains 57 bp of pvt-1 sequence (pvt-1a) spliced to a novel sequence of 2.1 kb. We report here that this 3' segment (termed AJ-IX) maps more than 60 kb telomeric to pvt-1a and is encoded by a novel locus (AJ-I) on mouse chromosome 15. The AJ-IX probe detects a transcript that is expressed only in normal mouse brain and testis. Several mast-cell tumors, Ly-I+ B-lymphocytic cell lines and a neuroblastoma also display abundant levels of AJ-IX-specific mRNA. However, splicing of pvt-1a to AJ-IX is found exclusively in Ly-I+ B-cell lines that contain amplified c-myc/pvt-1. We conclude that some features in the generation of this amplicon facilitates the synthesis of a pvt-1/AJ-IX chimeric mRNA that may play a role in immortalization of these Ly-I+ B-cell lines.

Animals↗
PubMed1993

Association of tumorigenic and nontumorigenic (immunogenic) variants in a mouse T-cell lymphoma with two distinct p53 mutations.

An in vitro model system for xenogenization has been developed in which an immunogenic, nonmalignant phenotype was selected from a highly malignant T-cell line (S49). We showed by single-strand conformation polymorphism and DNA sequence analysis that specific point mutations in the p53 tumor suppressor gene correlated with a change from a tumorigenic to a nontumorigenic (immunogenic) phenotype. Specifically, we found that the highly malignant S49 cell line T-60 contains an Arg-->Gln substitution at residue 246 in exon 7 of p53. In contrast, nontumorigenic (immunogenic) variants (T-25-Adh and Rev-1) exhibited a Gly-->Ser substitution at residue 242 of p53. In two subsequent tumorigenic revertants derived from Rev-1, we again found the Arg-->Gln substitution at residue 246 that was found initially in the T-60 cells. Thus, mutation at residue 246 of p53 was associated with a highly malignant phenotype, whereas a novel mutation at residue 242 of p53 appeared to be associated with a nonmalignant phenotype and may have actually protected the host through immunization. We conclude that mutation of residue 242 may represent a new class of permissive (nonmalignant) mutations in the mouse that are analogous to the Li-Fraumeni mutation in humans.

Amino Acid Sequence↗
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↗
PubMed1992

The pattern of p53 mutations in Burkitt's lymphoma differs from that of solid tumors.

Available evidence suggests that, among hematological malignancies, p53 is most often mutated in Burkitt's lymphoma (BL). However, much of the published data is based on cell lines. We have, therefore, analyzed BL biopsies to determine more accurately the frequency and pattern of p53 mutations in primary tumors and to determine whether there are differences among the various subtypes of BL. Among 27 BL biopsies from South Africa, we have observed mutations in the p53 gene (exons 5 through 8) in 37% of tumors. The higher frequency of mutations in cell lines (70%) suggests that mutation of p53 may be associated with tumor progression. Summarizing available data we conclude that the presence of mutated p53 in BL is independent of the geographic origin of the tumor, the 8;14 chromosomal breakpoint locations and Epstein-Barr virus association. We also find that the mutational spectrum of p53 in BL differs from that observed in nonlymphoid tumors. More than 50% of mutations in BL are clustered in a small stretch of 33 amino acids (codons 213 to 248). Interestingly, codon 213 appears to be as frequently mutated as codon 248. Conversely, codon 273, often mutated in solid tumors, is rarely involved in BL.

Amino Acid Sequence↗
PubMed1992

Infrequent p53 mutation in mouse tumors with deregulated myc.

An invariant genetic lesion in mouse plasmacytomas is deregulated expression of c-myc as a consequence of chromosomal translocation. However, retroviral and transgenic studies suggest that additional genetic lesions may contribute to the genesis of plasmacytomas. The p53 tumor suppressor gene is a likely contributor to this genetic lesion, since there is a high incidence of p53 mutation in Burkitt's lymphomas and B-ALL (L3), both of which contain translocations involving c-myc analogous to those in plasmacytomas. In addition, p53 has been shown to be a transcriptional modulator of c-myc expression. In a survey of 27 mouse plasmacytomas by single-strand conformation polymorphism, we identified a single mutation (3.7% incidence), suggesting that p53 lesions are not frequent contributors to plasmacytomagenesis. A similar study of macrophage-monocyte tumors generated by a c-myc-containing retrovirus also indicates a lack of p53 involvement in deregulated c-myc expression. These results suggest that the specific maturation stage of transformed B-lymphocytes, independent of c-myc deregulation, may be the critical factor which determines the involvement of mutant p53.

Amino Acid Sequence↗
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

Pvt-1 transcripts are found in normal tissues and are altered by reciprocal(6;15) translocations in mouse plasmacytomas.

The mouse Pvt-1 (for plasmacytoma variant translocation) region maps to a chromosome 15 breakpoint region that is frequently interrupted by "variant" reciprocal chromosome translocations, rcpt(6;15), in plasmacytomas. This region lies several hundred kilobases (kb) 3' of the mouse c-myc gene (Myc) which is deregulated in both rcpt(6;15) and rcpt(12;15) plasmacytomas. rcpt(12;15) translocations apparently activate c-myc directly by interrupting the gene itself, but the mechanism causing c-myc deregulation in tumors bearing rcpt(6;15) translocations remains unknown. The indirect activation of c-myc by Pvt-1 interruption has remained an appealing possibility, but heretofore it has not been possible to establish such a connection. Furthermore, no genes from the Pvt-1 locus have been shown to be transcribed in normal tissues or in tumors with rcpt(6;15) translocations. We report the isolation of a cDNA clone, Pvt-1-1, from mouse spleen mRNA that is specific to the Pvt-1 region. This cDNA probe detects low levels of large (ca. 14 kb) RNA transcripts in normal mouse tissues. In plasmacytomas with rcpt(6;15) translocations, the Pvt-1 transcripts are elevated in abundance and truncated in size. Both changes are apparently induced by the chromosomal translocation. Expression of 14-kb Pvt-1 RNA is elevated in B-cell tumor lines that express immunoglobulin light chain genes; thus, we postulate that these translocations are facilitated by the increased DNA accessibility of immunoglobulin kappa light chain and Pvt-1 genes when they are simultaneously expressed at certain times during B-cell ontogeny.

Amino Acid Sequence↗
PubMed1989

Gene mapping of the three subunits of the high affinity FcR for IgE to mouse chromosomes 1 and 19.

The high affinity receptor for IgE (Fc epsilon RI) is a tetrameric structure consisting of a single IgE-binding alpha subunit, a single beta subunit, and two disulfide-linked gamma subunits. The alpha subunit of Fc epsilon RI and most Fc receptors are homologous members of the Ig superfamily. By contrast, the beta and gamma subunits from Fc epsilon RI are not homologous to the Ig superfamily. The gamma-chains do share a region of high homology with the zeta-chain of the TCR. No homology has been found to date for beta with any published sequence. Here, we report that a single copy gene encodes Fc epsilon RI beta and that the locus for Fc epsilon RI beta is found on mouse chromosome 19, genetically linked to the Ly-1 (Ly-12) locus and in a region that also contains Ly-10 and Ly-44 (CD20). Homology comparisons among these molecules reveal limited regions of homology between Fc epsilon RI beta and Ly-44 (CD20) as well as other striking similarities: both molecules have four putative transmembrane segments and a probably topology where both amino- and carboxytermini protrude into the cytoplasm. In addition, we show that a single gene for FC epsilon RI gamma is found at the distal end of mouse chromosome 1, clustered in a region where Fc epsilon RI alpha has also been linked to Fc gamma RII. At least one of the two forms of Fc gamma RII has recently been shown to contain gamma subunits identical to the gamma subunits of Fc epsilon RI. The close association of the genes for Fc epsilon RI alpha, FC gamma RII, and their shared gamma subunits raises interesting implications regarding coordinate regulation of gene expression.

Amino Acid Sequence↗
PubMed1989

Sequence and organization of the mouse poly (ADP-ribose) polymerase gene.

Using a human cDNA probe, we have isolated murine genomic and cDNA clones corresponding to the nuclear enzyme poly (ADP-ribose) polymerase (ADPRP). Northern analysis with the mouse cDNA clones reveals transcripts of 3.7-3.8 kb corresponding in size to the human ADPRP transcript. DNA sequence comparisons between mouse and human clones reveals extensive amino acid sequence conservation within regions harboring DNA binding, NAD+ binding or automodification domains. A survey among mouse inbred strains for restriction fragment length polymorphism (RFLP) reveals at least three distinct ADPRP alleles. The segregation of alleles among mouse genetic recombinants positions ADPRP on mouse chromosome 1 between the complement receptor-related gene At-3 and the Fc receptor locus FcR. Furthermore, ADPRP is closely associated with the autoimmune locus gld (generalized lymphadenopathy).

Amino Acid Sequence↗
PubMed1975

Cellular microcytotoxicity in human tumor systems: analysis of results.

Using the tritiated-proline microcytotoxicity assay with cultured target cells, we tested a large series of melanoma, breast cancer, and bladder cancer patients for the presence of cell-mediated immunity. Specific, disease-related activity was infrequently observed, since the patients' lymphocytes exhibited selective activity against both disease-related and non-disease-related target cells. Most normal controls also demonstrated selective activity against these target cells. Neither the length of time the target cells had been cultured in vitro nor technical aspects of the assay, including the lymphocyte preparation methods, seemed to account for our results. We concluded that the experimental design of these tests may be the critical factor responsible for many of the disparate results being observed in different laboratories.

Breast Neoplasms↗
PubMedDate not supplied

Double producers of kappa and lambda define a subset of B cells in mouse plasmacytomas.

Rearrangement of the light chain locus is believed to be an ordered process in which Iglambda rearrangements only occur if Igkappa rearrangements are found to be non-productive or self-reactive. Secondary rearrangements of the B-cell receptor (BCR) have shown, however, that rescue of abortive Igkappa rearrangements or autoreactive B cells can be achieved through receptor editing using upstream V-regions as the template sequences. Since secondary rearrangement can occur in the periphery, possibly in a subset of B cells maintaining constitutive Rag activity, it is conceivable that two light chains (kappa:kappa or kappa:lambda) could be expressed in these cells, apparently in violation of allelic exclusion. Previously, we have reported that silicone-induced plasmacytomas (SIPCs) exhibit dual expression and ongoing rearrangements of Igkappa and Iglambda. In this paper, we show by ELISA that both Igkappa and Iglambda are found at the protein level, but are secreted in different amounts. Furthermore, we demonstrate by micro-manipulation and RT-PCR amplification that Igkappa and Iglambda are simultaneously expressed in a single SIPC cell. We propose that these dual-expressing cells, found intermittently in cases of plasmacytomas (PCs), may have originally been immature B cells when transformed but now are maintained as a long-lived mature B cell found infrequently in the tumor population.

Animals↗