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J F Mushinski

Publications and source records attributed to J F Mushinski.

At least 109 records · Page 6Linked to original sources
PubMed1986

Two modes of c-myb activation in virus-induced mouse myeloid tumors.

Two modes of disruption of the protooncogene c-myb by viral insertional mutagenesis in mouse myeloid tumor cells are described. The first mode was found in six tumors in which a Moloney murine leukemia virus component had inserted in the same transcriptional orientation upstream of the 5'-most exon with v-myb homology (vE1). cDNA sequence data indicate the presence of a truncated c-myb mRNA that is initiated in the upstream 5' long terminal repeat of the integrated provirus and processed via a cryptic splice donor sequence in the gag region to the splice acceptor site in vE1 of the c-myb gene, thus removing the remaining downstream viral and myb intronic sequences. Unlike most gag-onc transcripts, the gag and myb sequences in the hybrid transcript were not in the same reading frame. It is presumed that the gag sequence provides a cryptic translation initiation site for the novel amino-truncated c-myb protein. The second mode of disruption was by downstream virus insertion at the 3' side of the c-myb, which results in the synthesis of a small (approximately 2 kilobase) myb transcript. The 5' long terminal repeat of the inserted provirus provides a TGA termination codon that results in the elimination of 240 normal c-myb amino acid residues from the carboxyl terminus of the tumor-specific myb protein. These results suggest that truncated myb proteins play a role in neoplastic transformation of myeloid cells.

Amino Acid Sequence↗
PubMed1985

Tumor-specific, hypomodified phenylalanyl-tRNA is utilized in translation in preference to the fully modified isoacceptor of normal cells.

Phenylalanine transfer RNA (tRNAPhe) of mammalian tissues contains the hypermodified guanine derivative Y (Wye) adjacent to the 3'-end of the anticodon and two O-methylated bases in the 5' portion of the anticodon loop. These positions are hypomodified in a variety of tumor cells including a mouse neuroblastoma. The normal and tumor-specific Phe-tRNAPhe iso-acceptors were prepared from mouse liver and mouse neuroblastoma cells and compared for their activity in incorporating phenylalanine into each phenylalanine site of rabbit globin in a reticulocyte cell-free protein synthesizing system. The hypomodified Phe-tRNAPhe of neuroblastoma cells is generally preferred to the fully modified tRNAPhe of liver in globin synthesis by about 15%. This preference is the same in the translation of both phenylalanine codons, UUC and UUU, but the ratios of incorporation by the Phe-tRNAPhe species vary from site to site within a 2-fold range. Only 2 of 16 phenylalanine residues are donated preferentially by the fully modified Phe-tRNAPhe. One such residue occurs in beta-42, the second of two tandem phenylalanine residues (both encoded by UUC), while the hypomodified isoacceptor is preferred in translation of the first residue. This result indicates that the translation of tandem residues is particularly affected by the tRNAs available. Since the tumor-specific hypomodified Phe-tRNAPhe is generally utilized preferntially, it appears that the bulky Y base and/or other modifications of normal tRNAPhe may modulate protein synthesis and that tumor cells may achieve a growth advantage if their tRNAPhe is hypomodified.

Animals↗
PubMed1985

Chromosome translocations clustered 5' of the murine c-myc gene qualitatively affect promoter usage: implications for the site of normal c-myc regulation.

Five novel murine plasma cell (PC) tumors with chromosome translocations 350-500 bp 5' of the first c-myc exon are described. The t(12;15)s of TEPC 1194, ABPC 33 and TEPC 1165 position the intact c-myc locus 5' of the Cu, C gamma 2a and C alpha IgCH genes respectively. In ABPC 17, the IgH enhancer element and adjacent switch (Su) sequences were found 5' of the first c-myc exon while this enhancer is associated with the reciprocal products of the TEPC 1194, ABPC 33 and TEPC 1033 translocations. Quantitative S1 nuclease analyses demonstrate that the ratios of transcription from the two c-myc promoters (P1 and P2) are increased 4-to 7-fold in these five tumors. With the exception of TEPC 1165, (which contains a small deletion in exon 1), such increases in P1:P2 ratios appear to be manifested by a reduction in P2 usage in comparison to other tumors without such promoter shifts. A survey of 27 additional PC and non-PC B lymphoid tumors and cell lines revealed that myc promoter shifts of this magnitude are unique to PC tumors with 5'-proximal translocations. We propose that (i) these clustered breakpoints identify a normal c-myc regulatory element located at least 350 bp 5' of c-myc exon 1; (ii) the loss or disruption of this cis-acting upstream element and the linkage of c-myc to the IgCH locus would result in abnormal expression of this oncogene in these as well as most other PC tumors.

Animals↗
PubMed1985

The c-myc oncogene is translocated to the involved chromosome 12 in mouse plasmacytoma.

Although it is known that the c-myc oncogene is rearranged in a head-to-head fashion with the immunoglobulin heavy chain locus in mouse plasmacytomas, it has not been clear whether the c-myc oncogene is translocated to the heavy chain locus on mouse chromosome 12 or whether the heavy chain locus is translocated to the c-myc locus on mouse chromosome 15. To determine which of these two possibilities is correct, we hybridized Chinese hamster fibroblasts with J558 mouse plasmacytoma cells that carry a reciprocal chromosome translocation between chromosomes 12 and 15, and we examined the segregating hybrids for the presence of the normal and rearranged mouse c-myc genes, for the presence of different regions of the mouse heavy chain locus, and for the presence of genes located on mouse chromosomes 12 and 15. The results of this analysis indicate that, as in human Burkitt lymphomas with the 8;14 chromosome translocation, the c-myc gene is translocated to the heavy chain locus in mouse plasmacytomas. Thus the orientation of the heavy chain locus on mouse chromosome 12 and of the c-myc gene on mouse chromosome 15 is the same as the orientation of the homologous loci in man.

Animals↗
PubMed1985

Oncogene expression in autoimmune mice.

Systemic autoimmune disease states are known to be associated with abnormal cell growth or differentiation. In the murine models of systemic lupus erythematosus (SLE), specific genotypes result in dysregulated growth of certain lymphocyte subpopulations. Although genes underlying autoimmune syndromes have been characterized by mendelian genetics, it has not yet been possible to characterize them at the molecular level. Recently, it has become clear that cellular proto-oncogenes can regulate cell growth and differentiation. Therefore, we have studied the expression of five different proto-oncogenes; myc, myb, abl, bas, and raf, in organs and cells of various autoimmune strains. These genes were selected because each has previously been associated with abnormal hemopoietic cell growth, and because each has been at least partially characterized at the molecular and functional level. We have found selective abnormal proto-oncogene expression associated with the characteristic abnormal cell growth or differentiation of lymphocytes of autoimmune mice. The lymph nodes of MRL-lpr/lpr mice are packed with unusual T cells. These had a marked increase in myb expression. There was a 20-40-fold increase in myb RNA in lymph nodes of lpr/lpr mice on several different genetic backgrounds. The gld/gld mouse has a very similar unusual T cell in the lymph nodes: it also had a comparable increase in myb RNA in the nodes. In contrast, myb expression was not elevated in the other autoimmune mouse strains lacking these abnormal T cells. Whereas such lpr/lpr mice had increased myb expression in the lymph nodes and splenic T cells, they had markedly subnormal myb expression in the thymus, an organ with high myb in normal and in the other autoimmune strains. These results suggest that one phase of intrathymic differentiation in other mice occurs in the periphery of lpr/lpr mice. The spleens of NZB and male BXSB mice had increased myc expression which was found to be associated with B cells upon cell separation. Similarly, increased bas and abl expression was associated with autoimmune B cells. The xid gene, which retards or prevents the expression of murine lupus by retarding B cell maturation, was associated in BXSB.xid, NZB.xid, and MRL-lpr/lpr.xid congenic mice with marked reduction in expression of myc, bas, and abl in the spleens containing B cells, but not of myb in the lpr/lpr.xid nodes containing primarily the unusual T cells. Raf expression was found to be associated in lpr/lpr and gld/gld mice with both the unusual T cells and splenic B cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Mouse IgD half molecules with shortened IgD heavy chain result from alterations within C delta locus.

An unusually small (51 KD) IgD myeloma protein was isolated from secretions of TEPC 1017 generation (gen) 24. The delta-chain mRNA and the delta-chain gene in this tumor were compared with those of TEPC 1017 of earlier generations. The gen 24 protein contained one normal-sized kappa-type light chain (21 KD) and one unusually short delta-heavy chain (30 KD). The delta-heavy chain was 15 KD shorter than that of TEPC 1017 of earlier generations, owing to a delta-mRNA (1.15 kb) which was 600 bp shorter than that of TEPC 1017 of earlier generations. TEPC 1017 is a tetraploid tumor, and the gen 24 appears to contain at least two different deletions on different chromosomes. The short mRNA was produced from one of these altered delta-chain genes which had a productive VDJ rearrangement but which had lost the C delta 3 domain and perhaps the C delta H domain as well. Despite these genetic insults, RNA splicing produced delta-mRNA with secreted termini and mRNA with membrane-binding termini. It is suggested that the mouse C delta gene has an unusual predilection for deletions because it normally lacks any vestige of C delta 2 and, during i.p. passage, it suffered further deletions or alterations.

Animals↗
PubMed1985

Modulation of c-myb transcription in autoimmune disease by cyclophosphamide.

This study explores the relationship between autoimmunity and the myb proto-oncogene, a gene important for T cell development. The lpr/lpr mice had very large amounts of myb RNA in the lymph node (LN) cells; but unexpectedly, they had abnormally low levels of myb RNA in the thymus, an organ normally rich in myb RNA. Mice with the gld/gld genotype had high myb RNA levels in peripheral LN, similar to lpr/lpr mice, but had normal thymic myb RNA levels. Both lpr/lpr and gld/gld mice and an AILD patient with lymphadenopathy and high myb RNA in peripheral blood cells were treated with cyclophosphamide (CY). In all cases, the CY eliminated the lymphadenopathy and corrected the abnormal myb expression. However, there were significant differences in the clinical and cellular responses to this drug. A single large dose of CY led to marked regression of the lymphadenopathy of gld/gld mice and long-term amelioration of their autoimmune syndrome. In contrast, similar treatment of lpr/lpr mice failed to alter either the lymphadenopathy or the disease process. Consistent with these clinical findings, LN myb was normalized in gld/gld mice by a single injection of CY, whereas there was no effect on myb expression in lpr/lpr mice. The AILD patient reacted much like the gld/gld mice in that myb RNA levels in the peripheral blood, and bone marrow returned to normal after only three doses of CY. The lymphadenopathy and high levels of LN myb mRNA of the lpr/lpr mice could be normalized; this occurred only after long-term treatment with CY. These events were accompanied by an increase in thymic myb mRNA from low levels. These studies have combined a molecular probe with CY therapy to provide insights into the cellular bases for lymphoproliferative autoimmune diseases.

Animals↗
PubMed1984

Activation of the c-myb locus by viral insertional mutagenesis in plasmacytoid lymphosarcomas.

Rearrangement in the c-myb locus of each of four independently derived BALB/c plasmacytoid lymphosarcoma (ABPL's) is due to the insertion of a defective Moloney murine leukemia virus (M-MuLV) into a 1.5-kilobase-pair stretch of cellular DNA at the 5' end of the v-myb-related sequences. This retroviral insertion is associated with abnormal transcription of myb sequences and probably represents a step in the neoplastic transformation of ABPL cells.

Animals↗
PubMed1984

Autoimmunity and increased c-myb transcription.

A single recessive gene, lpr, induces an autoimmune-lymphoproliferative syndrome in several strains of mice. The lymphoid organs of lpr/lpr mice contained cells with increased amounts of myb RNA, which codes for a protein found in the nucleus. A similar human lymphoproliferative disorder also had an increase in c-myb expression. Mouse T cells induced by mitogens to proliferate did not express large amounts of myb RNA, indicating that marked myb expression is not a general feature of lymphocyte activation and proliferation.

Animals↗
PubMed1984

Chromosomal translocations activating myc sequences and transduction of v-abl are critical events in the rapid induction of plasmacytomas by pristane and abelson virus.

Plasmacytomas with short latent periods can be induced in BALB/c mice by a single intraperitoneal (i.p.) injection of 0.5 ml pristane followed 20-40 d later by an injection of Abelson virus. The karyotypes of 18 such tumors were determined; 10 of these had rcpt 12;15, 5 had rcpt 6;15 and 3 had no translocations, but two of these have been shown to have interstitial deletions of chromosome 15. The specific breakpoints were the same as described in pristane-induced plasmacytomas, i.e., at 15D2 /3, 6C2 , and 12F2 . Near diploid karyotypes and trisomy of chromosome 11 were frequently seen. All of the Abelson-plus-pristane-induced plasmacytomas (ABPC) were studied as transplanted tumors, contained integrated v- abl sequences, and actively transcribed v- abl mRNA. All but one of these tumors contained abundant myc RNA transcripts. The shortness of the latent periods of the ABPC suggests that the rcpt 12;15 and rcpt 6;15 occur soon after pristane administration and are present at the time Abelson virus is introduced. In this form of plasmacytomagenesis , activated v- abl genes appear to bypass other genetic changes that require a much longer period of time in pristane plasmacytomagenesis . Nonetheless, the consistent finding of chromosome-15 alterations and abundant myc expression in these plasmacytomas emphasize the apparent need for multiple events even in the genesis of some tumors induced by rapid transforming viruses.

Abelson murine leukemia virus↗
PubMed1984

Illegitimate recombination generates a class switch from C mu to C delta in an IgD-secreting plasmacytoma.

We present here the sequence characterization of a C mu----C delta immunoglobulin (Ig) heavy chain class switch. In the murine IgD-secreting plasmacytoma TEPC 1017, deletion of most of the mu switch recombination region (S mu) and the entire C mu gene occurred in the absence of switch region sequences 5' to C delta. This unique rearrangement resulted from an illegitimate recombination of sequences with only patchy homology to each other. The infrequent and variable nature of illegitimate recombination may explain the low frequency of IgD-secreting plasma cells in normal mouse tissues.

Alleles↗
PubMed1984

Hemizygous interstitial deletion of chromosome 15 (band D) in three translocation-negative murine plasmacytomas.

Three murine plasmacytomas that were exceptional in lacking the characteristic (12;15) or (6;15) translocations were studied by G banding and high-resolution banding. One of every two chromosomes 15 (two of four in tetraploid tumors) was shortened in all three tumors. High-resolution banding analysis revealed that this was due to an interstitial deletion in the 15D band region. The two breaks responsible for the deletion have been tentatively localized to the interface of bands D2/3' and within band D2. One of the three plasmacytomas, ABPC45, had a rearranged c-myc gene. All three tumors contained a greater abundance of 2.4-kilobase myc RNA transcripts than normal spleen or thymus. The c-myc gene is located in the 15 D2/3 band region. We suggest that it may have joined the centromeric portion in the deletion plasmacytomas. This transposition may have led to its constitutive activation, as in the more frequent translocation-carrying plasmacytomas.

Animals↗