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D S Ucker

Publications and source records attributed to D S Ucker.

26 records · Page 2Linked to original sources
PubMed1989

Activation-driven T cell death. I. Requirements for de novo transcription and translation and association with genome fragmentation.

We have observed that stimuli that are mitogenic for normal T cells can induce cell death in transformed T cell hybridomas. "Activation-driven cell death" can be triggered by the presentation of appropriate Ag as well as by treatment with lectins and antibodies specific for the T cell Ag receptor complex and other activation structures on the T cell surface, such as Thy-1 and Ly-6. The activation-driven lethal process is cell autonomous, is associated with a fragmentation of the cell's genome characteristic of the "suicide process" induced in immature T cells by glucocorticoids and in target cells by cytotoxic T lymphocytes, and is dependent upon transcription and translation, presumably associated with the expression of new gene products. We hypothesize that activation-driven cell death may be involved in vivo in the clonal deletion of auto-reactive T cells during T cell ontogeny.

Animals↗
PubMed1985

An unusual clonotypic determinant on a cytotoxic T lymphocyte line is encoded by an immunoglobulin heavy chain variable region gene.

We have detected, in a CTL clone, an mRNA homologous to an immunoglobulin heavy chain variable region (VH) gene segment. A full-length copy of this mRNA was cloned and sequenced, revealing that it is the transcript of an authentic, unrearranged VH gene. The predicted protein product of this expressed VH gene is an approximately 12-kilodalton polypeptide, with secretory signal peptide leader and no membrane-anchoring sequences. Using immunologic reagents generated against a synthetic peptide representing the carboxyl terminus of the VH protein, we detect this protein as a clonotypic cell surface molecule. Strikingly, the anti-peptide reagents also exert effects on CTL function clonotypically. Immunoprecipitation experiments suggest that the VH protein may be associated noncovalently with the consensus, major histocompatibility complex-restricted, antigen-specific T cell receptor alpha- and beta-chains on the cell surface of this CTL. We detect weakly cross-reactive material similar to the VH protein in electrophoretic mobility in other CTL clones and suggest the possibility that small VH-like molecules may constitute a novel class of receptor components with variable determinants involved in the binding of nominal antigen and contributing to overall receptor diversity.

Animals↗
PubMed1984

Early events in the stimulation of mammary tumor virus RNA synthesis by glucocorticoids. Novel assays of transcription rates.

Two procedures were devised to examine initial events in the glucocorticoid-regulated transcription of integrated murine mammary tumor virus (MTV) DNA sequences. First, cells in monolayer culture were exposed for brief periods to dexamethasone and then permeabilized in situ with digitonin to allow entry of 32P-labeled ribonucleoside triphosphates and measurement of transcription rates. The results revealed that the rate of MTV RNA synthesis is stimulated selectively by dexamethasone after an apparent lag of approximately equal to 1 min and is half-maximal by 8-9 min. Second, the time course of transcription elongation was monitored by quantitating in single strand nuclease protection assays the accumulation of RNA sequences from different regions of the 7.8-kilobase MTV transcription unit. These experiments suggested that the rate of MTV RNA elongation in the presence of hormone does not differ substantially from elongation rates calculated for other genes transcribed by RNA polymerase II. Moreover, dexamethasone increased in parallel and to the same extent the levels of RNA from various segments of the transcription unit, implying that transcripts are elongated across the MTV element at a constant rate. We conclude that glucocorticoids stimulate MTV transcription solely via a rapid and selective increase in the efficiency of transcription initiation.

Animals↗
PubMed1983

Glucocorticoids and chromosomal position modulate murine mammary tumor virus transcription by affecting efficiency of promoter utilization.

The rate of transcription of murine mammary tumor virus (MTV) sequences in MTV-infected rat hepatoma tissue culture cells is strongly affected by both glucocorticoid hormones and the chromosomal position of provirus integration. We have characterized MTV RNAs produced in J2.17 and M1.54, independent isolates containing, respectively, 1 and 10 proviruses integrated at distinct chromosomal loci. M1.54, but not J2.17, synthesized MTV RNA in the absence of glucocorticoids; the rate of hormone-stimulated viral gene transcription in M1.54 was 50- to 100-fold higher than in J2.17. In each case in which MTV genes were expressed (J2.17 induced, M1.54 basal and induced), the viral RNAs produced were indistinguishable. RNA blotting revealed accumulation of two transcripts, 7.8 and 3.8 kilobases; the latter was likely produced from the former by RNA splicing. Sites used for transcription initiation, polyadenylation, and splicing have been identified from the sizes of end-labeled hybridization probes protected from digestion with mung bean nuclease; the unique initiation and polyadenylation sites were both encoded within the MTV long-terminal-repeat sequence. The efficiencies of splicing and of utilization of the polyadenylation signal did not appear to vary as functions of chromosomal position or hormonal stimulation. Differences in rates of viral gene transcription were reflected in the differential accumulation of the 5'-terminal 136 nucleotides of MTV RNA. Thus, glucocorticoids and chromosomal position appeared to affect solely the efficiency of utilization of the MTV promoter, leaving unchanged the sites of initiation, splicing, and polyadenylation, as well as the efficiencies of the latter two processes.

Animals↗
PubMed1981

Mammary tumor virus DNA contains sequences required for its hormone-regulated transcription.

Glucocorticoids regulate the rate of transcription of integrated murine mammary tumor virus (MTV) genes in most clones of MTV-infected rat hepatoma tissue culture (HTC) cells. To determine whether hormonal regulation is mediated from flanking cellular sequences or rather from within the viral DNA, we analyzed the relative rates of transcription of MTV and adjacent HTC sequences in two lines of infected HTC cells, J2.15 and J2.17, each of which contains a single insertion of MTV DNA. In addition, we measured in uninfected HTC cells the transcriptional rates of the corresponding "preinsertion fragments," which may be viewed as the equivalent sequences bearing deletions of MTV DNA; the two genomic segments into which integration occurred in the two lines are unrelated. Previous work showed that glucocorticoids induce the accumulation of MTV RNA in J2.17, whereas viral transcripts are not detected in J2.15, RNA pulse-labeling experiments indicate that glucocorticoids stimulate that rate of MTV gene transcription in J2.17 but not in J2.15; in contrast, no labeled RNA hybridizing to flanking sequences was detected either in the uninfected or in the infected cells. We conclude that the host site of integration cells. We conclude that the host site of integration of MTV need not be transcriptionally active or hormonally responsive to permit viral gene expression. Furthermore, these rate measurements indicate that glucocorticoid-stimulated MTV RNA synthesis in J2.17 does not reflect readthrough transcription from a regulated cellular promoter. This notion is independently supported by transcript mapping experiments showing that the 5' terminus of nuclear MTV RNA is at a site on MTV DNA approximately 1.2 kb downstream from the host-viral junction. Thus our data are consistent with the presence of a hormone-responsive element within the provirus.

Animals↗
PubMed1978

Catabolite-repression-like phenomenon in Rhizobium meliloti.

We report a phenomenon similar to catabolite repression in Rhizobium meliloti. Succinate, which allows the highest observed rate of growth of R. meliloti, caused an immediate reduction of beta-galactosidase activity when added to cells growing in lactose. A Lac- mutant was unaltered in nodulation and nitrogen fixation capacities, but a pleiotropic mutant deficient in several catabolic properties was unable to produce effective nitrogen-fixing nodules.

Cyclic AMP↗
PubMedDate not supplied

Cytotoxic T lymphocytes and glucocorticoids activate an endogenous suicide process in target cells.

Cytotoxic T lymphocytes (CTL) induce a cytolytic process in target cells which, like the glucocorticoid-mediated cytolysis of immature thymocytes, effects a rapid and characteristic degradation of chromosomal DNA. I have explored the possibility that these two lethal processes share a common pathway by studying the susceptibility of glucocorticoid-resistant mutants to CTL-mediated killing. Here, I report that an unusual thymoma mutant, which has normal hormone receptor activity, is resistant to both glucocorticoids and CTL. The failure to be killed by CTL is not due to an inability of this 'deathless' mutant to be recognized. Further, a single-step reversion can restore sensitivity to both glucocorticoids and CTL. The genetic locus thus identified may reveal one element of an endogenous suicide pathway that can be triggered by different effectors. Unlike complement-mediated lysis, the processes of glucocorticoid- and CTL-mediated cytolysis seem to require that target cells be active in their own death.

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