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4.1 - 10th August 1998


Nucleolar localization of the Werner syndrome protein in human cells.

Marciniak RA, Lombard DB, Johnson FB, Guarente L

Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Proc Natl Acad Sci U S A 1998 Jun 9;95(12):6887-6892

Werner Syndrome (WS) is a human genetic disorder with many features of premature aging. The gene defective in WS (WRN) has been cloned and encodes a protein homologous to several helicases, including Escherichia coli RecQ, the human Bloom syndrome protein (BLM), and Saccharomyces cerevisiae Sgs1p. To better define the function of WRN protein we have determined its subcellular localization. Indirect immunofluorescence using polyclonal anti-human WRN shows a predominant nucleolar localization. Studies of WRN mutant cells lines confirmed the specificity of antibody recognition. No difference was seen in the subcellular localization of the WRN protein in a variety of normal and transformed human cell lines, including both carcinomas and sarcomas. The nucleolar localization of human WRN protein was supported by the finding that upon biochemical subcellular fractionation, WRN protein is present in an increased concentration in a subnuclear fraction enriched for nucleolar proteins. We have also determined the subcellular localization of the mouse WRN homologue (mWRN). In contrast to human WRN protein, mWRN protein is present diffusely throughout the nucleus. Understanding the function of WRN in these organisms of vastly differing lifespan may yield new insights into the mechanisms of lifespan determination.

Effect of age and apoptosis on the mouse homologue of the huWRN gene.

Wu J, He J, Mountz JD

University of Alabama at Birmingham, Birmingham Veterans Administration Medical Center, 35294-0007, USA.

Mech Ageing Dev 1998 Jun 1;103(1):27-44

Werner's syndrome (WS) is an inherited disease with clinical symptoms which resemble premature aging. The Werner's syndrome gene (WRN), which is located on human chromosome 8p12, encodes a predicted protein of 1432 amino acids and shows significant similarity to DNA helicases. We have cloned the full-length mouse cDNA homologue of the human WRN gene encoding a predicted protein of 1320 amino acids and have obtained a full-length 70 kb genomic clone containing the moWRN gene. This gene has been mapped to chromosome 8A3 in mice. The expression of the moWRN gene was increased during apoptosis after IL-2 deprivation, and decreased in the spleen of aged mice. Lymphoid cells isolated from a patient with WS exhibited increased apoptosis after incubation with anti-Fas but not after incubation with the topoisomerase inhibitor VP16. RNase protection reviled dysregulation of the ICE family of apoptosis molecules in the WS cell line. These results indicate that the WS helicase is involved in certain pathways of apoptosis, and defective WS gene expression leads to accumulation of cells that are highly susceptibility to Fas-induced apoptosis.

Activation of p21ras/MAPK signal transduction molecules decreases with age in mitogen-stimulated T cells from rats.

Pahlavani MA, Harris MD, Richardson A

Geriatric Research, Education, and Clinical Center, Audie L. Murphy Veterans Hospital, San Antonio, Texas 78284, USA.

Cell Immunol 1998 Apr 10;185(1):39-48

Signal transduction is ubiquitously involved in the initiation of physiological signals that lead to growth and proliferation of cells. The signaling cascade mediated by the mitogen-activated protein kinase (MAPK) is considered essential for T cell growth and function. Therefore, it was of interest to determine the influence of age on the induction of MAPK in mitogen-activated T cells. T cells from young (4-6 months) and old (24-26 months) rats responded to concanavalin A (Con A) stimulation by increasing MAPK, c-jun amino terminal kinase (JNK), and p21ras activities. The time course of induction of MAPK/JNK and p21ras activities was similar in T cells isolated from young and old rats. The induction of JNK activity did not change significantly with age; however, the induction of MAPK and p21ras activities was significantly less (50 to 65%) in T cells from old rats than in T cells from young rats. Although the relative protein levels of p42 and p44 MAPK did not change with age, the proportion of the phosphorylated p44 MAPK decreased with age. In addition, it was found that the in vitro kinase activities of the T cell receptor-associated protein tyrosine kinase Lck (p56Lck) and ZAP-70 but not Fyn (p59Fyn) were lower in T cells from old rats than in T cells from young rats. The decline in activities of these signaling molecules with age was not associated with changes in their corresponding protein levels. Thus, our results demonstrate that aging alters the activation of the signal transduction cascade that leads to T cell activation.

Bypass of senescence after disruption of p21CIP1/WAF1 gene in normal diploid human fibroblasts.

Brown JP, Wei W, Sedivy JM

Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA.

Science 1997 Aug 8;277(5327):831-834

Most somatic cells die after a finite number of cell divisions, a phenomenon described as senescence. The p21(CIP1/WAF1) gene encodes an inhibitor of cyclin-dependent kinases. Inactivation of p21 by two sequential rounds of targeted homologous recombination was sufficient to bypass senescence in normal diploid human fibroblasts. At the checkpoint between the prereplicative phase of growth and the phase of chromosome replication, cells lacking p21 failed to arrest the cell cycle in response to DNA damage, but their apoptotic response and genomic stability were unaltered. These results establish the feasibility of using gene targeting for genetic studies of normal human cells.



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