Article

Signal recognition particle assembly in relation to the function of amplified nucleoli of Xenopus oocytes.

Division of Cell and Molecular Biology, School of Biology, University of St Andrews, KY16 9TS, UK.
Journal of Cell Science (Impact Factor: 5.33). 04/2005; 118(Pt 6):1299-307. DOI: 10.1242/jcs.01726
Source: PubMed

ABSTRACT The signal recognition particle (SRP) is a ribonucleoprotein machine that controls the translation and intracellular sorting of membrane and secreted proteins. The SRP contains a core RNA subunit with which six proteins are assembled. Recent work in both yeast and mammalian cells has identified the nucleolus as a possible initial site of SRP assembly. In the present study, SRP RNA and protein components were identified in the extrachromosomal, amplified nucleoli of Xenopus laevis oocytes. Fluorescent SRP RNA microinjected into the oocyte nucleus became specifically localized in the nucleoli, and endogenous SRP RNA was also detected in oocyte nucleoli by RNA in situ hybridization. An initial step in the assembly of SRP involves the binding of the SRP19 protein to SRP RNA. When green fluorescent protein (GFP)-tagged SRP19 protein was injected into the oocyte cytoplasm it was imported into the nucleus and became concentrated in the amplified nucleoli. After visiting the amplified nucleoli, GFP-tagged SRP19 protein was detected in the cytoplasm in a ribonucleoprotein complex, having a sedimentation coefficient characteristic of the SRP. These results suggest that the amplified nucleoli of Xenopus oocytes produce maternal stores not only of ribosomes, the classical product of nucleoli, but also of SRP, presumably as a global developmental strategy for stockpiling translational machinery for early embryogenesis.

0 Bookmarks
 · 
79 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Constitutive expression of interferons (IFNs) and activation of their signaling pathways have pivotal roles in host responses to malignant cells in the tumor microenvironment. IFNs are induced by the innate immune system and in tumors through stimulation of Toll-like receptors (TLRs) and through other signaling pathways in response to specific cytokines. Although in the oncologic context IFNs have been thought of more as exogenous pharmaceuticals, the autocrine and paracrine actions of endogenous IFNs probably have even more critical effects on neoplastic disease outcomes. Through high-affinity cell surface receptors, IFNs modulate transcriptional signaling, leading to regulation of more than 2,000 genes with varying patterns of temporal expression. Induction of the gene products by both unphosphorylated and phosphorylated STAT1 after ligand binding results in alterations in tumor cell survival, inhibition of angiogenesis, and augmentation of actions of T, natural killer (NK), and dendritic cells. The interferon-stimulated gene (ISG) signature can be a favorable biomarker of immune response but, in a seemingly paradoxical finding, a specific subset of the full ISG signature indicates an unfavorable response to DNA-damaging interventions such as radiation. IFNs in the tumor microenvironment thus can alter the emergence, progression, and regression of malignancies.
    Seminars in Oncology 04/2014; 41(2):156-173. DOI:10.1053/j.seminoncol.2014.02.002 · 3.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: BRCA2 mutations are significantly associated with early onset breast cancer, and the tumour suppressing function of BRCA2 has been attributed to its involvement in homologous recombination (HR)-mediated DNA repair. In order to identify additional functions of BRCA2, we generated BRCA2-knockout HCT116 human colorectal carcinoma cells. Using genome-wide microarray analyses, we have discovered a link between the loss of BRCA2 and the up-regulation of a subset of interferon (IFN)-related genes, including APOBEC3F and APOBEC3G. The over-expression of IFN-related genes was confirmed in different human BRCA2−/− and mouse Brca2−/− tumour cell lines, and was independent of senescence and apoptosis. In isogenic wild type BRCA2 cells, we observed over-expression of IFN-related genes after treatment with DNA-damaging agents, and following ionizing radiation. Cells with endogenous DNA damage because of defective BRCA1 or RAD51 also exhibited over-expression of IFN-related genes. Transcriptional activity of the IFN-stimulated response element (ISRE) was increased in BRCA2 knockout cells, and the expression of BRCA2 greatly decreased IFN-α stimulated ISRE reporter activity, suggesting that BRCA2 directly represses the expression of IFN-related genes through the ISRE. Finally, the colony forming capacity of BRCA2 knockout cells was significantly reduced in the presence of either IFN-β or IFN-γ, suggesting that IFNs may have potential as therapeutic agents in cancer cells with BRCA2 mutations.
    The Journal of Pathology 07/2014; 234(3). DOI:10.1002/path.4404 · 7.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Emerging evidence indicates that the redistribution of phosphatidylethanolamine (PE) across the bilayer of the plasma membrane is an important molecular marker for apoptosis. However, the effect of PE on apoptosis and the underlying mechanism of PE remain unclear. In the current study, MTT and flow cytometric assays were used to examine the effects of PE on apoptosis in SMMC‑7721 cells. The level of mitochondrial membrane potential (ΔΨm) and the expression of Bax, Bcl‑2, caspase‑3, phospho‑Erk and phospho‑Stat1/2 in SMMC‑7721 cells that were exposed to PE were also investigated. The results showed that PE inhibited proliferation, caused G0/G1 phase cell cycle arrest and induced apoptosis in SMMC‑7721 cells in a dose‑dependent manner. Rhodamine 123 staining showed that the treatment of SMMC‑7721 cells with different concentrations of PE for 24 h significantly decreased the level of ΔΨm and exerted dose‑dependent effects. Using immunofluorescence and western blotting, we found that the expression of Bax was upregulated, whereas that of Bcl‑2 was downregulated in PE‑induced apoptotic cells. In addition, these events were accompanied by an increase in caspase‑3 expression in a dose‑dependent manner following PE treatment. PE‑induced apoptosis was accompanied by a decrease in Erk phospho-rylation and by the activation of Stat1/2 phosphorylation in SMMC‑7721 cells. In conclusion, the results suggested that PE‑induced apoptosis is involved in upregulating the Bax/Bcl‑2 protein ratio and decreasing the ΔΨm. Moreover, the results showed that the Erk and Stat1/2 signalling pathways may be involved in the process of PE‑induced apoptosis.
    International Journal of Molecular Medicine 05/2014; 34(1). DOI:10.3892/ijmm.2014.1777 · 1.88 Impact Factor
    This article is viewable in ResearchGate's enriched format

Full-text (2 Sources)

Download
20 Downloads
Available from
May 21, 2014