Article

Cajal-body formation correlates with differential coilin phosphorylation in primary and transformed cell lines.

Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216, USA.
Journal of Cell Science (Impact Factor: 5.88). 07/2009; 122(Pt 11):1872-81. DOI: 10.1242/jcs.044040
Source: PubMed

ABSTRACT Cajal bodies (CBs) are nuclear structures that are thought to have diverse functions, including small nuclear ribonucleoprotein (snRNP) biogenesis. The phosphorylation status of coilin, the CB marker protein, might impact CB formation. We hypothesize that primary cells, which lack CBs, contain different phosphoisoforms of coilin compared with that found in transformed cells, which have CBs. Localization, self-association and fluorescence recovery after photobleaching (FRAP) studies on coilin phosphomutants all suggest this modification impacts the function of coilin and may thus contribute towards CB formation. Two-dimensional gel electrophoresis demonstrates that coilin is hyperphosphorylated in primary cells compared with transformed cells. mRNA levels of the nuclear phosphatase PPM1G are significantly reduced in primary cells and expression of PPM1G in primary cells induces CBs. Additionally, PPM1G can dephosphorylate coilin in vitro. Surprisingly, however, expression of green fluorescent protein alone is sufficient to form CBs in primary cells. Taken together, our data support a model whereby coilin is the target of an uncharacterized signal transduction cascade that responds to the increased transcription and snRNP demands found in transformed cells.

2 Bookmarks
 · 
99 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Protein translation initiation is a tightly controlled process responding to nutrient availability and mitogen stimulation. Serving as one of the most important negative regulators of protein translation, 4E binding protein 1 (4E-BP1) binds to translation initiation factor 4E and inhibits cap-dependent translation in a phosphorylation-dependent manner. While it has been demonstrated previously that the phosphosphorylation of 4E-BP1 is controlled by mTOR in the mTOR complex 1 (mTORC1), the mechanism underlying the dephosphorylation of 4E-BP1 remains elusive. Here, we report the identification of PPM1G as the phosphatase of 4E-BP1. Co-immunoprecipitation experiment reveals that PPM1G binds to 4E-BP1 in cells, and purified PPM1G dephosphorylates 4E-BP1 in vitro. Knockdown of PPM1G in 293E and colon cancer HCT116 cells results in an increase in the phosphorylation of 4E-BP1 at both Thr37/46 and Ser65 sites. Furthermore, the time course of 4E-BP1 dephosphorylation induced by amino acid starvation or mTOR inhibition is significantly slowed down in PPM1G knockdown cells. Functionally, the amount of 4E-BP1 bound to the cap-dependent translation initiation complex is decreased when the expression of PPM1G is depleted. As the result, the rate of cap-dependent translation, cell size, and protein content are increased in PPM1G knockdown cells. Taken together, our study has identified protein phosphatase PPM1G as a novel regulator of cap-dependent protein translation by negatively controlling the phosphorylation of 4E-BP1.
    Journal of Biological Chemistry 06/2013; · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Eukaryotic cells enclose their genome within a dedicated organelle, the nucleus, which is the site of major cellular events such as messenger RNA synthesis and processing, ribosome subunit biogenesis and DNA replication. Like the cytoplasm, the nucleus is compartmentalized to facilitate efficient coordination of these pathways, although subnuclear compartments form without the use of membranes. Numerous disease states have been linked to dysfunction of these compartments or 'nuclear bodies'. Recent advances have shed light on the formation and maintenance of key structures, including nucleoli, splicing speckles, paraspeckles, Cajal bodies, histone locus bodies and promyelocytic leukemia bodies. Here, we review the impact of these findings, which provide major insights into dynamic processes that affect both structure and function within the nucleus.
    Current opinion in cell biology 04/2014; 28C:76-83. · 14.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Spliceosomal small nuclear ribonucleoproteins (snRNPs) are enriched in the Cajal body (CB). Guide RNAs, known as small Cajal body-specific RNAs (scaRNAs), direct modification of the small nuclear RNA (snRNA) component of the snRNP. The protein WRAP53 binds a sequence motif (the CAB box) found in many scaRNAs and the RNA component of telomerase (hTR) and targets these RNAs to the CB. We have previously reported that coilin, the CB marker protein, associates with certain non-coding RNAs. For a more comprehensive examination of the RNAs associated with coilin, we have sequenced the RNA isolated from coilin immunocomplexes. A striking preferential association of coilin with the box C/D scaRNAs 2 and 9, which lack a CAB box, was observed. This association varied by treatment condition and WRAP53 knockdown. In contrast, reduction of WRAP53 did not alter the level of coilin association with hTR. Additional studies showed that coilin degrades/processes scaRNA 2 and 9, associates with active telomerase and can influence telomerase activity. These findings suggest that coilin plays a novel role in the biogenesis of box C/D scaRNPs and telomerase.
    Biology open. 03/2014;

Full-text

Download
27 Downloads
Available from
Jun 4, 2014