Biomedical subjects

Sonia Delgado

Publications and source records attributed to Sonia Delgado.

5 recordsLinked to original sources

PubMed2006

Oncogenic activity of Cdc6 through repression of the INK4/ARF locus.

The INK4/ARF locus encodes three tumour suppressors (p15(INK4b), ARF and p16(INK4a)) and is among the most frequently inactivated loci in human cancer. However, little is known about the mechanisms that govern the expression of this locus. Here we have identified a putative DNA replication origin at the INK4/ARF locus that assembles a multiprotein complex containing Cdc6, Orc2 and MCMs, and that coincides with a conserved noncoding DNA element (regulatory domain RD(INK4/ARF)). Targeted and localized RNA-interference-induced heterochromatinization of RD(INK4/ARF) results in transcriptional repression of the locus, revealing that RD(INK4/ARF) is a relevant transcriptional regulatory element. Cdc6 is overexpressed in human cancers, where it might have roles in addition to DNA replication. We have found that high levels of Cdc6 result in RD(INK4/ARF)-dependent transcriptional repression, recruitment of histone deacetylases and heterochromatinization of the INK4/ARF locus, and a concomitant decrease in the expression of the three tumour suppressors encoded by this locus. This mechanism is reminiscent of the silencing of the mating-type HM loci in yeast by replication factors. Consistent with its ability to repress the INK4/ARF locus, Cdc6 has cellular immortalization activity and neoplastic transformation capacity in cooperation with oncogenic Ras. Furthermore, human lung carcinomas with high levels of Cdc6 are associated with low levels of p16(INK4a). We conclude that aberrant expression of Cdc6 is oncogenic by directly repressing the INK4/ARF locus through the RD(INK4/ARF) element.

Animals↗

PubMed2006

Variants of Peach latent mosaic viroid inducing peach calico: uneven distribution in infected plants and requirements of the insertion containing the pathogenicity determinant.

Previous characterization of Peach latent mosaic viroid (PLMVd) variants from a single peach calico (PC) isolate showed that PC symptoms are induced by variants with a 12-13 nt insertion at a specific position and folding into a hairpin with a U-rich loop. Here, this study was extended to two other PC isolates. PLMVd variants with insertions similar to those reported previously (type 1), predominated in one isolate (PC-P2). The second (PC-P1), in addition to these variants, contained others with insertions in the same position and of the same size, but with the hairpin capped by a GA-rich loop (type 2). When symptomatic and non-symptomatic tissues from both isolates were used to inoculate GF-305 peach seedlings, they reproduced the phenotype of the inoculum source, indicating that variants differing in pathogenicity are unevenly distributed within single plants. Moreover, characterization of the progeny from inoculations with the PC-P1 source showed that variants with insertions of type 1 and 2 were predominant in the symptomatic and non-symptomatic seedlings, respectively, confirming the association between PC and variants with type 1 but not type 2 insertions. Inoculations with dimeric in vitro transcripts from PLMVd variants with type 1, type 2 and with a chimeric insertion showed that the variant with type 2 insertion was latent and established that the U-rich capping loop has a major role in PC, although the adjacent stem may also have some influence. Insertions can be acquired and lost during infection, suggesting that latent variants can evolve into pathogenic variants and vice versa.

Genetic Variation↗

PubMed2005

A short double-stranded RNA motif of Peach latent mosaic viroid contains the initiation and the self-cleavage sites of both polarity strands.

The transcription initiation sites of viroid RNAs, despite their relevance for replication and in vivo folding, are poorly characterized. Here we have examined this question for Peach latent mosaic viroid (PLMVd), which belongs to the family of chloroplastic viroids with hammerhead ribozymes (Avsunviroidae), by adapting an RNA ligase-mediated rapid amplification of cDNA ends methodology developed for mapping the genuine capped 5' termini of eukaryotic messenger RNAs. To this aim, the characteristic free 5'-triphosphate group of chloroplastic primary transcripts from PLMVd-infected young fruits was previously capped in vitro with GTP and guanylyltransferase. PLMVd plus and minus initiation sites map at similar double-stranded motifs of 6 to 7 bp that also contain the conserved GUC triplet preceding the self-cleavage site in both polarity strands. Within the branched secondary structures predicted for the two PLMVd strands, this motif is located at the base of a similar long hairpin that presumably contains the promoters for a chloroplastic RNA polymerase. The transcription templates could be the circular viroid RNAs or their most abundant linear counterparts, assuming the involvement of an RNA polymerase able to jump over template discontinuities. Both PLMVd initiation sites were confirmed by applying the same methodology to two purified PLMVd subgenomic RNAs and by primer extension, and they therefore likely reflect the in vivo situation. The location of the PLMVd initiation sites provides a mechanistic view into how the nascent strands may fold and self-cleave during transcription. The approach described here may be extended to other chloroplastic RNA replicons and transcripts accumulating at low levels.

Chloroplasts↗

PubMed2004

Viroids: the minimal non-coding RNAs with autonomous replication.

Viroids are small (246-401 nucleotides), non-coding, circular RNAs able to replicate autonomously in certain plants. Viroids are classified into the families Pospiviroidae and Avsunviroidae, whose members replicate in the nucleus and chloroplast, respectively. Replication occurs by an RNA-based rolling-circle mechanism in three steps: (1). synthesis of longer-than-unit strands catalyzed by host DNA-dependent RNA polymerases forced to transcribe RNA templates, (2). processing to unit-length, which in family Avsunviroidae is mediated by hammerhead ribozymes, and (3). circularization either through an RNA ligase or autocatalytically. Disease induction might result from the accumulation of viroid-specific small interfering RNAs that, via RNA silencing, could interfere with normal developmental pathways.

Base Sequence↗

PubMedDate not supplied

Role of prostacyclin (epoprostenol) as anticoagulant in continuous renal replacement therapies: efficacy, security and cost analysis.

BACKGROUND: Heparin remains the drug most commonly used for anticoagulation in continuous renal replacement therapies (CRRTs). However, in patients with hypercoagulability, heparin is insufficient or, in cases with an increased risk of bleeding or thrombocytopenia, it may be contraindicated. Epoprostenol, a potent vasodilator, antithrombotic and antiplatelet agent, could be an alternative. PATIENTS AND METHODS: We studied the records of patients treated under continuous venovenous hemodiafiltration in an academic tertiary hospital of 900 beds, between January 2000 and June 2003. Epoprostenol was prescribed to patients with (i) filter hypercoagulability, defined as consumption of 2 or more filters in the last 24 hours; (ii) low platelet count; or (iii) recent severe hemorrhage. RESULTS: Thirty-eight out of 248 (15%) patients who were under CRRT received epoprostenol for more than 72 hours. Epoprostenol was indicated due to filter hypercoagulability in 48%, thrombocytopenia in 68% (7 patients both) and hemorrhage in 3% of cases. The overall time for epoprostenol therapy was 9,749 hours. The mean filter duration previous to epoprostenol was 23 +/- 12 hours and after administering this drug 38.2 +/- 11.9 hours (p = 0.0001). In 6 patients, heparin and epoprostenol were simultaneously administered. The adverse effects were hemorrhage, which presented in 7 patients (18%) and a fall in blood pressure in another 7 (18%), which recovered in the next 24 hour after starting treatment. Cost analysis demonstrates some advantage with epoprostenol in patients with increased tendency to clotting. CONCLUSIONS: Epoprostenol may be safely used to prevent clotting of the extracorporeal circuits, either alone in patients with thrombocytopenia and/or increased risk of bleeding, or in combination with heparin in states of hypercoagulability.

Anticoagulants↗