Recognition of internal (TTAGGG)n repeats by telomeric protein TRF1 and its role in maintenance of chromosomal stability in Chinese hamster cells

Mammalian telomeres contain long tandem (TTAGGG)n repeats, which are protected by a complex of different proteins. Telomeric repeat-binding factors TRF1 and TRF2 play the key role in protection of telomeres through the formation of terminal loops (called T-loop). A T-loop isolates the 3' strand telomeric end and with this mechanism protects telomeres from the influence of enzymes of DNA reparation and telomere fusions and also interferes with the interaction of telomerase with telomeres. Many vertebrate species also contain large blocks of (TTAGGG)n sequences in pericentric and interstitial chromosome bands. The Chinese hamster genome contains a total of 18 arrays of these non-telomeric internal (TTAGGG)n sequences (ITs). Chromosome bands containing these arrays are unstable and should be protected with the help of another mechanism, rather than that using telomeres. In this study we analysed association of Green Fluorescent Protein (GFP)-tagged TRF1 in Chinese hamster V79 cells with ITs. We found that in these cells GFP-TRF1 associates with ITs in the interphase nucleus. We detected a little overlap between IT-associated GFP-TRF1 and random DSB sites visualized after the treatment of V79 cells with ionizing radiation. We found that the treatment of V79 cells with WM significantly increases the frequency of spontaneous chromosome aberrations. These WM effects are possible due to inhibiting phosphorylation of TRF1 by ATM. TRF1 is known to be eliminated from telomeres by overexpression of TANK1, which induces TRF1 poly(ADP-ribosyl)ation. We transfected V79 cells by plasmid encoding TANK1 and found that the frequency of chromosome rearrangements increased in these cells independently of their treatment by IR. Taken together, our results suggest that TRF1 may be involved in the sequence-specific protection of internal non-telomeric (TTAGGG)n repeats.     

Activated fibronectin-secretory phenotype of mesenchymal stromal cells in pre-fibrotic myeloproliferative neoplasms

We characterized bone marrow stromal cells (BMSC) from patients with pre-fibrotic myeloproliferative neoplasms (MPN). MPN-BMSC showed decreased capacity to stimulate the proliferation of colony-forming units of normal hematopoietic stem and progenitor cells and displayed increased matrix remodelling (in particular fibronectin deposition) compared to control BMSC. This finding was confirmed in pre-fibrotic MPN bone marrow biopsies in a tissue microarray (n?=?34), which stained positive for fibronectin in the absence of reticulin as a standard myelofibrosis marker. Fibronectin expression correlated significantly with reduced haemoglobin levels in MPN-patients (p?=?0.007; R2?=?0.42). Our data show significant cell-intrinsic alterations in MPN-MSC and suggest that Fibronectin expression might be applicable as a biomarker for the identification of early myelofibrotic transformation in reticulin-negative MPN.     

Levels of acute phase proteins remain stable after ischemic stroke

Background  

Inflammation and inflammatory biomarkers play an important role in atherosclerosis and cardiovascular disease. Little information is available, however, on time course of serum markers of inflammation after stroke.     

Butyrate inhibits mouse fibroblasts at a control point in the G1 phase

Butyrate block 3T6 cells in the G1 phase of the cell cycle approximately 5--6 h prior to the start of the S phase. Serum factors are required before as well as after the butyrate-sensitive steps in G1 in order to allow cells to start DNA synthesis. 3T6 cells infected with SV40 or with polyoma virus are also blocked at the same stage in G1 in the presence of the fatty acid. However, events before as well as after the butyrate-sensitive step do not require serum in virus-infected cells. The sensitivity of the initiation of cellular DNA synthesis to increasing concentrations of butyrate is the same for serum-stimulated or for virus-infected cells. A similar and parallel effect on DNA synthesis is observed if cells are incubated in the presence of very small amounts of cycloheximide. After release of the cycloheximide-induced G1 arrest about 4--6 h have to pass before cells enter the S phase. Cells stably transformed by SV40 are considerably more resistant to low cycloheximide concentrations and to butyrate. These data are discussed in the light of the hypothesis that both low concentrations of cycloheximide and sodium butyrate block cells at a control point in G1 by interference with the synthesis of one or more rapidly turning over, cell cycle-specific proteins.