No abstract

Telomerase is essential for telomere maintenance, and its activation is thought to be a critical step in cellular immortalization and tumorigenesis. Human telomerase reverse transcriptase (hTERT) is a major component of telomerase activity. We show here that hTERT is expressed soon after lymphocyte activation and that its expression is inhibited by rapamycin, wortmannin, and FK506, which was the most potent inhibitor. These results suggest a potential role for the transcription factor nuclear factor of activated T cells (NFAT) in the regulation of hTERT expression. Five putative NFAT-binding sites were identified in the hTERT promoter. In luciferase assays, the hTERT promoter was activated by overexpressed NFAT1. Moreover, serial deletions revealed that the promoter activation was mainly due to a ؊40 NFAT1-binding site flanked by two SP1-binding sites. Mutation of the ؊40 NFAT-binding site caused a 53% reduction in the transcriptional activity of hTERT promoter. Simultaneous mutations of the ؊40 NFAT-responsive element together with one or both SP1-binding sites led to a more dramatic decrease in luciferase activity than single mutations, suggesting a functional synergy between NFAT1 and SP1 in hTERT transcriptional regulation. NFAT1 overexpression in MCF7 and Jurkat cell lines induced an increase in endogenous hTERT mRNA expression. Inversely, its down-regulation was induced by NFAT1 silencing. Furthermore, chromatin immunoprecipitation assay demonstrated that NFAT1 directly binds to two sites (؊40 and ؊775) in the endogenous hTERT promoter. Thus, we show for the first time the direct involvement of NFAT1 in the transcriptional regulation of hTERT.Telomeres are specialized structures located at the ends of linear mammalian chromosomes (1). The erosion of human telomeres at each cycle of cellular division is compensated for by de novo synthesis catalyzed by human telomerase reverse transcriptase (hTERT), 3 the catalytic subunit of a ribonucleoprotein complex called telomerase (2). Telomerase maintains telomeres by protecting them from exonucleases and ligases and by preventing illegitimate recombination (3). However, hTERT is also implicated in cell immortalization and tumorigenesis (4) through its telomere-lengthening activity, as well as by a mechanism independent of telomere length (5).Most normal human somatic tissues do not express hTERT, but germinal cells, several types of normally activated or proliferating cells, and tumor cells do (6 -13). In particular, lymphocytes exhibit telomerase activity in response to stimulation (14). Regulation of telomerase expression in these cells is likely to occur in the G 1 phase of the cell cycle as telomerase is inhibited by rapamycin, a compound that affects the mammalian target of rapamycin (mTOR) but is not inhibited by aphidicolin or hydroxyurea, substances that inhibit DNA synthesis (14 -16). Phosphorylation of hTERT and the resulting effects on its nuclear translocation and telomerase activity have been well described (17, 18). These post-translational modificati...

SummaryNormal lymphocytes represent examples of somatic cells that are able to induce telomerase activity when stimulated. As previously reported, we showed that, during lymphocyte long-term culture and repeated stimulations, the appearance of senescent cells is associated with telomere shortening and a progressive drop in telomerase activity. We further showed that this shortening preferentially occured at long telomeres and was interrupted at each stimulation by a transitory increase in telomere length. In agreement with the fact that telomere uncapping triggers lymphocyte senescence, we observed an increase in γ γ γ γ -H2AX and 53BP1 foci as well as in the percentage of cells exhibiting DNA damage foci in telomeres. Such a DNA damage response may be related to the continuous increase of p16 ink4a upon cell stimulation and cell aging. Remarkably, at each stimulation, the expression of shelterin genes, such as hTRF1 , hTANK1 , hTIN2 , hPOT1 and hRAP1 , was decreased. We propose that telomere dysfunction during lymphocyte senescence caused by iterative stimulations does not only result from an excessive telomere shortening, but also from a decrease in shelterin content. These observations may be relevant for T-cell biology and aging.

B-cell chronic lymphocytic leukaemia (B-CLL) is a lymphoproliferative disorder characterized by clonal expansion of B lymphocytes. The present study aimed to determine whether there is an association between the polymorphic features located within the promoter/enhancer region of tumour necrosis factor-alpha (TNFA) gene and susceptibility to B-CLL. TNFA (-308 G/A) promoter single nucleotide polymorphism (SNP) was determined by polymerase chain reaction with sequence-specific primers (PCR-SSP) using commercial oligonucleotides. No significant association was found between the distribution of TNFA alleles and B-CLL in Polish patients with B-CLL. Our single centre results were compared with other literature data and combined in a cumulative analysis employing the Mantel-Haenszel method. Among 183 B-CLL patients, 47 (26%) were carrying TNFA*2 allele and this allele was present in 98 out of 348 controls (28%). Also, the results of the Mantel-Haenszel test did not show a significant correlation [Mantel-Haenszel estimate of approximate relative risk (RMH) = 0.86, P = 0.294]. These results suggest that TNFA (-308) alleles are not involved in the predisposition to the development of B-CLL.

No abstract

The pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) has been linked with the production and activity of certain growth factors. However a significant proportion of CLL patients display immune abnormalities suggestive of aberrant cytokine secretion and/or response. In contrast to B lymphocytes, T cells of B-CLL patients characterise with the increased production of interferon-gamma (IFN-gamma) and this cytokine has been indicated to prevent malignant cells from entering apoptosis including the slowly expanding population of CD5+ B cells that characterizes chronic lymphocytic leukemia. The aim of the present study was to assess whether functionally relevant interferon-gamma gene (IFNG) polymorphism (+847 A/T) contributes to the pathogenesis of B-CLL. In total 110 individuals was investigates, including 61 CLL patients and 50 healthy individuals. The presence of the IFNG AA genotype was found to be associated with susceptibility to CLL (23/61 vs. 7/50, p < 0.005, for patients and controls, respectively). This results suggest that individuals rather prone to the lower level of IFN-gamma production (associated with the presence of the A allele) appear to be more susceptible to this malignant disease.

Aplastic anemia (AA) is a rare, life-threatening syndrome of bone marrow failure resulted from bone marrow hypoplasia or aplasia, leading to pancytopenia (not only anemia). The most common cause is an autoimmune reaction of T lymphocytes against hematopoietic stem cells or, less frequently, a congenital defect or acquired damage to these cells, which leads to inhibition of their division and differentiation. AA can develop quickly (within a few days) or slowly (several weeks or months). The signs and symptoms are related to anemia, neutropenia, and thrombocytopenia. The concepts of treatment of patients with AA have significantly evolved in recent years. This is due to improved outcomes of both family and unrelated donor hematopoietic stem cell transplantations (HSCTs) as well as to revised results of immunosuppressive therapy (IST). The choice of the method depends essentially on three factors: the severity of AA, the age of the patient, matched sibling donor. All patients diagnosed with AA require appropriate supportive treatment adapted to the current clinical situation. Supportive treatment is necessary both before, during and after invasive causal treatment, it mainly involves the transfusion of leukocyte-depleted blood components, the use of anti-infectious prophylaxis or treatment of infections. In many cases AA, supportive therapy is the only therapeutic option, especially in elderly patients with comorbidities. In this paper we present current supportive treatment in this life-threatening disease.

This article has been peer reviewed and published immediately upon acceptance.It is an open access article, which means that it can be downloaded, printed, and distributed freely, provided the work is properly cited. Articles in "Cardiology Journal" are listed in PubMed.