Ilona Tárkányi

Immunodetection of human telomerase reverse-transcriptase (hTERT) re-appraised: nucleolin and telomerase cross paths

The involvement of telomerase in cellular immortalization and senescence has often been assessed by means of telomerase expression at the RNA level and quantification of telomerase activity by the telomeric repeat amplification protocol assay. However, these methods either neglected the existence of various telomerase splice variants, or ignored the nonconventional functions of telomerase independent of its ability to elongate and maintain telomere length. Immunodetection of telomerase is now being recognized as a necessary approach to precisely elucidate its roles in oncogenesis and senescence. A few antibodies directed against the catalytic subunit of the human telomerase (hTERT) are currently used but their specificity is not always demonstrated. A survey of the literature showed inconsistencies and led us to comparatively re-evaluate the most frequently used antibodies. Surprisingly, mass spectrometry, two-dimensional gel analysis and immunofluorescent experiments revealed that the most frequently used hTERT immunoprobe, a mouse monoclonal antibody that was claimed to be directed against an hTERT protein epitope, in fact recognizes nucleolin rather than telomerase. Our findings have interesting implications regarding the biology of nucleolin and telomerase in the context of pathophysiological investigations recently carried out.

Retinoid/arsenic combination therapy of promyelocytic leukemia: induction of telomerase-dependent cell death

Acute promyelocytic leukemia (APL) is efficiently treated with a cell differentiation inducer, all-trans retinoic acid (ATRA). However, a significant percentage of patients still develop resistance to this treatment. Recently, arsenic trioxide (As2O3), alone or in combination with ATRA, has been identified as an alternative therapy in patients with both ATRA-sensitive and ATRA-resistant APL. Previous investigations restricted the mechanism of this synergism to the modulation and/or degradation of PML-RARα oncoprotein through distinct pathways. In this study, using several ATRA maturation-resistant APL cell lines, we demonstrate in vitro that the success of ATRA/As2O3 treatment in APL pathology can be explained, at least in part, by a synergistic effect of these two drugs in triggering downregulation of telomerase efficient enough to cause telomere shortening and subsequent cell death. Such long-term low-dose combinatorial therapy strategies, developed also to avoid acute side effects, reinforce the notion that the antitelomerase strategy, based on a combination of active agents, should now be considered and evaluated not only in APL but also in other malignancies.

Epigenetic plasticity of hTERT gene promoter determines retinoid capacity to repress telomerase in maturation-resistant acute promyelocytic leukemia cells

The expression of hTERT gene, encoding the catalytic subunit of telomerase, is a feature of most cancer cells. Changes in the chromatin environment of its promoter and binding of transcriptional factors have been reported in differentiating cells when its transcription is repressed. However, it is not clear whether these changes are directly involved in this repression or only linked to differentiation. In a maturation-resistant acute promyelocytic leukemia (APL) cell line (NB4-LR1), we have previously identified a new pathway of retinoid-induced hTERT repression independent of differentiation. Using a variant of this cell line (NB4-LR1SFD), which resists to this repression, we show that although distinct patterns of histone modifications and transcription factor binding at the proximal domain of hTERT gene promoter could concur to modulate its expression, this region is not sufficient to the on/off switch of hTERT by retinoids. DNA methylation analysis of the hTERT promoter led to the identification of two distinct functional domains, a proximal one, fully unmethylated in both cell lines, and a distal one, significantly methylated in NB4-LR1SFD cells, whose methylation was further re-enforced by retinoid treatment. Interestingly, we showed that the binding to this distal domain of a known hTERT repressor, WT1, was defective only in NB4-LR1SFD cells. We propose that epigenetic modifications targeting this distal region could modulate the binding of hTERT repressors and account either for hTERT reactivation and resistance to retinoid-induced hTERT downregulation.

Inhibition of human telomerase by oligonucleotide chimeras, composed of an antisense moiety and a chemically modified homo‐oligonucleotide

Most tumor cells attain their immortality by reactivating telomerase. We report here the telomerase inhibitory potential of chimeric oligonucleotides composed of a 13mer antisense sequence targeting the telomerase RNA template region and a (s4dU) n moiety at its 3′ or 5′‐end. The increase of the thiolated chain length enhances the telomerase inhibitory potential, but decreases specificity, indicated by HIV reverse transcriptase inhibition. Chimeras with 5′ (s4dU) n s were more potent inhibitors than the antisense alone or the 3′ modified ones. Cy5‐labeled (s4dU)4AS and (s4dU)8AS proved the internalization of the oligonucleotides, raising the possibility to be tested as cellular anti‐telomerase agents.

Retrospective Analysis of the Prognostic Role of Tissue Eosinophil and Mast Cells in Hodgkin's Lymphoma

The composition of reactive cell populations, which constitute the majority of tumor load in Hodgkin’s lymphoma (HL), can influence the prognosis of the disease. Besides widely accepted and applied prognostic scores, the authors evaluate biological factors that may have a prognostic impact. Previous data indicate that the rate of eosinophils and mast cells in the reactive cell population, determined already at diagnosis, can be used for this purpose. Histological samples from 104 patients with HL with an average follow-up period of 110 (24–214) months were retrospectively analyzed. Mast cell positivity was associated with better overall survival, although this difference was only of borderline statistical significance (p=0.092). No significant difference was found in parameters like overall survival (OS, p=0.906) or event-free survival (EFS, p=0.307) of eosinophil-positive vs. -negative cases or in EFS (p=0.742) of mast cell-positive vs. -negative individuals (criterion for a positive specimen was more than 5% of appropriate cells in the reactive cell population). Looking at the effect of eosinophilia and mastocytosis together, there was no significant difference between the subgroups categorized according to the combined presence of the two cell types. It seems that tissue eosinophil and mast cell predominance have no prognostic value that could be used in clinical practice, although a tendency for correlation of mast cell positivity with overall survival could be seen. For a definitive statement, multicenter studies should be performed involving a higher number of patients suffering from HL.

In vitro and in vivo activity of 4-thio-uridylate against JY cells, a model for human acute lymphoid leukemia.

We have previously reported the in vitro anti-proliferative effect of 4-thio-uridylate (s(4)UMP) on OCM-1 uveal melanoma cells. Here, we assessed the efficacy of s(4)UMP on JY cells. Treatment of JY cells with s(4)UMP suppressed their colony forming activity and induced apoptosis; healthy human bone marrow granulocyte-macrophage progenitor cells were 14-fold less sensitive to the nucleotide. In vivo effectiveness of s(4)UMP was determined using xenograft SCID mouse model. s(4)UMP decreased the cell number and colony forming activity of the total cell content of the femur of SCID mice transplanted with JY cells without affecting the bone marrow of healthy mice. These results suggest that s(4)UMP alone or in combination with other clinically approved anti-leukemic remedies should be further explored as a potential novel therapeutic agent.