Research Article: The Regulation of Telomerase in Oncogenesis

Date Published: April , 2009

Publisher: A.I. Gordeyev

Author(s): D. A. Skvortzov, M. P. Rubzova, M. E. Zvereva, F. L. Kiselev, O. A. Donzova.

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Abstract

The influence that the expression of the human (glial-derived neurotrophic factor (GDNF)) neurotrophic factor has on the morphology and proliferative activity of embryonic stem cells (SC) of a mouse with R1 lineage, as well as their ability to form embroid bodies (EB), has been studied. Before that, using a PCR (polymerase chain reaction) coupled with reverse transcription, it was shown that, in this very lineage of the embryonic SC, the expression of the receptors’ genes is being fulfilled for the neurotropfic RET and GFRα1 glia factor. The mouse′s embryonic SC lineage has been obtained, transfected by the human GDNF gene, and has been fused with the “green” fluorescent protein (GFP) gene. The presence of the expression of the human GDNF gene in the cells was shown by northern hybridization and the synthesis of its albuminous product by immunocitochemical coloration with the use of specific antibodies. The reliable slowing-down of the embriod-body formation by the embryonic SC transfected by the GDNF gene has been shown. No significant influence of the expression of the GDNF gene on the morphology and the proliferative activity of the transfected embryonic SCs has been found when compared with the control ones.

Partial Text

Telomerase is active in most (80-90%) tumor cells (Table 1), and this activity is the main instrument for supporting the telomeres length. There are non-malignant types of tumors and other types of non-cancer lesions that demonstrate telomerase activity almost 100% of the time, but there are others without any activity [19-21]. Tumor cell of some cell types can use an alternative mechanism of telomeres length support that is based on recombination [22]. In case of the transaction of cells with an alternative telomere-supporting mechanism by the gene hTERT, both mechanisms are active; however, in the case of the hybridization of cell lines with different mechanisms, telomerase is present in hybrids, and indications of an alternative mechanism of telomere lengthening disappear [23]. It should be noted that telomerase itself is not oncogene. Cell lines that were tranfected by the hTERT gene do not demonstrate indications of malignant transformation for a long time [24, 25].

The hTR gene has one copy and is located in the Chromosome 3 at the position 3q26.3. This chromosomal region is amplified, for example, in the case of cervical cancer, lung cancer, and squamous cell carcinoma of the head and neck. The number of copies of the hTR gene increases in tumor cells more than in normal cells, and, correspondingly, the hTR expression increases in the case of cervical cancer, lung cancer, and squamous cell carcinoma of the head and neck [42].

hTERT transcription is very low or not detected at all in most human tissues, but it often appears in these tissues after neoplastic transformation [44].

The hTERT promoter does not contain TATA or CAAT, which are typical for the binding of RNA-polymerase II, and it is GC-rich. There are different data on the position of the region of the transcription′s initiation. Note that, now and further in this paper, we use the numeration of nucleotides (point + 1 bp (nucleotide base pairs)) from point A in the triplet ATG, which is the beginning of translation. It was shown [45] (using the method of anti-RNAse protection) that there are several protected regions in different hTERT-positive cell lines, which indicates the possibility of several sites of transcription initiation (in the region of from -40 to 100 bp). The most commonly protected region in the region of transcription initiation is at the position -55 G from the beginning of translation. It was shown [46] by analyzing caped mRNA from the HeLa cell line that the site of transcription start is at position -77 bp. Recently, most authors have accepted this view.

 

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