[Protein CD133 as a tumor stem cell marker]. / Belok CD133 kak marker opukholevykh stvolovykh kletok.

The CD133 protein is a large transmembrane glycoprotein. Despite multiple studies, the role of CD133 protein in cells is still poorly understood. Nevertheless, there is an association of CD133 protein with neoplastic transformation. This review summarizes data on CD133 protein, its structure, regulation of expression, molecular interactions and representation in cells that have undergone malignant transformation. Available data suggest that CD133 may have a great potential for predicting survival in various solid tumors. This protein can also be a marker of glioma.

Recombinogenic telomeres in diploid Sorex granarius (Soricidae, Eulipotyphla) fibroblast cells.

The telomere structure in the Iberian shrew Sorex granarius is characterized by unique, striking features, with short arms of acrocentric chromosomes carrying extremely long telomeres (up to 300 kb) with interspersed ribosomal DNA (rDNA) repeat blocks. In this work, we investigated the telomere physiology of S. granarius fibroblast cells and found that telomere repeats are transcribed on both strands and that there is no telomere-dependent senescence mechanism. Although telomerase activity is detectable throughout cell culture and appears to act on both short and long telomeres, we also discovered that signatures of a recombinogenic activity are omnipresent, including telomere-sister chromatid exchanges, formation of alternative lengthening of telomeres (ALT)-associated PML-like bodies, production of telomere circles, and a high frequency of telomeres carrying marks of a DNA damage response. Our results suggest that recombination participates in the maintenance of the very long telomeres in normal S. granarius fibroblasts. We discuss the possible interplay between the interspersed telomere and rDNA repeats in the stabilization of the very long telomeres in this organism.

[High level of expression and nuclear localization of RNA, transcribed from genome region, containing repetitive elements].

The non-coding and repetitive sequences constitute a great amount of higher eukaryotes genomes, but the elucidation of its role and mechanisms of action is now at the very beginning. Here we found, that internal telomeric repeats in Danio rerio are colocalized with some repetitive elements, namely, hAT and EnSpm repeats, which are highly represented in vertebrate genome. While investigating one of genome regions, containing two pairs of such repeats in close proximity we found, that it is transcribed. RNA-dependent structures, containing this sequence, were revealed in D. rerio fibroblast nuclei, which may serve as evidence of functional relevance of repetitive elements in genomes or of their transcripts.

Assays for detection of telomerase activity.

Progressive loss of the telomeric ends of chromosomes caused by the semi-conservative mechanism of DNA replication is an important timing mechanism which controls the number of cells doubling. Telomerase is an enzyme which elongates one chain of the telomeric DNA and compensates for its shortening during replication. Therefore, telomerase activity serves as a proliferation marker. Telomerase activity is not detected in most somatic cells, with the exception of embryonic tissues, stem cells, and reproductive organs. In most tumor cells (80-90%), telomerase is activated and plays the role of the main instrument that supports the telomere length, which can be used for the diagnostics of neoplastic transformation. This is the primary reason why assays regarding the development of telomerase activity have attracted the attention of researchers. Telomerase activity testing may be useful in the search for telomerase inhibitors, which have the potential to be anti-cancer drugs. Moreover, telomerase activation may play a positive role in tissue regeneration; e.g., after partial removal of the liver or cardiac infarction. All telomerase activity detection assays can be divided into two large groups: those based on direct detection of telomerase products, and those based on different systems of amplification of the signals from DNA that yield from telomerase. The methods discussed in this review are suitable for testing telomerase activity in different samples: in protozoa and mammalian cells, mixed cellular populations, and tissues.

Cervical intraepithelial neoplasia: Telomerase activity and splice pattern of hTERT mRNA.

Cervical cancers are characterized by the persistence of human papilloma virus (HPV) genome that is found in tissue samples starting from the early stages of tumor progression. Just like in other tumors, the activation of telomerase was observed in cervical carcinomas, but information about its expression was controversial. The aim of this study is to find possible correlations between the presence of HPV sequences, activity of telomerase and expression of different spliced forms of hTERT RNA in cervical intraepithelial neoplasias (CIN). The results show that HPV DNA is present in 60% of normal tissue adjacent to CIN lesions and up to 84% in CIN samples. Telomerase activity was found in 28% of adjacent normal tissue and in 68% of CIN II-III. hTERT RNA that encodes an active enzyme was present almost in all CIN samples. Variations in levels of telomerase activity are possibly not regulated by the splicing forms of hTERT mRNA with deletions.

[Telomerase level versus spliced hTERT-specific RNA forms in cervical carcinoma].

An attempt was made to identify molecular markers of different clinical stages of cervical carcinoma caused by papilloma virus (HPV). Presence of viral genome, telomerase level and expression of a gene, which coded the catalytic activity of that enzyme (hTERT), were assayed in 89 patients. HPV (type 16) genome harboring tumors were detected in 73% which was in conformity with the literature and our own data. Telomerase was identified (TRAP) in all tumors and tumor cells cultured in vitro. hTERT-specific RNA was found in all tumor samples, however, increase in its expression was insignificant. As far as the three markers are concerned, no significant differences between clinical stages of tumor were reported.

The regulation of telomerase in oncogenesis.

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.

[Telomerase: structure and properties of the enzyme, characteristics of the yeast telomerase].

Telomerase is a ribonucleoprotein that extends the telomeric ends of the chromosomes to counterbalance the natural shortening due to incomplete DNA replication in eukaryotic cells. The core enzyme consists of catalytic reverse transcriptase subunit TERT (Telomerase Reverse Transcriptase) and RNA subunit TER (Telomerase RNA), a short specific region of which serves as a template for synthesis of the telomeric repeats. In this review we focus on the telomerase from yeast Saccharomyces cerevisiae. Despite the intensive research of telomerase in different organisms, the enzyme mechanism remains unclear. The observed peculiarities of the yeast telomerase is of great interest too. Unlike ciliate and human telomerases, yeast enzyme can add only one telomeric repeat to a DNA oligonucleotide (primer) imitating the single-stranded telomeric end of the chromosome and remains stably bound to it after elongation. This review is an attempt to summarise results of numerous studies of the structure and functions of the core enzyme components, their interactions between each other and with a primer, telomerase activity on different substrates in vitro. Also the peculiarities of the telomerase functioning in a cell and accessory proteins of the telomerase complex are discussed.