World Cancer, Oncology and Therapeutics Congress

Biography

Biography: Shah Rucksana Akhter Urme

Abstract

Telomerase, an RNA-dependent DNA polymerase that adds telomeric DNA to telomeres which is involved in several essential biological functions and in vertebrates, telomeres are composed of the sequence TTAGGG. Maintenance of telomere stability may require for the long-term proliferation of tumors. Telomerase activity has been found in almost all human tumors but not in adjacent normal cells and escape from cellular senescence and becoming immortal by activating telomerase, or an alternative mechanism to maintain telomeres constitutes an additional step in oncogenesis that most tumors require for their ongoing proliferation. Telomerase an eukaryotic ribonucleoprotein (RNP) complex, contains both an essential RNA and a protein reverse transcriptase subunit. By reverse transcription, the telomerase RNP maintains telomere length stability in almost all cancer cells. Telomeres maintain genomic integrity in normal cells, and their progressive shortening during successive cell divisions whereas the large majority of cancer cells, telomere length is maintained by telomerase. Thus, telomere length and telomerase activity are crucial for cancer initiation and the survival of tumors. The main objective of this review paper is to suggest secondary facts for proving relationship between telomerase and cancer and information collected from various sources. Recent studies demonstrated that expression of human telomerase alone is sufficient for the immortalization of diverse cell types and for allowing transformed cells to escape from crisis. Importantly, telomerase can cooperate with oncogenes or with inactivation of tumor suppressor genes to induce tumorigenic conversion of normal human cells thus telomerase plays an important role in cellular aging and tumorigenesis. Telomerase consists of two essential components: one is the functional RNA component (in humans called hTR or hTERC), which serves as a template for telomeric DNA synthesis; the other is a catalytic protein (hTERT) with reverse transcriptase activity. hTR is highly expressed in all tissues regardless of telomerase activity, with cancer cells generally having fivefold-higher expression than normal cells . In contrast, the expression (mRNA) of the human catalytic component hTERT is estimated at less than 1 to 5 copies per cell and is closely associated with telomerase activity in cells. hTERT is generally repressed in normal cells and upregulated in immortal cells, suggesting that hTERT is the primary determinant for the enzyme activity. Since modulation of telomerase activity may have important implication for the development of diagnostic and therapeutic strategies, the mechanisms of telomerase regulation are of great interest. There is mounting evidence for the existence of an important co-relationship between telomeres and telomerase in cancer. Telomerase activity was found to be absent in most normal human somatic cells but present in over 90% of cancerous cells and in vitro-immortalized cells.

Key words: Telomerase, Telomere, Cancerous cells