Alternative splicing of telomerase catalytic subunit hTERT pre-mRNA (human Telomerase Reverse Transcriptase) regulates telomerase activity. Increased expression of non-active splice variant hTERT results in inhibition of telomerase. Apoptotic endonuclease EndoG is known to participate in hTERT alternative splicing. Expression of EndoG can be induced in response to DNA damages. The aim of this study was to determine the ability of a DNA-damaging compound, cisplatin, to induce EndoG and its influence on alternative splicing of hTERT and telomerase activity in human CD4+ Т lymphocytes. Overexpression of EndoG in CD4+ T cells downregulated the expression of active full-length hTERT variant and upregulated its non-active spliced variant. Reduction of full-length hTERT caused downregulation of telomerase activity, shortening of telomeres length during cell divisions, converting cells to the replicative senescence state, activation of apoptosis and finally cell death. Few cells survived and underwent malignant transformation. Transformed cells have increased telomerase activity and proliferative potential compare to initial CD4+ T cells. These cells have phenotype of T lymphoblastic leukemic cells and are able to form tumors and cause death in experimental mice.
Al'ternativnyĭ splaĭsing pre-mRNK kataliticheskoĭ sub"edinitsy hTERT (human Telomerase Reverse Transcriptase) igraet vazhnuiu rol' v reguliatsii aktivnosti telomerazy. Uvelichenie kolichestva neaktivnoĭ splaĭs-formy hTERT ingibiruet telomeraznuiu aktivnost'. Izvestno, chto apoptoticheskaia éndonukleaza EndoG prinimaet uchastie v protsesse al'ternativnogo splaĭsinga hTERT. Ékspressiia EndoG vozrastaet v otvet na povrezhdeniia DNK. Tsel'iu raboty bylo izuchenie vliianiia povrezhdaiushchego DNK agenta tsisplatina na induktsiiu EndoG, al'ternativnyĭ splaĭsing hTERT i aktivnost' telomerazy v CD4+ T-limfotsitakh cheloveka. Inkubatsiia CD4+ T-kletok s tsisplatinom vyzyvaet povrezhdeniia DNK i induktsiiu EndoG. Ékspressiia EndoG soprovozhdaetsia snizheniem sinteza polnorazmernogo aktivnogo varianta hTERT i uvelicheniem ékspressii neaktivnogo splaĭs-varianta. Umen'shenie kolichestva polnorazmernogo varianta hTERT privodit k snizheniiu telomeraznoĭ aktivnosti, ukorocheniiu dliny telomer do kriticheskikh znacheniĭ, perekhodu kletok v sostoianie replikativnogo stareniia, aktivatsii apoptoticheskikh protsessov i gibeli kletok. Nekotorye kletki ostaiutsia zhivymi i preterpevaiut zlokachestvennuiu transformatsiiu. Zlokachestvenno transformirovannye kletki obladaiut povyshennoĭ telomeraznoĭ aktivnost'iu i replikativnym potentsialom, po sravneniiu s iskhodnymi CD4+ T-kletkami. Oni imeiut fenotip T-kletochnoĭ limfomy, a takzhe obladaiut sposobnost'iu formirovat' opukholi i vyzyvat' gibel' éksperimental'nykh zhivotnykh.
Keywords: EndoG; alternative splicing; cisplatin; hTERT; malignant transformation; telomerase.