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Antisense telomerase treatment: induction of two distinct pathways, apoptosis and differentiation
1Department of Neurosurgery, Brain Tumor/Neuro-Oncology Center, The Cleveland Clinic Foundation, Ohio 44195, USA. kondos@cesmtp.ccf.org
Abstract:
Telomerase, the enzyme that elongates telomeric DNA (TTAGGG)n, may be involved in cellular immortality and oncogenesis. To investigate the effect of inhibition of telomerase on tumor cells, we transfected the antisense vector against the human telomerase RNA into human malignant glioma cells exhibiting telomerase activity. After 30 doublings, some subpopulations of transfectants expressed a high level of interleukin-1beta-converting enzyme (ICE) protein and underwent apoptosis. In contrast, other subpopulations also showed enhanced ICE protein but escaped from apoptotic crisis and continued to grow, although their DNA synthesis, invasive ability, and tumorigenicity in nude mice were significantly reduced. Surviving cells demonstrated increased expression of glial fibrillary acidic protein and decreased motility, consistent with a more differentiated state. These cells also contained enhanced expression of the cyclin-dependent kinase inhibitors (CDKIs) p21 and p27. Treatment of surviving nonapoptotic cells with antisense oligonucleotides against p27, but not p21, induced apoptotic cell death, suggesting that p27 may have protected differentiating glioma cells from apoptosis. These data show that treatment with antisense telomerase inhibits telomerase activity and subsequently induces either apoptosis or differentiation. Regulation of these two distinct pathways may be dependent on the expression of ICE or CDKIs.
Insights
Inhibiting telomerase in glioma cells triggered either cell death (apoptosis) or differentiation. This suggests telomerase inhibition is a potential cancer therapy, impacting cell immortality and oncogenesis.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Telomerase, an enzyme elongating telomeric DNA, is implicated in cellular immortality and cancer.
- Understanding telomerase's role is crucial for developing targeted cancer therapies.
Purpose of the Study:
- To investigate the effects of inhibiting telomerase activity in human malignant glioma cells.
- To explore the mechanisms by which telomerase inhibition influences tumor cell fate, including apoptosis and differentiation.
Main Methods:
- Human malignant glioma cells with telomerase activity were transfected with an antisense vector targeting human telomerase RNA.
- Cellular responses, including apoptosis, differentiation markers, and protein expression (ICE, CDKIs), were analyzed after 30 cell doublings.
- The role of cyclin-dependent kinase inhibitors (CDKIs) p21 and p27 in cell survival and apoptosis was assessed.
Main Results:
- Telomerase inhibition led to apoptosis in some glioma cell subpopulations.
- Other subpopulations survived, exhibiting reduced DNA synthesis, invasion, and tumorigenicity, alongside increased glial fibrillary acidic protein expression and decreased motility, indicating differentiation.
- Surviving cells showed increased expression of p21 and p27; antisense oligonucleotides against p27 induced apoptosis in these cells, suggesting p27's protective role in differentiation.
Conclusions:
- Antisense telomerase treatment effectively inhibits telomerase activity, leading to either apoptosis or differentiation in glioma cells.
- The balance between apoptosis and differentiation appears regulated by interleukin-1beta-converting enzyme (ICE) and cyclin-dependent kinase inhibitors (CDKIs).
- Targeting telomerase offers a potential strategy for cancer therapy by inducing cell death or promoting a less aggressive, differentiated tumor phenotype.