Induced telomerase activity in primary aortic endothelial cells by low-LET gamma-radiation is mediated through NF-kappaB activation.
Our objective was to understand the mechanism through which cells that initially survive irradiation could acquire survival advantage. In this study, we show evidence that low-linear energy transfer gamma-radiation can induce telomerase enzyme activity in primary aortic endothelial cells, and that an upstream regulator, nuclear factor kappa B (NF-kappaB), controls this activation. Telomeric repeat amplification protocol (TRAP) assay showed that cells exposed to a dose of 2 Gy induce telomerase activity. Subsequent analysis revealed that radiation-induced telomeric activity is regulated at the transcriptional level by triggering activation of the promoter of the telomerase catalytic subunit, telomerase reverse transcriptase (TERT). A mechanistic study revealed that NF-kappaB becomes functionally activated upon radiation exposure and mediates the upregulation of telomerase activity by binding to the kappaB-binding region in the promoter region of the TERT gene. More significantly, elimination of the NF-small ka, CyrillicB recognition site on the telomerase promoter or inhibition of NF-small ka, CyrillicB by ectopically expressing the inhibitor protein IkappaBalpha mutant (Ismall ka, CyrillicBalpha(S32A/S36A))) compromises radiation-induced telomerase promoter activation. Consistent with the notion that NF-kappaB mediates gamma-ray-induced telomerase responses, TRAP assay revealed that ectopically expressed IkappaBalpha(S32A/S36A)) also attenuated telomerase enzyme activity. These findings indicate that NF-kappaB activation following ionizing radiation exposure may elicit a survival advantage by upregulating and maintaining telomerase activity.
Department of Radiation Oncology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. Natarajan@uthscsa.edu
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Natarajan
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Mohan
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Konopinski
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Otto
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Herman
D000818:Animals; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D042783:Endothelial Cells / Q000201:enzymology* / Q000528:radiation effects; D004790:Enzyme Induction / Q000528:radiation effects; D019317:Evidence-Based Medicine; D005720:Gamma Rays; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D018499:Linear Energy Transfer / Q000235:genetics; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D011401:Promoter Regions, Genetic; D019098:Telomerase / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D015854:Up-Regulation / Q000528:radiation effects
D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D000072000:NF-KappaB Inhibitor alpha; D051550:I-kappa B Kinase; C509186:TERT protein, human; D019098:Telomerase