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.
Natarajan
M
M
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
Mohan
S
S
Konopinski
R
R
Otto
R A
RA
Herman
T S
TS
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