Stress-induced premature senescence in a human glioma cell line after irradiation with heavy ion beam

Abstract

Cellular senescence is generally defined as the physiological program of irreversible growth arrest, which can be caused either by telomere shortening (replicative senescence) or by telomere-independent signals (stress-induced premature senescence). In this study, we examined whether irradiation with carbon ion beam induces senescence of a human glioma-derived cell line, NP-2. The development of morphological phenotypes consistent with cellular senescence, that is, enlarged and flattened appearance was observed in irradiated NP-2 cells. This senescent nature was supported by positive staining for senescence-associated β-galactosidase (SA-β-Gal) activity, accumulation of lipofuscin, and increased lysosomal mass. Double labeling for 5-bromodeoxyuridine and SA-β-Gal indicated that most SA-β-Gal-positive NP-2 cells did not synthesize DNA. The mean telomere length of unirradiated NP-2 cells was approximately 4.5 kbp and its length did not significantly vary in SA-β-Gal-positive NP-2 cells. Since the status for p53 in NP-2 cells was determined as a mutant type, p53-independent growth arrest mechanism might be involved in induction of senescence-like phenotype in NP-2 cells. We conclude that carbon ion beam irradiation can induce a senescence-like phenotype associated with terminal growth arrest in human glioma-derived cells. Elucidation of gene(s) and regulatory mechanism(s) of cellular senescence in response to carbon ion beam irradiation should contribute for designing new therapeutic approaches to improve the efficacy for cancer radiation therapy.