title: Effects of hypoxia on radiation-responsive stress-activated protein kinase, p53, and caspase 3 signals in TK6 human lymphoblastoid cells.
abstract: Despite significant evidence of a role of hypoxia in cellular resistance to ionizing radiation-induced toxicity, the underlying molecular mechanisms remain unclear. This study focused on the influence of hypoxia on radiation-induced signals in TK6 human lymphoblastoid cells. Hypoxic (<10 ppm oxygen) and aerobic cells were exposed to equilethal doses of ionizing radiation, radiation dose ratio, 3:1 (hypoxia:air). Hypoxia alone or radiation treatment under aerobic or hypoxic conditions led to increased levels of phospho-p44/42 mitogen-activated protein kinase. Levels of phospho-p38 mitogen-activated protein kinase did not change as a result of either hypoxia or irradiation. Hypoxia alone had no effect on expression of phospho-stress-activated protein kinase (SAPK), wild-type p53, or cleaved caspase 3. Irradiation under aerobic conditions resulted in an increase in the phospho-SAPK signal, whereas hypoxia suppressed the irradiation-induced increase in the level of phospho-SAPK. Both hypoxic and aerobic cells showed increases in p53 levels in response to radiation. Hypoxia blocked radiation-induced cleavage of caspase 3 and poly-ADP-ribose polymerase. Irradiation of aerobic and hypoxic TK6 cells using 6 and 18 Gy, respectively, resulted in a similar and significant increase in fraction of apoptotic cells within 24 hours postirradiation. In contrast, basal levels of apoptosis were observed at 24 hours postirradiation in aerobic and hypoxic NH32 cells, a p53 null derivative of TK6 cells. These results suggest that radiation-induced apoptosis under hypoxia occurs independent of phospho-SAPK and caspase 3, and the p53 response is an obligatory apoptotic signal in TK6 cells.
authors.affiliation: Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
authors.forename: Ayelet M
authors.initials: AM
authors.lastname: Samuni
authors.forename: Usha
authors.initials: U
authors.lastname: Kasid
authors.forename: Eric Y
authors.initials: EY
authors.lastname: Chuang
authors.forename: Simeng
authors.initials: S
authors.lastname: Suy
authors.forename: William
authors.initials: W
authors.lastname: Degraff
authors.forename: Murali C
authors.initials: MC
authors.lastname: Krishna
authors.forename: Angelo
authors.initials: A
authors.lastname: Russo
authors.forename: James B
authors.initials: JB
authors.lastname: Mitchell
mesh_terms: D000332:Aerobiosis; D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism* / Q000528:radiation effects; D015687:Cell Hypoxia / Q000502:physiology; D002460:Cell Line; D005434:Flow Cytometry; D006801:Humans; D008214:Lymphocytes / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D020935:MAP Kinase Signaling System / Q000502:physiology / Q000528:radiation effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism* / Q000528:radiation effects; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism* / Q000528:radiation effects; D010766:Phosphorylation / Q000528:radiation effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D016159:Tumor Suppressor Protein p53; D011065:Poly(ADP-ribose) Polymerases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases