TY - JOUR
T1 - AMPK-independent autophagy promotes radioresistance of human tumor cells under clinical relevant hypoxia in vitro
AU - Chaachouay, Hassan
AU - Fehrenbacher, Birgit
AU - Toulany, Mahmoud
AU - Schaller, Martin
AU - Multhoff, Gabriele
AU - Rodemann, H. Peter
N1 - Publisher Copyright:
© 2015 Elsevier Ireland Ltd.
PY - 2015/9
Y1 - 2015/9
N2 - Background and purpose Blocking of the autophagy-signaling has the potential to improve cancer therapy. In the present study, the role of autophagy for radioresistance of human tumor cells was tested under clinically relevant hypoxia (1% O2). Materials and methods Non-small cell lung cancer cell lines A549 and H460, head and neck squamous cell carcinoma FaDu, colon carcinoma cell line HCT116 and mouse-embryo-fibroblasts were analyzed under normoxic (21% O2) and hypoxic (0.01% and 1% O2) conditions with respect to clonogenic cell survival and hypoxia-induced autophagy. Immunofluorescence and electron microscopy were used to monitor the autophagy process and Western blotting of LC3, AMPK, and BNIP3 was applied to analyze autophagy signaling. Results Clinically relevant hypoxia stimulated autophagy in tumor cells as indicated by enhanced LC3-I to LC3-II conversion. Furthermore, hypoxia stimulated autophagy was approved by Immunofluorescence staining and electron-microscopy analysis of autophagosome vacuoles. Preconditioning of tumor cells to moderate-hypoxia increased their radioresistance that was significantly reversed following pretreatment with autophagy inhibitor, chloroquine. Using siRNA against AMPK as well as AMPK deficient cells, autophagy stimulation by 1% O2 was shown to be AMPK-independent. However, a correlation between the expression of BNIP3 and autophagy-stimulation was observed under this condition. Conclusion Under clinically relevant hypoxia (1% O2) the stimulation of autophagy mediates resistance of hypoxic tumor cells to ionizing radiation, which is independent of AMPK signaling.
AB - Background and purpose Blocking of the autophagy-signaling has the potential to improve cancer therapy. In the present study, the role of autophagy for radioresistance of human tumor cells was tested under clinically relevant hypoxia (1% O2). Materials and methods Non-small cell lung cancer cell lines A549 and H460, head and neck squamous cell carcinoma FaDu, colon carcinoma cell line HCT116 and mouse-embryo-fibroblasts were analyzed under normoxic (21% O2) and hypoxic (0.01% and 1% O2) conditions with respect to clonogenic cell survival and hypoxia-induced autophagy. Immunofluorescence and electron microscopy were used to monitor the autophagy process and Western blotting of LC3, AMPK, and BNIP3 was applied to analyze autophagy signaling. Results Clinically relevant hypoxia stimulated autophagy in tumor cells as indicated by enhanced LC3-I to LC3-II conversion. Furthermore, hypoxia stimulated autophagy was approved by Immunofluorescence staining and electron-microscopy analysis of autophagosome vacuoles. Preconditioning of tumor cells to moderate-hypoxia increased their radioresistance that was significantly reversed following pretreatment with autophagy inhibitor, chloroquine. Using siRNA against AMPK as well as AMPK deficient cells, autophagy stimulation by 1% O2 was shown to be AMPK-independent. However, a correlation between the expression of BNIP3 and autophagy-stimulation was observed under this condition. Conclusion Under clinically relevant hypoxia (1% O2) the stimulation of autophagy mediates resistance of hypoxic tumor cells to ionizing radiation, which is independent of AMPK signaling.
KW - Autophagy
KW - Clinical relevant hypoxia
KW - Ionizing radiation
KW - Solid tumor cells
UR - http://www.scopus.com/inward/record.url?scp=84944177567&partnerID=8YFLogxK
U2 - 10.1016/j.radonc.2015.08.012
DO - 10.1016/j.radonc.2015.08.012
M3 - Article
C2 - 26318663
AN - SCOPUS:84944177567
SN - 0167-8140
VL - 116
SP - 409
EP - 416
JO - Radiotherapy and Oncology
JF - Radiotherapy and Oncology
IS - 3
ER -