Basal HIF-1α expression levels are not predictive for radiosensitivity of human cancer cell lines.
OBJECTIVE
High levels of hypoxia inducible factor (HIF)-1α in tumors are reported to be associated with tumor progression and resistance to therapy. To examine the impact of HIF-1α on radioresistance under normoxia, the sensitivity towards irradiation was measured in human tumor cell lines that differ significantly in their basal HIF-1α levels.


METHODS
HIF-1α levels were quantified in lysates of H1339, EPLC-272H, A549, SAS, XF354, FaDu, BHY, and CX- tumor cell lines by ELISA. Protein levels of HIF-1α, HIF-2α, carbonic anhydrase IX (CA IX), and GAPDH were assessed by Western blot analysis. Knock-down experiments were performed using HIF-1α siRNA. Clonogenic survival after irradiation was determined by the colony forming assay.


RESULTS
According to their basal HIF-1α status, the tumor cell lines were divided into low (SAS, XF354, FaDu, A549, CX-), intermediate (EPLC-272H, BHY), and high (H1339) HIF-1α expressors. The functionality of the high basal HIF-1α expression in H1339 cells was proven by reduced CA IX expression after knocking-down HIF-1α. Linear regression analysis revealed no correlation between basal HIF-1α levels and the survival fraction at either 2 or 4 Gy in all tumor cell lines investigated.


CONCLUSIONS
Our data suggest that basal HIF-1α levels in human tumor cell lines do not predict their radiosensitivity under normoxia.
Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, Munich, Germany.
D
D
Schilling
C
C
Bayer
K
K
Emmerich
M
M
Molls
P
P
Vaupel
R M
RM
Huber
G
G
Multhoff
D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D004797:Enzyme-Linked Immunosorbent Assay; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics* / Q000528:radiation effects*; D055785:Gene Knockdown Techniques; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics*; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D010039:Otorhinolaryngologic Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D034741:RNA, Small Interfering / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000528:radiation effects*; D014410:Tumor Stem Cell Assay
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering