Radiation-induced HIF-1alpha cell survival pathway is inhibited by soy isoflavones in prostate cancer cells.
We previously showed that treatment of prostate cancer cells with soy isoflavones and radiation resulted in greater cell killing in vitro, and caused downregulation of NF-kappaB and APE1/Ref-1. APE1/Ref-1 functions as a redox activator of transcription factors, including NF-kappaB and HIF-1alpha. These molecules are upregulated by radiation and implicated in radioresistance of cancer cells. We extended our studies to investigate the role of HIF-1alpha survival pathway and its upstream Src and STAT3 molecules in isoflavones and radiation interaction. Radiation induced phosphorylation of Src and STAT3 leading to induction of HIF-1alpha. Genistein, daidzein or a mixture of soy isoflavones did not activate this pathway. These data were observed both in PC-3 (AR-) and C4-2B (AR+) androgen-independent cell lines. Pretreatment with isoflavones inhibited Src/STAT3/HIF-1alpha activation by radiation and nuclear translocation of HIF-1alpha. These findings correlated with decreased expression of APE1/Ref-1 and DNA binding activity of HIF-1alpha and NF-kappaB. In APE1/Ref-1 cDNA transfected cells, radiation caused a greater increase in HIF-1alpha and NF-kappaB activities but this effect was inhibited by pretreatment with soy prior to radiation. Transfection experiments indicate that APE1/Ref-1 inhibition by isoflavones impairs the radiation-induced transcription activity of NF-kappaB and HIF-1alpha. This mechanism could result in the inhibition of genes essential for tumor growth and angiogenesis, as demonstrated by inhibition of VEGF production and HUVECs tube formation. Our novel findings suggest that the increased responsiveness to radiation mediated by soy isoflavones could be due to pleiotropic effects of isoflavones blocking cell survival pathways induced by radiation including Src/STAT3/HIF-1alpha, APE1/Ref-1 and NF-kappaB.
Singh-Gupta
Vinita
V
Department of Radiation Oncology, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, MI.
Zhang
Hao
H
Banerjee
Sanjeev
S
Kong
Dejuan
D
Raffoul
Julian J
JJ
Sarkar
Fazlul H
FH
Hillman
Gilda G
GG
D015153:Blotting, Western; D045744:Cell Line, Tumor; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000187:drug effects / Q000528:radiation effects; D024202:Electrophoretic Mobility Shift Assay; D005455:Fluorescent Antibody Technique; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D007529:Isoflavones / Q000494:pharmacology*; D008297:Male; D016328:NF-kappa B / Q000187:drug effects / Q000528:radiation effects; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000187:drug effects / Q000528:radiation effects; D015398:Signal Transduction / Q000187:drug effects* / Q000528:radiation effects*; D013025:Glycine max / Q000737:chemistry; D042461:Vascular Endothelial Growth Factor A / Q000187:drug effects; D019061:src-Family Kinases / Q000187:drug effects / Q000528:radiation effects
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007529:Isoflavones; D016328:NF-kappa B; D050796:STAT3 Transcription Factor; D042461:Vascular Endothelial Growth Factor A; D019061:src-Family Kinases; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase