Siah1 proteins enhance radiosensitivity of human breast cancer cells.
BACKGROUND
Siah proteins play an important role in cancer progression. We evaluated the effect of Siah1, its splice variants Siah1L and the Siah1 mutant with the RING finger deleted (Siah1DeltaR) on radiosensitization of human breast cancer cells.


METHODS
The status of Siah1 and Siah1L was analysed in five breast cancer cell lines. To establish stable cells, SKBR3 cells were transfected with Siah1, Siah-1L and Siah1DeltaR. Siah1 function was suppressed by siRNA in MCF-7 cells. The impact of Siah1 overexpression and silencing on apoptosis, proliferation, survival, invasion ability and DNA repair was assessed in SKBR3 and MCF-7 cells, also in regards to radiation.


RESULTS
Siah1 and Siah1L mRNA expression was absent in four of five breast cancer cells lines analysed. Overexpression of Siah1 and Siah1L enhanced radiation-induced apoptosis in stable transfected SKBR3 cells, while Siah1DeltaR failed to show this effect. In addition, Siah1 and Siah1L significantly reduced cell clonogenic survival and proliferation. Siah1L sensitization enhancement ratio values were over 1.5 and 4.0 for clonogenic survival and proliferation, respectively, pointing to a highly cooperative and potentially synergistic fashion with radiation. Siah1 or Siah1L significantly reduced invasion ability of SKBR3 and suppressed Tcf/Lef factor activity. Importantly, Siah1 siRNA demonstrated opposite effects in MCF-7 cells. Siah1 and Siah1L overexpression resulted in inhibition of DNA repair as inferred by increased levels of DNA double-strand breaks in irradiated SKBR3 cells.


CONCLUSIONS
Our results reveal for the first time how overexpression of Siah1L and Siah1 can determine radiosensitivity of breast cancer cells. These findings suggest that development of drugs augmenting Siah1 and Siah1L activity could be a novel approach in improving tumor cell kill.
He
Hai-Tao
HT
Department of Radiotherapy and Radiation Oncology, Philipps-University Marburg, Baldingerstr, D-35043 Marburg, Germany.
Fokas
Emmanouil
E
You
An
A
Engenhart-Cabillic
Rita
R
An
Han-Xiang
HX
D017209:Apoptosis / Q000528:radiation effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy*; D002448:Cell Adhesion / Q000528:radiation effects; D002465:Cell Movement / Q000528:radiation effects*; D049109:Cell Proliferation / Q000528:radiation effects; D005260:Female; D005455:Fluorescent Antibody Technique; D005720:Gamma Rays; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D009361:Neoplasm Invasiveness; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D011836:Radiation Tolerance; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000098563:Seven in Absentia Proteins
D009687:Nuclear Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D008156:Luciferases; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins