Overexpression of the cytoprotective protein clusterin decreases radiosensitivity in the human LNCaP prostate tumour model.
OBJECTIVE
To evaluate the effect of clusterin overexpression on radiation-induced tumour growth rates and apoptosis in human prostate LNCaP cells, as prostate cancer cells are relatively resistant to radiation-induced apoptosis and local recurrences are common, but overexpression of the anti-apoptotic protein clusterin can accelerate progression to androgen-independence and to confer a chemoresistant phenotype in various prostate cancer models.


METHODS
Western blot analysis and immunohistochemistry were used to compare clusterin expression levels in parental (P) and clusterin-transfected (T) LNCaP cells in vitro and in vivo. The effects of radiation on clusterin-expression in both parental LNCaP/P and clusterin-transfected LNCaP/T tumours were analysed by Northern blot analysis. The cellular response to radiation was determined up to 3 weeks after irradiation using tetrazolium and re-growth assays, and cell-cycle analysis by flow cytometry.


RESULTS
Clusterin mRNA expression increased from undetectable to low levels in LNCaP/P tumours after radiation and more than three-fold in LNCaP/T tumours. Clusterin overexpression decreased the radiosensitivity in a time-dependent manner, reducing the extent of growth arrest and apoptosis by up to 54%. Re-growth assays showed that the improved survival rates of LNCaP/T cells after radiation did not change after 3 days, remaining constant over 3 weeks.


CONCLUSIONS
These results identify clusterin as a promoter of cell survival that may help mediate resistance to radiation-induced apoptosis. Furthermore, clusterin overexpression seems to provide an extended protection against radiation-induced cell cycle arrest and apoptosis.
Zellweger
T
T
The Prostate Centre, Vancouver General Hospital, BC, Canada.
Kiyama
S
S
Chi
K
K
Miyake
H
H
Adomat
H
H
Skov
K
K
Gleave
M E
ME
D017209:Apoptosis / Q000528:radiation effects*; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division / Q000528:radiation effects; D051152:Clusterin; D005434:Flow Cytometry; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018832:Molecular Chaperones / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured
C495242:CLU protein, human; D051152:Clusterin; D006023:Glycoproteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D012333:RNA, Messenger