Survivin gene silencing sensitizes prostate cancer cells to selenium growth inhibition.
BACKGROUND
Prostate cancer is a leading cause of cancer-related death in men worldwide. Survivin is a member of the inhibitor of apoptosis (IAP) protein family that is expressed in the majority of human tumors including prostate cancer, but is barely detectable in terminally differentiated normal cells. Downregulation of survivin could sensitize prostate cancer cells to chemotherapeutic agents in vitro and in vivo. Selenium is an essential trace element. Several studies have shown that selenium compounds inhibit the growth of prostate cancer cells. The objective of this study is to investigate whether survivin gene silencing in conjunction with selenium treatment could enhance the therapeutic efficacy for prostate cancer and to elucidate the underlying mechanisms.


METHODS
Expression of survivin was analyzed in a collection of normal and malignant prostatic tissues by immunohistochemical staining. In vitro studies were conducted in PC-3M, C4-2B, and 22Rv1 prostate cancer cells. The effect of selenium on survivin expression was analyzed by Western blotting and semi-quantitative RT-PCR. Survivin gene knockdown was carried out by transfecting cells with a short hairpin RNA (shRNA) designed against survivin. Cell proliferation was quantitated by the 3-(4,5-Dimethylthiazol-2-yl)- 2,5-Diphenyltetrazolium Bromide (MTT) assay and apoptosis by propidium iodide staining followed by flow cytometry analysis. Finally, in vivo tumor growth assay was performed by establishing PC-3M xenograft in nude mice and monitoring tumor growth following transfection and treatment.


RESULTS
We found that survivin was undetectable in normal prostatic tissues but was highly expressed in prostate cancers. Survivin knockdown or selenium treatment inhibited the growth of prostate cancer cells, but the selenium effect was modest. In contrast to what have been observed in other cell lines, selenium treatment had little or no effect on survivin expression in several androgen-independent prostate cancer cell lines. Survivin knockdown sensitized these cells to selenium growth inhibition and apoptosis induction. In nude mice bearing PC-3M xenografts, survivin knockdown synergizes with selenium in inhibiting tumor growth.


CONCLUSIONS
Selenium could inhibit the growth of hormone-refractory prostate cancer cells both in vitro and in vivo, but the effects were modest. The growth inhibition was not mediated by downregulating survivin expression. Survivin silencing greatly enhanced the growth inhibitory effects of selenium.
Liu
Xichun
X
Prostate Diseases Prevention and Treatment Research Center and Department of Pathophysiology, Norman Bethune College of Medicine, Jilin University, Xinmin Street, Changchun, 130021, PR China.
Gao
Ruijuan
R
Dong
Yan
Y
Gao
Lifang
L
Zhao
Yanying
Y
Zhao
Lijuan
L
Zhao
Xuejian
X
Zhang
Haitao
H
D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003545:Cysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015536:Down-Regulation; D004357:Drug Synergism; D020868:Gene Silencing; D006801:Humans; D007124:Immunoenzyme Techniques; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D016566:Organoselenium Compounds / Q000494:pharmacology*; D011379:Prognosis; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017279:Selenocysteine / Q000031:analogs & derivatives; D015996:Survival Rate; D000077022:Survivin
D016588:Anticarcinogenic Agents; C117749:Birc5 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D016566:Organoselenium Compounds; D012333:RNA, Messenger; D012097:Repressor Proteins; D000077022:Survivin; D017279:Selenocysteine; C008493:methylselenic acid; D003545:Cysteine; C002979:selenomethylselenocysteine