Lithium suppresses cell proliferation by interrupting E2F-DNA interaction and subsequently reducing S-phase gene expression in prostate cancer.
BACKGROUND
Lithium is an existing drug for bipolar disorder and its uptake was recently linked to reduced tumor incidence compared to the general population. The major target of lithium action is glycogen synthase kinase 3 (GSK-3). Since GSK-3 expression and activation are associated with prostate cancer progression, the anti-cancer potential of lithium on prostate cancer was investigated in this study.


METHODS
Multiple prostate cancer cell lines were treated with lithium chloride (LiCl). Cell proliferation and cell cycle distribution were analysed. DNA replication was determined using BrdU labeling assay. Genome-wide screening of gene expression was performed using cDNA microarray assay. GSK-3beta gene-specific silencing was conducted using small interferencing RNA (siRNA) transfection. E2 factor (E2F) transactivation was evaluated using reporter gene assay and E2F-DNA interaction was determined with chromatin-immunoprecipitation assay (ChIP).


RESULTS
LiCl significantly inhibited cell proliferation, which was associated with reduced DNA replication and S-phase cell cycle arrest. LiCl significantly decreased the expression of multiple DNA replication-related genes, including cell division cycle 6 (cdc6), cyclin A, cyclin E, and cdc25C, which are regulated by E2F factor during cell cycle. A novel GSK-3-specific inhibitor TDZD-8 and GSK-3beta siRNA also suppressed the expression of these E2F target genes, indicating that LiCl-induced anti-cancer effect was associated with GSK-3beta inhibition. Furthermore, LiCl suppressed E2F transactivation by interrupting the interaction of E2F1 factor with its target gene promoter.


CONCLUSIONS
These data indicated that LiCl suppresses cancer cell proliferation by disrupting E2F-DNA interaction and subsequent E2F-mediated gene expression in prostate cancer.
Sun
Aijing
A
Department of Pathology, Shaoxing People's Hospital and the First Affiliated Hospital of Shaoxing University, Shaoxing, Zhejiang, China.
Shanmugam
Ilanchezian
I
Song
Jiawu
J
Terranova
Paul F
PF
Thrasher
J Brantley
JB
Li
Benyi
B
D002455:Cell Division / Q000187:drug effects*; D045744:Cell Line, Tumor; D017931:DNA Primers; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008094:Lithium / Q000494:pharmacology*; D008297:Male; D009363:Neoplasm Proteins / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D011471:Prostatic Neoplasms / Q000235:genetics / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase / Q000187:drug effects / Q000235:genetics*
D017931:DNA Primers; D009363:Neoplasm Proteins; D008094:Lithium