Thiazolidinediones downregulate Wnt/beta-catenin signaling via multiple mechanisms in breast cancer cells.
BACKGROUND
Thiazolidinediones (TZDs) have been demonstrated to possess antitumor effects in breast cancer cells, although the mechanisms are not well established. We sought to better define TZDs' antitumor effects and molecular mechanisms to permit rational utilization of these agents.


METHODS
We studied the effects of TZDs on DNA synthesis (BrdU enzyme-linked immunosorbent assay), gene expression (microarray, quantitative reverse transcription-polymerase chain reaction, and immunoblot), serine phosphorylation and localization of beta-catenin (nuclear/cytoplasmic fractionation and immunoblot), transactivation activity of beta-catenin/T cell factor 4 (TCF4) (luciferase assay with wild-type and mutant TCF4 responsive element), and beta-catenin/TCF4 complex (immunoprecipitation) in human breast cancer cells MDA-MB-231 and T47D.


RESULTS
Troglitazone (TG) down-regulated DNA synthesis in MDA-MB-231 and T47D and decreased mRNA expression of the Wnt co-receptors frizzled-1 and low-density lipoprotein-related protein 6 (LRP6) as well as protein level of LRP6. TG also targets downstream Wnt signaling molecules in T47D cells. TG down-regulates p-beta-catenin (S33/S37/T41) and promotes translocation of beta-catenin into the nucleus. However, TG inhibits beta-catenin-mediated transactivation by down-regulating TCF4 protein levels, thereby inhibiting beta-catenin/TCF4 complex formation. Finally, we found that inhibition of Akt augments TG-mediated down-regulation of DNA synthesis and this result was accompanied with the decreased protein levels of Wnt signaling molecules: LRP6, beta-catenin, and TCF4.


CONCLUSIONS
These results suggest that the Wnt/beta-catenin signaling pathway, which plays an important role in breast cancer pathogenesis, may be a target for TZD treatment. Moreover, a combination of TZDs and a specific Akt inhibitor may serve as a new approach to target Wnt/beta-catenin directly and via PI3K/Akt action on glycogen synthase-3beta.
Wang
Pei-Shan
PS
Department of Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA.
Chou
Fu-Sheng
FS
Bloomston
Mark
M
Vonau
Martin S
MS
Saji
Motoyasu
M
Espinosa
Allan
A
Pinzone
Joseph J
JJ
D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D051157:Frizzled Receptors / Q000378:metabolism; D006801:Humans; D026502:LDL-Receptor Related Proteins / Q000378:metabolism; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects*; D045162:Thiazolidinediones / Q000494:pharmacology* / Q000627:therapeutic use; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000378:metabolism; D015854:Up-Regulation; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
D000970:Antineoplastic Agents; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C489740:FZD1 protein, human; D051157:Frizzled Receptors; D026502:LDL-Receptor Related Proteins; C555475:LRP6 protein, human; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C532096:TCF4 protein, human; D045162:Thiazolidinediones; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; D051057:Proto-Oncogene Proteins c-akt