Rosiglitazone induces caveolin-1 by PPARgamma-dependent and PPRE-independent mechanisms: the role of EGF receptor signaling and its effect on cancer cell drug resistance.
BACKGROUND
Caveolin-1, a key component of plasma membrane caveolae, has been implicated in the regulation of cancer cell growth and survival. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a ligand-activated nuclear receptor which plays a pivotal role in many cellular processes. Activation of PPARgamma by its ligand rosiglitazone upregulates caveolin-1 mRNA and protein in human carcinoma cells.


METHODS
We have used specific signaling inhibitors to dissect the mechanisms of caveolin-1 mRNA and protein induction by rosiglitazone, determined by RT-PCR and Western blotting, respectively. ROS generation was measured by flow cytometry and cell survival was determined by the MTT assay.


RESULTS
We show that in HT-29 human colon cancer cells the induction ofcaveolin-1 by rosiglitazone is inhibited by the EGF receptor (EGFR) blocker AG1478. Moreover, rosiglitazone stimulates EGFR phosphorylation, while direct activation of EGFR by EGF up-regulates caveolin-1 mRNA. Inhibitors of Src and the Mek1-Erk1/2 and p38 MAP kinase pathways also inhibit up-regulation of caveolin-1 by rosiglitazone. Furthermore, rosiglitazone stimulates formation of superoxide anions, whereas induction of caveolin-1 expression by rosiglitazone is attenuated by the antioxidant N-acetyl-cysteine. Finally, rosiglitazone increases the resistance of HT-29 cells to doxorubicin and to hydrogen peroxide. The caveolin-1 gene promoter lacks a canonical PPARgamma response element (PPRE) and a PPRE-reporter construct is not sensitive to EGF or EGFR inhibition.


CONCLUSIONS
Our findings indicate that up-regulation of caveolin-1 by rosiglitazone requires superoxide formation and the activation of Src, EGFR, and the Mek1-Erk1/2 and p38 MAP kinase pathways. We suggest a novel mode of action of PPARgamma ligands in the regulation of caveolin-1, and possibly other genes devoid of a PPRE in their promoters, which involves the coordinate activation of PPARgamma and intracellular signaling pathways.
Tencer
Lilach
L
Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel.
Burgermeister
Elke
E
Ebert
Matthias P
MP
Liscovitch
Mordechai
M
D051242:Caveolin 1 / Q000378:metabolism*; D002470:Cell Survival; D019008:Drug Resistance, Neoplasm; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000502:physiology*; D019073:HT29 Cells; D006801:Humans; D047495:PPAR gamma / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D000077154:Rosiglitazone; D015398:Signal Transduction; D013481:Superoxides / Q000378:metabolism; D045162:Thiazolidinediones / Q000494:pharmacology*
D051242:Caveolin 1; D047495:PPAR gamma; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D013481:Superoxides; D004815:Epidermal Growth Factor; D066246:ErbB Receptors