title: PPARgamma inhibitors reduce tubulin protein levels by a PPARgamma, PPARdelta and proteasome-independent mechanism, resulting in cell cycle arrest, apoptosis and reduced metastasis of colorectal carcinoma cells.
abstract: The nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma) has been identified as an important therapeutic target in murine models of colorectal cancer (CRC). To examine whether PPARgamma inhibition has therapeutic effects in late-stage CRC, the effects of PPARgamma inhibitors on CRC cell survival were examined in CRC cell lines and a murine CRC model. Low doses (0.1-1 microM) of PPARgamma inhibitors (T0070907, GW9662 and BADGE) did not affect cell survival, while higher doses (10-100 microM) of all 3 PPARgamma inhibitors caused caspase-dependent apoptosis in HT-29, Caco-2 and LoVo CRC cell lines. Apoptosis was preceded by altered cell morphology, and this alteration was not prevented by caspase inhibition. PPARgamma inhibitors also caused dual G and M cell cycle arrest, which was not required for apoptosis or for morphologic alterations. Furthermore, PPARgamma inhibitors triggered loss of the microtubule network. Notably, unlike other standard antimicrotubule agents, PPARgamma inhibitors caused microtubule loss by regulating tubulin post-transcriptionally rather than by altering microtubule polymerization or dynamics. Proteasome inhibition by epoxomicin was unable to prevent tubulin loss. siRNA-mediated reduction of PPARgamma and PPARdelta proteins did not replicate the effects of PPARgamma inhibitors or interfere with the inhibitors' effects on apoptosis, cell cycle or tubulin. PPARgamma inhibitors also reduced CRC cell migration and invasion in assays in vitro and reduced both the number and size of metastases in a HT-29/SCID xenograft metastatic model of CRC. These results suggest that PPARgamma inhibitors are a novel potential antimicrotubule therapy for CRC that acts by directly reducing microtubule precursors.
authors.affiliation: Section of Gastroenterology and Hepatology, University of Rochester Medical Center, Rochester, NY 14642, USA. katherie_schaefer@urmc.rochester.edu
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Schaefer
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Takahashi
authors.forename: Victor M
authors.initials: VM
authors.lastname: Morales
authors.forename: Gianni
authors.initials: G
authors.lastname: Harris
authors.forename: Susan
authors.initials: S
authors.lastname: Barton
authors.forename: Emi
authors.initials: E
authors.lastname: Osawa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nakajima
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Saubermann
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000813:Anilides / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology; D001559:Benzhydryl Compounds; D018938:Caco-2 Cells; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D004852:Epoxy Compounds / Q000494:pharmacology; D019073:HT29 Cells; D006801:Humans; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009362:Neoplasm Metastasis; D047494:PPAR delta / Q000378:metabolism; D047495:PPAR gamma / Q000037:antagonists & inhibitors* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D014404:Tubulin / Q000235:genetics / Q000378:metabolism*; D023041:Xenograft Model Antitumor Assays; D000098826:Bisphenol A Compounds
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000813:Anilides; D001549:Benzamides; D001559:Benzhydryl Compounds; D061945:Caspase Inhibitors; D020169:Caspases; D004852:Epoxy Compounds; D047494:PPAR delta; D047495:PPAR gamma; D046988:Proteasome Endopeptidase Complex; D011725:Pyridines; D014404:Tubulin; C457499:2-chloro-5-nitrobenzanilide; C458508:T 0070907; C476093:z-Val-Ala-Asp(Ome)-fluoromethylketone; C019273:bisphenol A diglycidyl ether; D000098826:Bisphenol A Compounds