title: Signaling pathways involved in induction of GADD45 gene expression and apoptosis by troglitazone in human MCF-7 breast carcinoma cells.
abstract: We previously reported that the PPARgamma agonist troglitazone (TRO) inhibits proliferation and induces apoptosis in human MCF-7 breast carcinoma cells. To understand the mechanisms of antiproliferative and pro-apoptotic effects of TRO, we screened a limited DNA array containing 23 genes involved in regulating either the cell cycle and/or apoptosis. Four of the 23 genes screened exhibited regulation by TRO, with growth arrest and DNA damage-inducible gene 45 (GADD45) being the most strongly upregulated. TRO induced GADD45 mRNA expression in a time- and dose-dependent manner. Depletion of GADD45 by siRNA abrogated TRO-induced apoptosis in MCF-7 cells demonstrating the physiological relevance of GADD45 upregulation. Signaling pathways mediating TRO-induced GADD45 were also investigated. Several mitogen-activated protein kinase (MAPK) pathways were involved in the induction of GADD45 by TRO. Inhibition of the c-jun N-terminal kinase MAPK pathway by SP600125 partially abolished TRO-induced GADD45 mRNA, and protein expression and apoptosis. In contrast, inhibition of the p38 MAPK pathway by SB203580, or through overexpression of a dominant-negative mutant of p38 MAPK, augmented GADD45 mRNA induction and GADD45 promoter activation as well as cell apoptosis by TRO. Blockade of the extracellular signal-regulated kinase MAPK pathway by PD98059 also enhanced TRO's effects on GADD45 and apoptosis. Two other PPARgamma agonists pioglitazone and rosiglitazone did not induce GADD45 expression. Our finding of GADD45 induction by TRO may provide a new insight concerning the mechanisms for TRO's antiproliferative and pro-apoptotic effects in breast cancer cells.
authors.affiliation: Division of Endocrinology, Diabetes and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, California, CA 90095, USA. fyin@mednet.ucla.edu
authors.forename: Fen
authors.initials: F
authors.lastname: Yin
authors.forename: Dennis
authors.initials: D
authors.lastname: Bruemmer
authors.forename: Florian
authors.initials: F
authors.lastname: Blaschke
authors.forename: Willa A
authors.initials: WA
authors.lastname: Hsueh
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Law
authors.forename: Andre J Van
authors.initials: AJ
authors.lastname: Herle
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D002277:Carcinoma / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D002453:Cell Cycle / Q000235:genetics; D002839:Chromans / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D034741:RNA, Small Interfering; D015398:Signal Transduction; D045162:Thiazolidinediones / Q000494:pharmacology*; D000077288:Troglitazone; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases; D000097642:GADD45 Proteins
chemical_list: D000970:Antineoplastic Agents; D002839:Chromans; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D011506:Proteins; D011725:Pyridines; D034741:RNA, Small Interfering; D045162:Thiazolidinediones; D000077288:Troglitazone; D048051:p38 Mitogen-Activated Protein Kinases; D000097642:GADD45 Proteins; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one