title: Peroxisome proliferator-activated receptor gamma-independent activation of p38 MAPK by thiazolidinediones involves calcium/calmodulin-dependent protein kinase II and protein kinase R: correlation with endoplasmic reticulum stress.
abstract: The thiazolidinediones (TZDs) are synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands that promote increased insulin sensitivity in type II diabetic patients. In addition to their ability to improve glucose homeostasis, TZDs also exert anti-proliferative effects by a mechanism that is unclear. Our laboratory has shown that two TZDs, ciglitazone and troglitazone, rapidly induce calcium-dependent p38 mitogen-activated protein kinase (MAPK) phosphorylation in liver epithelial cells. Here, we further characterize the mechanism responsible for p38 MAPK activation by PPARgamma ligands and correlate this with the induction of endoplasmic reticulum (ER) stress. Specifically, we show that TZDs rapidly activate the ER stress-responsive pancreatic eukaryotic initiation factor 2alpha (eIF2alpha) kinase or PKR (double-stranded RNA-activated protein kinase)-like endoplasmic reticulum kinase/pancreatic eIF2alpha kinase, and that activation of these kinases is correlated with subsequent eIF2alpha phosphorylation. Interestingly, PPARgamma ligands not only activated calcium/calmodulin-dependent kinase II (CaMKII) 2-fold over control, but the selective CaMKII inhibitor, KN-93, attenuated MKK3/6 and p38 as well as PKR and eIF2alpha phosphorylation. Although CaMKII was not affected by inhibition of PKR with 2-aminopurine, phosphorylation of MKK3/6 and p38 as well as eIF2alpha were significantly reduced. Collectively, these data provide evidence that CaMKII is a regulator of PKR-dependent p38 and eIF2alpha phosphorylation in response to ER calcium depletion by TZDs. Furthermore, using structural derivatives of TZDs that lack PPARgamma ligand-binding activity as well as a PPARgamma antagonist, we show that activation of these kinase signaling pathways is PPARgamma-independent.
authors.affiliation: Curriculum in Toxicology, University of North Carolina at Chapel Hill, North Carolina, 27599, USA.
authors.forename: Olivia S
authors.initials: OS
authors.lastname: Gardner
authors.forename: Chung-Wai
authors.initials: CW
authors.lastname: Shiau
authors.forename: Ching-Shih
authors.initials: CS
authors.lastname: Chen
authors.forename: Lee M
authors.initials: LM
authors.lastname: Graves
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001596:Benzylamines / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D002839:Chromans / Q000494:pharmacology; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000166:cytology; D015151:Immunoblotting; D047468:Immunoprecipitation; D008024:Ligands; D008099:Liver / Q000166:cytology; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D008954:Models, Biological; D008956:Models, Chemical; D047495:PPAR gamma / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D015398:Signal Transduction; D013449:Sulfonamides / Q000378:metabolism; D045162:Thiazolidinediones / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors; D000077288:Troglitazone; D019892:eIF-2 Kinase / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D000096926:Benzenesulfonamides
chemical_list: D000970:Antineoplastic Agents; D001596:Benzylamines; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002839:Chromans; D016895:Culture Media, Serum-Free; D008024:Ligands; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D047495:PPAR gamma; D013449:Sulfonamides; D045162:Thiazolidinediones; D000077288:Troglitazone; D019892:eIF-2 Kinase; D048051:p38 Mitogen-Activated Protein Kinases; C072105:KN 93; D000096926:Benzenesulfonamides; C089946:2,4-thiazolidinedione; C482566:MAP2K6 protein, human; C039671:ciglitazone