title: Genetic downregulation of receptor-interacting protein 140 uncovers the central role of Akt signalling in the regulation of fatty acid oxidation in skeletal muscle cells.
abstract: The role of the nuclear co-repressor receptor-interacting protein 140 (RIP140) in metabolic regulation, gene and protein expression and insulin signalling in skeletal muscle cells remains to be delineated. To study this question, L6 myotubes were treated with or without an RNA interference oligonucleotide sequence to downregulate RIP140 expression and incubated with or without insulin (1 μM). Downregulation of RIP140 increased (P < 0.05) basal palmitate uptake (by 20%) and decreased (P < 0.05) basal palmitate oxidation (by 38%). In control small interfering RNA-treated cells, insulin increased (P < 0.05) glucose (by 31%) and palmitate uptake (by 20%) and decreased (P < 0.05) palmitate oxidation (by 35%). However, in RIP140 small interfering RNA-treated cells, insulin did not affect (P > 0.05) palmitate uptake and increased (P < 0.05) palmitate oxidation (by 79%). In insulin-mediated conditions, downregulation of RIP140 decreased (P < 0.05) Akt(Ser473) and atypical protein kinase C-ζ(Thr403/410) phosphorylation. As expected, downregulation of RIP140 was accompanied by an increase (P < 0.05) in cytochrome c oxidase subunit 4 isoform 1 and peroxisome proliferator-activated receptor receptor γ coactivator-1α mRNA content. Downregulation of RIP140 increased (P < 0.05) fatty acid transport protein 1 mRNA content and carnitine palmitoyltransferase 1b protein content and decreased (P < 0.05) medium chain acyl-CoA dehydrogenase mRNA content in basal conditions. In insulin-mediated conditions, downregulation of RIP140 increased (P < 0.05) carnitine palmitoyltransferase 1b, fatty acid transport protein 1 and fibroblast growth factor 21 mRNA content and decreased (P < 0.05) medium chain acyl-CoA dehydrogenase mRNA content and plasma membrane fatty acid translocase/cluster of differentiation 36 protein content. Our data show that, in skeletal muscle cells, RIP140 expression significantly impacts palmitate uptake and oxidation and that alterations in gene expression and Akt-atypical protein kinaseC-ζ signalling can partly explain these changes.
authors.affiliation: Department of Biological Sciences, Dana and David Dornsife College of Arts, Letters and Sciences, University of Southern California, Los Angeles, CA 90089-652, USA.
authors.forename: Silvana
authors.initials: S
authors.lastname: Constantinescu
authors.forename: Lorraine P
authors.initials: LP
authors.lastname: Turcotte
mesh_terms: D042964:Acyl-CoA Dehydrogenase / Q000235:genetics / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D015536:Down-Regulation; D003576:Electron Transport Complex IV / Q000378:metabolism; D050556:Fatty Acid-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D000078723:Nuclear Receptor Interacting Protein 1; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000378:metabolism*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D000074121:Protein Kinase C-theta; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018955:CD36 Antigens; C008132:Cd36 protein, rat; C493321:Fabp1 protein, rat; D050556:Fatty Acid-Binding Proteins; D007328:Insulin; D007527:Isoenzymes; D009687:Nuclear Proteins; D000078723:Nuclear Receptor Interacting Protein 1; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; C501429:Ppargc1a protein, rat; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D014157:Transcription Factors; C414620:fibroblast growth factor 21; D019308:Palmitic Acid; D005346:Fibroblast Growth Factors; D042964:Acyl-CoA Dehydrogenase; D003576:Electron Transport Complex IV; D002334:Carnitine O-Palmitoyltransferase; D051057:Proto-Oncogene Proteins c-akt; C489591:Prkcq protein, rat; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta; D005947:Glucose