Identification of Glucose Transporter 4 Knockdown-dependent Transcriptional Activation Element on the Retinol Binding Protein 4 Gene Promoter and Requirement of the 20 S Proteasome Subunit for Transcriptional Activity

• Published in: The Journal of biological chemistry Vol. 285; no. 33; pp. 25545 - 25553
• Main Authors: Inoue, Erina, Yamashita, Aoi, Inoue, Hirofumi, Sekiguchi, Mariko, Shiratori, Asuka, Yamamoto, Yuji, Tadokoro, Tadahiro, Ishimi, Yoshiko, Yamauchi, Jun
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13.08.2010; American Society for Biochemistry and Molecular Biology
• Subjects: 3T3-L1 Cells; Animals; Blotting, Western; Chromatin Immunoprecipitation; Electrophoretic Mobility Shift Assay; Gene Regulation; Glucose Transport; Glucose Transporter Type 4 - genetics; Glucose Transporter Type 4 - physiology; Insulin Resistance; Lentivirus - genetics; Metabolism; Mice; Promoter Regions, Genetic - genetics; Proteasome Endopeptidase Complex - metabolism; Retinoid Binding Protein; Retinol-Binding Proteins, Plasma - genetics; RNA Interference - physiology; Transcription, Genetic - genetics; Transcription, Genetic - physiology; Transcription/Regulation; Transcriptional Activation - genetics; Transcriptional Activation - physiology; Transcription/Regulation; Glucose Transport; Retinoid Binding Protein; Insulin Resistance; Gene/Regulation
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.M109.079152

Retinol binding protein 4 (RBP4) is the transport protein that carries retinol in blood. RBP4 was described recently as a new adipokine that reduced insulin sensitivity. Mice lacking glucose transporter 4 (GLUT4) in adipocytes have enhanced Rbp4 gene expression; however, the molecular mechanism is unknown. We found a G4KA (GLUT4knockdown-dependent transcriptional activation) element located ∼1.3 kb upstream of the Rbp4 promoter. Mutations within the G4KA sequence significantly reduced expression of the Rbp4 promoter-reporter construct in G4KD-L1 (GLUT4knockdown 3T3-L1) adipocyte cells. In a yeast one-hybrid screen of a G4KD-L1 cell cDNA library, using the G4KA element as bait, we identified subunits of the 20 S proteasome, PSMB1 and PSMA4, as binding partners. In chromatin immunoprecipitation assays, both subunits bound to the G4KA element; however, only PSMB1 was tightly bound in the GLUT4 knockdown model. PSMB1 RNA interference, but not PSMA4, significantly inhibited Rbp4 transcription. Nuclear transportation of PSMB1 was increased in G4KD-L1 cells. These results provide evidence for an exclusive proteasome subunit-related mechanism for transcriptional activation of RBP4 within a GLUT4 knockdown model.