The beta2ARs (beta(2)-adrenergic receptors) undergo ligand-induced internalization into early endosomes, but then are rapidly and efficiently recycled back to the plasma membrane, restoring the numbers of functional cell-surface receptors. Gathering evidence suggests that, during prolonged exposure to agonist, some beta2ARs also utilize a slow recycling pathway through the perinuclear recycling endosomal compartment regulated by the small GTPase Rab11. In the present study, we demonstrate by co-immunoprecipitation studies that there is a beta2AR-Rab11 association in HEK-293 cells (human embryonic kidney cells). We show using purified His(6)-tagged Rab11 protein and beta2AR intracellular domains fused to GST (glutathione transferase) that Rab11 interacts directly with the C-terminal tail of beta2AR, but not with the other intracellular domains of the receptor. Pull-down and immunoprecipitation assays revealed that the beta2AR interacts preferentially with the GDP-bound form of Rab11. Arg(333) and Lys(348) in the C-terminal tail of the beta2AR were identified as crucial determinants for Rab11 binding. A beta2AR construct with these two residues mutated to alanine, beta2AR RK/AA (R333A/K348A), was generated. Analysis of cell-surface receptors by ELISA revealed that the recycling of beta2AR RK/AA was drastically reduced when compared with wild-type beta2AR after agonist washout, following prolonged receptor stimulation. Confocal microscopy demonstrated that the beta2AR RK/AA mutant failed to co-localize with Rab11 and recycle to the plasma membrane, in contrast with the wild-type receptor. To our knowledge, the present study is the first report of a direct interaction between the beta2AR and a Rab GTPase, which is required for the accurate intracellular trafficking of the receptor.

[18F]FTHA is sensitive to insulin-induced modifications of free fatty acid oxidative metabolism in rats but is insensitive to changes in nonoxidative fatty acid metabolism.

Background Data on the association of ustekinumab (UST) drug concentrations and clinical outcomes are conflicting. We assessed serum UST drug and anti-UST antibody concentrations using three commercially available assays. Methods Sixty-one blood samples were analyzed for serum UST drug and anti-UST antibody concentrations using three assays: one homogeneous mobility shift assay (HMSA, Prometheus, Assay A), and two enzyme-linked immunosorbent assays (ELISA; Progenika, Dynacare, Assay B and Theradiag, Assay C). Results The median (IQR) serum UST concentrations for the three assays were: Assay A 7.50 (5.35 to 12.88) µg/mL, Assay B 4.02 (2.46 to 6.95) µg/mL and Assay C 4.35 (2.62 to 7.50) µg/mL. A Kruskal–Wallis test confirmed a statistically significant difference between the different assays, X2(2) = 30.606, p < 0.001. Linear regression showed near twofold increased difference in the absolute drug concentrations between the HMSA and either ELISA. Linear quantitative correlation was observed for all three assays (r = 0.836 for A versus B, r = 0.792 for A versus C, r = 0.936 for B versus C; p < 0.01). The intraclass correlation coefficient (ICC) between assay A and B was 0.649 (95% confidence interval [CI] −0.208 to 0.874); assay A and C was 0.671 (95% CI −0.165 to 0.878); and assay B and C was 0.958 (95% CI 0.928 to 0.975); p < 0.001. No anti-UST antibodies were detected. Conclusion A good correlation was observed for serum UST drug concentrations and a good agreement was observed between the ELISA tests. However, agreement was poor between the HMSA and each ELISA tests. Clinical recommendations regarding drug concentrations should be based on assay type used.

Background:Interacting partners and regulation of Rab geranylgeranyltransferase are poorly characterized. Mechanisms of GPCR maturation and anterograde trafficking are not fully understood. Results: RGGTA interacts with a dileucine motif in the ␤ 2 AR to regulate ␤ 2 AR maturation/anterograde trafficking and ␤ 2 ARmediated Rab geranylgeranylation. Conclusion: RGGTA and the ␤ 2 AR interact functionally. Significance: This is the first demonstration of a functional interaction between RGGTA and a transmembrane receptor. Previous reports by us and others demonstrated that G protein-coupled receptors interact functionally with Rab GTPases.Here, we show that the ␤ 2 -adrenergic receptor (␤ 2 AR) interacts with the Rab geranylgeranyltransferase ␣-subunit (RGGTA). Confocal microscopy showed that ␤ 2 AR co-localizes with RGGTA in intracellular compartments and at the plasma membrane. Site-directed mutagenesis revealed that RGGTA binds to the L 339 L 340 motif in the ␤ 2 AR C terminus known to be involved in the transport of the receptor from the endoplasmic reticulum to the cell surface. Modulation of the cellular levels of RGGTA protein by overexpression or siRNA-mediated knockdown of the endogenous protein demonstrated that RGGTA has a positive role in the maturation and anterograde trafficking of the ␤ 2 AR, which requires the interaction of RGGTA with the ␤ 2 AR L 339 L 340 motif. Furthermore, the ␤ 2 AR modulates the geranylgeranylation of Rab6a, Rab8a, and Rab11a, but not of other Rab proteins tested in this study. Regulation of Rab geranylgeranylation by the ␤ 2 AR was dependent on the RGGTA-interacting L 339 L 340 motif. Interestingly, a RGGTA-Y107F mutant was unable to regulate Rab geranylgeranylation but still promoted ␤ 2 AR maturation, suggesting that RGGTA may have functions independent of Rab geranylgeranylation. We demonstrate for the first time an interaction between a transmembrane receptor and RGGTA which regulates the maturation and anterograde transport of the receptor, as well as geranylgeranylation of Rab GTPases.