Transmembrane domain IV of the Gallus gallus VT2 vasotocin receptor is essential for forming a heterodimer with the corticotrophin releasing hormone receptor.

Corticotropin releasing hormone receptor (CRHR) and the VT2 arginine vasotocin receptor (VT2R) are vital links in the hypothalamic-pituitary-adrenal axis that enable a biological response to stressful stimuli in avian species. CRHR and VT2R are both G-protein coupled receptors (GPCRs), and have been shown by us to form a heterodimer via fluorescent resonance energy transfer (FRET) analysis in the presence of their respective ligands, corticotrophin releasing hormone (CRH) and arginine vasotocin (AVT). The dimerization interface of the heterodimer is unknown, but computational analyses predict transmembrane domains (TMs) as likely sites of the interaction. We constructed chimerical VT2Rs, tagged at the C-terminal ends with either cyan fluorescent protein (CFP) or yellow fluorescent protein (YFP), by replacing the fourth transmembrane region (TM4) of VT2R with TM4 of the beta2-adrenergic receptor (beta2AR). The VT2R/beta2AR chimeras were expressed in HeLa cells and proper trafficking is confirmed by observing cell membrane localization using confocal microscopy. VT2R/beta2AR-YFP chimera functionality was confirmed with a Fura-2 acetoxymethyl ester (Fura-2AM) assay. FRET analysis was then performed on VT2/beta2AR-chimera/CRHR pairs, and the calculated distance was observed to be >10 nm apart, indicating that heterodimerization was partly disrupted by mutating TM4 of the VT2R. Therefore, TM4 may form one region of the possible dimerization interfaces between the VT2R and CRHR.

Enhanced beta2-adrenergic receptor (beta2AR) signaling by adeno-associated viral (AAV)-mediated gene transfer.

BACKGROUND: Beta2-adrenergic receptors (beta2AR) play important regulatory roles in a variety of cells and organ systems and are important therapeutic targets in the treatment of airway and cardiovascular disease. Prolonged use of beta-agonists results in tolerance secondary to receptor down-regulation resulting in reduced therapeutic efficiency. The purpose of this work is to evaluate the signaling capabilities of the beta2AR expressed by a recombinant adeno-associated viral (AAV) vector that also included an enhanced green fluorescent protein (EGFP) gene (AAV-beta2AR/EGFP). RESULTS: By epifluorescence microscopy, approximately 40% of infected HEK 293 cells demonstrated EGFP expression. beta2AR density measured with [3H]dihydroalprenolol ([3H]DHA) increased either 13- or 77-fold in infected cells compared to mock infected controls depending on the culture conditions used. The [3H]DHA binding was to a single receptor population with a dissociation constant of 0.42 nM, as would be expected for wild-type beta2AR. Agonist competition assays with [3H]DHA showed the following rank order of potency: isoproterenol>epinephrine> norepinephrine, consistent with beta2AR interaction. Isoproterenol-stimulated cyclic AMP levels were 5-fold higher in infected cells compared to controls (314 +/- 43 vs. 63.4 +/- 9.6 nmol/dish; n = 3). Receptor trafficking demonstrated surface expression of beta2AR with vehicle treatment and internalization following isoproterenol treatment. CONCLUSIONS: We conclude that HEK 293 cells infected with AAV-beta2AR/EGFP effectively express beta2AR and that increased expression of these receptors results in enhanced beta2AR signaling. This method of gene transfer may provide an important means to enhance function in in vivo systems.