Regulation of the Cellular Localization and Signaling Properties of the α_1B- and α_1D-Adrenoceptors by Agonists and Inverse Agonists

Abstract

The regulation of the cellular distribution and intracellular signaling properties of the alpha(1B)- and alpha(1D)- adrenoceptor (alpha(1)-AR) subtypes was examined in stably transfected Rat 1 fibroblasts. In unstimulated cells, alpha(1B)-AR expression was noted primarily on the cell surface. Treatment with phenylephrine induced internalization of the alpha(1B)-AR and promoted association with arrestin 2. The internalized alpha(1B)-AR colocalized with the transferrin receptor, an endosomal marker. In unstimulated fibroblasts, the alpha(1D)-AR was detected in a perinuclear orientation and was colocalized with arrestin 2 in a compartment also containing the transferrin receptor. After treatment with prazosin, which exhibits inverse agonist properties, the alpha(1D)-AR was redistributed from intracellular sites to the cellular periphery and was no longer associated with the transferrin receptor or arrestin 2. alpha(1D)-AR-expressing cells exhibited a high degree of basal activity for both inositol phosphate formation and extracellular signal regulated kinase (ERK), which was reduced by treatment with prazosin. In these cells, phenylephrine induced a dose-dependent increase in inositol phosphate formation but had no effect on ERK activity. In alpha(1B) -AR-expressing cells, phenylephrine stimulated both inositol phosphate formation and ERK activity. These data show that: 1) there are differences in the cellular localization of the alpha(1)-AR subtypes; 2) the alpha(1B)-AR exhibits expected G protein-coupled receptor activity regarding cellular localization, agonist-mediated internalization, and coupling to second messengers; and 3) the alpha(1D)-AR is constitutively active and, as a result, is localized to intracellular compartments involved in receptor recycling.

Differential Cardiovascular Regulatory Activities of the α1B- and α1D-Adrenoceptor Subtypes

“…In previous work, it has been shown that this receptor is expressed mainly in intracellular compartments (McCune et al, 2000;Chalothorn et al, 2002). We do not yet know the reason for this atypical localization pattern or if the regulatory activities of the ␣ 1D -AR are accomplished by these intracellular receptors.…”

Ligand Modulation of the Epstein-Barr Virus-induced Seven-transmembrane Receptor EBI2

“…3), and it will be interesting to see whether EBI2, like GPR109A, regulates distinct processes via these different effectors. Moreover, GSK682753A is able to suppress this activity with high potency and is thus an inverse agonist at both pathways, as seen in the ␣ 1D -adrenergic receptor, where the inverse agonist prazosin suppresses the activity of the G␣ q as well as the ERK pathways (36). On the other hand, the results are contradictory to the biased pharmacological profile of the ␤ 2 -adrenergic ligand ICI118551 that functions as an inverse agonist at the G␣ s pathway and as an agonist at the ERK pathway (37).…”

Alpha‐1D adrenoceptors are involved in reserpine‐induced supersensitivity of rat tail artery

“…Alpha-1D AR subtype is known to be constitutively active and undergo phosphorylation or sequestration, as compared with the alpha-1A and alpha-1B AR subtypes (Gisbert et al, 2000;McCune et al, 2000). From these data, together with the high affinity of the alpha-1D AR subtype for catecholamines, it is possible that most of the alpha-1D AR subtype is sequestered or downregulated under sympathetically innervated conditions and that this process may be reversed by sympathetic denervation, resulting in an upregulation of the alpha-1D AR.…”