Regulation of Receptor Fate by Ubiquitination of Activated β ₂ -Adrenergic Receptor and β-Arrestin

Abstract

Although trafficking and degradation of several membrane proteins are regulated by ubiquitination catalyzed by E3 ubiquitin ligases, there has been little evidence connecting ubiquitination with regulation of mammalian G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) function. Agonist stimulation of endogenous or transfected beta2-adrenergic receptors (beta2ARs) led to rapid ubiquitination of both the receptors and the receptor regulatory protein, beta-arrestin. Moreover, proteasome inhibitors reduced receptor internalization and degradation, thus implicating a role for the ubiquitination machinery in the trafficking of the beta2AR. Receptor ubiquitination required beta-arrestin, which bound to the E3 ubiquitin ligase Mdm2. Abrogation of beta-arrestin ubiquitination, either by expression in Mdm2-null cells or by dominant-negative forms of Mdm2 lacking E3 ligase activity, inhibited receptor internalization with marginal effects on receptor degradation. However, a beta2AR mutant lacking lysine residues, which was not ubiquitinated, was internalized normally but was degraded ineffectively. These findings delineate an adapter role of beta-arrestin in mediating the ubiquitination of the beta2AR and indicate that ubiquitination of the receptor and of beta-arrestin have distinct and obligatory roles in the trafficking and degradation of this prototypic GPCR.

Inhibitors of phosphoinositide 3-kinase cause defects in the postendocytic sorting of β2-adrenergic receptors

“…Proteins with these domains play a role in sorting various ubiquitinated receptors from late endosomes to lysosomes. Agonist induced β 2 AR degradation could occur by this mechanism, because these receptors are ubiquitinated after agonist activation, and removal of all potential sites of β 2 AR ubiquitination reduces receptor downregulation [34]. Our finding that LY294002 inhibits β 2 AR degradation supports this possibility.…”

Picropodophyllin induces downregulation of the insulin-like growth factor 1 receptor: potential mechanistic involvement of Mdm2 and β-arrestin1

“…Transfections with DN-MDM (MDM2 1-400 ) (kindly obtained from Dr Robert J Lefkowitz) were performed as described elsewhere (Shenoy et al, 2001). …”

Role of insulin-like growth factor 1 receptor signalling in cancer

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