Novel Mechanisms in the Regulation of G Protein-coupled Receptor Trafficking to the Plasma Membrane*

Abstract

␤ 2 -Adrenergic receptors (␤ 2 -AR) are low abundance, integral membrane proteins that mediate the effects of catecholamines at the cell surface. Whereas the processes governing desensitization of activated ␤ 2 -ARs and their subsequent removal from the cell surface have been characterized in considerable detail, little is known about the mechanisms controlling trafficking of neo-synthesized receptors to the cell surface. Since the discovery of the signal peptide, the targeting of the integral membrane proteins to plasma membrane has been thought to be determined by structural features of the amino acid sequence alone. Here we report that localization of translationally silenced ␤ 2 -AR mRNA to the peripheral cytoplasmic regions is critical for receptor localization to the plasma membrane. ␤ 2 -AR mRNA is recognized by the nucleocytoplasmic shuttling RNA-binding protein HuR, which silences translational initiation while chaperoning the mRNA-protein complex to the cell periphery. When HuR expression is down-regulated, ␤ 2 -AR mRNA translation is initiated prematurely in perinuclear polyribosomes, leading to overproduction of receptors but defective trafficking to the plasma membrane. Our results underscore the importance of the spatiotemporal relationship between ␤ 2 -AR mRNA localization, translation, and trafficking to the plasma membrane, and establish a novel mechanism whereby G protein-coupled receptor (GPCR) responsiveness is regulated by RNA-based signals.

Norepinephrine Modulates the Motility of Resting and Activated Microglia via Different Adrenergic Receptors

“…6, A and C). It is known that ␤ 2 receptor expression is controlled at multiple levels, including mRNA translation and protein trafficking (43,44). Thus, one possible explanation for the lack of functional effects of ␤ 2 agonists in activated microglia is the existence of post-translational mechanisms of expression regulation, but their elucidation is beyond the scope of this study.…”

C5aR Expression in a Novel GFP Reporter Gene Knockin Mouse: Implications for the Mechanism of Action of C5aR Signaling in T Cell Immunity

“…To our knowledge, this is only the second example of a 3′-UTR sequence critically regulating cell surface expression of a GPCR protein. Previously, it has been reported that disruption of the 3′-UTR of the β 2 -adrenergic receptor (β 2 -AR) mRNA interfered with its recognition by the RNA-binding protein HuR, and this in turn led to impaired cell surface expression of β 2 -AR (51, 52). Nuclear binding of HuR to the 3′UTR of β 2 -AR mRNA is thought to prevent translation of the β 2 -AR mRNA while allowing its transit to the cell periphery where unknown mechanisms release the translational block and the locally-translated β 2 -AR protein can efficiently traffic to the cell surface.…”

“…Nuclear binding of HuR to the 3′UTR of β 2 -AR mRNA is thought to prevent translation of the β 2 -AR mRNA while allowing its transit to the cell periphery where unknown mechanisms release the translational block and the locally-translated β 2 -AR protein can efficiently traffic to the cell surface. Disruption of the 3′ UTR of β 2 -AR mRNA or knockdown of HuR led to premature initiation of translation, resulting in overproduction of β 2 -AR protein in perinuclear polyribosomes but defective trafficking to the cell surface (51). This is reminiscent of the increase in C5aR protein in the GFP-KI +/+ cytosol seen by Western blot and its perinuclear localization on immunofluorescence microscopy in our study.…”

Relationships among variables and their equilibrium values: caveats of time‐less interpretation

“…A variable cannot quantum‐tunnel to another state in zero time, so Y will start moving towards its new equilibrium value. In the case of noradrenergic activity, this value will depend on time‐dependent shifts in mRNA transport and translation (Tholanikunnel et al , 2010), as well as protein internalization and recycling (Luttrell & Gesty‐Palmer, 2010; Vayttaden et al , 2010). But then one can argue that what X actually controls is not the equilibrium value of Y , but rather its direction of movement.…”