Enhanced Phosphorylation-Independent Arrestins and Gene Therapy

Abstract

A variety of heritable and acquired disorders is associated with excessive signaling by mutant or overstimulated GPCRs. Since any conceivable treatment of diseases caused by gain-of-function mutations requires gene transfer, one possible approach is functional compensation. Several structurally distinct forms of enhanced arrestins that bind phosphorylated and even non-phosphorylated active GPCRs with much higher affinity than parental wild-type proteins have the ability to dampen the signaling by hyperactive GPCR, pushing the balance closer to normal. In vivo this approach was so far tested only in rod photoreceptors deficient in rhodopsin phosphorylation, where enhanced arrestin improved the morphology and light sensitivity of rods, prolonged their survival, and accelerated photoresponse recovery. Considering that rods harbor the fastest, as well as the most demanding and sensitive GPCR-driven signaling cascade, even partial success of functional compensation of defect in rhodopsin phosphorylation by enhanced arrestin demonstrates the feasibility of this strategy and its therapeutic potential.

Uncovering missing pieces: duplication and deletion history of arrestins in deuterostomes

“…As expected, known key functional motifs such as the phosphate sensing residues [6], the polar core residues [20], the residues involved in the three element interaction, and the sequence of the receptor-binding finger loop [32] are conserved in all ARR0 and vertebrate arrestins (Fig. 9).…”

“…Scanning the Pfam28.0 database using hmmscan confirmed that more than 95% of all annotated deuterostome arrestins possess an arrestin_C and an arrestin_N domain (see Additional file 1 : Appendix 6 for details about other domains). As expected, known key functional motifs such as the phosphate sensing residues [ 6 ], the polar core residues [ 20 ], the residues involved in the three element interaction, and the sequence of the receptor-binding finger loop [ 32 ] are conserved in all ARR0 and vertebrate arrestins (Fig. 9 ).…”

“…Beyond their “arresting”-function that gave the protein family its name, diverse other biological functions of arrestins have been described in the last two decades. Among them are the scaffolding, subcellular localization, and regulation of kinases, phosphatases and ubiquitin ligases, G protein independent signaling and GPCR trafficking (for review see [5, 6]). In recent years, considerable efforts were made towards the design of arrestins that modulate GPCR signaling and facilitate biased signaling [7].…”

The Diverse Roles of Arrestin Scaffolds in G Protein–Coupled Receptor Signaling

“…Several customized arrestins have been developed, and one has even been tested in gene therapy rescue experiments (Gurevich et al, 2014). As noted, arrestin activation is triggered by the interaction between phosphate residues on the GPCR C terminus and the arrestin phosphate sensor, and point mutations within the phosphate sensor produce an arrestin molecule that binds activated receptors independent of their phosphorylation state Benovic, 1995, 1997).…”

“…Conversely, a K 296 E point mutation in the opsin binding site of rhodopsin that leads to constitutive GRK1 phosphorylation and desensitization in vivo underlies one autosomal dominant form of retinitis pigmentosa (Li et al, 1995). The capacity to customize arrestin function suggests that a strategy of compensatory gene therapy could be a viable means of restoring lost arrestin function (Gurevich et al, 2014). As proof-of-concept, introducing a phosphorylation-independent visual arrestin mutant into GRK1 null rods, which would replace the normal two-step process of GRK phosphorylation followed by visual arrestin binding with a one-step process that bypasses the defect, was able to suppress rhodopsin signaling and enhance photoreceptor survival, functional performance, and photoresponse recovery (Song et al, 2009b).…”