Although regulation of G protein-coupled receptor signaling by receptor kinases and arrestins is a well established biochemical process, the physiological significance of such regulation remains poorly understood. To better understand the in vivo consequences of arrestin function, we have examined the function of the sole arrestin in Caenorhabditis elegans (ARR-1). ARR-1 is primarily expressed in the nervous system, including the HSN neuron and various chemosensory neurons involved in detecting soluble and volatile odorants. arr-1 null mutants exhibit normal chemotaxis but have significant defects in olfactory adaptation and recovery to volatile odorants. In contrast, adaptation is enhanced in animals overexpressing ARR-1. Both the adaptation and recovery defects of arr-1 mutants are rescued by transgenic expression of wild-type ARR-1, whereas expression of a C-terminally truncated ARR-1 effectively rescues only the adaptation defect. A potential mechanistic basis for these findings is revealed by in vitro studies demonstrating that wild-type ARR-1 binds proteins of the endocytic machinery and promotes receptor endocytosis, whereas C-terminally truncated ARR-1 does not. These results demonstrate that ARR-1 functions to regulate chemosensory signaling, enabling organisms to adapt to a variety of environmental cues, and provide an in vivo link between arrestin, receptor endocytosis, and temporal recovery from adaptation.

Arrestins are multifunctional adaptor proteins best known for their role in regulating G protein-coupled receptor signaling. Arrestins also regulate other types of receptors, including the insulin-like growth factor receptor (IGF-1R), although the mechanism by which this occurs is not well understood. In Caenorhabditis elegans, the IGF-1R ortholog DAF-2 regulates dauer formation, stress resistance, metabolism, and lifespan through a conserved signaling cascade. To further elucidate the role of arrestin in IGF-1R signaling, we employed an in vivo approach to investigate the role of ARR-1, the sole arrestin ortholog in C. elegans, on longevity. Here, we report that ARR-1 functions to positively regulate DAF-2 signaling in C. elegans. arr-1 mutant animals exhibit increased longevity and enhanced nuclear localization of DAF-16, an indication of decreased DAF-2 signaling, whereas animals overexpressing ARR-1 have decreased longevity. Genetic and biochemical analysis reveal that ARR-1 functions to regulate DAF-2 signaling via direct interaction with MPZ-1, a multi-PDZ domain-containing protein, via a C-terminal PDZ binding domain in ARR-1. Interestingly, ARR-1 and MPZ-1 are found in a complex with the phosphatase and tensin homolog (PTEN) ortholog DAF-18, which normally serves as a suppressor of DAF-2 signaling, suggesting that these three proteins work together to regulate DAF-2 signaling. Our results suggest that the ARR-1-MPZ-1-DAF-18 complex functions to regulate DAF-2 signaling in vivo and provide insight into a novel mechanism by which arrestin is able to regulate IGF-1R signaling and longevity.The fundamental process of aging is regulated by a diverse number of genetic and environmental factors; however, one well established factor contributing to longevity is the insulin/ IGF-1 (IIS) 2 signaling pathway (1). Mutations that reduce IIS signaling have been demonstrated to extend lifespan in a wide range of organisms including Drosophila, Caenorhabditis elegans, mice, and humans (2, 3). For example, mutation of DAF-2, the sole insulin/IGF-1 receptor in C. elegans, doubles the normal lifespan of these animals (4, 5). The IIS signaling pathway in worms regulates longevity through a highly conserved set of components (6). Upon ligand binding, the DAF-2 receptor recruits and activates the phosphatidylinositol 3-kinase (PI3K) homolog AGE-1, resulting in the production of phosphatidylinositol 3,4,5-trisphosphate (7). This activates PDK-1, which in turn leads to activation of the serine/threonine protein kinases AKT-1, AKT-2, and SGK-1 (8 -10). These kinases phosphorylate the forkhead transcription factor DAF-16 and prevent it from entering the nucleus, an event that represses the ability of DAF-16 to regulate the transcription of genes involved in longevity (11-13). DAF-2 signaling is negatively regulated by the lipid phosphatase DAF-18, the ortholog of the human tumor suppressor PTEN (14 -16). DAF-18 catalyzes the dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate, thereby antagonizing AGE-1 and disrupting t...