G protein–coupled receptors (GPCRs) use diverse mechanisms to regulate the mitogen-activated protein kinases ERK1/2. β-Arrestins (βArr1/2) are ubiquitous inhibitors of G protein signaling, promoting GPCR desensitization and internalization and serving as scaffolds for ERK1/2 activation. Studies using CRISPR/Cas9 to delete βArr1/2 and G proteins have cast doubt on the role of β-arrestins in activating specific pools of ERK1/2. We compared the effects of siRNA-mediated knockdown of βArr1/2 and reconstitution with βArr1/2 in three different parental and CRISPR-derived βArr1/2 knockout HEK293 cell pairs to assess the effect of βArr1/2 deletion on ERK1/2 activation by four Gs-coupled GPCRs. In all parental lines with all receptors, ERK1/2 stimulation was reduced by siRNAs specific for β-Arr2 or β-Arr1/2. In contrast, variable effects were observed with CRISPR-derived cell lines both between different lines and with activation of different receptors. For β2-adrenergic receptors (β2ARs) and β1ARs, βArr1/2 deletion increased, decreased, or had no effect on isoproterenol-stimulated ERK1/2 activation in different CRISPR clones. ERK1/2 activation by the vasopressin V2 and follicle-stimulating hormone receptors was reduced in these cells but was enhanced by reconstitution with βArr1/2. Loss of desensitization and receptor internalization in CRISPR βArr1/2 knockout cells caused β2AR-mediated stimulation of ERK1/2 to become more dependent on G proteins, which was reversed by reintroducing βArr1/2. These data suggest that βArr1/2 function as a regulatory hub, determining the balance between mechanistically different pathways that result in activation of ERK1/2, and caution against extrapolating results obtained from βArr1/2- or G protein–deleted cells to GPCR behavior in native systems.

β-arrestin1 (or arrestin2) and β-arrestin2 (or arrestin3) are ubiquitously expressed cytosolic adaptor proteins that were originally discovered for their inhibitory role in G protein-coupled receptor (GPCR) signaling via heterotrimeric G proteins. However, further biochemical characterization revealed that β-arrestins do not just ‘block’ the activated GPCRs, but trigger endocytosis and kinase activation leading to specific signaling pathways that can be localized on endosomes. The signaling pathways initiated by β-arrestins were also found to be independent of G protein activation by GPCRs. The discovery of ligands that blocked G protein activation but promoted β-arrestin binding, or vice-versa, suggested the exciting possibility of selectively activating intracellular signaling pathways. Additionally, it is becoming increasingly evident that β-arrestin-dependent signaling is extremely diverse and provokes distinct cellular responses through different GPCRs even when the same effector kinase is involved. In this review, we summarize various signaling pathways mediated by β-arrestins and highlight the physiologic effects of β-arrestin-dependent signaling.

BACKGROUND: Previous research reports that 48% of veterans regularly experience and express concern over pain. Outpatient service use is higher for veterans with pain than for veterans without pain. Our study objective was to identify differences in outpatient utilization between men and women veterans with chronic pain. METHODS:We identified all men and women veterans at the Durham Veterans Affairs Medical Center in fiscal year (FY) 2002 between the ages of 21 and 60 that had two visits for the same pain location at least 6 weeks apart as determined by ICD-9 coding. Men and women were age-matched at a 2:1 ratio. We then compared the number of outpatient visits between genders in FY 2003. RESULTS:We identified 406 female and 812 male veterans. The mean number of clinic visits for women was 25.2 (SD 30.2) and for men 17.6 (SD 24.1). After adjusting for multiple pain sites, psychiatric diagnoses, age, and comorbidities, women veterans had a 27% higher rate of outpatient visits than men (incidence rate ratio [RR] 1.27, 95% confidence [CI] 1.15 to 1.41). Specifically, women had higher rates of visits to primary care (RR 1.36, 95% CI 1.24 to 1.50), physical therapy (RR 1.67, 95% CI 1.20 to 2.33), and other clinics (RR 1.28, 95% CI 1.14 to 1.44), and had a higher rate of visits to address pain (RR 1.15, 95% CI 1.02 to 1.30) than men.CONCLUSIONS: This is the first study to examine gender differences in chronic pain and utilization in the veteran population. Women veterans with chronic pain may need more resources to adequately manage chronic pain conditions as well as associated comorbidities and psychiatric disease.KEY WORDS: women veterans; chronic pain; health care utilization; mental health.