Inhibition of G Protein–Coupled Receptor Kinase 2 Promotes Unbiased Downregulation of IGF1 Receptor and Restrains Malignant Cell Growth

Abstract

The ability of a receptor to preferentially activate only a subset of available downstream signal cascades is termed biased signaling. Although comprehensively recognized for the G proteincoupled receptors (GPCR), this process is scarcely explored downstream of receptor tyrosine kinases (RTK), including the cancerrelevant insulin-like growth factor-1 receptor (IGF1R). Successful IGF1R targeting requires receptor downregulation, yet therapymediated removal from the cell surface activates cancer-protective b-arrestin-biased signaling (b-arr-BS). As these overlapping processes are initiated by the b-arr/IGF1R interaction and controlled by GPCR-kinases (GRK), we explored GRKs as potential anticancer therapeutic targets to disconnect IGF1R downregulation and b-arr-BS. Transgenic modulation demonstrated that GRK2 inhibition or GRK6 overexpression enhanced degradation of IGF1R, but both scenarios sustained IGF1-induced b-arr-BS. Pharmacologic inhibition of GRK2 by the clinically approved antidepressant, serotonin reuptake inhibitor paroxetine (PX), recapitulated the effects of GRK2 silencing with dose-and timedependent IGF1R downregulation without associated b-arr-BS.In vivo, PX treatment caused substantial downregulation of IGF1R, suppressing the growth of Ewing's sarcoma xenografts. Functional studies reveal that PX exploits the antagonism between b-arrestin isoforms; in low ligand conditions, PX favored b-arrestin1/Mdm2-mediated ubiquitination/degradation of IGF1R, a scenario usually exclusive to ligand abundancy, making PX more effective than antibody-mediated IGF1R downregulation. This study provides the rationale, molecular mechanism, and validation of a clinically feasible concept for "system bias" targeting of the IGF1R to uncouple downregulation from signaling. Demonstrating system bias as an effective anticancer approach, our study reveals a novel strategy for the rational design or repurposing of therapeutics to selectively cross-target the IGF1R or other RTK.Significance: This work provides insight into the molecular and biological roles of biased signaling downstream RTK and provides a novel "system bias" strategy to increase the efficacy of anti-IGF1Rtargeted therapy in cancer.

G Protein-Coupled Receptor Kinase 2 as Novel Therapeutic Target in Fibrotic Diseases

“…Subsequently, tyrosine kinases and various types of receptors are investigated as downstream targets of GRK2. Furthermore, it is also engaged in regulation of protein kinases, transcription factors and their regulatory proteins (Smad2/3, IκBα) ( 38 ). Increasing evidence suggests that GRK2, which exhibits the abnormal expression or activity, participates in the regulation of fibrosis-associated pathways, thus may as an essential role engages in the development of fibrotic diseases ( Figure 2 ).…”

Neddylation inhibition induces glutamine uptake and metabolism by targeting CRL3SPOP E3 ligase in cancer cells

“…6h, i ). We then used pharmacological and genetic approaches to inactivate or deplete GRK2 and found that paroxetine (PX), a GRK2 small molecule inhibitor 53 , or siRNA-based GRK2 knockdown rescued SPOP reduction induced by glutamine-deprivation (Fig. 5k, l and Supplementary Fig.…”

It Takes Two to Tango: IGF-I and TSH Receptors in Thyroid Eye Disease

“…GRK2/β-arrestin 2 pairing occurs at low ligand concentrations, has transient signaling effects maintaining receptor homeostasis, and prevents GRK6/β-arrestin 1 complex formation. GRK6/β-arrestin 1 represents a very powerful activator of IGF-IR-mediated β-arrestin 1 signaling and promotes cell proliferation and survival ( 70-72 , 74 ). This type of signaling is triggered by IGF-IR, not only under conditions of abundant natural ligand availability ( 66 ), but also during oncogenic IGF-IR hyperactivation (eg, by Mdm2).…”

“…This type of signaling is triggered by IGF-IR, not only under conditions of abundant natural ligand availability ( 66 ), but also during oncogenic IGF-IR hyperactivation (eg, by Mdm2). It can occur with noncanonical ligands, such as IGF-IR-targeting therapeutic antibodies and LL-37 ( 59 , 65 , 67 , 70-72 , 74 , 75 ). GRK6/β-arrestin 1 signaling downstream IGF-IR not only activates robust MAPK/AKT survival pathways but also inhibits tumor suppressor p53 signaling; however, this occurs at the cost of substantial IGF-IR internalization and degradation ( Fig.…”