Endogenously expressed TSH receptors (TSHRs) on orbital fibroblasts of patients with Graves ophthalmopathy (GO) use crosstalk with IGF1 receptors (IGF1R) to synergistically stimulate secretion of hyaluronan (HA), a major component of GO pathology. We previously showed crosstalk occurred upstream of mitogen-activated protein kinase (ERK) phosphorylation. Because other G protein-coupled receptors engage arrestin-β-1 (ARRB1) and ERK, we tested whether ARRB1 was a necessary component of TSHR/IGF1R crosstalk. HA secretion was stimulated by the TSHR-stimulating monoclonal antibodies M22 and KSAb1, or immunoglobulins from patients with GO (GO-Igs). Treatment with M22, as previously shown, resulted in biphasic dose-response stimulation of HA secretion. The high-potency phase was IGF1R dependent, and the low-potency phase was partly IGF1R independent. KSAb1 produced a monophasic dose-response stimulation of HA secretion, whose potency was lowered >20-fold after IGF1R knockdown. ARRB1 knockdown abolished M22's high-potency phase and lowered KSAb1's potency and efficacy. ARRB1 knockdown inhibited GO-Ig stimulation of HA secretion and of ERK phosphorylation. Last, ARRB1 was shown to be necessary for TSHR/IGF1R proximity. In contrast, ARRB2 knockdowns did not show these effects. Thus, TSHR must neighbor IGF1R for crosstalk in GO fibroblasts to occur, and this depends on ARRB1 acting as a scaffold. Similar scaffolding of TSHR and IGF1R by ARRB1 was found in human osteoblast-like cells and human thyrocytes. These findings support a model of TSHR/IGF1R crosstalk that may be a general mechanism for G-protein-coupled receptor/receptor tyrosine kinase crosstalk dependent on ARRB1.
Published by Oxford University Press on behalf of the Endocrine Society 2019.