β-Arrestin 1 down-regulation after insulin treatment is associated with supersensitization of β2 adrenergic receptor Gαs signaling in 3T3-L1 adipocytes

β-Arrestin 1 is required for internalization and mitogen-activated protein (MAP) kinase activation by the β2 adrenergic receptor (β2AR). Our previous studies have shown that chronic insulin treatment down-regulates cellular β-arrestin 1 levels, leading to a marked impairment in G protein-coupled receptor and insulin-like growth factor-1 receptor-mediated MAP kinase and mitogenic signaling. In this study, we show that chronic insulin-treated, β-arrestin 1depleted 3T3-L1 adipocytes display (i) increased isoproterenol-induced cAMP generation (53 ± 38% at 1.5 min, 25 ± 19% at 5 min, 63 ± 14% at 30 min, and 59 ± 2% at 60 min), a Gα(s)-associated pathway; (ii) impaired isoproterenol-induced β2AR internalization (reduced by 98 ± 4%), which is required for MAP kinase signaling, a Gα(i)-associated pathway; and (iii) increased β-arrestin 1 phosphorylation at Ser-412. Taken together, these findings represent a hitherto unknown mechanism (degradation and phosphorylation of β-arrestin, whereby the activation of the insulin receptor, belonging to the family of receptor tyrosine kinases, causes supersensitization of Gα(s)-associated signaling and inhibition of Gα(i)-associated signaling by the β2AR, a prototypical G protein-coupled receptor.