Insulin-Like Growth Factor-I Induces α1B-Adrenergic Receptor Phosphorylation through Gβγ and Epidermal Growth Factor Receptor Transactivation

Abstract

IGF-I induces alpha(1B)-adrenoceptor (alpha(1B)-AR) phosphorylation. The effect of IGF-I was rapid and transient, reaching near-maximal values at 10 min and decreasing after 30 min; it was observed at low IGF-I concentrations (EC(50) approximately 10 ng/ml) and was associated to receptor desensitization as evidenced by a decreased alpha(1B)-adrenergic effect on intracellular calcium and production of inositol phosphates. The effect of IGF-I was markedly decreased in cells treated with pertussis toxin suggesting involvement of pertussis toxin-sensitive G proteins. Transfection of the carboxyl terminus of the beta-adrenergic receptor kinase or the Deltap85 mutant of phosphoinositide 3-kinase (PI3K) markedly decreased the alpha(1B)-AR phosphorylation induced by IGF-I without decreasing the receptor phosphorylation induced by noradrenaline. Inhibitors of PI3K and protein kinase C blocked IGF-I-induced alpha(1B)-AR phosphorylation. In addition, it was observed that AG1478, an inhibitor of the epidermal growth factor (EGF) receptor kinase, and BB-94, a metalloproteinase inhibitor, also diminished IGF-I-induced adrenoceptor phosphorylation. The data clearly show that IGF-I triggers a complex signaling pathway, which leads to the phosphorylation and desensitization of a serpentine G protein-coupled receptor, suggesting the following hypothetical model: 1) stimulation of IGF-I receptors activate pertussis toxin-sensitive G proteins; 2) the growth factor action activates metalloproteinases, which catalyze heparin binding-EGF shedding, and transactivation of EGF receptors, and 3) dissociated Gbetagamma subunits and phosphotyrosine residues seem to trigger PI3K activity, which leads to activation of protein kinase C, resulting in alpha(1B)-AR phosphorylation and desensitization.

Insulin Modulates Protease-Activated Receptor 2 Signaling: Implications for the Innate Immune Response

“…More recently, it has been demonstrated that for certain G protein-coupled receptor-mediated increases in intracellular calcium concentration (vasopressin, bradykinin, angiotensin II, neurotensin, and bombesin) insulin can enhance rather than inhibit signaling via a mammalian target of rapamycin-dependent pathway (32,33). However, our data demonstrating an insulin-mediated decrease rather than an increase in PAR 2 -triggered calcium signaling are in keeping with the ability of insulin-like growth factor I and insulin to induce phosphorylation and desensitization of the G protein-coupled a 1B and a 1D adrenergic receptors (34,35). In those studies, as in ours, inhibitors of PI3K and PKC blocked receptor phosphorylation (on serines in the a 1D adrenoceptor) caused by the growth factors.…”

Sphingosine 1-phosphate-mediated α1B-adrenoceptor desensitization and phosphorylation. Direct and paracrine/autocrine actions

“…The procedure employed to study α 1B -AR phosphorylation, has been previously described in detail [15, 16, 18]. In brief, cells were maintained overnight in phosphate-free Dulbecco’s modified Eagle’s medium without serum.…”

“…These proteases cause shedding of HB-EGF from the plasma membrane and subsequent activation of EGF receptor intrinsic tyrosine kinase, resulting in the triggering of intracellular signaling [20, 21]. Surprisingly, this process is much more general than we could have anticipated and is involved in both homologous and heterologous desensitization and phosphorylation of α 1B -ARs [9, 10, 15, 16]. …”

“…In our study on IGF-I-induced α 1B -AR desensitization and phosphorylation we observed that EGF receptor transactivation as well as pertussis toxin-sensitive G proteins were involved [16]; in fact, the action of other hormones/growth factors that act through receptor tyrosine kinase receptors also share these characteristics [16]. These data suggest the possibility that receptor tyrosine kinases could couple to pertussis toxin-sensitive G proteins and in this way activate metalloproteinases and the EGF receptor transactivation process [16].…”

“…These data suggest the possibility that receptor tyrosine kinases could couple to pertussis toxin-sensitive G proteins and in this way activate metalloproteinases and the EGF receptor transactivation process [16]. G protein involvement in receptor tyrosine kinase action has been frequently observed, but the mechanisms have been elusive [22].…”