S. Dalle et al., Insulin and insulin-like growth factor I receptors utilize different G protein signaling components, J BIOL CHEM, 276(19), 2001, pp. 15688-15695
We examined the role of heterotrimeric G protein signaling components in in
sulin and insulin-like growth factor I (IGF-I) action. In HIRcB cells and i
n 3T3L1 adipocytes, treatment with the G alpha (i) inhibitor (pertussis tox
in) or microinjection of the G beta gamma inhibitor (glutathione S-transfer
ase-beta ARK) inhibited IGF-I and lysophosphatidic acid-stimulated mitogene
sis but had no effect on epidermal growth factor (EGF) or insulin action. I
n basal state, G alpha (i) and G beta were associated with the IGF-I recept
or (IGF-IR), and after ligand stimulation the association of IGF-IR with G
alpha (1) increased concomitantly with a decrease in G beta association. No
association of Ga-i was found with either the insulin or EGF receptor. Mic
roinjection of anti-beta -arrestin-1 antibody specifically inhibited IGF-I
mitogenic action but had no effect on EGF or insulin action. beta -Arrestin
-1 was associated with the receptors for IGF-I, insulin, and EGF in a ligan
d-dependent manner. We demonstrated that G alpha (i), beta gamma subunits,
and beta -arrestin-1 all play a critical role in IGF-I mitogenic signaling.
In contrast, neither metabolic, such as GLUT4 translocation, nor mitogenic
signaling by insulin is dependent on these protein components. These resul
ts suggest that insulin receptors and IGF-IRs can function as G protein-cou
pled receptors and engage different G protein partners for downstream signa
ling.