S. Farah et al., A RHO-ASSOCIATED PROTEIN-KINASE, ROK-ALPHA, BINDS INSULIN-RECEPTOR SUBSTRATE-1 AND MODULATES INSULIN SIGNALING, The Journal of biological chemistry, 273(8), 1998, pp. 4740-4746
Insulin receptor substrate-1 (IRS-1) is physphorylated on multiple tyr
osine residues by ligand-activated insulin receptors. These tyrosine p
hosphorylation sites serve to dock several Src homology 2-containing s
ignaling proteins, In addition, IRS-1 contains a pleckstrin homology d
omain and a phosphotyrosine binding domain (PTB) implicated in protein
-protein and protein-lipid interactions, In a yeast two-hybrid screeni
ng using Xenopus IRS-1 (xIRS-1) pleekstrin homology-PTB domains as bai
t, we identified a Xenopus homolog of Rho-associated kinase alpha (xRO
K alpha) as a potential xIRS-1-binding protein, The original clone con
tained. the carboxyl terminus of xROK alpha (xROK-C) including the put
ative Rho binding domain but lacking the amino-terminal kinase domain.
Further analyses in yeast indicated that xROK-C bound to the putative
PTB domain of xIRS-1. Binding of xROK-C to xIRS-1 was confirmed in Xe
nopus oocytes after microinjection of mRNA corresponding to xROK-C. Fu
rthermore, microinjection of xROK-C mRNA inhibited insulin-induced mit
ogen-activated protein kinase activation with a concomitant inhibition
of oocyte maturation. In contrast, microinjection of xROK-C mRNA did
not inhibit mitogen-activated protein kinase activation or oocyte matu
ration induced by progesterone or by microinjection of viral. Ras (v-R
as) mRNA, These results suggest that xROK alpha may play a role in ins
ulin signaling via a direct interaction with xIRS-1.