Compartmentalization of SHC, GRB2 and mSOS, and hyperphosphorylation of Raf-1 by EGF but not insulin in liver parenchyma.
Rat liver parenchyma harbors equal numbers of epidermal growth factor (EGF) and insulin receptors. Following administration of a saturating dose of EGF (10 micrograms/100 g body weight), there was a rapid (t1/2 approximately 1.1 min) internalization of receptor coincident with its tyrosine phosphorylation at residue 1173 and receptor recruitment of the adaptor protein SHC, its tyrosine phosphorylation and its association with GRB2 and the Ras guanine nucleotide exchange factor, mSOS, largely in endosomes. This led to a cytosolic pool of a complex of tyrosine-phosphorylated SHC, GRB2 and mSOS. It was demonstrated that these constituents were linked to Ras activation by the characteristic decrease in Raf-1 mobility on SDS-PAGE, which was maintained for 60 min after a single bolus of administered EGF. While insulin administration (15 micrograms/100 g body weight) led to insulin receptor beta-subunit tyrosine phosphorylation and internalization, there was little detectable tyrosine phosphorylation of SHC, recruitment of GRB2, association of a complex with mSOS or any detectable change in the mobility of Raf-1. Therefore, in normal physiological target cells in vivo, distinct signaling pathways are realized after EGF or insulin receptor activation, with regulation of this specificity most probably occurring at the locus of the endosome.
Di Guglielmo
G M
GM
Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
Baass
P C
PC
Ou
W J
WJ
Posner
B I
BI
Bergeron
J J
JJ
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002451:Cell Compartmentation; D004705:Endocytosis; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000502:physiology*; D008297:Male; D008566:Membranes / Q000378:metabolism; D008958:Models, Molecular; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D020663:ras Guanine Nucleotide Exchange Factors
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495950:Grb2 protein, rat; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin; D011506:Proteins; D011518:Proto-Oncogene Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D020663:ras Guanine Nucleotide Exchange Factors; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011972:Receptor, Insulin; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf