Two different protein kinase activities are associated with the insulin receptor

Abstract

In intact rat hepatocytes insulin stimulates the phosphorylation of the beta-subunit of its receptor exclusively on serine residues, which are also phosphorylated in the absence of insulin. In contrast, in partially purified insulin receptors derived from these same cells and in highly purified insulin receptors obtained by immunoprecipitation with anti-receptor antibodies, the receptor beta-subunit is phosphorylated solely on tyrosine residues. For both cell-free systems, insulin's stimulatory action on receptor phosphorylation leads to an increase in phosphotyrosine. When partially purified receptors were used to phosphorylate two exogenous substrates, casein and histone, insulin was found to stimulate the phosphorylation of both tyrosine and serine. However, the basal and insulin-stimulated kinase activity of immunoprecipitated receptors was only tyrosine-specific. From these observations we propose that the insulin-receptor complex consists of two different insulin-stimulatable kinase activities: (1) a tyrosine-specific kinase, which is a constituent of the insulin-receptor structure and whose activation is likely to be the first post-binding event in insulin action; and (2) a serine-specific kinase, which is closely associated with the receptor in the cell membrane.

Protein kinase activity of the insulin receptor

“…These purified receptor preparations exhibited insulinstimulated protein kinase activity which catalysed phosphorylation of both the f-subunit and exogenous substrates like casein, histones and synthetic tyrosinecontaining peptides. In contrast with the partially purified receptor, the phosphorylation occurred exclusively on tyrosine residues in highly purified receptors under basal conditions, and the insulin stimulatory action was accounted for by a several-fold increase in phosphotyrosine (Avruch et al, 1982;Petruzzelli et al, 1982Petruzzelli et al, , 1984Gazzano et al, 1983;Kasuga et al, 1983a;Roth & Cassell, 1983;. Thus, the tyrosine kinase is a constituent of the insulin receptor, whereas the serine kinase is non-covalently associated with the receptor (Fig.…”

“…in labelling of phosphoserine (Kasuga et al, 1982c;Gazzano et al, 1983;Zick et al, 1983a;Pang et al, 1985;White et al, 1985). The insulin receptor exhibits insulin-dependent tyrosine-kinase activity.…”

“…In the proteins, phosphoaminoacid analysis showed only phosphorylation on tyrosine residues. Among the synthetic peptides, even the dipeptide Tyr-Arg was a substrate, although with very high Km (Stadtmauer & Rosen, 1983 Kasuga et al (1982a-c), Van Obberghen et al (1983, Haring et al (1982Haring et al ( , 1984b, Velicelebi & Aiyer (1984), Burant et al (1984), Petruzzelli et al (1982, Roth & Cassell (1983), (1982b, 1983a,b), Van Obberghen et al (1983), Roth et al (1982, Petruzzelli et al (1984 Gazzano et al (1983, Kasuga et al (1983b), Pike et al (1984), Stadtmauer & Rosen (1983), Sadoul et al (1985), …”

“…Furthermore, in a cellfree system of partially purified insulin receptor, some laboratories have reported that insulin stimulates phosphorylation of both tyrosine and serine residues on its receptor (Kasuga et al, 1982c;Zick et al, 1983a;Yu & Czech, 1984) as well as on exogenous substrates . The serine kinase is non-covalently associated with the receptor, and is removed during further purification, because the highly purified receptor displayed only tyrosine kinase activity (Kasuga et al, 1982cGazzano et al, 1983;Petruzzelli et al, 1984;Nemenoff et al, 1984). The relationship between the two protein kinase activities associated with the (Fig.…”

Insulin receptor : tyrosine kinase activity and insulin action

“…Despite this progress, the molecular mechanism of in- (Denton, 1986). In addition, a promising discovery was made by the demonstration that the insulin receptor is an insulinsensitive protein kinase (Kasuga et aL, 1982a;Van Obberghen & Kowalski, 1982;Petruzzelli et al, 1982 (Kasuga et al, 1982;Gazzano et al, 1983;White et al, 1985b;Ballotti et aL, 1987 Shia & Pilch, 1983;Petruzzelli et al, 1982;1984 Shia & Pilch, 1983;Roth & Cassell, 1983). The simultaneous presence of phosphorylation sites and an ATP binding site on the receptor p subunit indicates that the insulin receptor acts as its own tyrosine kinase.…”