Protein kinase activity of the insulin receptor

Abstract

The insulin receptor is an integral membrane glycoprotein (Mr approximately 300,000) composed of two alpha-subunits (Mr approximately 130,000) and two beta-subunits (Mr approximately 95,000) linked by disulphide bonds. This oligomeric structure divides the receptor into two functional domains such that alpha-subunits bind insulin and beta-subunits possess tyrosine kinase activity. The amino acid sequence deduced from cDNA of the single polypeptide chain precursor of human placental insulin receptor revealed that alpha- and beta-subunits consist of 735 and 620 residues, respectively. The alpha-subunit is hydrophilic, disulphide-bonded, glycosylated and probably extracellular. The beta-subunit consists of a short extracellular region which links the alpha-subunit through disulphide bridges, a hydrophobic transmembrane region and a longer cytoplasmic region which is structurally homologous with other tyrosine kinases like the src oncogene product and EGF receptor kinases. The cellular function of insulin receptors is dual: transmembrane signalling and endocytosis of hormone. The binding of insulin to its receptor on the cell membrane induces transfer of signal from extracellular to cytoplasmic receptor domains leading to activation of cell metabolism and growth. In addition, hormone-receptor complexes are internalized leading to intracellular proteolysis of insulin, whereas receptors are recycled to the membrane. These phenomena are kinetically well-characterized, but their molecular mechanisms remain obscure. Insulin receptor in different tissues and animal species are homologous in their structure and function, but show also significant differences regarding size of alpha-subunits, binding kinetics, insulin specificity and receptor-mediated degradation. We suggest that this heterogeneity of receptors may be linked to the diversity in insulin effects on metabolism and growth in various cell types. The purified insulin receptor phosphorylates its own beta-subunit and exogenous protein and peptide substrates on tyrosine residues, a reaction which is insulin-sensitive, Mn2+-dependent and specific for ATP. Tyrosine phosphorylation of the beta-subunit activates receptor kinase activity, and dephosphorylation with alkaline phosphatase deactivates the kinase. In intact cells or impure receptor preparations, a serine kinase is also activated by insulin. The cellular role of two kinase activities associated with the insulin receptor is not known, but we propose that the tyrosine- and serine-specific kinases mediate insulin actions on metabolism and growth either through dual-signalling or sequential pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of gene expression by insulin

“…Two classes of pancreatic-specific amylase genes, designated Amy-2. 1 and Amy-2.2, are present in the mouse genome. Pancreatic amylase mRNA is reduced to < 0% of normal in diabetic rats [82] and mice [83,84] but can be restored to normal by insulin administration.…”

“…Insulin initiates its action by binding to a specific cell-surface receptor that is ubiquitously distributed [1]. The insulin receptor possesses an intrinsic tyrosine kinase activity [1,2] which is stimulated by insulin binding [3].…”

“…The insulin receptor possesses an intrinsic tyrosine kinase activity [1,2] which is stimulated by insulin binding [3]. Evidence suggests a crucial role for this enzyme in mediating insulin's action [3], although physiologically important substrates, apart from the receptor itself, have yet to be identified [4].…”

Insulin receptor : tyrosine kinase activity and insulin action

“…Several insulin analogues stimulated receptor phosphorylation with potencies relative to porcine insulin and identical with their relative binding affinities and with potencies in other assay systems (Kasuga et aL, 1982a;Grigorescu et aL, 1983). Finally, polyclonal antisera to insulin receptor, which exert insulin-like effects in several cell types, were also able to stimulated the receptor tyrosine kinase (Gammeltoft & Van Obberghen, 1986;Gherzi et al, 1987). In conclusion, the insulin effect on receptor phosphorylation has the affinity and specificity of a typical insulin receptor mediated event.…”

Orientations et coordination hormonale du métabolisme protéique chez les ruminants

“…Wangsness, 1983 ; Metcalf et al, 1986), il n'y a encore aucun résultat concernant la tyrosine-kinase qui est portée par ce récepteur et dont l'activité est détermi-nante dans l'action de l'insuline (Gammeltoft et Van Obberghen, 1986 Weekes, 1986 ;Oddy et Lindsay, 1986 ; Laarveld, 1986 ;Grizard, Balage et Manin, 1986). Brièvement, l'hormone de croissance accroît la masse des protéines dans les tissus ; son action passe en partie par la sécrétion hépatique de facteurs de croissance (lGF 1 ) (Hart et Johnsson, 1986).…”