Catalysis of serine and tyrosine autophosphorylation by the human insulin receptor.

Abstract

The protein kinase activity of human insulin receptors purified from Sf9 insect cells after infection with a recombinant baculovirus was evaluated. The following exper-imental observations led to the unexpected conclusion that this receptor protein catalyzes both serine and tyrosine autophos- The insulin receptor is one of a number of growth factor receptors with intrinsic tyrosine kinase activity that can be activated upon binding of appropriate peptide ligands (1). Binding of insulin to its receptor also causes rapid phosphorylation of the tyrosine residues of the insulin receptor (3 subunit itself (2-4), which in turn further activates the tyrosine kinase activity (5, 6). In intact cells, insulin causes receptor phosphorylation on tyrosine as well as serine and threonine residues (2). Protein kinase C or protein kinases activated by this enzyme can phosphorylate the serine and threonine residues of the insulin receptor in intact cells (7,8). Stimulation of serine phosphorylation of the insulin receptor by phorbol esters appears to correlate with inhibition of the insulin-stimulated tyrosine kinase activity ofthe receptor (8).Thus, phosphorylation ofthe serine and threonine residues of the insulin receptor may regulate insulin signaling by modulating receptor tyrosine kinase activity. Several laboratory groups have reported the detection of an insulin-stimulated and receptor-associated serine/ threonine kinase activity using the receptor itself as substrate, in partially purified (9-14) or affinity-purified (15) insulin receptor preparations.

The insulin receptor is essential for virus-induced tumorigenesis of Kaposi's sarcoma

“…To examine whether signaling by the IR is required for KSHV-mediated postconfluent growth, we used the IR-specific inhibitor HNMPA-(AM 3 ) [hydroxy-2-naphthalenyl-methyl phosphonic acid trisacetoxymethyl ester] (Saperstein et al, 1989;Baltensperger et al, 1992). Treatment with 25, 50 and 100 mM HNMPA-(AM 3 ) inhibited the development of spindle cell-containing foci ( Figure 4a) over a period of 14 days.…”

Phosphoryl exchange is involved in the mechanism of the insulin receptor kinase

“…However, the position of the exchangeable tyrosine phosphates in the primary sequence have still to be elucidated. Recently, the insulin receptor has been characterized as a protein kinase with dual specificity [20,21]. Therefore, a phosphoenzyme intermediate could play a role in catalyzing phosphoryl transfer during the autophosphorylation reaction to tyrosine as well as to serine.…”

In IGF-I receptor-deficient leiomyosarcoma cells autocrine IGF-II induces cell invasion and protection from apoptosis via the insulin receptor isoform A

“…Either insulin, or IGF-II (10 nM) in 0.5 ml of medium was added to the lower compartment. Parallel wells were incubated with 0.5 mM HNMPA (hydroxy-2-naphthalenylmethyl phosphonic acid triacetoxymethyl ester), a specific IR tyrosine kinase inhibitor (Baltensperger et al, 1992), with or without 10 nM insulin or IGF-II.…”