Untitled

Abstract

The insulin-like growth factor 1 (IGF1) receptor is closely related to the insulin receptor. However, the unique biological functions of IGF1 receptor make it a target for therapeutic intervention in human cancer. Using its isolated tyrosine kinase domain, we show that the IGF1 receptor is regulated by intermolecular autophosphorylation at three sites within the kinase activation loop. Steady-state kinetic analyses of the isolated phosphorylated forms of the IGF1 receptor kinase (IGF1RK) reveal that each autophosphorylation event increases enzyme turnover number and decreases Km for ATP and peptide. We have determined the 2.1 A-resolution crystal structure of the tris-phosphorylated form of IGF1RK in complex with an ATP analog and a specific peptide substrate. The structure of IGF1RK reveals how the enzyme recognizes peptides containing hydrophobic residues at the P+1 and P+3 positions and how autophosphorylation stabilizes the activation loop in a conformation that facilitates catalysis. Although the nucleotide binding cleft is conserved between IGF1RK and the insulin receptor kinase, sequence differences in the nearby interlobe linker could potentially be exploited for anticancer drug design.

Crystal Structures of the Phosphorylated and Unphosphorylated Kinase Domains of the Cdc42-associated Tyrosine Kinase ACK1

“…This increase in activity is low compared with kinases that are autoinhibited by their unphosphorylated activation loop. For example, the insulin-like growth factor-1 receptor kinase exhibits a Ͼ120-fold increase in catalytic efficiency when fully phosphorylated (47). The current structural results suggest that the activation loop of ACK1 is not autoinhibitory, that phosphorylation is not necessary for reorganization of the catalytic machinery, and that the binding of ATP and substrate should be largely unaffected by the phosphorylation state.…”

The insulin-like growth factor-1 receptor inhibitor PPP produces only very limited resistance in tumor cells exposed to long-term selection

“…However, in the approach of targeting the IGF-1R they may face the problem to crossreact with the highly homologous insulin receptor. In order to solve this problem crystallographic studies of the tyrosine kinase domain of the IGF-IR have been performed (Favelyukis et al, 2001;Pautsch et al, 2001). Such studies may reveal subtle structural difference between the kinases of the two receptors and this way enable the design and production of small molecules acting as specific antagonists for the IGF-1R and therewith inhibiting its antiapoptotic effects (De Meyts and Whittaker, 2002).…”

Growth factor receptors as therapeutic targets: strategies to inhibit the insulin-like growth factor I receptor

“…Recent advances in the characterization of the threedimensional structures of IGF-IR and IR greatly facilitated the design of specific IGF-IR inhibitors (De Meyts and Whittaker, 2002). Most importantly, crystallographic studies revealed conformational differences in the phosphorylated forms of IGF-IR and IR kinases, the feature allowing the development of selective therapeutics (Favelyukis et al, 2001;Pautsch et al, 2001). Several new compounds with enhanced specificity towards IGF-IR and low crossreactivity with IR entered into preclinical studies.…”