Assessing the range of kinase autoinhibition mechanisms in the insulin receptor family

Abstract

To investigate the range of autoinhibitory mechanisms used by TKDs (tyrosine kinase domains) from the insulin receptor family of RTKs (receptor tyrosine kinases), we determined crystal structures of TKDs from TrkA (tropomyosin receptor kinase A, a nerve growth factor receptor) and Ror2 (receptor tyrosine kinase-like orphan receptor 2, an unconventional Wnt receptor). TrkA autoinhibition closely resembles that seen for the insulin receptor, relying on projection of an activation loop tyrosine residue into the substrate-binding site and occlusion of the ATP-binding site by the activation loop. Ror2 employs similar mechanisms, but the unusual replacement of the phenylalanine residue in its Asp-Phe-Gly motif with leucine necessitates occlusion of the ATP-binding site by other means. The unusual Asp-Leu-Gly motif in Ror2 is displaced compared with other inactive kinases, allowing the activation loop to interact directly with the TKD's αC helix, in another mode of autoinhibition that is characteristic of the other extreme of this receptor family: ALK (anaplastic lymphoma kinase) and Met. These findings provide insight into the expected range of activating mutations in these TKDs in cancer. We also describe symmetrical dimers of the inactive TrkA TKD resembling those found in other RTKs, possibly reflecting an arrangement of kinase domains in a pre-formed TrkA dimer.

The Insulin Receptor: Both a Prototypical and Atypical Receptor Tyrosine Kinase

“…That is, because of the finite length of the activation loop, it is not sterically possible to bind simultaneously ATP in its binding cleft and Y1162 in the active site in cis. This cis-inhibitory/pseudosubstrate (Y1162) conformation first viewed in IRK has now been observed in several other RTKs, including IGF1R (Munshi et al 2002), TrkA-B (Artim et al 2012;Bertrand et al 2012), MuSK (Till et al 2002), and Ror2 (Artim et al 2012). The activation loops of all of these RTKs ) and D1132 and R1136 are shown by black dashed lines as is the salt bridge between conserved residues K1030 (b3) and E1047 (aC).…”

Obesity and thyroid cancer

“…The insulin signal transduction is dependent on two insulin receptors: IR-A (which has greater affinity for insulin-like growth factors 1 and 2 (IGF1 and IGF2), although it also recognizes insulin), and IR-B (insulin specific) (Artim et al 2012). Blood glucose homeostasis in healthy subjects requires a very delicate adjustment of insulin production by pancreatic b-cells and insulinmediated glucose uptake in tissues (Kern et al 1990, Dimitriadis et al 2008.…”

Insulin resistance and cancer: the role of insulin and IGFs

“…IGFs have characteristics of both hormones and tissue growth factors, and consequently, they can induce both local and systemic responses (Blundell et al 1978, Sajid et al 2011. Tissues that classically respond to IGFs preferentially express the IGF1R, and nonclassic target tissues including cancer cells express both the latter receptor and IR-A genes and may display hybrid receptors as well, which probably account in carcinogenesis and chemoresistance (Artim et al 2012, Pierre-Eugene et al 2012.…”

“…1). Other ILP receptors include the IGF1 receptor (IGF1R) that recognizes both IGF1 and IGF2; holoreceptors made up of combinations of half IGF1R and IR isoforms or other tyrosine kinases; and finally the IGF2R that recognizes only IGF2 (Rinderknecht & Humbel 1978) and attenuates IGF2 signaling by clearing the ligand from cell surface without signal transduction (Artim et al 2012). IGFs also bind to carrier proteins named 'IGF-binding proteins' (IGFBP).…”

“…Insulin signal transduction occurs through two insulin receptor (IR) isoforms resulting from transcriptional alternative splicing: the 'A' isoform (IR-A) that recognizes insulin and IGFs, with a greater affinity for IGF2 than IGF1, and the IR 'B' isoform (IR-B), which is insulin specific and mainly involved in glucose homeostasis (Zhang & Roth 1991, Artim et al 2012. In healthy individuals, blood glucose concentrations are maintained within narrow physiological range by a state of balance between insulin production by specialized pancreatic b-cells and insulin-mediated glucose uptake in target tissues, which is further determined by the translocation of glucose transporters, of which GLUT-4 is the most abundant, to the cell surface (Kern et al 1990).…”