Conserved roles for receptor tyrosine kinase extracellular regions in regulating receptor and pathway activity

Abstract

Receptor Tyrosine Kinases (RTKs) comprise a diverse group of cell-surface receptors that mediate key signaling events during animal development and are frequently activated in cancer. We show here that deletion of the extracellular regions of 10 RTKs representing 7 RTK classes or their substitution with the dimeric immunoglobulin Fc region results in constitutive receptor phosphorylation but fails to result in phosphorylation of downstream signaling effectors Erk or Akt. Conversely, substitution of RTK extracellular regions with the extracellular region of the Epidermal Growth Factor Receptor (EGFR) results in increases in effector phosphorylation in response to EGF. These results indicate that the activation signal generated by the EGFR extracellular region is capable of activating at least 7 different RTK classes. Failure of phosphorylated Fc-RTK chimeras or RTKs with deleted extracellular regions to stimulate phosphorylation of downstream effectors indicates that either dimerization and receptor phosphorylation per se are insufficient to activate signaling or constitutive dimerization leads to pathway inhibition.

Molecular basis of VEGFR1 autoinhibition at the plasma membrane

“…3f, g ). As shown previously 76 , the VEGFR2 ΔECD construct was constitutively activated (Supplementary Fig. 3f ) and linearly phosphorylates Y1175 in the single-cell assay (Fig.…”

“…Perhaps the polarized electrostatic surface of the ECD (D4-D7) prevents receptor dimerization in the absence of ligand 24 , 65 , 67 , and mutation of C471 does not induce autophosphorylation of the receptor. Therefore, we speculate that removing ECD inhibition might spontaneously activate the VEGFR1, as observed in many RTKs 73 – 76 and is often linked to pathological manifestations 77 .…”

“…Unlike other RTKs 59 , 76 , removal of the ECD does not spontaneously activate the VEGFR1 (Fig. 4c ).…”

Systematic pharmacological analysis of agonistic and antagonistic fibroblast growth factor receptor 1 MAbs reveals a similar unique mode of action

“…For a FGFR agonist, designing molecules that target different epitopes and/or possess various geometries will be required to maximize pathway activation. For example, several reports observe diverse signaling profiles for RTK and cytokine receptors in the presence of mAbs or other engineered molecules capable of inducing ECD dimerization ( 50 , 51 , 52 , 53 ). In some cases, dimerization alone does not suffice to trigger a full agonistic response ( 52 ).…”

Molecular basis of VEGFR1 autoinhibition at the plasma membrane

“…In summary, our data indicate that VEGFR1 remains predominantly an inactive monomer in the basal state, and the ECD is likely the dominant negative regulator of VEGFR1 activation. Therefore, removing ECD inhibition might spontaneously activate the VEGFR1, as observed in many RTKs (71)(72)(73)(74) and is often linked to pathological manifestations (75).…”