The deleted in brachydactyly B domain of ROR2 is required for receptor activation by recruitment of Src

The transmembrane receptor 'ROR2' resembles members of the receptor tyrosine kinase family of signalling receptors in sequence but its' signal transduction mechanisms remain enigmatic. This problem has particular importance because mutations in ROR2 are associated with two human skeletal dysmorphology syndromes, recessive Robinow Syndrome (RS) and dominant acting Brachydactyly type B (BDB). Here we show, using a constitutive dimerisation approach, that ROR2 exhibits dimerisation-induced tyrosine kinase activity and the ROR2 C-terminal domain, which is deleted in BDB, is required for recruitment and activation of the non-receptor tyrosine kinase Src. Native ROR2 phosphorylation is induced by the ligand Wnt5a and is blocked by pharmacological inhibition of Src kinase activity. Eight sites of Src-mediated ROR2 phosphorylation have been identified by mass spectrometry. Activation via tyrosine phosphorylation of ROR2 receptor leads to its internalisation into Rab5 positive endosomes. These findings show that BDB mutant receptors are defective in kinase activation as a result of failure to recruit Src

Regulation of FGF Receptor signalling by SPROUTY and SPRED

Signalling from Fibroblast Growth Factor Receptors (FGFRs) is under tight control by a wide variety of extrinsic and intrinsic regulatory mechanisms, many of which remain poorly defined. Sproutys and their related Spred proteins constitute two such families of signalling regulators with multiple developmental roles as well as potential tumour suppressive functions. However, the molecular mechanisms of these proteins have remained unclear and subject to many unresolved controversies. Using a mass spectrometry approach, several novel interacting partners of Sprouty with roles in endocytosis are identified here, suggestive of a potential endocytic-related function for Sproutys. In addition, comprehensive analysis of Sprouty phosphorylations and their dynamics by mass spectrometry reveal previously unknown but potentially crucial sites that might regulate Sproutys function. Next, a novel late-endosomal protein that directly binds to Spred is identified using a different approach. Neighbor of BRCA1-1 (NBR1) is shown to be necessary for attenuation of FGF signaling by Spred, and this is demonstrated to be via modulation of the trafficking itinerary of FGFRs. Finally, NBR1 is established as a novel regulator of RTK trafficking and signalling, and the interplay between its various regions for protein localisation and function is revealed