Congenital insensitivity to pain with anhidrosis (CIPA): effect of TRKA (NTRK1) missense mutations on autophosphorylation of the receptor tyrosine kinase for nerve growth factor

Human TRKA (NTRK1) encodes the receptor tyrosine kinases (RTKs) for nerve g rowth factor (NGF) and is the gene responsible for congenital insensitivity to pain with anhidrosis (CIPA), an autosomal recessive disorder characteri zed by a lack of pain sensation and anhidrosis, We reported 11 putative mis sense mutations in 31 CIPA families from various ethnic groups. Here we hav e introduced the corresponding mutations into the TRKA cDNA and examined NG F-stimulated autophosphorylation, We find that wildtype TRKA precursor prot eins in a neuronal and a non-neuronal cell line were differentially process ed and phosphorylated in an NGF-dependent and -independent manner, respecti vely. Two mutants (L93P and L213P) in the extracellular domain were aberran tly processed and showed diminished autophosphorylation in neuronal cells. Five mutants (G516R, G571R, R643W, R648C and G708S) in the tyrosine kinase domain were processed as wild-type TRKA but showed significantly diminished autophosphorylation in both neuronal and non-neuronal cells. In contrast, R85S and (H598Y; G607V), detected previously as double and triple mutations , are probably polymorphisms in a particular ethnic background. The other p utative mutant D668Y might be a rare polymorphism or might impair the funct ion of TRKA without compromising autophosphorylation, Mutated residues in t he tyrosine kinase domain are conserved in various RTKs and probably contri bute to critical function of these proteins. Thus, naturally occurring TRKA missense mutations with loss of function provide considerable insight into the structure-function relationship in the RTK family, Our data may aid in developing a drug which targets the clinically devastating 'complex region al pain syndrome'.