W-N MUTATION OF C-KIT RECEPTOR AFFECTS ITS POSTTRANSLATIONAL PROCESSING AND EXTRACELLULAR EXPRESSION

The W locus of mice encodes the c-kit receptor tyrosine kinase. Recent ly, we characterized a novel mutant allele, W-n, and demonstrated that the c-kit protein synthesized in W-n/W-n cultured mast cells (CMC) wa s reduced in size and not expressed on their surface (Tsujimura et al. , 1993). In this study, we further examined biochemical nature of the mutant form of c-kit protein, by using W-n/W-n CMC and 293T cells tran sfected with W-n-type c-kit cDNA (c-kit(Wn)). The c-kit product synthe sized in W-n/W-n CMC was truncated almost all cytoplasmic domain and w as less glycosylated. In c-kif(Wn)-tranfected cells, both glycosylatio n and extracellular expression of c-kit protein was also impaired, how ever, no truncation was detected. These results indicate that W-n-muta nt form of c-kit product is insufficient in maturation, which is assoc iated with impairments in the transport to the plasma membrane, and re tention of the mutant protein in endoplasmic reticulum is suggested. T his is the first demonstration of the c-kit mutation affecting posttra nslational processing its product.