Complementary DNA cloning and characterization of truncated form of c-kit in human colon carcinoma cells.

We have obtained a novel c-kit complementary DNA (cDNA) from a colon carcinoma cell line, Colo201, and characterized its structure. The size of the transcript in Colo201 was approximately 3.5 kilobases and it hybridized to the c-kit cDNA fragments encompassing the kinase domain, but not to the cDNA fragments encoding extracellular and transmembrane domains. The predicted protein encoded by those cDNAs was composed of 257 amino acids containing the NH2-terminal 25 unique amino acids in frame by the COOH terminal of the KIT protein. Of interest, these 25 amino acids were encoded by intron 15 of the c-kit gene. The aberrant mRNA was also detected in another colon carcinoma cell line, BM314. The translation of this message in Colo201 was confirmed by flow cytometry and immunoblot analysis. This is the first report describing the aberrant transcript of c-kit in human tumor cells, and it is suggested that truncated form of c-kit might play a role in the onset and development of human colon carcinoma.