Expression in human lung tumor cells of the proprotein processing enzyme PC1/PC3. Cloning and primary sequence of a 5 kb cDNA.

Northern blot analysis of human lung tumors indicated that the gene, which encodes the subtilisin-like proprotein processing enzyme PC1/PC3, was highly expressed in almost all carcinoid tumors tested. In small cell lung carcinomas (SCLCs), expression varied. In non-SCLCs and normal lung, no expression was found. Analysis of SCLC cell lines revealed that expression was restricted preferentially to cell lines of the classical type. In lung tumor cells expressing the PC1/PC3 gene, transcripts of 3 kb and 5 kb were detected, the 5 kb mRNA always being the most abundant species. We isolated a cDNA corresponding to the 5 kb human PC1/PC3 transcript, determined the nucleotide sequence of it and deduced the amino acid sequence of the corresponding protein. Furthermore, we conclude that the two PC1/PC3 transcripts have 3' non-coding regions of different size and encode the same protein.