IDENTIFICATION OF 2 NEW EXONS AND MULTIPLE TRANSCRIPTION START POINTSIN THE 5'-UNTRANSLATED REGION OF THE HUMAN CATHEPSIN-B-ENCODING GENE

Transcripts for cysteine protease cathepsin B (CTSB) were found to be highly variable in the 5'-UTR (untranslated region). In cDNA clones fr om a human gastric adenocarcinoma cDNA library, we have identified two new exons (designated 2a and 2b) between exons 2 and 3 in the 5'-UTR of the gene. All of the exons of the 5'-UTR could be alternatively spl iced to produce several transcript species, In addition, transcription was initiated from more than one promoter region. Using RT-PCR (rever se transcription-polymerase chain reaction) and primer extension assay s, CTSB mRNA species were found to differ among tissues and between a glioblastoma sample and a cell line derived from it. Exons 2a and 2b w ere detected more frequently in tumor samples than in matched normal s amples. Thus. factors related to the cell differentiation and environm ent seem likely to determine the types of transcripts that are express ed which in turn could influence the overall steady-state level of CTS B mRNAs and their rate of translation. Interestingly, at least three u pstream translation initiation codons were observed and could constitu te a means of controlling translation initiation.