CHARACTERIZATION OF THE CATHEPSIN-B GENE AND MULTIPLE MESSENGER-RNAS IN HUMAN TISSUES - EVIDENCE FOR ALTERNATIVE SPLICING OF CATHEPSIN-B PREMESSENGER RNA
Qm. Gong et al., CHARACTERIZATION OF THE CATHEPSIN-B GENE AND MULTIPLE MESSENGER-RNAS IN HUMAN TISSUES - EVIDENCE FOR ALTERNATIVE SPLICING OF CATHEPSIN-B PREMESSENGER RNA, DNA and cell biology, 12(4), 1993, pp. 299-309
We have cloned and characterized multiple messages for cathepsin B tha
t differ in their 5' and 3' untranslated regions (UTRs) from human kid
ney and the hepatoma cell line HepG2. A comparison of these messages w
ith the cloned human cathepsin B gene reveals that they arise by alter
native splicing of a single gene. Processing at a cryptic intron donor
site in exon 11 and splicing to exon 12 produces a 4.0-kb message wit
h an alternate 3' UTR in addition to the 2.3-kb message described prev
iously by Chan et al. (1986). Variable removal of exon 2 produces cath
epsin B mRNAs which differ by 88 nucleotides in their 5'-UTRs. The rat
io of the 2.3-kb to 4.0-kb transcript is about 2:1 in most of the tiss
ues examined, but the ratio of mRNAs with variant 5' UTRs differs wide
ly. Cathepsin B mRNAs lacking exon 2 are predominant in human tumors.
In addition, human breast and colon carcinomas and a human melanoma co
ntain a cathepsin B transcript that is also missing exon 3 encoding th
e signal peptide and 7 residues of the activation propeptide. An in vi
tro transcription/translation assay was used to demonstrate that this
message could be translated from an internal methionine codon (residue
52), producing a 32-kD product lacking the signal peptide and more th
an half the propeptide. The transcription/translation assay also demon
strated that the variant messages differ in their rates of translation
. The relative rates are about 8:2:1 for mRNA lacking exons 2 and 3 co
mpared to mRNA lacking exon 2 and mRNA containing the full-length 5' e
nd, respectively. These results suggest that the expression of catheps
in B in human tissues may be regulated in part at the level of mRNA pr
ocessing.