A novel proteolytically processed CDP/Cux isoform of 90 kDa is generated by cathepsin L.
The Cut-like genes code for multiple isoforms of the CDP/Cux transcription factor. The full-length protein contains four DNA-binding domains: Cut repeats 1, 2 and 3 (CR1, CR2 and CR3) and the Cut homeodomain (HD). The p75 isoform is expressed from an mRNA that is initiated within intron 20 and contains only CR3 and HD. The p110 isoform is generated by proteolytic processing by cathepsin L and contains CR2, CR3 and HD. In the present study, we show that an additional isoform of 90 kDa is expressed in many cell lines of epithelial origin. Mapping experiments with deletion mutants indicated that the N-terminus of p90 is located upstream of CR2, between amino acids 918 and 938. Indeed, p90 and p110 displayed similar DNA-binding and transcriptional activities. The p90 isoform, like p110, was found to be generated by proteolytic processing. The steady-state level of both p90 and p110 correlated with the level of cathepsin L activity. Importantly, co-expression with a cathepsin L mutant that is initiated at downstream AUG sites also stimulated the generation of p90 and p110. These results strongly suggest that p90, like p110, is generated by cathepsin L isoforms that are devoid of a signal peptide.
Goulet
Brigitte
B
Molecular Oncology Group, McGill University Health Center, McGill University, Montreal H3A 1A1, Canada.
Truscott
Mary
M
Nepveu
Alain
A
D000818:Animals; D019556:COS Cells; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008970:Molecular Weight; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors
C080632:CUX1 protein, human; C000624101:Cux1 protein, mouse; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012097:Repressor Proteins; D014157:Transcription Factors; D004247:DNA; D002403:Cathepsins; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C534280:Ctsl protein, rat