Goulet Brigitte, Truscott Mary, Nepveu Alain
Molecular Oncology Group, McGill University Health Center, McGill University, Montreal H3A 1A1, Canada.
Biol Chem. 2006 Sep;387(9):1285-93. doi: 10.1515/BC.2006.159.
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.
Cut样基因编码CDP/Cux转录因子的多种亚型。全长蛋白包含四个DNA结合结构域：Cut重复序列1、2和3（CR1、CR2和CR3）以及Cut同源结构域（HD）。p75亚型由起始于内含子20内的mRNA表达，仅包含CR3和HD。p110亚型由组织蛋白酶L进行蛋白水解加工产生，包含CR2、CR3和HD。在本研究中，我们发现一种90 kDa的额外亚型在上皮来源的多种细胞系中表达。用缺失突变体进行的定位实验表明，p90的N端位于CR2上游，在氨基酸918和938之间。事实上，p90和p110表现出相似的DNA结合和转录活性。发现p90亚型与p110一样，是由蛋白水解加工产生的。p90和p110的稳态水平与组织蛋白酶L的活性水平相关。重要的是，与在下游AUG位点起始的组织蛋白酶L突变体共表达也刺激了p90和p110的产生。这些结果强烈表明，p90与p110一样，是由缺乏信号肽的组织蛋白酶L亚型产生的。
