O'Donoghue Anthony J, Ivry Sam L, Chaudhury Chaity, Hostetter Daniel R, Hanahan Douglas, Craik Charles S
Biol Chem. 2016 Sep 1;397(9):871-81. doi: 10.1515/hsz-2016-0138.
The cathepsin family of lysosomal proteases is increasingly being recognized for their altered expression in cancer and role in facilitating tumor progression. The aspartyl protease cathepsin E is overexpressed in several cancers and has been investigated as a biomarker for pancreatic ductal adenocarcinoma (PDAC). Here we show that cathepsin E expression in mouse PDAC tumors is increased by more than 400-fold when compared to healthy pancreatic tissue. Cathepsin E accumulates over the course of disease progression and accounts for more than 3% of the tumor protein in mice with end-stage disease. Through immunoblot analysis we determined that only procathepsin E exists in mouse PDAC tumors and cell lines derived from these tumors. By decreasing the pH, this procathepsion E is converted to the mature form, resulting in an increase in proteolytic activity. Although active site inhibitors can bind procathepsin E, treatment of PDAC mice with the aspartyl protease inhibitor ritonavir did not decrease tumor burden. Lastly, we used multiplex substrate profiling by mass spectrometry to identify two synthetic peptides that are hydrolyzed by procathepsin E near neutral pH. This work represents a comprehensive analysis of procathepsin E in PDAC and could facilitate the development of improved biomarkers for disease detection.
溶酶体蛋白酶组织蛋白酶家族因其在癌症中表达改变以及在促进肿瘤进展中的作用而日益受到认可。天冬氨酸蛋白酶组织蛋白酶E在多种癌症中过表达，并已作为胰腺导管腺癌（PDAC）的生物标志物进行研究。在此我们表明，与健康胰腺组织相比，小鼠PDAC肿瘤中组织蛋白酶E的表达增加了400多倍。组织蛋白酶E在疾病进展过程中积累，在终末期疾病小鼠的肿瘤蛋白中占比超过3%。通过免疫印迹分析，我们确定在小鼠PDAC肿瘤及源自这些肿瘤的细胞系中仅存在组织蛋白酶E原。通过降低pH值，这种组织蛋白酶E原可转化为成熟形式，导致蛋白水解活性增加。尽管活性位点抑制剂可与组织蛋白酶E原结合，但用天冬氨酸蛋白酶抑制剂利托那韦治疗PDAC小鼠并未减轻肿瘤负担。最后，我们使用质谱多重底物分析来鉴定两种在接近中性pH值时被组织蛋白酶E原水解的合成肽。这项工作代表了对PDAC中组织蛋白酶E原的全面分析，并可能有助于开发用于疾病检测的改进生物标志物。
