Active Recombinant Rat Dipeptidyl Aminopeptidase I (Cathepsin C) Produced Using the Baculovirus Expression System

An active form of rat dipeptidyl aminopeptidase I (DPPI, cathepsin C) was obtained by heterologous expression in insect cells. Baculoviruses carrying a cDNA sequence encoding the entire rat DPPI precursor was used to infect High Five cells in a serum-free medium. Recombinant DPPI (rDPPI) was secreted into the medium from which it was purified by a combination of ammonium sulfate fractionation, hydrophobic interaction chromatography (HIC), and ion-exchange chromatography. A polyhistidine-tagged form of the enzyme (HT-rDPPI) was purified from the medium by immobilized metal affinity chromatography (IMAC).In vivoactivation of native rat DPPI involves at least three chain cleavages per subunit and the ability of the expression system to imitate this processing was investigated. Both rDPPI and HT-rDPPI were secreted into the medium as unprocessed and inactive proenzymes and gradually converted into their active forms in the medium. This process was not completed at the time of harvest but mature enzyme processed similarly to native rat and human DPPI could be obtained by incubating the eluates from the HIC and IMAC columns at pH 4.5 and 5°C for 18–40 h. The yield of purified and matured enzyme was approximately 50 mg/liter, and it was shown that rDPPI and HT-rDPPI were active against both a dipeptide–p-nitroanilide substrate and human growth hormone N-terminally extended with an Ala-Glu dipeptide.     

Comparative localization of cathepsin B protein and activity in colorectal cancer.

Cathepsin B is a lysosomal cysteine proteinase that may participate in cancer progression. We compared localization of its protein and activity during progression of human colorectal cancer. In adenomas and carcinomas, protein expression and, particularly, activity were elevated compared with those in normal colorectal mucosa. In normal mucosa, cathepsin B protein expression was moderate in stroma and variable in epithelium, whereas activity was mainly present in distinct areas of stroma directly underneath the surface of the colon and in epithelium at the surface of the colon. Stroma in adenomas and carcinomas contained moderate to high protein levels but little activity except for areas of angiogenesis, inflammation, and necrosis, in which activity was high. In adenomas and the majority of well-differentiated carcinomas and moderately differentiated carcinomas, cathepsin B protein and activity were found in granular form in the epithelium, close to the basement membrane. Protein and activity levels were low and diffusely distributed in cancer cells in the remainder of the well-differentiated and moderately differentiated carcinomas and in all poorly differentiated carcinomas. Invasive fronts in most cancers contained moderate protein levels but high activity. We conclude that (a) activity localization is essential to understand the role of cathepsin B in cancer progression, and (b) cathepsin B activity in human colon is associated with invasion of cancer cells, endothelial cells, and inflammatory cells, and in cell death, both apoptotic and necrotic.