A high-level mammalian expression system based on the Madin-Darby canine kidney cell line

In this report, we demonstrate that a combination of the Madin-Darby canine kidney (MDCK) cell line and a cytomegalovirus promoter-based expression vector can achieve high-level expression of secretory recombinant proteins in mammalian cells. The matrix metalloproteinase MMP13, a secretory protein, was expressed in MDCK cells at a level high enough to be detectable in crude supernatants without concentration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis stained with Coomassie brilliant blue R-250. The secreted MMP-13 accounts for about 15 to 20% of the total secreted proteins and reaches a concentration of at least 10 mg/liter of unconcentrated conditioned medium harvested from confluent monolayer culture. Furthermore, the recombinant protein appears to be properly folded and modified posttranslationally. This system may be employed for the production of human proteins of special interests, such as those for structural determination or therapeutical development.