The CCT Promoter Directs High-Level Transgene Expression in Distal Lung Epithelial Cell Lines

Abstract

Gene therapy requires the presence of a robust and yet small promoter to drive high-level expression of desired proteins. In comparative analysis, we investigated the promoter strength of the CTP:phosphocholine cytidylyltransferase promoter (CCTα) with other commonly used promoters, which were all cloned into a similar background vector (PGL3 basic). Transient promoter-reporter assays in murine lung epithelial (MLE-12) cells revealed that the core CCTα promoter (240 bp) was observed to exhibit a 40-fold, 8-fold, and 3-fold higher level of activity compared with the simian virus 40, human cytomegalovirus, and Rous sarcoma virus promoters, respectively. The CCTα promoter was significantly more active than the Clara cell 10, thymidine kinase, and phosphoglycerate kinase promoters. This pattern of high-level expression for CCTα was detected primarily in cell lines of distal lung epithelial origin (MLE-12, RLE, H441) and was reduced in other cell lines (A549, CHO, HepG 2). CCTα promoter-reporter activity, CCTα transcript levels, and immunoreactive protein levels increased significantly in the presence of all-trans retinoic acid. The CCTα promoter, in a retinoic acid-inducible manner, efficiently directed expression of murine erythropoietin in MLE-12 cells. Collectively, these observations suggest that the CCTα construct might be useful to drive high-level, regulatable expression of heterologous proteins in alveolar epithelia.