Conserved elements within first intron of aquaporin-5 (Aqp5) function as transcriptional enhancers

A 4.3 kb rat aquaporin-5 (Aqp5) promoter that directs lung and salivary cell-specific expression in vitro directs low level expression of a GFP reporter in lungs of transgenic mice. Alignment of rat, mouse, and human AQP5 genomic sequences identified a highly conserved region in the 3' portion of intron 1, here termed cil. To investigate the role of cil in Aqp5 expression, transient transfections were undertaken in AQP5-expressing mouse lung epithelial (MLE-15) and rat salivary (Pa-4) cells and AQP5-non-expressing NIH/3T3 cells. A 536 bp cil fragment enhanced transcriptional activity of the rat Aqp5 minimal promoter specifically in MLE-15 cells in an orientation-independent manner. Enhancer activity was Aqp5 promoter-specific, since no increase in activity was detected with the TK promoter. These results suggest that expression of transgenes in mouse lungs under direction of the 4.3 kb rat Aqp5 promoter may be augmented by inclusion of cil in transgenic constructs. (c) 2007 Elsevier Inc. All rights reserved.