title: Differential regulation of rat aquaporin-5 promoter/enhancer activities in lung and salivary epithelial cells.
abstract: Aquaporin-5 (AQP5) is a water channel protein that is selectively expressed in respiratory, salivary, and lacrimal tissues. In order to establish the tissue-specific transcriptional programs that underlie its lung- and salivary-specific expression, a 4.5-kilobase pair DNA fragment encompassing the 5'-flanking region of the rat AQP5 gene has been characterized in detail. A major transcription start site utilized in lung and salivary glands has been localized downstream of a TATAA-like motif. Transient transfection assays of -4.3- and -1.7-AQP5-luciferase constructs in AQP5-expressing lung (MLE-15) and salivary (Pa-4) cells and nonexpressing fibroblast (NIH3T3) and epithelial (HeLa) cells demonstrate preferential transcriptional enhancement of reporter activities in MLE-15 and Pa-4 cells. Transient transfection assays of a series of 5' --> 3' deletion constructs of -4.3-AQP5-luciferase suggest that a common salivary and lung enhancer is located between nucleotides -274 and -139, and a lung-specific enhancer is located between nucleotides -894 and -710. There is one putative lung-specific repressor located in the region of nucleotides -1003/-894 and a common lung and salivary repressor located at nucleotides -503/-385. Moreover, 3' --> 5' deletions up to -171 and -127 base pairs almost abolish transcriptional activation in salivary and lung cells, respectively. Together, our findings indicate that the combination of enhancer/repressor elements within the proximal 5'-flanking region of rat AQP5 gene dictates its restricted expression in both lung and salivary cells.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Will Rogers Institute Pulmonary Research Center, Los Angeles, CA 90033, USA. zborok@hsc.usc.edu
authors.forename: Z
authors.initials: Z
authors.lastname: Borok
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: V F
authors.initials: VF
authors.lastname: Fernandes
authors.forename: B
authors.initials: B
authors.lastname: Zhou
authors.forename: D K
authors.initials: DK
authors.lastname: Ann
authors.forename: E D
authors.initials: ED
authors.lastname: Crandall
mesh_terms: D016475:3T3 Cells; D000818:Animals; D051402:Aquaporin 5; D020346:Aquaporins / Q000235:genetics*; D001483:Base Sequence; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D008168:Lung / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012463:Saliva / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: C496038:Aqp5 protein, mouse; C496040:Aqp5 protein, rat; D051402:Aquaporin 5; D020346:Aquaporins; D008565:Membrane Proteins; D012333:RNA, Messenger