Systems Level Analysis of Cell‐Specific AQP2 Gene Expression in Collecting Duct

Abstract

We investigated the basis of cell‐specific expression of aquaporin‐2 (AQP2) in the collecting duct. Bioinformatic analysis of the 5′‐flanking region of the AQP2 gene (GenomatixTM) revealed 11 conserved transcriptional regulator (TR) binding element (BE) motifs corresponding to SF1, NFAT, Forkhead, AP2, SRF, CREB, GATA, Ets, E‐Box, RXR and Homeobox TR families. To identify TRs that potentially bind to these sites, we carried out mRNA profiling (Affymetrix) in mouse mpkCCDc14 collecting duct cells, revealing expression of 25 TR from these families that are also expressed in native inner medullary collecting duct (IMCD). One showed a significant positive correlation with AQP2 mRNA abundance among mpkCCD clones expressing various levels of AQP2 protein (Ets1) and two showed a significant negative correlation (Elf1 and Nr1h2). Affymetrix profiling in native proximal tubules (PT), thick ascending limbs (TAL), and IMCDs from kidney identified 14 TRs (including Ets1 and HoxD3) expressed in the IMCD but not PT or TAL (candidate AQP2 enhancers), and 5 TRs (including HoxA5, HoxA9,and HoxA10) expressed in PT and TAL but not in IMCD (candidate AQP2 repressors). The results point to Ets and Homeobox as potentially important BEs in cell‐specific expression of AQP2 in the collecting duct. Full transcriptomic data are available online (Google "transcriptome database").