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Pax Transactivation-Domain Interacting Protein Is Required for Urine Concentration and Osmotolerance in Collecting Duct Epithelia

Doyeob Kim^*, Min Wang^*, Qi Cai, Heddwen Brooks and Gregory R. Dressler^*

^* Department of Pathology, University of Michigan, Ann Arbor, Michigan; and Department of Physiology, University of Arizona, Tucson, Arizona

Address correspondence to: Dr. Gregory R. Dressler, 2049 BSRB, 109 Zina Pitcher Place, Ann Arbor, MI 48109. Phone: 734-764-6490; Fax: 734-763-2162; E-mail: dressler{at}umich.edu

Received for publication June 16, 2006. Accepted for publication March 1, 2007.

Pax transactivation-domain interacting protein (PTIP) is a widely expressed nuclear protein that is essential for early embryonic development. PTIP was first identified on the basis of its interactions with the developmental regulator Pax2 but can also bind to other nuclear transcription factors. The Pax2 protein is essential for development of the renal epithelia and for regulating the response of mature collecting ducts to hyperosmotic stress. For determination of whether PTIP also functions in more differentiated cell types, the Cre-LoxP system was used to delete the ptip gene in the renal collecting ducts using Ksp-Cre driver mice. Collecting duct–specific ptip knockout mice were viable with little discernible phenotype under normal physiologic conditions. However, collecting duct–specific ptip mutants were unable to concentrate urine after the treatment of desamino-cis, D-arginine vasopressin, an antidiuretic hormone. Furthermore, aquaporin-2 (AQP2) expression in the inner medulla of the ptip knockout mice was decreased approximately 10-fold compared with that of wild-type littermates. Expression level of tonicity responsive enhancer binding protein, a transcription factor of AQP2, is not altered in the mutant mice, but its nuclear localization in the inner medulla is unresponsive after treatment with vasopressin agonists. This was due, at least in part, to decreased expression of the arginine vasopressin receptor 2 in ptip mutants. Furthermore, ptip null inner medullary collecting duct cells were sensitive to hyperosmolality in vitro. Thus, ptip is required for the urine concentration mechanism by modulating arginine vasopressin receptor 2 and AQP2 expression in the inner medulla. The data suggest an essential role for ptip in regulating urine concentration and in controlling survival of collecting duct epithelial cells in high osmolality.

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				Y.-W. Cho, T. Hong, S. Hong, H. Guo, H. Yu, D. Kim, T. Guszczynski, G. R. Dressler, T. D. Copeland, M. Kalkum, et al. PTIP Associates with MLL3- and MLL4-containing Histone H3 Lysine 4 Methyltransferase Complex J. Biol. Chem., July 13, 2007; 282(28): 20395 - 20406. [Abstract] [Full Text] [PDF]

Copyright © 2008 by the American Society of Nephrology. Online ISSN: 1533-3450 Print ISSN: 1046-6673