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

Abstract

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.

In situ histone landscape of nephrogenesis

“…Recent studies in which KMT cofactors were disrupted in the mature heart and kidney have shown that H3K4me3 is important in specific aspects of adult terminally differentiated tissues, such as cardiac electrophysiology and renal concentrating mechanisms. 42,43 Given its strong association with actively transcribed genes, the broad distribution of H3K4me3 and its KMT, Ash2l, in nephron progenitors and derivatives is not surprising. Our studies in clonal MM-like cells have demonstrated that H3K4me3 peaks decorate not only actively transcribed metabolic and housekeeping genes, but also promoters of developmental renal regulators such as Six2 and Osr1.…”

PTIP Associates with MLL3- and MLL4-containing Histone H3 Lysine 4 Methyltransferase Complex

“…Primary PTIP flox/flox MEFs were isolated from E13.5 embryos of PTIP conditional knock-out mice (26) and immortalized by transfection with pcDNA3 expressing SV40T following 3T3 protocol (27). Retrovirus infection of immortalized MEFs was performed as described (28).…”

The DNA Damage- and Transcription-Associated Protein Paxip1 Controls Thymocyte Development and Emigration

“…Paxip1 f/f (Kim et al, 2007), TCRβ transgenic (Shinkai et al, 1993), and Lck Cre transgenic (Hennet et al, 1995) and S1PR1 transgenic (Liu et al, 2009) mice were generated as previously described. Rag2 −/− mice were obtained from Taconic Laboratories.…”