Submitted on May 15, 2008
Revised on August 18, 2008
Accepted on August 24, 2008
Localization of Phosphatidylinositol phosphate Kinase II
in kidney to a membrane trafficking compartment within specialized cells of the nephron
Jonathan H Clarke1*, Piers C Emson2, and Robin F. Irvine3
1 Cambridge University
2 Babraham Institute, UK
3 Cambridge UK
* To whom correspondence should be addressed. E-mail: jhc30{at}cam.ac.uk.
PIP4Ks (Type II PIP kinases) are PtdIns5P 4-kinases, believed primarily to regulate cellular PtdIns5P levels. In this study we have investigated the expression, localization and associated biological activity of the least-studied PIP4K isoform, PIP4K
. Quantitative RT-PCR and in situ hybridization revealed that compared to PIP4K
and PIP4K
, PIP4K is expressed at exceptionally high levels in the kidney, especially the cortex and outer medulla. A specific antibody was raised to PIP4K and immunohistochemistry with this and with antibodies to specific kidney cell markers showed a restricted expression, primarily distributed in epithelial cells in the thick ascending limb, and in the intercalated cells of the collecting duct. In these cells PIP4K had a vesicular appearance, and transfection of kidney cell lines revealed a partial Golgi localization (primarily the matrix of the cis-Golgi) with an additional presence in an unidentified vesicular compartment. In contrast to PIP4K, bacterially-expressed recombinant PIP4K was completely inactive, but did have the ability to associate with active PIP4K in vitro. Overall our data suggest that PIP4K may have a function in the regulation of vesicular transport in specialized kidney epithelial cells.
