Localization of phosphatidylinositol phosphate kinase IIγ in kidney to a membrane trafficking compartment within specialized cells of the nephron

Clarke JH, Emson PC, Irvine RF. Localization of phosphatidylinositol phosphate kinase II gamma in kidney to a membrane trafficking compartment within specialized cells of the nephron. Am J Physiol Renal Physiol 295: F1422-F1430, 2008. First published August 27, 2008; doi:10.1152/ajprenal.90310.2008.-PIP4Ks (type II phosphatidylinositol 4-phosphate kinases) are phosphatidylinositol 5-phosphate (PtdIns5P) 4-kinases, believed primarily to regulate cellular PtdIns5P levels. In this study, we investigated the expression, localization, and associated biological activity of the least-studied PIP4K isoform, PIP4K gamma. Quantitative RT-PCR and in situ hybridization revealed that compared with PIP4K alpha and PIP4K beta, PIP4K gamma is expressed at exceptionally high levels in the kidney, especially the cortex and outer medulla. A specific antibody was raised to PIP4K gamma, 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 gamma 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 alpha, bacterially expressed recombinant PIP4K gamma was completely inactive but did have the ability to associate with active PIP4K alpha in vitro. Overall our data suggest that PIP4K gamma may have a function in the regulation of vesicular transport in specialized kidney epithelial cells.