Abstract
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, PIP4Kgamma. Quantitative RT-PCR and in situ hybridization revealed that compared with PIP4Kalpha and PIP4Kbeta, PIP4Kgamma is expressed at exceptionally high levels in the kidney, especially the cortex and outer medulla. A specific antibody was raised to PIP4Kgamma, 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, PIP4Kgamma 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 PIP4Kalpha, bacterially expressed recombinant PIP4Kgamma was completely inactive but did have the ability to associate with active PIP4Kalpha in vitro. Overall our data suggest that PIP4Kgamma may have a function in the regulation of vesicular transport in specialized kidney epithelial cells.