A novel neuronal-specific splice variant of Type I phosphatidylinositol 4-phosphate 5-kinase isoform gamma.

Type I PIPkins (phosphatidylinositol 4-phosphate 5-kinases) are the enzymes that catalyse the major cellular route of synthesis of PtdIns(4,5) P2, and three isoforms (alpha, beta and gamma) with several splice variants have been found to date. In the present paper, we describe the discovery of a novel splice variant of the gamma isoform, which we call PIPkin Igammac, and which is characterized by the inclusion of a 26-amino-acid insert near the C-terminus. Its transcript appears to be selectively expressed in brain, where it locates in the neurons of restricted regions, such as cerebellum, hippocampus, cortex and olfactory bulb, as indicated by in situ hybridization studies. Overexpression of two different catalytically inactive constructs of PIPkin Igammac in rat cerebellar granule cells causes a progressive loss of their neuronal processes, whereas equivalent kinase-dead versions of PIPkin Igammaa did not induce any such effect, suggesting the possible existence of a specific PtdIns(4,5) P2 pool synthesized by PIPkin Igammac, which is involved in the maintenance of some neuronal cellular processes

Localization of phosphatidylinositol phosphate kinase II␥ 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␥ in kidney to a membrane trafficking compartment within specialized cells of the nephron. Am J Physio

CHARACTERIZATION AND CONTENT OF VIP AND VIP MESSENGER-RNA IN RAT FORE-BRAIN NEURONS

HPLC, gel chromatography, Northern analysis and non-isotopic in situ hybridization have been used to characterize for the first time the nature of vasoactive intestinal polypeptide mRNA and peptide in the rat thalamus and suprachiasmatic nucleus. Both these hitherto unstudied areas were shown to contain VIP-like immunoreactivity and VIP mRNA indistinguishable from those found in the rat cerebral cortex. Non-isotopic in situ hybridization with an alkaline phosphatase labelled antisense oligonucleotide specific for VIP mRNA and densitometry revealed that relative levels of VIP mRNA per cell were highest in the suprachiasmatic nucleus and lowest per cell in the thalamus of the rat brain areas investigated

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

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, PIP4Kγ. Quantitative RT-PCR and in situ hybridization revealed that compared with PIP4Kα and PIP4Kβ, PIP4Kγ is expressed at exceptionally high levels in the kidney, especially the cortex and outer medulla. A specific antibody was raised to PIP4Kγ, 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, PIP4Kγ 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 PIP4Kα, bacterially expressed recombinant PIP4Kγ was completely inactive but did have the ability to associate with active PIP4Kα in vitro. Overall our data suggest that PIP4Kγ may have a function in the regulation of vesicular transport in specialized kidney epithelial cells