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

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, 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.

In B cells, phosphatidylinositol 5-phosphate 4-kinase–α synthesizes PI(4,5)P2to impact mTORC2 and Akt signaling

“…No Akt phenotype was found in PIP4K2A knockout mice (21), but as far as we are aware, cells of the hematopoietic lineage were not studied there; another study from the same group elegantly showed the tissue variability of gene knockouts, with PIP4K2B knockout mice having enhanced insulininduced Akt phosphorylation in skeletal muscle and liver but not in white fat (22). Certainly, it is not unreasonable to suggest a particular role of PI5P4Kα in blood cells given that these are the only cells reported so far to have an excess of this enzyme over the other isoforms (23). Our data from exploring a simple, single-cell type system highlight how difficult it can be to interpret primary protein function from knockout phenotypes.…”

Involvement of phosphatidylinositol 5-phosphate in insulin-stimulated glucose uptake in the L6 myotube model of skeletal muscle

“…However, it has recently emerged that PIP4Kβ makes only a minor contribution to total cellular PtdIns5P 4-kinase activity. Specifically, PIP4Kβ is 2,000-fold less active than the closely related PIP4Kα [2,33], whilst the only other mammalian PtdIns5P 4-kinase, PIP4Kg, is catalytically inactive [4]. It has been suggested that PIP4Kβ and PIP4Kγ largely act to recruit PIP4Kα to different subcellular compartments through hetero-dimerisation [4,22].…”

“…Specifically, PIP4Kβ is 2,000-fold less active than the closely related PIP4Kα [2,33], whilst the only other mammalian PtdIns5P 4-kinase, PIP4Kg, is catalytically inactive [4]. It has been suggested that PIP4Kβ and PIP4Kγ largely act to recruit PIP4Kα to different subcellular compartments through hetero-dimerisation [4,22]. Indeed, endogenous PIP4Kβ, which localises to the nucleus [22], has been shown to target PIP4Kα to this location [2,33].…”

Phosphatidylinositol 5-phosphate 4-kinase (PIP4K) regulates TOR signaling and cell growth during Drosophila development

“…Expression of PIP4Kβ in CHO cells results in down-regulation of PIP 3 production and AKT (protein kinase B) phosphorylation in response to insulin stimulation (17), whereas skeletal muscle cells from PIP4Kβ −/− mice show enhanced sensitivity to insulin stimulation (18). PIP4Kγ encodes a protein that appears to localize to endomembrane compartments whose identity is unclear (19). Whereas these studies suggest important cellular functions for PIP4K enzymes, the physiological significance and the mechanism by which this unique class of lipid kinase exerts its effects remain unclear.…”