Nucleolar localization of phosphatidylinositol 4‐kinase PI4K230 in various mammalian cells

Abstract

Background: Previous immunohistochemical investigations could not detect PI4K230, an isoform of mammalian phosphatidylinositol 4-kinases (also called type III a), in the nucleus and nucleolus of cells in spite of its predicted nuclear localization signals. Methods: Immunofluorescent detection of PI4K230 and other PI4K isoforms was performed on formaldehyde (PFA) or ethanol fixed cells and rat brain cryosections. Costaining with nucleolin and the effect of siRNA, Triton X-100, DNase, and RNase treatments were also tested to determine the localization of PI4K230. Results: PI4K230 gives a prominent signal in the nucleolus of ethanol fixed rat brain cryosections and of several cell types in addition to its presence in the nucleus and cytoplasm. The PI4K230 immunoreactivity of the nucleolus is masked in PFA fixed cells, but it can be restored by

Mapping of Functional Domains of the Lipid Kinase Phosphatidylinositol 4-Kinase Type III Alpha Involved in Enzymatic Activity and Hepatitis C Virus Replication

“…In previous reports, we and others found a more distinct localization of the endogenous kinase in punctate structures throughout the cytoplasm, consistent with an ER association (7,16,21). In brain cells, PI4KIII␣ was prominently detected in the nucleus and nucleolus (21). Therefore, the subcellular localization might depend on cell type and expression level of PI4KIII␣.…”

“…While the yeast orthologue of PI4KIII␣ is located at the plasma membrane (17), mammalian PI4KIII␣ mainly resides at the ER (18) but is also located at Golgi membranes (19) and at nucleoli upon exogenous expression (20). The localization of PI4KIII␣ also differs among cell types, since in neuronal cells and other cell types, like COS-7 or B50 cells, it is prominently found in the nuclei (21). The exact role of PI4KIII␣ at the ER still is unknown, but it was demonstrated that PI4KIII␣ is responsible mainly for PI4P synthesis at the ER, the plasma membrane (22,23), and partly at the Golgi compartment (24).…”

Phosphatidylinositol 4-Phosphate Negatively Regulates Chloroplast Division in Arabidopsis

“…PI4Ka1 has a PH domain, which binds specifically to PI4P, and the GFP fusion protein is localized in perinuclear membranes when it is expressed in Sf9 insect cells (StevensonPaulik et al, 2003). Our results suggest that PI4Ka1 localizes in membranes and the cytosol, as does PI4KIIIa in mammalian cells (Kakuk et al, 2006). The localization of PI4Kb2 has not been demonstrated, although it was reported that the novel homology domain of PI4Kb2 interacts with RabA4b as does that of PI4Kb1 (Preuss et al, 2006).…”

Phosphoinositides: Tiny Lipids With Giant Impact on Cell Regulation

“…It is notable that PI4KA shows the highest expression in the brain both during development and in adult rodents (1107,1828). At the cellular level, the enzyme was also found associated with nucleoli, but the biological significance of this finding is not known (748). A series of recent studies using RNAi screens to search for cellular host factors required for the infection cycle of hepatitic C virus (HCV), identified PI4KA as a critical protein for HCV replication in the liver (122,166,1513,1577,1597).…”

“…With the cloning of the various PI lipid metabolizing enzymes and the availability of antibodies for immunofluorescence, it has become clear that many enzymes of the PI cycle do localize to the nucleus. These include several isoforms of PLC enzymes [␤1 (451,952,987), ␦1 (302, 1448), and ␦4 (925)], both forms of the type III PI4Ks [PI4KA (748) and PI4KB/Pik1 (332, 343,1478)], the yeast PIP 5-kinase Mss4 (62) and the mammalian PIP 5-kinase I␣ (168,1029), and the type II PIPK␤ (263). In addition to the kinases, inositide phosphatases were also shown to move in and out of the nucleus.…”