ARTICLE |
Correspondence to: Sharon F. Suchy, Genetic Diseases Res. Branch, National Human Genome Research Institute, NIH, 49 Convent Dr., Room 4A66, Bethesda, MD 20892-4472.
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
PtdIns(4,5)P2 and PtdIns(4,5)P2 5-phosphatases play important roles in diverse aspects of cell metabolism, including protein trafficking. However, the relative importance of the PtdIns(4,5)P2 5-phosphatases in regulating PtdIns(4,5)P2 levels for specific cell processes is not well understood. Ocrl1 is a PtdIns(4,5)P2 5-phosphatase that is deficient in the oculocerebrorenal syndrome of Lowe, a disorder characterized by defects in kidney and lens epithelial cells and mental retardation. Ocrl1 was originally localized to the Golgi in fibroblasts, but a subsequent report suggested a lysosomal localization in a kidney epithelial cell line. In this study we defined the localization of ocrl1 in fibroblasts and in two kidney epithelial cell lines by three methods: immunofluorescence, subcellular fractionation, and a dynamic perturbation assay with brefeldin A. We found that ocrl1 was a Golgi-localized protein in all three cell types and further identified it as a protein of the trans-Golgi network (TGN). The TGN is a major sorting site and has the specialized function in epithelial cells of directing proteins to the apical or basolateral domains. The epithelial cell phenotype in Lowe syndrome and the localization of ocrl1 to the TGN imply that this PtdIns(4,5)P2 5-phosphatase plays a role in trafficking. (J Histochem Cytochem 48:179189, 2000)
Key Words: Golgi apparatus, Lowe syndrome, phosphatidylinositol 4,5- bisphosphate 5-phosphatase, renal proximal tubules, trans-Golgi network
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A GROWING BODY OF EVIDENCE has demonstrated that phosphatidylinositol 4,5 bisphosphate [PtdIns (4,5)P2] plays important roles in regulating a number of diverse aspects of cell metabolism (
Recently, attention has focused on the role of PtdIns (4,5)P2 phosphatases in vesicle trafficking (
![]() |
Materials and Methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell Culture
Normal human fibroblast cell lines (CRL1489) and Vero monkey kidney epithelial cells (CCL81) were obtained from American Type Culture Collection (Manassas, VA). Human fibroblasts, Vero cells, and mouse fibroblasts derived in our laboratory (
Antibodies
The antibodies used for immunofluorescence studies were anti--tubulin, anti-
-adaptin (Sigma Chemical; St Louis, MO), anti-lamp1 (clone H4A3) (Developmental Studies Hybridoma Bank; University of Iowa, Ames, IA), and an affinity-purified polyclonal anti-ocrl1 antibody (
Immunofluorescence microscopy
Fibroblasts and Vero cells were grown on LabTek chamber slides (Naperville, IL) coated with 0.01% poly-L-lysine (Sigma) for 2448 hr until cells reached 6080% confluence. NHK cells were plated on the coated chamber slides and switched from 33C to 37C for 35 days to allow differentiation before immunocytochemistry. Immunocytochemistry was performed at room temperature. Cells were fixed and permeabilized with 1% paraformaldehyde, 0.1% Triton X-100 in PBS for 5 min, washed with PBS, and blocked with 5% goat serum (Gibco/BRL; Gaithersburg, MD) for 30 min. The cells were incubated with primary antibody for 1.5 hr washed 3 times with PBS, and incubated with secondary antibody, Alexa 488, or Alexa 594 (Molecular Probes) for 30 min. Fluorescence was visualized on a Leica DMR fluorescence microscope.
Sucrosome Formation and Vital Staining of Cell Lysosomes
Cells were incubated in 100 mM sucrose in growth medium for 13 days and washed with PBS (
Subcellular Fractionation
Human kidney (NHK) and mouse fibroblasts were homogenized with a ball-bearing homogenizer in 0.25 M sucrose, 10 mM Tris-HCl (pH 7.4) with 4 µg/ml aprotinin, 4 µg/ml leupeptin, and 100 mg/ml phenylmethylsulfonylfluoride (
The fractions were tested to confirm their enrichment for specific organelles by Western analysis (
Golgi Perturbation Studies
For the Golgi perturbation studies, fibroblasts were incubated with 5 µg/ml brefeldin A (BFA) (Epicentre Technologies; Madison, WI) for 1 hr at 37C in a humidified atmosphere of 95% air, 5% CO2, as reported previously (
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Immunofluorescence
To compare the localization of ocrl1 in fibroblasts and kidney epithelial cells, three cell lines were studied by immunofluorescence with the ocrl1 antibody, an antibody to the TGN protein -adaptin, and two lysosomal markers, lamp1 antibody and LysoTrackerTM. Figure 1 shows double-label immunofluorescence of ocrl1 (green) and
-adaptin staining (red) of normal human fibroblasts (Figure 1A1C) and of kidney epithelial cells of monkey (Vero cells) (Figure 1D1F) and human origin (NHK cells) (Figure 1G1I). In human fibroblasts, ocrl1 staining (Figure 1A) was distributed in a juxtanuclear reticular pattern typical of a Golgi complex protein, very similar to that of
-adaptin staining (Figure 1B). In fact, there appeared to be significant co-localization (yellow staining) of ocrl1 and
-adaptin to the juxtanuclear region of fibroblasts and kidney epithelial cells, as shown in the double exposures (Figure 1C, Figure 1F, and Figure 1I). The overlap of ocrl1 with
-adaptin was more striking than that with ß-COP reported previously (
|
In addition to the predominantly juxtanuclear ocrl1 staining, there was a small amount of punctate staining in the cytoplasm of fibroblasts and Vero cells. This staining is specific because it was not observed in fibroblasts from Lowe syndrome patients, which lack ocrl1 (not shown). Punctate cytoplasmic staining was also observed with -adaptin (Figure 1) and clathrin immunofluorescence (data not shown), but the cytoplasmic
-adaptin and clathrin staining were not coincident with the cytoplasmic ocrl1 staining.
Because a previous report proposed a lysosomal localization of ocrl1 in NHK cells (
|
To confirm that ocrl1 was not localized to lysosomes in fibroblasts and Vero cells, we performed immunocytochemistry with a second lysosomal marker, the vital lysosomal dye LysoTrackerTM. As with the lamp1 staining, the LysoTrackerTM staining was cytoplasmic, with a patchy distribution in both fibroblasts (Figure 2H) and Vero cells (Figure 2K). The double exposures (Figure 2I and Figure 2K) show a distinct separation between the two staining patterns, with ocrl1 exhibiting a more polarized staining pattern than the LysoTrackerTM staining. These immunofluorescence studies clearly demonstrate that ocrl1 is not localized to lysosomes in these cells.
We then compared the staining of ocrl1 and lamp1 in NHK cells, the cells used in a previous report to localize ocrl1 to lysosomes (-adaptin in these cells (Figure 1I). This made it clear that immunofluorescence studies alone were inadequate to determine the subcellular localization of ocrl1 in NHK cells. We therefore performed subcellular fractionation and Golgi perturbation experiments to determine the localization of ocrl1 in these cells.
Subcellular Fractionation
Subcellular fractionation was performed with the NHK human kidney cells and with mouse fibroblasts. The latter were used because of their rapid growth rate to test consistency of the fractionation procedure. Fractionation was performed to isolate nuclear, mitochondrial/lysosomal, Golgi/microsomal and cytosolic fractions. For confirmation of the fractions, Western analysis was performed with antibodies to proteins with a well-established subcellular localization. Western analysis confirmed that nuclei, mitochondria, and Golgi were consistently found in the expected fractions based on their separation by differential centrifugation (
The NHK cell fractionation results were similar to those of the mouse fibroblasts and are shown in Figure 3. Lamp1 and the mitochondrial marker hsp-70 were highly enriched in the mitochondrial/lysosomal fraction (Figure 3d). A small amount of lamp1, estimated at about 10%, was also present in the Golgi/microsomal fraction (Figure 3e). The integral Golgi membrane protein golgin-84 and the TGN protein -adaptin were enriched in the Golgi/microsomal fraction (Figure 3b and Figure 3c). These proteins were also present in the mitochondrial/lysosomal fraction. The fact that the TGN and Golgi markers were in the mitochondrial/lysosomal fraction indicates that there may be some contamination of this fraction with Golgi or TGN elements. The Golgi/microsomal and mitochondrial/lysosomal fractions also contained the mannose 6-phosphate receptor (M6PR), indicating that endosomes were present in these fractions as well (Figure 3f). M6PRs are not found on lysosomes but are found on prelysosomes, late and early endosomes, and the TGN (
-adaptin in the fractions (Figure 3c). These subcellular fractionation data clearly demonstrated that ocrl1 and lamp1 were in different subcellular compartments in NHK cells and indicated that, as in other cell types, ocrl1 is a Golgi-associated protein.
|
Golgi Perturbation Experiments
We performed dynamic Golgi perturbation experiments with two purposes in mind. First, we wanted to provide independent evidence to confirm in NHK cells the immunofluorescence and subcellular fractionation data indicating that ocrl1 was a Golgi-associated protein. Second, we sought to identify the localization of ocrl1 within the Golgi apparatus. The fungal metabolite BFA disrupts the Golgi and redistributes components from Golgi stacks to the endoplasmic reticulum, while the TGN and early endosomes redistribute to the microtubule organizing center (MTOC) (-adaptin (red) to a concentrated spot near the nucleus. Photographs of untreated fibroblasts (Figure 4A4C) and Vero cells (Figure 4G4I) from the same experiment are provided for comparison. The computer overlays show that the ocrl1 and
-adaptin staining condense to the same spot (Figure 4F and Figure 4L). To demonstrate that the intense spot of perinuclear staining corresponds to the MTOC, we double-labeled BFA-treated fibroblasts with ocrl1 (green) (Figure 4M) and the microtubule protein
-tubulin (red) (Figure 4N). Microtubules converge at the MTOC, and immunofluorescence staining with
-tubulin results in a concentrated juxtanuclear spot of staining. A computer overlay demonstrates that the spot of intense ocrl1 staining near the nucleus corresponds to the MTOC (Figure 4O, yellow staining).
|
Since a previous study has demonstrated that lysosomal proteins do not redistribute to the MTOC with BFA treatment (
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
There is ample evidence that PtdIns(4,5)P2 is an activator or cofactor for a number of membrane-trafficking events at the plasma membrane and in the Golgi complex (-adaptin antibody.
We first studied the localization of ocrl1 by immunofluorescence experiments with several markers. In fibroblasts and Vero cells, ocrl1 immunostaining co-localized with that of the TGN protein -adaptin. Furthermore, ocrl1 and lysosomal marker localizations were nonoverlapping, making the Golgi localization of ocrl1 clear. In human kidney epithelial cells (NHK), we likewise observed co-localization of ocrl1 and
-adaptin, which is in contrast to a previous report (
-adaptin, lamp1, and ocrl1 staining in immunofluorescence experiments led us to the conclusion that this method was inadequate for localization of ocrl1 in NHK cells and that additional methods had to be employed.
To further investigate the localization of ocrl1 in NHK cells, in which the co-localization staining patterns were ambiguous, subcellular fractionation experiments were done. Ocrl1 was concentrated in the Golgi/microsomal fraction as was the TGN protein, -adaptin, whereas lamp1 was concentrated in the mitochondrial/lysosomal fraction. The presence of a smaller amount of ocrl1 and
-adaptin in the mitochondrial/lysosomal fraction may represent limited TGN material in that fraction. The presence of a small percentage of lamp1 in the Golgi/microsomal fraction is expected because electron microscopic studies have found that about 1030% of lamp1 is present in the TGN (
To confirm the evidence for a Golgi localization of ocrl1 in NHK cells and to identify the specific Golgi compartment in which ocrl1 was located, we performed perturbation assays using the fungal metabolite BFA. BFA disrupts the Golgi complex and causes transport of Golgi proteins back to the endoplasmic reticulum, resulting in a diffuse cytoplasmic distribution of Golgi proteins. BFA also causes the TGN to tubulate, merge with endosomes, and reversibly condense around the MTOC (-adaptin to the MTOC region, whereas no change was detected in lamp1 distribution. On the basis of these dynamic Golgi perturbation experiments, subcellular fractionation studies, and co-localization of ocrl1 with known Golgi proteins, we are able to conclude that ocrl1 is localized to the Golgi in NHK cells, fibroblasts, and Vero cells. The Golgi perturbation experiments more specifically pinpoint the localization of ocrl1 to the TGN.
The overlap between immunofluorescence staining with ocrl1 and lamp1 that we and others (
Ocrl1 is a member of an enzyme family that hydrolyzes the 5-position phosphate from phosphatidylinositol polyphosphate (
The precise cellular role for ocrl1 is unknown. Furthermore, it is not clear how ocrl1 associates with or is targeted to cell membranes. Sequence analysis of the ocrl1 protein indicates that it has no transmembrane domains nor does it contain a consensus sequence for myristolation or prenylation for membrane attachment. Its association with membranes appears to be weak because ocrl1 is not found with Golgi membranes when fractionation is performed under hypotonic conditions (
The localization of ocrl1 to the TGN is particularly interesting given the special function played by the TGN in epithelial cells. The TGN is the site from which proteins are sorted into vesicles destined for secretory vesicles or lysosomes. In polarized cells, the TGN also serves as the key sorting site for proteins destined for either the apical or basolateral membrane. The localization of ocrl1 to the TGN, its function as a PtdIns(4,5)P2 5-phosphatase, and the restriction of the Lowe syndrome phenotype to certain polarized cells all support the hypothesis that ocrl1 is a second member of the PtdIns 5-phosphatase family that is involved in membrane trafficking, in this case in the TGN. Understanding its role in this specific subcellular compartment may help us to understand the tissue-specific phenotype in Lowe syndrome. It will also prove useful to elucidate more general questions, such as the compensatory capability of other PtdIns (4,5)P2 5-phosphatases and the role of PtdIns (4,5)P2 5-phosphatases in protein sorting in polarized cells.
![]() |
Footnotes |
---|
1 Present address: Novartis Pharmaceuticals, Gaithersburg, MD.
![]() |
Acknowledgments |
---|
We thank Edwin Arnold, Nancy Theriault, and Darryl Leja for assistance in the preparation of the photomicrographs. We also thank Drs Deborah Cabin and Christian Lavedan for critical reading of the manuscript.
Received for publication July 2, 1999; accepted October 11, 1999.
![]() |
Literature Cited |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Akasaki K, Michihara A, Mibuka K, Fujiwara Y, Tsufi H (1995) Biosynthetic transport of a major lysosomal membrane glycoprotein, lamp-1: convergence of biosynthetic and endocytic pathways occurs at three distinctive points. Exp Cell Res 220:464-473[Medline]
Balch WE, Beckers CJ, Keller DS (1988) Reconstitution of protein transport from the endoplasmic reticulum to the Golgi using a cell free system. Prog Clin Biol Res 270:333-342[Medline]
Bascom R, Srinivasan S, Nussbaum RL (1999) Identification and characterization of golgin-84, a novel Golgi integral membrane protein with a cytoplasmic coiled-coil domain. J Biol Chem 274:2953-2962
Chen JW, Chen GL, D'Souza MP, Murphy TL, August JT (1986) Lysosomal membrane glycoproteins: properties of lamp-1 and lamp-2. Biochem Soc Symp 51:97-112[Medline]
Chen JW, Murphy TL, Willingham MC, Pastan I, August JT (1985) Identification of two lysosomal membrane glycoproteins. J Cell Biol 101:85-95[Abstract]
Chung J, Sekiya F, Kang H, Lee C, Han J, Kim S, Bae Y, Morris A, Rhee SG (1997) Synaptojanin inhibition of phospholipase D activity by hydrolysis of phosphatidylinositol 4,5-bisphosphate. J Biol Chem 272:15980-15985
DeCamilli P, Emr SD, McPherson PS, Novick P (1996) Phosphoinositides as regulators in membrane traffic. Science 271:1533-1539[Abstract]
DeCourcy K, Storrie B (1991) Osmotic swelling of endocytic compartments induced by internalized sucrose is restricted to mature lysosomes in cultured mammalian cells. Exp Cell Res 192:52-60[Medline]
De Smedt F, Boom A, Pesesse X, Schiffmann SN, Erneaux C (1996) Post-translational modification of human brain type I inositol-1,4,5-trisphosphate 5-phosphatase by farnesylation. J Biol Chem 271:10419-10424
Dinter A, Berger EG (1998) Golgi disturbing agents. Histochem Cell Biol 109:571-590[Medline]
Erneaux C, Govaerts C, Communi D, Pesesse D (1999) The diversity and possible functions of the inositol polyphosphate 5-phosphatases. Biochim Biophys Acta 1436:185-199
Fang M, Rivas MP, Bankaitis VA (1998) The contribution of lipids and lipid metabolism to cellular functions of the Golgi complex. Biochim Biophys Acta 1404:85-100[Medline]
Geuze H, Stoorvogel W, Strous G, Slot J, Bleekmolen J, Mellman I (1988) Sorting of mannose 6-phosphate receptors and lysosomal membrane proteins in endocytic vesicles. J Cell Biol 107:2491-2501[Abstract]
Griffiths G (1989) The structure and function of a mannose 6-phosphate receptor-enriched, pre-lysosomal compartment in animal cells. J Cell Sci Suppl 11:139-147
Griffiths G, Hoflack B, Simons K, Mellman I, Kornfeld S (1988) The mannose 6-phosphate receptor and the biogenesis of lysosomes. Cell 52:329-341[Medline]
Griffiths G, Matteoni R, Back R, Hoflack B (1990) Characterization of the cation-independent mannose 6-phosphate receptor enriched prelysosomal compartment in NRK cells. J Cell Sci 95:441-461[Abstract]
Griffiths G, Simons K (1986) The trans Golgi network: sorting at the exit site of the Golgi complex. Science 234:438-443[Medline]
Honing S, Griffith J, Geuze HJ, Hunziker W (1996) The tyrosine-based lysosomal targeting signal in lamp-1 mediates sorting into Golgiderived clathrin-coated vesicles. EMBO J 15:5230-5239[Abstract]
Hsuan JJ, Minogue S, dos Santos M (1998) Phosphoinositide 4- and 5-kinases and the cellular roles of phosphoinositol 4,5-bisphosphate. Adv Cancer Res 74:167-216[Medline]
Jamney PA (1994) Phosphoinositides and calcium as regulators of cellular actin assembly and disassembly. Annu Rev Physiol 56:169-191[Medline]
Jänne PA, Suchy SF, Bernard D, MacDonald M, Crawley J, Grinberg A, WynshawBoris A, Westphal H, Nussbaum RL (1998) Functional overlap between murine inpp5b and ocrl1 may explain why deficiency of the murine ortholog for OCRL1 does not cause Lowe syndrome. J Clin Invest 101:2042-2053
Karageorgos LE, Isaac EL, Brooks DA, Ravenscroft EM, Davey R, Hopwood JJ, Meikle PJ (1997) Lysosomal biogenesis in lysosomal storage disorders. Exp Cell Res 234:85-97[Medline]
Koenig H (1974) The isolation of lysosomes from brain. In Fleischer S, ed. Methods in Enzymology. Vol 31. New York, Academic Press, 457-477
Ktistakis NT, Brown HA, Waters MG, Sternweis PC, Roth M (1996) Evidence that phospholipase D mediates ADP ribosylation factor-dependent formation of Golgi coated vesicles. J Cell Biol 134:295-306[Abstract]
Ladinsky MS, Howell KE (1992) The trans-Golgi network can be dissected structurally and functionally from the cisternae of the Golgi complex by brefeldin A. Eur J Cell Biol 59:92-105[Medline]
Lee SB, Rhee SG (1995) Significance of PIP2 hydrolysis and regulation of phospholipase C isozymes. Curr Opin Cell Biol 7:183-189[Medline]
LippincottSchwartz J, Yuan L, Tipper C, Amherdt M, Orci L, Klausner RD (1991) Brefeldin A's effects on endosomes, lysosomes, and the TGN suggest a general mechanism for regulating organelle structure and membrane traffic. Cell 67:601-616[Medline]
Liscovitch M, Cantley LC (1995) Lipid second messengers. Cell 81:659-662[Medline]
Liscovitch M, Chalifa V, Pertile P, Chen CS, Cantley LC (1994) Novel function of phosphatidylinositol 4,5-bisphosphate as a cofactor for brain membrane phospholipase D. J Biol Chem 269:403-421
Lowe CU, Terrey M, MacLachan EA (1952) Organic aciduria, decreased renal ammonia production, hydrophthalmos, mental retardation: a clinical entity. Am J Dis Child 83:164-184
Martin TFJ (1998) Phosphoinositide lipids as signalling molecules. Annu Rev Cell Dev Biol 14:231-264[Medline]
Matzaris M, Jackson SP, Laxminarayan KM, Speed CJ, Mitchell CA (1994) Identification and characterization of the phosphatidylinositol-(4,5)-bisphosphate 5-phosphatase in human platelets. J Biol Chem 269:3397-3402
Matzaris M, O'Malley CJ, Badger A, Speed CJ, Bird PI, Mitchell CA (1998) Distinct membrane and cytosolic forms of inositol polyphosphate 5-phosphatase II. J Biol Chem 273:8256-8267
McPherson PS, Garcia EP, Slepnev VI, David C, Zhang X, Bauerfeind R, Nemoto Y, DeCamilli P (1995) A presynaptic inositol-5-phosphatase. Nature 379:353-357
Mullock BM, Perez JH, Kuwana T, Gray SR, Luzio JP (1994) Lysosomes can fuse with a late endosomal compartment in a cell-free system from rat liver. J Cell Biol 126:1173-1182[Abstract]
OlivosGlander IM, Jänne PA, Nussbaum RL (1995) The oculocerebrorenal syndrome gene product is a 105-kD protein localized to the Golgi complex. Am J Hum Genet 57:817-823[Medline]
Racusen LC, Wilson PD, Hartz PA, Fivush BA, Burrow CR (1995) Renal proximal tubular epithelium from patients with nephropathic cystinosis: immortalized cell lines as in vitro model systems. Kidney Int 48:536-543[Medline]
Ramjaun AR, McPherson PS (1996) Tissue-specific alternative splicing generates two synaptojanin isoforms with differential membrane binding properties. J Biol Chem 271:24856-24861
Reaves B, Banting G (1992) Perturbation of the morphology of the trans-Golgi network following brefeldin A treatment: redistribution of a TGN-specific integral membrane protein, TGN38. J Cell Biol 116:85-94[Abstract]
Rhee SG, Choi KD (1992) Regulation of inositol phospholipid-specific phospholipase C isozymes. J Biol Chem 267:12393-12396
Sandvig K, Prydz K, Hansen SH, van Deurs B (1991) Ricin transport in brefeldin A-treated cells: correlation between Golgi structure and toxic effect. J Biol Chem 115:971-981
Stossel TP (1989) From signal to pseudopod. How cells control cytoplasmic actin assembly. J Biol Chem 264:261-264
Suchy SF, Nussbaum RL (1998) Subcellular localization of the Lowe syndrome protein (ocrl1) by differential centrifugation: comparison of its distribution to Golgi-associated proteins. Mol Biol Cell 9S:101A
Suchy SF, OlivosGlander IM, Nussbaum RL (1995) Lowe syndrome, a deficiency of a phosphatidylinositol 4,5-bisphosphate 5-phosphatase in the Golgi apparatus. Hum Mol Genet 4:2245-2250[Abstract]
Tjelle TE, Brech A, Juvet LK, Griffiths G, Berg T (1996) Isolation and characterization of early endosomes, late endosomes and terminal lysosomes: their role in protein degradation. J Cell Sci 109:2905-2914
Terui T, Kahn RA, Randazzo PA (1994) Effects of acid phospholipids on nucleotide exchange properties of ADP-ribosylation factor 1. Evidence for specific interaction with phosphatidylinositol 4,5-bisphosphate. J Biol Chem 269:130-135
Willison K, Lewis V, Zuckerman KS, Cordell J, Dean C, Miller K, Lyon MF, Marsh M (1989) The t complex polypeptide 1 (TCP-1) is associated with the cytoplasmic aspect of Golgi membranes. Cell 57:621-632[Medline]
Wood SA, Park JE, Brown WJ (1991) Brefeldin A causes a microtubule-mediated fusion of the trans-Golgi network and early endosomes. Cell 67:591-600[Medline]
Zhang X, Hartz PA, Philip E, Racusen LC, Majerus PW (1998) Cell lines from kidney proximal tubules of a patient with Lowe syndrome lack OCRL inositol polyphosphate 5-phosphatase and accumulate phosphatidylinositol 4,5-bisphosphate. J Biol Chem 273:1574-1582
Zhang X, Jefferson AB, Auethavekiat V, Majerus PW (1995) The protein deficient in Lowe syndrome is a phosphatidylinositol 4,5,-bisphosphate 5-phosphatase. Proc Natl Acad Sci USA 92:4853-4856[Abstract]