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Yang Sun - One of the best experts on this subject based on the ideXlab platform.
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ocrl regulates lysosome positioning and mtorc1 activity through ssx2ip mediated microtubule anchoring
EMBO Reports, 2021Co-Authors: Biao Wang, Jorge A Alvarado, Yang Sun, Philipp P Prosseda, Tia J Kowal, Qing WangAbstract:Lysosomal positioning and mTOR (mammalian target of rapamycin) signaling coordinate cellular responses to nutrient levels. Inadequate nutrient sensing can result in growth delays, a hallmark of Lowe Syndrome. OCRL mutations cause Lowe Syndrome, but the role of OCRL in nutrient sensing is unknown. Here, we show that OCRL is localized to the centrosome by its ASH domain and that it recruits microtubule-anchoring factor SSX2IP to the centrosome, which is important in the formation of the microtubule-organizing center. Deficiency of OCRL in human and mouse cells results in loss of microtubule-organizing centers and impaired microtubule-based lysosome movement, which in turn leads to mTORC1 inactivation and abnormal nutrient sensing. Centrosome-targeted PACT-SSX2IP can restore microtubule anchoring and mTOR activity. Importantly, boosting the activity of mTORC1 restores the nutrient sensing ability of Lowe patients' cells. Our findings highlight mTORC1 as a novel therapeutic target for Lowe Syndrome.
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loss of ocrl increases ciliary pi 4 5 p2 in Lowe oculocerebrorenal Syndrome
PMC, 2017Co-Authors: Philipp P Prosseda, Na Luo, Jorge A Alvarado, Yang Sun, Biao WangAbstract:ABSTRACT Lowe Syndrome is a rare X-linked disorder characterized by bilateral congenital cataracts and glaucoma, mental retardation, and proximal renal tubular dysfunction. Mutations in OCRL, an inositol polyphosphate 5-phosphatase that dephosphorylates PI(4,5)P 2 , cause Lowe Syndrome. Previously we showed that OCRL localizes to the primary cilium, which has a distinct membrane phospholipid composition, but disruption of phosphoinositides in the ciliary membrane is poorly understood. Here, we demonstrate that cilia from Lowe Syndrome patient fibroblasts exhibit increased levels of PI(4,5)P 2 and decreased levels of PI4P. In particular, subcellular distribution of PI(4,5)P 2 build-up was observed at the transition zone. Accumulation of ciliary PI(4,5)P 2 was pronounced in mouse embryonic fibroblasts (MEFs) derived from Lowe Syndrome mouse model as well as in Ocrl -null MEFs, which was reversed by reintroduction of OCRL. Similarly, expression of wild-type OCRL reversed the elevated PI(4,5)P 2 in Lowe patient cells. Accumulation of sonic hedgehog protein in response to hedgehog agonist was decreased in MEFs derived from a Lowe Syndrome mouse model. Together, our findings show for the first time an abnormality in ciliary phosphoinositides of both human and mouse cell models of Lowe Syndrome.
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ocular pathology of oculocerebrorenal Syndrome of Lowe novel mutations and genotype phenotype analysis
Scientific Reports, 2017Co-Authors: Emilie Song, Jorge A Alvarado, Maria Lim, Cathleen Walnuss, Daniel Neely, Dan Spandau, Alireza Ghaffarieh, Yang SunAbstract:Mutations in the OCRL1 gene result in the oculocerebrorenal Syndrome of Lowe, with symptoms including congenital bilateral cataracts, glaucoma, renal failure, and neurological impairments. OCRL1 encodes an inositol polyphosphate 5-phosphatase which preferentially dephosphorylates phosphatidylinositide 4,5 bisphosphate (PI(4,5)P2). We have identified two novel mutations in two unrelated Lowe Syndrome patients with congenital glaucoma. Novel deletion mutations are detected at c.739-742delAAAG in Lowe patient 1 and c.1595-1631del in Lowe patient 2. End stage glaucoma in patient 2 resulted in the enucleation of the eye, which on histology demonstrated corneal keloid, fibrous infiltration of the angle, ectropion uvea, retinal gliosis, and retinal ganglion cell loss. We measured OCRL protein levels in patient keratinocytes and found that Lowe 1 patient cells had significantly reduced OCRL protein as compared to the control keratinocytes. Genotype-phenotype correlation of OCRL1 mutations associated with congenital glaucoma revealed clustering of missense and deletion mutations in the 5-phosphatase domain and the RhoGAP-like domain. In conclusion, we report novel OCRL1 mutations in Lowe Syndrome patients and the corresponding histopathologic analysis of one patient's ocular pathology.
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ocrl localizes to the primary cilium a new role for cilia in Lowe Syndrome
Human Molecular Genetics, 2012Co-Authors: Na Luo, Clark D. Wells, Robert N. Weinreb, Callah West, Carlos Murgazamalloa, Lou Sun, Ryan M Anderson, Jeffrey B Travers, Hemant Khanna, Yang SunAbstract:Oculocerebral renal Syndrome of Lowe (OCRL or Lowe Syndrome), a severe X-linked congenital disorder characterized by congenital cataracts and glaucoma, mental retardation and kidney dysfunction, is caused by mutations in the OCRL gene. OCRL is a phosphoinositide 5-phosphatase that interacts with small GTPases and is involved in intracellular trafficking. Despite extensive studies, it is unclear how OCRL mutations result in a myriad of phenotypes found in Lowe Syndrome. Our results show that OCRL localizes to the primary cilium of retinal pigment epithelial cells, fibroblasts and kidney tubular cells. Lowe Syndrome-associated mutations in OCRL result in shortened cilia and this phenotype can be rescued by the introduction of wild-type OCRL; in vivo, knockdown of ocrl in zebrafish embryos results in defective cilia formation in Kupffer vesicles and cilia-dependent phenotypes. Cumulatively, our data provide evidence for a role of OCRL in cilia maintenance and suggest the involvement of ciliary dysfunction in the manifestation of Lowe Syndrome.
Joël Lunardi - One of the best experts on this subject based on the ideXlab platform.
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Bleeding disorders in Lowe Syndrome patients: evidence for a link between OCRL mutations and primary haemostasis disorders.
British Journal of Haematology, 2010Co-Authors: Dominique Lasne, Joël Lunardi, Marion Egot, T Mirault, Rémi Salomon, Geneviève Baujat, Françoise Grelac, Christilla Bachelot-lozaAbstract:Lowe Syndrome (LS) is a rare X-linked disorder caused by mutations in the oculocerebrorenal gene (OCRL), encoding OCRL, a phosphatidylinositol 5-phosphatase with a RhoGAP domain. An abnormal rate of haemorrhagic events was found in a retrospective clinical survey. Herein, we report the results of exploration of haemostasis in six LS patients. All patients had normal coagulation tests but prolonged closure times (CTs) in the PFA-100 system. Healthy donors' blood samples incubated with a RhoA kinase inhibitor had prolonged CTs. This suggests that an aberrant RhoA pathway in platelets contributes to CT prolongation and primary haemostasis disorders in LS.
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Two closely related endocytic proteins that share a common OCRL-binding motif with APPL1.
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Laura Swan, Michelle Pirruccello, Livia Tomasini, Joël LunardiAbstract:Mutations of the inositol 5' phosphatase oculocerebrorenal Syndrome of Lowe (OCRL) give rise to the congenital X-linked disorders oculocerebrorenal Syndrome of Lowe and Dent disease, two conditions giving rise to abnormal kidney proximal tubule reabsorption, and additional nervous system and ocular defects in the case of Lowe Syndrome. Here, we identify two closely related endocytic proteins, Ses1 and Ses2, which interact with the ASH-RhoGAP-like (ASPM-SPD-2-Hydin homology and Rho-GTPase Activating Domain-like) domain of OCRL. The interaction is mediated by a short amino acid motif similar to that used by the rab-5 effector APPL1 (Adaptor Protein containing pleckstrin homology [PH] domain, PTB domain and Leucine zipper motif 1) APPL1 for OCRL binding. Ses binding is mutually exclusive with APPL1 binding, and is disrupted by the same missense mutations in the ASH-RhoGAP-like domain that also disrupt APPL1 binding. Like APPL1, Ses1 and -2 are localized on endosomes but reside on different endosomal subpopulations. These findings define a consensus motif (which we have called a phenylalanine and histidine [F&H] motif) for OCRL binding and are consistent with a scenario in which Lowe Syndrome and Dent disease result from perturbations at multiple sites within the endocytic pathway.
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Lowe Syndrome protein Ocrl1 is translocated to membrane ruffles upon Rac GTPase activation: a new perspective on Lowe Syndrome pathophysiology.
Human Molecular Genetics, 2005Co-Authors: Adèle Faucherre, Véronique Satre, Pierrette Desbois, Joël Lunardi, Gérard Gacon, Fumiko Nagano, Olivier DorseuilAbstract:Oculocerebrorenal Lowe Syndrome is a rare X-linked disorder characterized by bilateral cataract, mental retardation and renal Fanconi Syndrome. The Lowe Syndrome protein Ocrl1 is a PIP2 5-phosphatase, primarily localized to the trans-Golgi network (TGN), which 'loss of function' mutations result in PIP2 accumulation in patient's cells. Although PIP2 is involved in many cell functions including signalling, vesicle trafficking and actin polymerization, it has been difficult so far to decipher molecular/cellular mechanisms responsible for Lowe Syndrome phenotype. We have recently shown that, through its C-terminal RhoGAP domain, Ocrl1 forms a stable complex with Rac GTPase within the cell. In line with this finding, we report here that upon epidermal growth factor induced Rac activation in COS-7 cells, a fraction of Ocrl1 translocates from TGN to plasma membrane and concentrates in membrane ruffles. In order to investigate the functionality of Ocrl1 in plasma membrane, we have analysed PIP2 distribution in human dermal fibroblasts (HDFs) from Lowe patients versus control HDFs. As revealed by both immunodetection and green fluorescent protein-PH binding, PIP2 was found strikingly to accumulate in PDGF induced ruffles in Lowe HDFs when compared with control. This suggests that Ocrl1 is active as a PIP2 5-phosphatase in Rac induced membrane ruffles. Cellular properties such as cell migration and establishment of cell-cell contacts, which depend on ruffling and lamellipodia formation, should be further investigated to understand the pathophysiology of Lowe Syndrome.
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Lowe Syndrome protein OCRL1 interacts with Rac GTPase in the trans-Golgi network
Human molecular genetics, 2003Co-Authors: Adèle Faucherre, Véronique Satre, Pierrette Desbois, Joël Lunardi, Olivier Dorseuil, Gérard GaconAbstract:The oculocerebrorenal Syndrome of Lowe (OCRL) is a rare X-linked disorder characterized by severe mental retardation, congenital cataracts and renal Fanconi Syndrome. OCRL1 protein is a phosphatidylinositol 4,5-bisphosphate 5-phosphatase with a C-terminal RhoGAP domain. Considering the pleiotropic cellular functions of Rho GTPases (Rho, Rac and Cdc42) and their dysregulation in several forms of mental retardation, we have investigated the so far unexplored function of the RhoGAP domain of OCRL1. Activated Rac GTPase was found to stably associate with the OCRL1 RhoGAP domain in vitro and to co-immunoprecipitate with endogenous OCRL1. Contrasting with other GAPs, OCRL1 RhoGAP exhibited a significant interaction with GDP bound Rac in vitro. As compared to Rac, other Rho GTPases tested showed reduced (Cdc42) or no binding (RhoA, RhoG) to OCRL1 RhoGAP. Immunofluorescence studies in HEK and COS7 cells and Golgi perturbation assays with Brefeldin A demonstrated that a fraction of endogenous Rac co-localizes with OCRL1 and gamma-adaptin in the trans-Golgi network. The OCRL1 RhoGAP domain showed low Rac GAP activity in vitro, and when expressed in Swiss 3T3 cells induced specific inhibition of RacGTP dependent ruffles, consistent with OCRL1 being an active RacGAP. OCRL1 appears to be a bifunctional protein which, in addition to its PIP2 5-phosphatase activity, binds to Rac GTPase. This novel property may play a role in localizing OCRL1 to the trans-Golgi network. Moreover, loss of OCRL1 RhoGAP and the resulting alteration in Rho pathways may contribute to mental retardation in Lowe Syndrome, as illustrated in other forms of X-linked mental retardation.
Michael Ludwig - One of the best experts on this subject based on the ideXlab platform.
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The oculocerebrorenal Syndrome of Lowe: an update
Pediatric Nephrology, 2016Co-Authors: Arend Bökenkamp, Michael LudwigAbstract:The oculocerebrorenal Syndrome of Lowe is a rare X-linked multisystemic disorder characterized by the triad of congenital cataracts, intellectual disability, and proximal renal tubular dysfunction. Whereas the ocular manifestations and severe muscular hypotonia are the typical first diagnostic clues apparent at birth, the manifestations of incomplete renal Fanconi Syndrome are often recognized only later in life. Other characteristic features are progressive severe growth retardation and behavioral problems, with tantrums. Many patients develop a debilitating arthropathy. Treatment is symptomatic, and the life span rarely exceeds 40 years. The causative oculocerebrorenal Syndrome of Lowe gene ( OCRL ) encodes the inositol polyphosphate 5-phosphatase OCRL-1. OCRL variants have not only been found in classic Lowe Syndrome, but also in patients with a predominantly renal phenotype classified as Dent disease type 2 (Dent-2). Recent data indicate that there is a phenotypic continuum between Dent-2 disease and Lowe Syndrome, suggesting that there are individual differences in the ability to compensate for the loss of enzyme function. Extensive research has demonstrated that OCRL-1 is involved in multiple intracellular processes involving endocytic trafficking and actin skeleton dynamics. This explains the multi-organ manifestations of the disease. Still, the mechanisms underlying the wide phenotypic spectrum are poorly understood, and we are far from a causative therapy. In this review, we provide an update on clinical and molecular genetic findings in Lowe Syndrome and the cellular and physiological functions of OCRL-1.
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Lowe Syndrome dent 2 disease a comprehensive review of known and novel aspects
Journal of pediatric genetics, 2015Co-Authors: Florian Recker, Michael Ludwig, Heiko ReutterAbstract:The oculocerebrorenal Syndrome of Lowe is a rare X-linked multisystemic disorder characterized by the triad of congenital cataracts, cognitive and behavioral impairment and a renal proximal tubulopathy in almost all of the patients. Whereas the ocular manifestations and severe hypotonia are present at birth, the renal involvement appears within the first months of life. Patients show progressive growth retardation and may develop a debilitating arthropathy. Treatment is symptomatic and life span rarely exceeds 40 yr. The causative OCRL gene, encodes an inositol polyphosphate 5-phosphatase. OCRL mutations were not only found in classic Lowe Syndrome, but also in milder affected patients, classified as having Dent-2 disease. There is a phenotypic continuum within patients with Dent-2 disease and Lowe Syndrome, suggesting that there are individual differences in the ability to compensate for loss of enzyme function. Researchers have conducted a large amount of work to understand the etiology responsible for the disease. However, the mechanisms leading to the clinical manifestations are still poorly understood and we are far from an effective therapy. In this review, we have included well-established findings and the most recent progress in understanding Lowe Syndrome and Dent-2 disease.
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a premature termination mutation in a patient with Lowe Syndrome without congenital cataracts dropping the o in ocrl
Klinische Padiatrie, 2012Co-Authors: Sandra M Pasternack, Velibor Tasic, Detlef Böckenhauer, Heiko Reutter, Melanie Refke, Markus Draaken, C Conrad, Mark Born, Regina C Betz, Michael LudwigAbstract:The oculocerebrorenal Syndrome of Lowe is an X-linked recessive disorder characterized by the triad of congenital cataracts, mental retardation and a renal proximal tubulopathy. Although severity of phenotype might vary, congenital cataracts are part of the definition of this rare disorder. We report a 13-year-old patient with the typical cerebrorenal phenotype of Lowe Syndrome, that had remained undiagnosed due to absence of any ocular involvement. OCRL gene analysis was carried. DNA analysis revealed a c.C760T (p.Gln199X) nonsense mutation in exon 8 expected to cause complete disruption of OCRL function. After sequencing the parents of the index patient and his maternal grandparents, this mutation turned out to be de novo in the mother. Furthermore, a silent variant (p.Arg35=) was identified in exon 2, that could also be identified in the mother and her 3 sisters, but not in the grandparents assuming germ cell mosaicism in either of the grandparents. RNA analysis from the patient’s lymphocytes revealed presence of full-length OCRL transcripts. Western blotting from lymphocyte samples failed to detect OCRL protein even in controls. Our findings extend the phenotypic spectrum caused by OCRL mutations and illustrate that there may be selective organ involvement in Lowe Syndrome.
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Clinical and laboratory features of Macedonian children with OCRL mutations
Pediatric Nephrology, 2011Co-Authors: Velibor Tasic, Nadica Ristoska-bojkovska, Vesna Sabolic-avramovska, Petar Korneti, Vladimir J. Lozanovski, Zoran Gucev, Michael LudwigAbstract:OCRL mutations, which are a hallmark of Lowe Syndrome, have recently been found in patients with isolated renal phenotype (Dent-2 disease). In this report, we describe clinical and laboratory features in five Macedonian children with mutations in the OCRL gene. Children with a clinical diagnosis of Lowe Syndrome or Dent disease underwent complete neurological and ophthalmological examination, imaging of the kidney and urinary tract, assessment of renal tubular function, and mutation analysis of the OCRL gene. Two children (18 months and 11 years, respectively) were diagnosed with Lowe Syndrome on the basis of congenital cataracts, severe psychomotor retardation, and renal dysfunction. Both children had low molecular weight proteinuria (LMWP) and hypercalciuria, but not Fanconi Syndrome. The older one had bilateral nephrolithiasis due to associated hypocitraturia and mild hyperoxaluria. Three children with asymptomatic proteinuria were diagnosed with Dent-2 disease; none had cataracts or neurological deficit. One child showed mild mental retardation. All had LMWP, hypercalciuria, and elevated enzymes (creatine phosphokinase, lactic dehydrogenase). All three children had an abnormal Tc-99m DMSA scan revealing poor visualization of the kidneys with a high radionuclide content in the bladder; none had nephrolithiasis or nephrocalcinosis. In conclusion, children with OCRL mutations may present with very mild phenotype (asymptomatic proteinuria with/without mild mental retardation) or severe classic oculocerebrorenal Syndrome of Lowe. Elevated enzymes and abnormal results on the Tc-99m DMSA scan may be useful indicators for Dent-2 disease.
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dent 2 disease a mild variant of Lowe Syndrome
The Journal of Pediatrics, 2009Co-Authors: Arend Bökenkamp, Robert J Unwin, Velibor Tasic, Bernd Hoppe, Detlef Böckenhauer, Hae Il Cheong, Michael LudwigAbstract:Objective To compare the renal and extra-renal phenotypes of patients classified as having Dent disease, Dent-2 disease, or Lowe Syndrome. Study design Chart review of data from 93 patients with identified voltage-gated chloride channel and chloride/proton antiporter 5 gene and oculo-cerebro-renal Syndrome of Lowe gene mutations observed by the authors, complemented with published data. Results There was a wide overlap of renal symptoms. Nephrocalcinosis was more prevalent in Dent-1 disease, and renal tubular acidosis, aminoaciduria, and renal failure was more prevalent in patients with Lowe Syndrome. Patients with Lowe Syndrome were shorter than patients with Dent-1 disease, and patients with Dent-2 disease showed an intermediate phenotype. Three patients with Dent-2 disease had mild peripheral cataract, and 9 patients were noted to have some degree of mental retardation. Conclusion There is a phenotypic continuum within patients with Dent-2 disease and Lowe Syndrome, suggesting that there are individual differences in the ability to compensate for loss of oculo-cerebro-renal Syndrome of Lowe gene function.
Pierrette Desbois - One of the best experts on this subject based on the ideXlab platform.
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ocrl mutated fibroblasts from patients with dent 2 disease exhibit inpp5b independent phenotypic variability relatively to Lowe Syndrome cells
Human Molecular Genetics, 2015Co-Authors: Pierrette Desbois, Rodrick Montjean, Rifdat Aoidi, Julien RucciAbstract:OCRL mutations are associated with both Lowe Syndrome and Dent-2 disease, two rare X-linked conditions. LoweSyndromeisanoculo-cerebro-renaldisorder,whereasDent-2patientsmainlypresentrenalproximaltubulopathy. Loss of OCRL-1, a phosphoinositide-5-phosphatase, leads in Lowe patients’ fibroblasts to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) accumulation, with defects in F-actin network, a-actinin distribution and ciliogenesis, whereas fibroblasts of Dent-2 patients are still uncharacterized. To search for mechanisms linked to clinical variability observed between these twoOCRL mutation-associated pathologies, we compared dermalfibroblasts from independent patients,four affectedbyDent-2 diseaseandsixwith LoweSyndrome.For the first time, we describe that Dent-2 fibroblasts with OCRL loss-of-function (LOF) mutations exhibit decrease in actin stress fibers, appearance of punctate a-actinin signals and alteration in primary cilia formation. Interestingly, we quantified these phenotypes as clearly intermediate between Lowe and control fibroblasts, thus suggesting that levels of these defects correlate with clinical variations observed between patients with OCRL mutations. In addition, we show that Lowe and Dent-2 fibroblasts display similar PI(4,5)P2 accumulation levels. Finally, we analyzed INPP5B, a paralogous gene already reported to exhibit functional redundancy with OCRL,andreportneitherdifferencesinitsexpressionatRNAorproteinlevels,norspecificallelicvariationsbetween fibroblasts of patients. Altogether, we describe here differential phenotypes between fibroblasts from Lowe and Dent-2 patients, both associated with OCRL LOF mutations, we exclude direct roles of PI(4,5)P2 andINPP5Binthisphenotypicvariabilityandweunderlinepotentialkeyalterationsleadingtoocularandneurological clinical features in Lowe Syndrome.
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Lowe Syndrome protein Ocrl1 is translocated to membrane ruffles upon Rac GTPase activation: a new perspective on Lowe Syndrome pathophysiology.
Human Molecular Genetics, 2005Co-Authors: Adèle Faucherre, Véronique Satre, Pierrette Desbois, Joël Lunardi, Gérard Gacon, Fumiko Nagano, Olivier DorseuilAbstract:Oculocerebrorenal Lowe Syndrome is a rare X-linked disorder characterized by bilateral cataract, mental retardation and renal Fanconi Syndrome. The Lowe Syndrome protein Ocrl1 is a PIP2 5-phosphatase, primarily localized to the trans-Golgi network (TGN), which 'loss of function' mutations result in PIP2 accumulation in patient's cells. Although PIP2 is involved in many cell functions including signalling, vesicle trafficking and actin polymerization, it has been difficult so far to decipher molecular/cellular mechanisms responsible for Lowe Syndrome phenotype. We have recently shown that, through its C-terminal RhoGAP domain, Ocrl1 forms a stable complex with Rac GTPase within the cell. In line with this finding, we report here that upon epidermal growth factor induced Rac activation in COS-7 cells, a fraction of Ocrl1 translocates from TGN to plasma membrane and concentrates in membrane ruffles. In order to investigate the functionality of Ocrl1 in plasma membrane, we have analysed PIP2 distribution in human dermal fibroblasts (HDFs) from Lowe patients versus control HDFs. As revealed by both immunodetection and green fluorescent protein-PH binding, PIP2 was found strikingly to accumulate in PDGF induced ruffles in Lowe HDFs when compared with control. This suggests that Ocrl1 is active as a PIP2 5-phosphatase in Rac induced membrane ruffles. Cellular properties such as cell migration and establishment of cell-cell contacts, which depend on ruffling and lamellipodia formation, should be further investigated to understand the pathophysiology of Lowe Syndrome.
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Lowe Syndrome protein OCRL1 interacts with Rac GTPase in the trans-Golgi network
Human molecular genetics, 2003Co-Authors: Adèle Faucherre, Véronique Satre, Pierrette Desbois, Joël Lunardi, Olivier Dorseuil, Gérard GaconAbstract:The oculocerebrorenal Syndrome of Lowe (OCRL) is a rare X-linked disorder characterized by severe mental retardation, congenital cataracts and renal Fanconi Syndrome. OCRL1 protein is a phosphatidylinositol 4,5-bisphosphate 5-phosphatase with a C-terminal RhoGAP domain. Considering the pleiotropic cellular functions of Rho GTPases (Rho, Rac and Cdc42) and their dysregulation in several forms of mental retardation, we have investigated the so far unexplored function of the RhoGAP domain of OCRL1. Activated Rac GTPase was found to stably associate with the OCRL1 RhoGAP domain in vitro and to co-immunoprecipitate with endogenous OCRL1. Contrasting with other GAPs, OCRL1 RhoGAP exhibited a significant interaction with GDP bound Rac in vitro. As compared to Rac, other Rho GTPases tested showed reduced (Cdc42) or no binding (RhoA, RhoG) to OCRL1 RhoGAP. Immunofluorescence studies in HEK and COS7 cells and Golgi perturbation assays with Brefeldin A demonstrated that a fraction of endogenous Rac co-localizes with OCRL1 and gamma-adaptin in the trans-Golgi network. The OCRL1 RhoGAP domain showed low Rac GAP activity in vitro, and when expressed in Swiss 3T3 cells induced specific inhibition of RacGTP dependent ruffles, consistent with OCRL1 being an active RacGAP. OCRL1 appears to be a bifunctional protein which, in addition to its PIP2 5-phosphatase activity, binds to Rac GTPase. This novel property may play a role in localizing OCRL1 to the trans-Golgi network. Moreover, loss of OCRL1 RhoGAP and the resulting alteration in Rho pathways may contribute to mental retardation in Lowe Syndrome, as illustrated in other forms of X-linked mental retardation.
Kai S. Erdmann - One of the best experts on this subject based on the ideXlab platform.
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the role of the Lowe Syndrome protein ocrl in the endocytic pathway
Biological Chemistry, 2015Co-Authors: Shruti Sharma, Agnieszka Skowronek, Kai S. ErdmannAbstract:Mutations of the inositol-5-phosphatase OCRL cause Lowe Syndrome and Dent-II disease. Both are rare genetic disorders characterized by renal defects. Lowe Syndrome is furthermore characterized by defects of the eye (congenital cataracts) and nervous system (mental disabilities, hypotonia). OCRL has been localised to various endocytic compartments suggesting impairments in the endocytic pathway as possible disease mechanism. Recent evidence strongly supports this view and shows essential roles of OCRL at clathrin coated pits, transport of cargo from endosomes to the trans-Golgi network as well as recycling of receptors from endosomes to the plasma membrane. In particular in vitro and in vivo evidence demonstrates an important role of OCRL in recycling of megalin, a multi-ligand receptor crucial for reabsorption of nutrients in the proximal tubulus, a process severely impaired in Lowe Syndrome patients. Thus defects in the endocytic pathway are likely to significantly contribute to the kidney phenotype in Lowe Syndrome and Dent-II disease.
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a role of the Lowe Syndrome protein ocrl in early steps of the endocytic pathway
Developmental Cell, 2007Co-Authors: Yuxin Mao, Roberto Zoncu, Kai S. Erdmann, Heather J Mccrea, Sang Yoon LeeAbstract:Summary Mutations in the inositol 5-phosphatase OCRL are responsible for Lowe Syndrome, whose manifestations include mental retardation and renal Fanconi Syndrome. OCRL has been implicated in membrane trafficking, but disease mechanisms remain unclear. We show that OCRL visits late-stage, endocytic clathrin-coated pits and binds the Rab5 effector APPL1 on peripheral early endosomes. The interaction with APPL1, which is mediated by the ASH-RhoGAP-like domains of OCRL and is abolished by disease mutations, provides a link to protein networks implicated in the reabsorptive function of the kidney and in the trafficking and signaling of growth factor receptors in the brain. Crystallographic studies reveal a role of the ASH-RhoGAP-like domains in positioning the phosphatase domain at the membrane interface and a clathrin box protruding from the RhoGAP-like domain. Our results support a role of OCRL in the early endocytic pathway, consistent with the predominant localization of its preferred substrates, PI(4,5)P 2 and PI(3,4,5)P 3 , at the cell surface.
