The 5-phosphatase OCRL mediates retrograde transport of the mannose 6-phosphate receptor by regulating a Rac1-cofilin signalling module.
Mutations in the OCRL gene encoding the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) 5-phosphatase OCRL cause Lowe syndrome (LS), which is characterized by intellectual disability, cataracts and selective proximal tubulopathy. OCRL localizes membrane-bound compartments and is implicated in intracellular transport. Comprehensive analysis of clathrin-mediated endocytosis in fibroblasts of patients with LS did not reveal any difference in trafficking of epidermal growth factor, low density lipoprotein or transferrin, compared with normal fibroblasts. However, LS fibroblasts displayed reduced mannose 6-phosphate receptor (MPR)-mediated re-uptake of the lysosomal enzyme arylsulfatase B. In addition, endosome-to-trans Golgi network (TGN) transport of MPRs was decreased significantly, leading to higher levels of cell surface MPRs and their enrichment in enlarged, retromer-positive endosomes in OCRL-depleted HeLa cells. In line with the higher steady-state concentration of MPRs in the endosomal compartment in equilibrium with the cell surface, anterograde transport of the lysosomal enzyme, cathepsin D was impaired. Wild-type OCRL counteracted accumulation of MPR in endosomes in an activity-dependent manner, suggesting that PI(4,5)P(2) modulates the activity state of proteins regulated by this phosphoinositide. Indeed, we detected an increased amount of the inactive, phosphorylated form of cofilin and lower levels of the active form of PAK3 upon OCRL depletion. Levels of active Rac1 and RhoA were reduced or enhanced, respectively. Overexpression of Rac1 rescued both enhanced levels of phosphorylated cofilin and MPR accumulation in enlarged endosomes. Our data suggest that PI(4,5)P(2) dephosphorylation through OCRL regulates a Rac1-cofilin signalling cascade implicated in MPR trafficking from endosomes to the TGN.
Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Vanessa A
VA
van Rahden
Kristina
K
Brand
Juliane
J
Najm
Joerg
J
Heeren
Suzanne R
SR
Pfeffer
Thomas
T
Braulke
Kerstin
K
Kutsche
D051339:Actin Depolymerizing Factors / Q000378:metabolism*; D001190:Arylsulfonates / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism; D009800:Oculocerebrorenal Syndrome / Q000235:genetics / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D021381:Protein Transport; D034622:RNA Interference; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D015398:Signal Transduction; D054462:p21-Activated Kinases / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism
D051339:Actin Depolymerizing Factors; D001190:Arylsulfonates; D052118:Lysosomal-Associated Membrane Protein 1; D017527:Receptor, IGF Type 2; D054462:p21-Activated Kinases; D010744:Phosphoric Monoester Hydrolases; C075695:OCRL protein, human; D002402:Cathepsin D; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein