A role of OCRL in clathrin-coated pit dynamics and uncoating revealed by studies of Lowe syndrome cells.

Ramiro Nández,Liang Liang,Summer Paradise,Pietro De Camilli,Matthias Mann,Marco Y Hein,Heather Czapla,Daniel M Balkin,Mirko Messa,James S Duncan

doi:10.7554/elife.02975

Ramiro Nández, Liang Liang + Show 8 more

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https://doi.org/10.7554/elife.02975

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Abstract

Mutations in the inositol 5-phosphatase OCRL cause Lowe syndrome and Dent's disease. Although OCRL, a direct clathrin interactor, is recruited to late-stage clathrin-coated pits, clinical manifestations have been primarily attributed to intracellular sorting defects. Here we show that OCRL loss in Lowe syndrome patient fibroblasts impacts clathrin-mediated endocytosis and results in an endocytic defect. These cells exhibit an accumulation of clathrin-coated vesicles and an increase in U-shaped clathrin-coated pits, which may result from sequestration of coat components on uncoated vesicles. Endocytic vesicles that fail to lose their coat nucleate the majority of the numerous actin comets present in patient cells. SNX9, an adaptor that couples late-stage endocytic coated pits to actin polymerization and which we found to bind OCRL directly, remains associated with such vesicles. These results indicate that OCRL acts as an uncoating factor and that defects in clathrin-mediated endocytosis likely contribute to pathology in patients with OCRL mutations.

Highlights

Reversible phosphorylation of the inositol ring of phosphatidylinositol at the 3, 4 and 5 position generates seven phosphoinositide species, which play critical regulatory roles in cell physiology via their property to control interactions at the cytosolic surface of membranes
We examined the contribution of OCRL to clathrin-mediated endocytosis in Lowe syndrome patient fibroblasts
Our findings suggest that OCRL participates in uncoating and facilitates the recycling of endocytic factors, a process required for the normal progression of endocytosis

Summary

Introduction

Reversible phosphorylation of the inositol ring of phosphatidylinositol at the 3, 4 and 5 position generates seven phosphoinositide species, which play critical regulatory roles in cell physiology via their property to control interactions at the cytosolic surface of membranes. The human genome contains 10 genes encoding inositol 5-phosphatases, a group of enzymes that dephosphorylate the inositol ring at the 5 position, nine of which act on inositol phospholipids (Dyson et al, 2012; Pirruccello and De Camilli, 2012). Mutations in one such gene, OCRL, give rise to Oculo-Cerebro-Renal syndrome of Lowe (Lowe syndrome) and type 2 Dent's disease, two X-linked diseases (Attree et al, 1992; Hoopes et al, 2005). Patients with Dent's disease exhibit similar proximal tubule defects but no, or only mild, additional clinical defects (Bökenkamp et al, 2009; Shrimpton et al, 2009)

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