title: Post-Golgi supramolecular assembly of aquaporin-4 in orthogonal arrays.
abstract: The supramolecular assembly of aquaporin-4 (AQP4) in orthogonal arrays of particles (OAPs) involves N-terminus interactions of the M23-AQP4 isoform. We found AQP4 OAPs in cell plasma membranes but not in endoplasmic reticulum (ER) or Golgi, as shown by: (i) native gel electrophoresis of brain and AQP4-transfected cells, (ii) photobleaching recovery of green fluorescent protein-AQP4 chimeras in live cells and (iii) freeze-fracture electron microscopy (FFEM). We found that AQP4 OAP formation in plasma membranes, but not in the Golgi, was not related to AQP4 density, pH, membrane lipid composition, C-terminal PDZ domain interactions or α-syntrophin expression. Remarkably, however, fusion of AQP4-containing Golgi vesicles with (AQP4-free) plasma membrane vesicles produced OAPs, suggesting the involvement of plasma membrane factor(s) in AQP4 OAP formation. In investigating additional possible determinants of OAP assembly we discovered membrane curvature-dependent OAP assembly, in which OAPs were disrupted by extrusion of plasma membrane vesicles to ∼110 nm diameter, but not to ∼220 nm diameter. We conclude that AQP4 supramolecular assembly in OAPs is a post-Golgi phenomenon involving plasma membrane-specific factor(s). Post-Golgi and membrane curvature-dependent OAP assembly may be important for vesicle transport of AQP4 in the secretory pathway and AQP4-facilitated astrocyte migration, and suggests a novel therapeutic approach for neuromyelitis optica.
authors: Departments of Medicine and Physiology, University of California-San Francisco, CA 94143, USA.
authors: Andrea
authors: A
authors: Rossi
authors: Florian
authors: F
authors: Baumgart
authors: Alfred N
authors: AN
authors: van Hoek
authors: A S
authors: AS
authors: Verkman
mesh_terms: D000818:Animals; D051401:Aquaporin 4 / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D001253:Astrocytes / Q000378:metabolism / Q000648:ultrastructure; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D016466:CHO Cells; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D006224:Cricetinae; D003412:Cricetulus; D004591:Electrophoresis, Polyacrylamide Gel; D036681:Fluorescence Recovery After Photobleaching; D005614:Freeze Fracturing; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D015151:Immunoblotting; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D013347:Subcellular Fractions; D014162:Transfection
chemical_list: C496030:AQP4 protein, human; D051401:Aquaporin 4