TY - JOUR
T1 - Aquaporin-4 square array assembly
T2 - Opposing actions of M1 and M23 isoforms
AU - Furman, C. Sue
AU - Gorelick-Feldman, Daniel A.
AU - Davidson, Kimberly G.V.
AU - Yasumura, Thomas
AU - Neely, John D.
AU - Agre, Peter
AU - Rash, John E.
PY - 2003/11/11
Y1 - 2003/11/11
N2 - Osmotic homeostasis in the brain involves movement of water through aquaporin-4 (AQP4) membrane channels. Perivascular astrocyte end-feet contain distinctive orthogonal lattices (square arrays) assembled from 4- to 6-nm intramembrane particles (IMPs) corresponding to individual AQP4 tetramers. Two isoforms of AQP4 result from translation initiation at methionine residues M1 and M23, but no functional differences are known. In this study, Chinese hamster ovary cells were transfected with M1, M23, or M1+M23 isoforms, and AQP4 expression was confirmed by immunoblotting, immunocytochemistry, and immunogold labeling. Square array organization was examined by freeze-fracture electron microscopy. In astrocyte end-feet, >90% of 4- to 6-nm IMPs were found in square arrays, with 65% in arrays of 13-30 IMPs. In cells transfected with M23, 95% of 4- to 6-nm IMPs were in large assemblies (rafts), 85% of which contained >100 IMPs. However, in M1 cells, >95% of 4- to 6-nm IMPs were present as singlets, with <5% in incipient arrays of 2-12 IMPs. In M1+M23 cells, 4- to 6-nm IMPs were in arrays of intermediate sizes, resembling square arrays in astrocytes. Structural cross-bridges of 1 × 2 nm linked >90% of IMPs in M23 arrays (≈1,000 cross-bridges per μm2) but were rarely seen in M1 cells. These studies show that M23 and M1 isoforms have opposing effects on intramembrane organization of AQP4: M23 forms large square arrays with abundant cross-bridges; M1 restricts square array assembly.
AB - Osmotic homeostasis in the brain involves movement of water through aquaporin-4 (AQP4) membrane channels. Perivascular astrocyte end-feet contain distinctive orthogonal lattices (square arrays) assembled from 4- to 6-nm intramembrane particles (IMPs) corresponding to individual AQP4 tetramers. Two isoforms of AQP4 result from translation initiation at methionine residues M1 and M23, but no functional differences are known. In this study, Chinese hamster ovary cells were transfected with M1, M23, or M1+M23 isoforms, and AQP4 expression was confirmed by immunoblotting, immunocytochemistry, and immunogold labeling. Square array organization was examined by freeze-fracture electron microscopy. In astrocyte end-feet, >90% of 4- to 6-nm IMPs were found in square arrays, with 65% in arrays of 13-30 IMPs. In cells transfected with M23, 95% of 4- to 6-nm IMPs were in large assemblies (rafts), 85% of which contained >100 IMPs. However, in M1 cells, >95% of 4- to 6-nm IMPs were present as singlets, with <5% in incipient arrays of 2-12 IMPs. In M1+M23 cells, 4- to 6-nm IMPs were in arrays of intermediate sizes, resembling square arrays in astrocytes. Structural cross-bridges of 1 × 2 nm linked >90% of IMPs in M23 arrays (≈1,000 cross-bridges per μm2) but were rarely seen in M1 cells. These studies show that M23 and M1 isoforms have opposing effects on intramembrane organization of AQP4: M23 forms large square arrays with abundant cross-bridges; M1 restricts square array assembly.
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U2 - 10.1073/pnas.2235843100
DO - 10.1073/pnas.2235843100
M3 - Article
C2 - 14597700
AN - SCOPUS:0345659199
SN - 0027-8424
VL - 100
SP - 13609
EP - 13614
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 23
ER -