Rat Kidney Papilla Contains Abundant Synaptobrevin Protein that Participates in the Fusion of Antidiuretic Hormone-regulated Water Channel-containing Endosomes In Vitro
|Title:||Rat Kidney Papilla Contains Abundant Synaptobrevin Protein that Participates in the Fusion of Antidiuretic Hormone-regulated Water Channel-containing Endosomes In Vitro|
|Authors:||Harris, H. William; Amendt-Raduege, Amy M.; Majewski, Rebecca R.; Hammond, Timothy G.; Jo, Inho|
|Publisher:||Proceedings of the National Academy of Sciences of the United States of America|
|Date Published:||March 14, 1995|
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This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)
AQP2s are encased in small sacs called vesicles. It is these AQP2-containing vesicles that carry the AQP2s to the apical cell membrane and fuse with it so the AQP2s may be inserted in the membrane. Jo, et al., sought to identify the proteins responsible for taking and fusing the AQP2-containing vesicles to the apical membrane.
They thought that the protein, synaptobrevin, might be the protein that performs this function. First located in the central nervous system and related tissues (such as brain tissues), recent research has revealed that synaptobrevin and its homologues (proteins such as cellubrevin that are similar in form and function to synaptobrevin) are widespread in yeasts, flies and mammals where they act as parts of a complex of structures that are responsible for fusing intracellular vesicles to intracellular membranes.
Researchers have used a tetanus toxin on live experimental animals which specifically degrades both synaptobrevin and cellubrevin to provide support that these proteins do help endosomes (vesicles that have lost their coating of a protein called clathrin after they have returned to the cell from the cell membrane) travel to and fuse with membranes. But, as yet, researchers had not provided a direct demonstration of a functional role for synaptobrevin or its homologues in the fusion of endosomes in laboratory cell cultures.
In their paper, Jo, et al., demonstrate that the innermost part of the rat kidney, purified and made into a cell culture, contains abundant synaptobrevin protein that fuse the endosomes which they are in to rat kidney cell membranes. The authors infused rats with flourescein-conjugated dextran. This was absorbed by the apical endosomes in the rat kidney. This allowed the researchers to track the movement and function of the inner kidney endosomes after they homogenized, purified and recovered them.
The authors found two types of AQP2 containing endosomes: light endosomes (LE) and heavy endosomes (HE). Although both contained abundant AQP2, only LE possessed synaptobrevin. LE were tested to see if they fused with intracellular membranes in the laboratory cell culture, and about 50% of them did.
To determine if synaptobrevin protein in LE was an important part of the fusion process, the researchers pretreated LE with substances known to inhibit the function of synaptobrevin. Then they tested LE fusion and found it to be greatly inhibited. This data provides strong support for the involvement of synaptobrevin proteins in fusing AQP2-containing vesicles to the apical membrane.