MAL Decreases the Internalization of the Aquaporin-2 Water Channel
|Title:||MAL Decreases the Internalization of the Aquaporin-2 Water Channel|
|Authors:||Kamsteeg, Erik-Jan; Duffield, Amy S.; Konings, Irene B. M.; Spencer, Joanna; Pagel, Phillip; Deen, Peter M.T.; Caplan, Michael J.|
|Publisher:||Proceedings of the National Academy of Sciences of the United States of America|
|Date Published:||October 16, 2007|
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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)
Myelin and lymphocyte-associated protein (MAL) is a protein that may be involved in the transfer of proteins from the cell interior to the cell membrane. Caplan, et al., investigated to determine if MAL plays a role in the movement of AQP2 to the apical membrane. First, the researchers confirmed that MAL and AQP2 coexist in the kidney principal cells. Second, they determined that the two proteins interact in the principal cells. Interestingly, MAL prefers to interact with AQP2 that has been phosphorylated, that is, AQP2 that has had a phosphate group added to it, specifically to the serine amino acid residue that is the 256th amino acid residue in the chain of amino acids that comprise the AQP2. Phosphorylation is part of the molecular cascade that occurs when AVP and V2R bind.
By examining AQP2 delivery in cells that do not contain MAL, the research team discovered that AQP2 still was able to transfer from the cell interior to the apical membrane. Nor did the researchers find that MAL helps the AQP2 into the transport vesicles. These findings indicate that MAL is not involved in the translocation of AQP2. However, the researchers did find that when MAL and AQP2 are both expressed in a laboratory cell culture, it results in a two fold increase in AQP2 phosphorylation.
Significantly, the final stages of Caplan, et al’s. research indicated that MAL, though not involved in the delivery of AQP2 to the apical membrane, it slows the rate at which AQP2 returns to cell interior. This allows AQP2 to function as a channel through which water passes for a longer time than it could were MAL not present with it.