Functional Role of the NPxxY Motif in Internalization of the Type 2 Vasopressin Receptor in LLC-PK1 Cells
|Title:||Functional Role of the NPxxY Motif in Internalization of the Type 2 Vasopressin Receptor in LLC-PK1 Cells|
|Authors:||Bouley, Ph.D., Richard; Sun, Tian-Xiao; Chenard, Melissa; McLaughlin, M.D., Margaret Elise; McKee, Mary; Lin, M.D., Ph.D., Herbert Y.; Brown, Dennis; Ausiello, M.D., Dennis A.|
|Publisher:||American Journal of Physiology: Cell Physiology|
|Date Published:||October 01, 2003|
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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)
The V2R’s time dependent loss of sensitivity to AVP (downregulation) is believed to depend on changes in the shape of the V2R stimulated AVP. This allows the V2R to be phosphorylated (i.e., have a phosphate group attached to it), desensitized so it signals less when AVP binds with it, internalized (i.e., moved back into the cell interior), and once internalized, sequestered.
Though the exact details involved in V2R’s internalization (i.e., its movement from the cell membrane to the cell interior) are not known, Bouley, et al., had reason to think that the amino acid sequence NPxxY, consisting of the amino acid residue, Asparagine (N) linked to proline (P) followed by any two amino acids (represented by xx) and ending with the amino acid residue tyrosine (Y), plays an essential role in the internalization of V2R. NPxxY is located in the tail end of the V2R protein.
To determine the role of the NPxxY motif in the AVP induced internalization, cell surface expression, and molecular signaling of V2R, these researchers traced the movements in laboratory cell cultures of both V2R with the NPxxY motif intact and the movements of a mutant V2R where the motif was disrupted due to a phenylalanine amino acid residue (F) being in the spot occupied by tyrosine in a normal V2R. This mutant is called (V2R-Y325F). Bouley, et al., found that both the V2R and the V2R-Y325F were distributed through the cell membranes in a similar manner. They both were able to link and bind with AVP and initiate the molecular sequence that leads to urine concentration, but V2R-Y325F did not return to the cell interior.
The researchers conclude that the NPxxY motif in the V2R plays a major role in the V2R’s ability to return to the cell interior, but that it is not essential for the distribution of V2R in the cell membrane or for the molecular sequence that occurs when AVP and V2R bind. They also discovered that the protein, clathrin, plays a major role in the internalization of V2R.