1998 Global Conference Proceeding

March 02 - 04, 1998

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Conference: 1998 Global Conference
Title: Transport Defects of V2 Receptor Mutants Found in Patients with X-linked Nephrogenic Diabetes Insipidus
Authors: Rosenthal, Walter; Schulein, Ralf; Oksche, Alexander; Rutz, Claudia; Hermosilla, Ricardo
Institutions: Charite - Universitatsmedizin Berlin, Forschungsinstitut fur Molekulare Pharmakologie (FMP), Institut Fuer Pharmakologie, Justus-Liebig-Universitat Giessen
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Walter Rosenthal

Arginine vasopressin exerts its antidiuretic action via V2 receptors located on kidney epithelial (principal) cells. About 100 mutations in the V2 receptor gene have been described in patients with X-linked nephrogenic diabetes insipidus (NDI). The majority of the mutations are missense and nonsense mutations; frameshift mutations due to insertion or deletion of bases have also been described. Characterization of V2 receptor mutants revealed defects of processing, transport to the cell surface, ligand binding and G-protein coupling/activation (1).

Many mutant receptors show a substantially reduced cell surface delivery. We therefore investigated the structural requirement for this process. We found that a truncated receptor, similar to the Hopewell mutant (W71X), is inserted into the membrane of the endoplasmic reticulum (ER) and adopts the correct orientation. This indicates that the first transmembrane domain and the flanking hydrophilic regions of the V2 receptor are sufficient for both insertion and correct orientation (2). Point mutations in the first and fourth transmembrane domains lead to the expression of immature, presumably intracellularly retained proteins (3). A mutant receptor lacking a major portion of the intracellular C-terminus (R337X) was retained within the ER (4). Further analysis of the N-terminal portion of the intracellular C-terminus showed that a hydrophobic motif consisting of a di-leucine sequence and an upstream glutamate residue are essential for establishing a functional and transport-competent state (5). The C-terminal portion of the intracellular C-terminus seems to be required for efficient cell surface delivery but not for function (4). In addition, palmitoylated cysteine residues 341 and 342 were found to be required for cell surface delivery and receptor internalization upon agonist exposure (6).

References

  1. Rosenthal, W., Oksche, A., Bichet, D.G.: Two genes - one disease: the molecular basis of congenital nephrogenic diabetes insipidus. Adv. Mol. Cell. Endocrinol. Vol. 2, Ed.: Le Roith, D., JAI Press Inc., 143-167 (1998)
  2. Schülein, R., Rutz, C., Rosenthal, W.: Membrane targeting and determination of transmembrane topology of the human vasopressin V2 receptor. J. Biol. Chem. 271, 28844-28852 (1996)
  3. Oksche, A., Schülein, R., Rutz, C., Liebenhoff, U., Dickson, J., Müller, H., Birnbaumer, M., Rosenthal, W.: Vasopressin V2 receptor mutants causing X-linked nephrogenic diabetes insipidus: analysis of expression, processing and function. Mol. Pharmacol. 50, 820-828 (1996)
  4. Oksche, A., Dehe, Schülein, R., Wiesner, B., Rosenthal, W.: Folding and cell surface expression of the vasopressin V2 receptor: requirement of the intracellular C-terminus. FEBS Lett. (in press)
  5. Schülein, R., Hermosilla, R. and Rosenthal, W.: Sorting signals of G-Protein-coupled receptors - A glutamate/di-leucine motif is essential for cell surface expression of the vasopressin V2-receptor. Naunyn-Schmiedeberg´s Arch. Pharmacol. 355 (Suppl.), R 56 (1997)
  6. Schülein, R., Liebenhoff, U., Müller, H., Birnbaumer, M., Rosenthal, W.: Properties of the human arginine vasopressin V2 receptor after site-directed mutagenesis of its putative palmitoylation site. Biochem. J. 313, 611-616 (1996)

Most people with X-linked nephrogenic diabetes insipidus (NDI) have mutations in the V2 receptor genes, resulting in the synthesis of "wrong" receptor proteins which do not function as they should. About 100 different mutations in the V2 receptor gene have been described. How a receptor protein misfunctions depends on the mutation it has. Some mutations render the receptor incapable of responding to the hormone vasopressin by abolishing the receptor's capabilities to either recognize the hormone or to interact with the activate proteins of the signal transduction chain. Other mutations prevent it from reaching the surface of the cell (where the hormone is). This study examines the structural causes for the mutant receptors' reduced ability to get to the surface of the cell where it is needed to do its job.

All regions of the V2 receptor are susceptible to mutations. The authors found that a truncated V2 receptor, that is, a mutated receptor that is missing the major latter part of its genetic sequence, is still able to incorporate into the membrane of an intracellular structure (the endoplasmic reticulum or ER) and be faced in the right direction. This indicates that just the first transmembrane domain (the V2 receptor has seven of them) and the regions around it are sufficient for the V2 receptor to begin its journey to the cell surface. But more is required if the V2R is to move on from this intracellular structure (the first intermediate stop) to the cell surface. For example, a portion of the V2R, the intracellular "end" called the C-terminus, is required for the receptor to leave the ER and get to the cell surface. Specific single building blocks (amino acids) in the C-terminus must be present if the receptor is to transport and function properly. Also, mutations in which the V2 receptor lacks a major portion of its intracellular C-terminus render the receptor incapable of reaching the cell surface.