title: MDM2 E3 ubiquitin ligase mediates UT-A1 urea transporter ubiquitination and degradation.
abstract: UT-A1 is the primary urea transporter in the apical plasma membrane responsible for urea reabsorption in the inner medullary collecting duct. Although the physiological function of UT-A1 has been well established, the molecular mechanisms that regulate its activity are less well understood. Analysis of the UT-A1 amino acid sequence revealed a potential MDM2 E3 ubiquitin ligase-binding motif in the large intracellular loop of UT-A1, suggesting that UT-A1 urea transporter protein may be regulated by the ubiquitin-proteasome pathway. Here, we report that UT-A1 is ubiquitinated and degraded by the proteasome but not the lysosome proteolytic pathway. Inhibition of proteasome activity causes UT-A1 cell surface accumulation and concomitantly increases urea transport activity. UT-A1 interacts directly with MDM2; the binding site is located in the NH2-terminal p53-binding region of MDM2. MDM2 mediates UT-A1 ubiquitination both in vivo and in vitro. Overexpression of MDM2 promotes UT-A1 degradation. The mechanism is likely to be physiologically important as UT-A1 ubiquitination was identified in kidney inner medullary tissue. The ubiquitin-proteasome degradation pathway provides an important novel mechanism for UT-A1 regulation.
authors.affiliation: Renal Division, Department of Medicine, Emory University School of Medicine, WMRB Rm. 338, 1639 Pierce Dr., NE, Atlanta, GA 30322, USA. gchen3@emory.edu
authors.forename: Guangping
authors.initials: G
authors.lastname: Chen
authors.forename: Haidong
authors.initials: H
authors.lastname: Huang
authors.forename: Otto
authors.initials: O
authors.lastname: Fröhlich
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.forename: Janet D
authors.initials: JD
authors.lastname: Klein
authors.forename: S Russ
authors.initials: SR
authors.lastname: Price
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Sands
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010879:Piperazines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011485:Protein Binding; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017384:Sequence Deletion; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D014508:Urea / Q000378:metabolism; D000096982:Urea Transporters
chemical_list: D003513:Cycloheximide; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007976:Leupeptins; D026901:Membrane Transport Proteins; D010879:Piperazines; D011480:Protease Inhibitors; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D014508:Urea; D000096982:Urea Transporters; C482205:nutlin 3; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
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