title: Adaptor protein 1 complexes regulate intracellular trafficking of the kidney anion exchanger 1 in epithelial cells.
abstract: Distal renal tubular acidosis (dRTA) can be caused by mutations in the gene encoding the anion exchanger 1 (AE1) and is characterized by defective urinary acidification, metabolic acidosis, and renal stones. AE1 is expressed at the basolateral membrane of type A intercalated cells in the renal cortical collecting duct (kAE1). Two dRTA mutations result in the carboxyl-terminal truncation of kAE1; in one case, the protein trafficked in a nonpolarized way in epithelial cells. A recent yeast two-hybrid assay showed that the carboxyl-terminal cytosolic domain of AE1 interacts with adaptor protein complex 1 (AP-1A) subunit μ1A (mu-1A; Sawasdee N, Junking M, Ngaojanlar P, Sukomon N, Ungsupravate D, Limjindaporn T, Akkarapatumwong V, Noisakran S, Yenchitsomanus PT. Biochem Biophys Res Commun 401: 85-91, 2010). Here, we show the interaction between kAE1 and mu-1A and B in vitro by reciprocal coimmunoprecipitation in epithelial cells and in vivo by coimmunoprecipitation from mouse kidney extract. When endogenous mu-1A (and to a lesser extent mu-1B) was reduced, kAE1 protein was unable to traffic to the plasma membrane and was rapidly degraded via a lysosomal pathway. Expression of either small interfering RNA-resistant mu-1A or mu-1B stabilized kAE1 in these cells. We also show that newly synthesized kAE1 does not traffic through recycling endosomes to the plasma membrane, suggesting that AP-1B, located in recycling endosomes, is not primarily involved in trafficking of newly synthesized kAE1 when AP-1A is present in the cells. Our data demonstrate that AP-1A regulates processing of the basolateral, polytopic membrane protein kAE1 to the cell surface and that both AP-1A and B adaptor complexes are required for normal kAE1 trafficking.
authors: Department of Physiology, University of Alberta, Edmonton, Alberta, Canada.
authors: Ensaf Y
authors: EY
authors: Almomani
authors: Jennifer C
authors: JC
authors: King
authors: Janjuree
authors: J
authors: Netsawang
authors: Pa-Thai
authors: PT
authors: Yenchitsomanus
authors: Prida
authors: P
authors: Malasit
authors: Thawornchai
authors: T
authors: Limjindaporn
authors: R Todd
authors: RT
authors: Alexander
authors: Emmanuelle
authors: E
authors: Cordat
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004285:Dogs; D004847:Epithelial Cells / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D051379:Mice; D021381:Protein Transport / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering; D013552:Swine; D020798:Two-Hybrid System Techniques
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D017920:Antiporters; D034741:RNA, Small Interfering