title: Multifunctional ion transport properties of human SLC4A11: comparison of the SLC4A11-B and SLC4A11-C variants.
abstract: Congenital hereditary endothelial dystrophy (CHED), Harboyan syndrome (CHED with progressive sensorineural deafness), and potentially a subset of individuals with late-onset Fuchs' endothelial corneal dystrophy are caused by mutations in the SLC4A11 gene that results in corneal endothelial cell abnormalities. Originally classified as a borate transporter, the function of SLC4A11 as a transport protein remains poorly understood. Elucidating the transport function(s) of SLC4A11 is needed to better understand how its loss results in the aforementioned posterior corneal dystrophic disease processes. Quantitative PCR experiments demonstrated that, of the three known human NH2-terminal variants, SLC4A11-C is the major transcript expressed in human corneal endothelium. We studied the expression pattern of the three variants in mammalian HEK-293 cells and demonstrated that the SLC4A11-B and SLC4A11-C variants are plasma membrane proteins, whereas SLC4A11-A is localized intracellularly. SLC4A11-B and SLC4A11-C were shown to be multifunctional ion transporters capable of transporting H+equivalents in both a Na+-independent and Na+-coupled mode. In both transport modes, SLC4A11-C H+flux was significantly greater than SLC4A11-B. In the presence of ammonia, SLC4A11-B and SLC4A11-C generated inward currents that were comparable in magnitude. Chimera SLC4A11-C-NH2-terminus-SLC4A11-B experiments demonstrated that the SLC4A11-C NH2-terminus functions as an autoactivating domain, enhancing Na+-independent and Na+-coupled H+flux without significantly affecting the electrogenic NH3-H(n)+cotransport mode. All three modes of transport were significantly impaired in the presence of the CHED causing p.R109H (SLC4A11-C numbering) mutation. These complex ion transport properties need to be addressed in the context of corneal endothelial disease processes caused by mutations in SLC4A11.
authors: Division of Nephrology.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Liyo
authors: L
authors: Kao
authors: Division of Nephrology.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Rustam
authors: R
authors: Azimov
authors: Department of Neurobiology.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Xuesi M
authors: XM
authors: Shao
authors: Stein Eye Institute, and.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Ricardo F
authors: RF
authors: Frausto
authors: Division of Nephrology.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Natalia
authors: N
authors: Abuladze
authors: Division of Nephrology.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Debra
authors: D
authors: Newman
authors: Stein Eye Institute, and.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Anthony J
authors: AJ
authors: Aldave
authors: Division of Nephrology, ikurtz@mednet.ucla.edu.|Brain Research Institute.|David Geffen School of Medicine, University of California, Los Angeles, California.
authors: Ira
authors: I
authors: Kurtz
mesh_terms: D027321:Anion Transport Proteins / Q000235:genetics*; D017920:Antiporters / Q000235:genetics*; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics; D003317:Corneal Dystrophies, Hereditary / Q000235:genetics; D004728:Endothelium, Corneal / Q000378:metabolism; D014644:Genetic Variation / Q000235:genetics*; D057809:HEK293 Cells; D006319:Hearing Loss, Sensorineural / Q000235:genetics; D006801:Humans; D017136:Ion Transport / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D008875:Middle Aged; D009154:Mutation / Q000235:genetics
chemical_list: D027321:Anion Transport Proteins; D017920:Antiporters; D008565:Membrane Proteins; C425809:SLC4A11 protein, human
keywords: CHED; ammonia; cornea; endothelial cell; proton; transport