Phosphorylation and ankyrin-G binding of the C-terminal domain regulate targeting and function of the ammonium transporter RhBG.
RhBG, a human member of the Amt/Mep/Rh/superfamily of ammonium transporters, has been shown to facilitate NH(3) transport and to be anchored to the basolateral plasma membrane of kidney epithelial cells, via ankyrin-G. We showed here that triple alanine substitution of the (419)FLD(421) sequence, which links the cytoplasmic C-terminal domain of RhBG to ankyrin-G, not only disrupted the interaction of RhBG with the spectrin-based skeleton but also delayed its cell surface expression, decreased its plasma membrane stability, and abolished its NH(3) transport function in epithelial cell lines. Similarly, we demonstrated that both anchoring to the membrane skeleton and ammonium transport activity are regulated by the phosphorylation status of the C-terminal tail of RhBG. Tyrosine 429, which belongs to the previously reported YED basolateral targeting signal of RhBG, was demonstrated to be phosphorylated in vitro using purified Src and Syk kinases and ex vivo by analyzing the effect of pervanadate treatment on wild-type RhBG or Y429A mutants. Then, we showed that Y429D and Y429E mutations, mimicking constitutive phosphorylation, abolished NH(3) transport and enhanced Triton X-100 solubilization of RhBG from the cell membrane. In contrast, the nonphosphorylated/nonphosphorylatable Y429A and Y429F mutants behaved the same as wild-type RhBG. Conversely, Y/A or Y/F but not Y/E or Y/D mutations of residue 429 abolished the exclusive basolateral localization of RhBG in polarized epithelial cells. All these results led to a model in which targeting and ammonium transport function of RhBG are regulated by both phosphorylation and membrane skeleton binding of the C-terminal cytoplasmic domain.
Sohet
Fabien
F
INSERM, U665, Paris F-75015, the Institut National de la Transfusion Sanguine, 6 Rue Alexandre Cabanel, Paris F-75015, France.
Colin
Yves
Y
Genetet
Sandrine
S
Ripoche
Pierre
P
Métral
Sylvain
S
Le Van Kim
Caroline
C
Lopez
Claude
C
D019943:Amino Acid Substitution; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D017487:Ankyrins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D016764:Cell Polarity / Q000187:drug effects / Q000502:physiology; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013049:Spectrin / Q000235:genetics / Q000378:metabolism; D000072377:Syk Kinase; D014638:Vanadates / Q000494:pharmacology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
C490613:ANK3 protein, human; C094681:Ank3 protein, mouse; D017487:Ankyrins; D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; C422995:RHBG protein, human; C486033:RhBG protein, mouse; C076715:pervanadate; D013049:Spectrin; D014638:Vanadates; D000641:Ammonia; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D019061:src-Family Kinases