Regulation of epithelial Na+ channel activity by conserved serine/threonine switches within sorting signals.
The PY and YXXphi motifs are canonical sorting signals involved in trafficking. Nedd4-2 and the mu(2)-subunit of the AP-2 complex target these motifs to facilitate internalization. Epithelial Na(+) channel (ENaC) subunits contain both motifs in their cytosolic COOH termini where they overlap ((S/T)PPPXYX(S/T)phi). Just preceding the PY and embedded within the YXXphi motifs are conserved serine/threonine. We test here whether these conserved Ser/Thr modulate ENaC activity by influencing the function of the internalization domains. We find that co-expression of dominant-negative dynamin (K44A) with ENaC increases channel activity. Conversely, co-expression of Nedd4-2 and epsin with ENaC decrease activity. Alanine substitution of the conserved Thr(628) preceding the PY motif in gamma-mENaC had no effect on basal activity. Channels with this mutation, however, responded to K44A and epsin but not Nedd4-2. Similarly, mutation of the proline repeat in the PY motif of gamma-mENaC disrupted only Nedd4-2 regulation having no effect on regulation by K44A and epsin. Alanine substitution of the conserved Thr within the YXX motif of gamma-mENaC (T635A) increased basal activity. Channels containing this mutation responded to Nedd4-2 but not K44A and epsin. Channels containing the T635(D/E) substitution in gamma-mENaC did not have increased basal activity and responded to Nedd4-2 but not K44A. The double mutant T628A,T635A did not respond to Nedd4-2 or K44A. Mutation of Thr(628) and Thr(635) also disrupted ENaC precipitation with the mu(2)-subunit of the AP-2 complex. Moreover, the YXXphi motif, independent of the PY motif, was sufficient to target degradation with T635A disrupting this effect. These results demonstrate that the overlapping PY and YXXphi motifs in ENaC are, in some instances, capable of independent function and that the Ser/Thr just preceding and within these domains impact this function.
Staruschenko
Alexander
A
Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Pochynyuk
Oleh
O
Stockand
James D
JD
D033942:Adaptor Proteins, Vesicular Transport; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D017124:Conserved Sequence; D034281:Dynamins / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D005816:Genetic Complementation Test; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D046912:Multiprotein Complexes; D000075702:Nedd4 Ubiquitin Protein Ligases; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000737:chemistry; D050656:Transcription Factor AP-2 / Q000737:chemistry / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism
D033942:Adaptor Proteins, Vesicular Transport; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D046912:Multiprotein Complexes; D021122:Protein Subunits; D011994:Recombinant Proteins; D015222:Sodium Channels; D050656:Transcription Factor AP-2; D033921:Vesicular Transport Proteins; C114154:epsin; D013912:Threonine; D012694:Serine; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; C000618461:Nedd4l protein, mouse; D044767:Ubiquitin-Protein Ligases; D034281:Dynamins