Drosophila Nedd4 regulates endocytosis of notch and suppresses its ligand-independent activation.
BACKGROUND
Ligand-induced proteolytic cleavage and internalization of the plasma membrane receptor Notch leads to its activation. Ligand-independent, steady-state internalization of Notch, however, does not lead to activation. The mechanism by which downstream effectors discriminate between these bipartite modes of Notch internalization is not understood. Nedd4 is a HECT domain-containing E3 ubiquitin ligase that targets transmembrane receptors containing the PPSY motif for endocytosis. Deltex is a positive Notch signaling regulator that encodes a putative ubiquitin ligase of the ring finger type.


RESULTS
We used the Drosophila system to show that Notch is ubiquitinated and destabilized by Nedd4 in a manner requiring the PPSY motif in the Notch intracellular domain. Loss of Nedd4 function dominantly suppresses the Notch and Deltex mutant phenotypes, and its hyperactivation attenuates Notch activity. In tissue culture cells, the dominant-negative form of Nedd4 blocks steady-state Notch internalization and activates Notch signaling independently of ligand binding. This effect was further potentiated by Deltex. Nedd4 destines Deltex for degradation in a Notch-dependent manner.


CONCLUSIONS
Nedd4 antagonizes Notch signaling by promoting degradation of Notch and Deltex. This Nedd4 function may be important for protecting unstimulated cells from sporadic activation of Notch signaling.
Sakata
Tadashi
T
RIKEN Center for Developmental Biology, Chuo-ku, Kobe 650-0047, Japan.
Sakaguchi
Hiromi
H
Tsuda
Leo
L
Higashitani
Atsushi
A
Aigaki
Toshiro
T
Matsuno
Kenji
K
Hayashi
Shigeo
S
D000818:Animals; D002478:Cells, Cultured; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D056827:Endosomal Sorting Complexes Required for Transport; D005786:Gene Expression Regulation / Q000502:physiology*; D018398:Homeodomain Proteins; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D008954:Models, Biological; D000075702:Nedd4 Ubiquitin Protein Ligases; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D034622:RNA Interference; D051880:Receptors, Notch; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism* / Q000502:physiology; D014921:Wings, Animal / Q000033:anatomy & histology / Q000378:metabolism
C086679:DX protein, Drosophila; D029721:Drosophila Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D018398:Homeodomain Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C497759:N protein, Drosophila; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D051880:Receptors, Notch; D014157:Transcription Factors; D025801:Ubiquitin; C066381:ct protein, Drosophila; C064045:delta protein; D000075702:Nedd4 Ubiquitin Protein Ligases; D044767:Ubiquitin-Protein Ligases