Notch-induced Asb2 expression promotes protein ubiquitination by forming non-canonical E3 ligase complexes.
Notch signaling controls multiple developmental processes, thus demanding versatile functions. We have previously shown that this may be partly achieved by accelerating ubiquitin-mediated degradation of important regulators of differentiation. However, the underlying mechanism was unknown. We now find that Notch signaling transcriptionally activates the gene encoding ankyrin-repeat SOCS box-containing protein 2 (Asb2). Asb2 promotes the ubiquitination of Notch targets such as E2A and Janus kinase (Jak) 2, and a dominant-negative (DN) mutant of Asb2 blocks Notch-induced degradation of these proteins. Asb2 likely binds Jak2 directly but associates with E2A through Skp2. We next provide evidence to suggest that Asb2 bridges the formation of non-canonical cullin-based complexes through interaction with not only ElonginB/C and Cullin (Cul) 5, but also the F-box-containing protein, Skp2, which is known to associate with Skp1 and Cul1. Consistently, ablating the function of Cul1 or Cul5 using DN mutants or siRNAs protected both E2A and Jak2 from Asb2-mediated or Notch-induced degradation. By shifting monomeric E3 ligase complexes to dimeric forms through activation of Asb2 transcription, Notch could effectively control the turnover of a variety of substrates and it exerts diverse effects on cell proliferation and differentiation.
Immunobiology and Cancer Research Program, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, OK 73104, USA.
Lei
L
Nie
Ying
Y
Zhao
Wei
W
Wu
Yuan-Zheng
YZ
Yang
Hong-Cheng
HC
Wang
Xiao-Hong
XH
Sun
D000818:Animals; D044842:Cullin Proteins / Q000378:metabolism; D000075065:Elongin; D006367:HeLa Cells; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D041681:NIH 3T3 Cells; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D051880:Receptors, Notch / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
C437987:ASB2 protein, human; D044842:Cullin Proteins; D000075065:Elongin; D051880:Receptors, Notch; D044786:S-Phase Kinase-Associated Proteins; C108944:SOCS1 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; D053614:Janus Kinase 2