LNX functions as a RING type E3 ubiquitin ligase that targets the cell fate determinant Numb for ubiquitin-dependent degradation

• Published in: The EMBO journal Vol. 21; no. 1-2; pp. 93 - 102
• Main Authors: Nie, Jing, McGill, Melanie A., Dermer, Matt, Dho, Sascha E., Wolting, Cheryl D., McGlade, C. Jane
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 15.01.2002; Blackwell Publishing Ltd; Oxford University Press
• Subjects: Animals; Binding Sites; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Line; CHO Cells; Cricetinae; Dogs; Humans; Ligases - genetics; Ligases - metabolism; LNX; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mutagenesis, Site-Directed; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Numb; PDZ domain; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; RING finger; Substrate Specificity; Ubiquitin - metabolism; ubiquitin ligase; Ubiquitin-Protein Ligases
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/21.1.93

LNX is a RING finger and PDZ domain containing protein that interacts with the cell fate determinant Numb. To investigate the function of LNX, we tested its RING finger domain for ubiquitin ligase activity. The isolated RING finger domain was able to function as an E2‐dependent, E3 ubiquitin ligase in vitro and mutation of a conserved cysteine residue within the RING domain abolished its activity, indicating that LNX is the first described PDZ domain‐containing member of the E3 ubiquitin ligase family. We have identified Numb as a substrate of LNX E3 activity in vitro and in vivo. In addition to the RING finger, a region of LNX, including the Numb PTB domain‐binding site and the first PDZ domain, is required for Numb ubiquitylation. Expression of wild‐type but not mutant LNX causes proteasome‐dependent degradation of Numb and can enhance Notch signalling. These results suggest that the levels of mammalian Numb protein and therefore, by extension, the processes of asymmetric cell division and cell fate determination may be regulated by ubiquitin‐dependent proteolysis.