SUMO-1 Modification of the C-terminal KVEKVD of Axin Is Required for JNK Activation but Has No Effect on Wnt Signaling
Journal of Biological Chemistry
Axin is a multifunctional protein, regulating Wnt signaling and the c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK) pathway as well as tumorigenesis. In the present study, we found that Axin interacts with three SUMO-1 (small ubiquitin-related modifier) conjugating enzymes 3 (E3), PIAS1, PIASx␤, and PIASy. The extreme C-terminal six amino acid residues of Axin are critical for the Axin/E3 interaction as deletion of the six residues (Axin⌬C6) completely abolished the ability of Axin
... o interact with E3 enzymes. Axin⌬C6 also failed to activate JNK, although it was intact in both its interaction with MEKK1 and homodimerization. Consistent with the presence of a doublet of the KV(E/D) sumoylation consensus motif at the C-terminal end (KVEKVD), we found that Axin is heavily sumoylated. Deletion of the C-terminal six amino acids drastically reduced sumoylation, indicating that the C-terminal six amino acids stretch is the main sumoylation site for Axin. Sumoylation-defective mutants failed to activate JNK but effectively destabilized ␤-catenin and attenuated LEF1 transcriptional activity. In addition, we show that dominant negative Axin mutants blocked PIAS-mediated JNK activation, in accordance with the requirement of sumoylation for Axin-mediated JNK activation. Taken together, we demonstrate that sumoylation plays a role for Axin to function in the JNK pathway.