title: SUMOylation target sites at the C terminus protect Axin from ubiquitination and confer protein stability.
abstract: Axin is a scaffold protein for the beta-catenin destruction complex, and a negative regulator of canonical Wnt signaling. Previous studies implicated the six C-terminal amino acids (C6 motif) in the ability of Axin to activate c-Jun N-terminal kinase, and identified them as a SUMOylation target. Deletion of the C6 motif of mouse Axin in vivo reduced the steady-state protein level, which caused embryonic lethality. Here, we report that this deletion (Axin-DeltaC6) causes a reduced half-life in mouse embryonic fibroblasts and an increased susceptibility to ubiquitination in HEK 293T cells. We confirmed the C6 motif as a SUMOylation target in vitro, and found that mutating the C-terminal SUMOylation target residues increased the susceptibility of Axin to polyubiquitination and reduced its steady-state level. Heterologous SUMOylation target sites could replace C6 in providing this protective effect. These findings suggest that SUMOylation of the C6 motif may prevent polyubiquitination, thus increasing the stability of Axin. Although C6 deletion also caused increased association of Axin with Dvl-1, this interaction was not altered by mutating the lysine residues in C6, nor could heterologous SUMOylation motifs replace the C6 motif in this assay. Therefore, some other specific property of the C6 motif seems to reduce the interaction of Axin with Dvl-1.
authors.affiliation: Department of Genetics and Development, 701 W. 168th St., Columbia University Medical Center, New York, NY 10032, USA.
authors.forename: Min Jung
authors.initials: MJ
authors.lastname: Kim
authors.forename: Ian V
authors.initials: IV
authors.lastname: Chia
authors.forename: Frank
authors.initials: F
authors.lastname: Costantini
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D060466:Axin Protein; D002460:Cell Line; D000072261:Dishevelled Proteins; D006801:Humans; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D015398:Signal Transduction / Q000502:physiology; D054875:Ubiquitination / Q000502:physiology*; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D060466:Axin Protein; C000606578:DVL1 protein, human; D000072261:Dishevelled Proteins; C000606579:Dvl1 protein, mouse; D010750:Phosphoproteins; D012097:Repressor Proteins; D051153:Wnt Proteins