NARF, an Nemo-like Kinase (NLK)-associated Ring Finger Protein Regulates the Ubiquitylation and Degradation of T Cell Factor/Lymphoid Enhancer Factor (TCF/LEF)*
- Misato Yamada‡,1,
- Junji Ohnishi‡,1,
- Bisei Ohkawara‡,
- Shunichiro Iemura§,
- Kiyotoshi Satoh‡,
- Junko Hyodo-Miura¶,
- Kaoru Kawachi‡,
- Tohru Natsume§ and
- Hiroshi Shibuya‡∥,2
- ‡Department of Molecular Cell Biology, Medical Research Institute and School of Biomedical Science, Tokyo Medical and Dental University, and SORST, JST, Chiyoda-ku, Tokyo 101-0062, the ∥Center of Excellence Program for Research on Molecular Destruction and Reconstruction of Tooth and Bone, Tokyo Medical and Dental University, Chiyoda, Tokyo 101-0062, the §National Institutes of Advanced Industrial Science and Technology, Biological Information Research Center (JBIRC), Kohtoh-ku, Tokyo 135-0064, and the ¶Division of Morphogenesis, Department of Developmental Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan
- ↵2 To whom correspondence should be addressed: Dept. of Molecular Cell Biology, Medical Research Institute, Tokyo Medical and Dental University, Chiyoda, Tokyo 101-0062, Japan. Tel. and Fax: 81-3-5280-8062; E-mail: shibuya.mcb{at}mri.tmd.ac.jp.
Abstract
β-Catenin is a key player in the Wnt signaling pathway, and interacts with cofactor T cell factor/lymphoid enhancer factor (TCF/LEF) to generate a transcription activator complex that activates Wnt-induced genes. We previously reported that Nemo-like kinase (NLK) negatively regulates Wnt signaling via phosphorylation of TCF/LEF. To further evaluate the physiological roles of NLK, we performed yeast two-hybrid screening to identify NLK-interacting proteins. From this screen, we isolated a novel RING finger protein that we term NARF (NLK associated RING finger protein). Here, we show that NARF induces the ubiquitylation of TCF/LEF in vitro and in vivo, and functions as an E3 ubiquitin-ligase that specifically cooperates with the E2 conjugating enzyme E2-25K. We found that NLK augmented NARF binding and ubiquitylation of TCF/LEF, and this required NLK kinase activity. The ubiquitylated TCF/LEF was subsequently degraded by the proteasome. Furthermore, NARF inhibited formation of the secondary axis induced by the ectopic expression of β-catenin in Xenopus embryos. Collectively, our findings raise the possibility that NARF functions as a novel ubiquitin-ligase to suppress the Wnt-β-catenin signaling.
- Received March 6, 2006.
- Revision received May 19, 2006.
- The American Society for Biochemistry and Molecular Biology, Inc.
