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Molecular and Cellular Biology, March 2004, p. 2012-2024, Vol. 24, No. 5
0270-7306/04/$08.00+0 DOI: 10.1128/MCB.24.5.2012-2024.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Sonoka Sese,1,
Jong-Seo Lee,1,
Tadaoki Shirakawa,1 Takeshi Iwatsubo,2 Taisuke Tomita,2 and Shin-ichi Yanagawa1*
Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-Ku, Kyoto 606-85071,1 Department of Neuropathology and Neuroscience, Graduate School of Pharmaceutical Sciences, University of Tokyo, Bunkyo-Ku, Tokyo 113-00332, Japan2
Received 2 July 2003/ Returned for modification 12 August 2003/ Accepted 25 November 2003
Regulation of Armadillo (Arm) protein levels through ubiquitin-mediated degradation plays a central role in the Wingless (Wg) signaling. Although zeste-white3 (Zw3)-mediated Arm phosphorylation has been implicated in its degradation, we have recently shown that casein kinase I
(CKI
) also phosphorylates Arm and induces its degradation. However, it remains unclear how CKI
and Zw3, as well as other components of the Arm degradation complex, regulate Arm phosphorylation in response to Wg. In particular, whether Wg signaling suppresses CKI
- or Zw3-mediated Arm phosphorylaytion in vivo is unknown. To clarify these issues, we performed a series of RNA interference (RNAi)-based analyses in Drosophila S2R+ cells by using antibodies that specifically recognize Arm phosphorylated at different serine residues. These analyses revealed that Arm phosphorylation at serine-56 and at threonine-52, serine-48, and serine-44, is mediated by CKI
and Zw3, respectively, and that Zw3-directed Arm phosphorylation requires CKI
-mediated priming phosphorylation. Daxin stimulates Zw3- but not CKI
-mediated Arm phosphorylation. Wg suppresses Zw3- but not CKI
-mediated Arm phosphorylation, indicating that a vital regulatory step in Wg signaling is Zw3-mediated Arm phosphorylation. In addition, further RNAi-based analyses of the other aspects of the Wg pathway clarified that Wg-induced Dishevelled phosphoylation is due to CKI
and that presenilin and protein kinase A play little part in the regulation of Arm protein levels in Drosophila tissue culture cells.
H.M. and S.S. contributed equally to this study.
Present address: Lab Frontier Co., Ewha University, 120-750 Seoul, Korea.
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