Casein kinase I phosphorylates the Armadillo protein and induces its degradation in Drosophila.
Casein kinase I (CKI) was recently reported as a positive regulator of Wnt signaling in vertebrates and Caenorhabditis elegans. To elucidate the function of Drosophila CKI in the wingless (Wg) pathway, we have disrupted its function by double-stranded RNA-mediated interference (RNAi). While previous findings were mainly based on CKI overexpression, this is the first convincing loss-of-function analysis of CKI. Surprisingly, CKIalpha- or CKIepsilon-RNAi markedly elevated the Armadillo (Arm) protein levels in Drosophila Schneider S2R+ cells, without affecting its mRNA levels. Pulse-chase analysis showed that CKI-RNAi stabilizes Arm protein. Moreover, Drosophila embryos injected with CKIalpha double-stranded RNA showed a naked cuticle phenotype, which is associated with activation of Wg signaling. These results indicate that CKI functions as a negative regulator of Wg/Arm signaling. Overexpression of CKIalpha induced hyper-phosphorylation of both Arm and Dishevelled in S2R+ cells and, conversely, CKIalpha-RNAi reduced the amount of hyper-modified forms. His-tagged Arm was phosphorylated by CKIalpha in vitro on a set of serine and threonine residues that are also phosphorylated by Zeste-white 3. Thus, we propose that CKI phosphorylates Arm and stimulates its degradation.
Yanagawa
Shin-ichi
S
Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-Ku, Kyoto 606-8507, Japan. syanagaw@virus.kyoto-u.ac.jp
Matsuda
Yukihiro
Y
Lee
Jong-Seo
JS
Matsubayashi
Hiroko
H
Sese
Sonoka
S
Kadowaki
Tatsuhiko
T
Ishimoto
Akinori
A
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D051186:Armadillo Domain Proteins; D047388:Casein Kinases; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D000072261:Dishevelled Proteins; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism; D019476:Insect Proteins / Q000096:biosynthesis / Q000378:metabolism*; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016372:RNA, Antisense; D034741:RNA, Small Interfering; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013912:Threonine / Q000378:metabolism; D015534:Trans-Activators; D014157:Transcription Factors; D051155:Wnt1 Protein
C495305:ARM protein, Drosophila; D048868:Adaptor Proteins, Signal Transducing; D051186:Armadillo Domain Proteins; D004268:DNA-Binding Proteins; D000072261:Dishevelled Proteins; D029721:Drosophila Proteins; D019476:Insect Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D016372:RNA, Antisense; D034741:RNA, Small Interfering; D015534:Trans-Activators; D014157:Transcription Factors; D051155:Wnt1 Protein; C092937:ci protein, Drosophila; C000606588:dsh protein, Drosophila; C074622:wg protein, Drosophila; D013912:Threonine; D012694:Serine; D011494:Protein Kinases; D047388:Casein Kinases