Regulation of Ci-SCFSlimb binding, Ci proteolysis, and hedgehog pathway activity by Ci phosphorylation.
Hedgehog (Hh) proteins signal by inhibiting the proteolytic processing of Ci/Gli family transcription factors and by increasing Ci/Gli-specific activity. When Hh is absent, phosphorylation of Ci/Gli triggers binding to SCF ubiquitin ligase complexes and consequent proteolysis. Here we show that multiple successively phosphorylated CK1 sites on Ci create an atypical extended binding site for the SCF substrate recognition component Slimb. GSK3 enhances binding primarily through a nearby region of Ci, which might contact an SCF component other than Slimb. Studies of Ci variants with altered CK1 and GSK3 sites suggest that the large number of phosphorylation sites that direct SCF(Slimb) binding confers a sensitive and graded proteolytic response to Hh, which collaborates with changes in Ci-specific activity to elicit a morphogenetic response. We also show that when Ci proteolysis is compromised, its specific activity is limited principally by Su(fu), and not by Cos2 cytoplasmic tethering or PKA phosphorylation.
Smelkinson
Margery G
MG
Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
Zhou
Qianhe
Q
Kalderon
Daniel
D
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D047389:Casein Kinase I / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D053823:Hedgehog Proteins / Q000378:metabolism*; D016547:Kinesins / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D053823:Hedgehog Proteins; D014157:Transcription Factors; C092937:ci protein, Drosophila; C107452:cos protein, Drosophila; C110233:slmb protein, Drosophila; C077245:hh protein, Drosophila; D044767:Ubiquitin-Protein Ligases; D047389:Casein Kinase I; D017868:Cyclic AMP-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D016547:Kinesins