Phosphorylation by double-time/CKIepsilon and CKIalpha targets cubitus interruptus for Slimb/beta-TRCP-mediated proteolytic processing.
Hedgehog (Hh) proteins govern animal development by regulating the Gli/Ci family of transcription factors. In Drosophila, Hh signaling blocks proteolytic processing of full-length Ci to generate a truncated repressor form. Ci processing requires sequential phosphorylation by PKA, GSK3, and a casein kinase I (CKI) family member(s). Here we show that Double-time (DBT)/CKIepsilon and CKIalpha act in conjunction to promote Ci processing. CKI phosphorylates Ci at three clusters of serine residues primed by PKA and GSK3 phosphorylation. CKI phosphorylation of Ci confers binding to the F-box protein Slimb/beta-TRCP, the substrate recognition component of the SCF(Slimb/beta-TRCP) ubiquitin ligase required for Ci processing. CKI phosphorylation sites act cooperatively to promote Ci processing in vivo. Substitution of Ci phosphorylation clusters with a canonical Slimb/beta-TRCP recognition motif in beta-catenin renders Slimb/beta-TRCP binding and Ci processing independent of CKI. We propose that phosphorylation of Ci by CKI creates multiple Slimb/beta-TRCP binding sites that act cooperatively to recruit SCF(Slimb/beta-TRCP).
Jia
Jianhang
J
Center for Developmental Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA. jin.jiang@utsouthwestern.edu
Zhang
Lei
L
Zhang
Qing
Q
Tong
Chao
C
Wang
Bing
B
Hou
Fajian
F
Amanai
Kazuhito
K
Jiang
Jin
J
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D048149:Casein Kinase 1 epsilon / Q000235:genetics / Q000378:metabolism*; D048128:Casein Kinase Ialpha / Q000235:genetics / 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 / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D000071676:Zinc Finger Protein GLI1; D044844:beta-Transducin Repeat-Containing Proteins / Q000378:metabolism*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C400551:GLI1 protein, human; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D044844:beta-Transducin Repeat-Containing Proteins; C092937:ci protein, Drosophila; C110233:slmb protein, Drosophila; D044767:Ubiquitin-Protein Ligases; D048149:Casein Kinase 1 epsilon; D048128:Casein Kinase Ialpha; D017868:Cyclic AMP-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D010447:Peptide Hydrolases