Multisite Protein Kinase A and Glycogen Synthase Kinase 3{beta} Phosphorylation Leads to Gli3 Ubiquitination by SCF super({beta}TrCP)

• Published in: Molecular and cellular biology 2006-06, Vol.26 (11), p.4316-4326
• Main Authors: Tempe, Denis, Casas, Mariana, Karaz, Sonia, Blanchet-Tournier, Marie-Francoise, Concordet, Jean-Paul
• Format: Article
• Language: English
• ISSN: 0270-7306; 1098-5549

Gli3 is a zinc finger transcription factor proteolytically processed into a truncated repressor lacking C-terminal activation domains. Gli3 processing is stimulated by protein kinase A (PKA) and inhibited by Hedgehog signaling, a major signaling pathway in vertebrate development and disease. We show here that multisite glycogen synthase kinase 3{beta} (GSK3{beta}) phosphorylation and ubiquitination by SCF super({beta}TrCP) are required for Gli3 processing. We identified multiple {beta}TrCP-binding sites related to the DSGX sub(2) sub(-) sub(4)S motif in Gli3, which are intertwined with PKA and GSK3{beta} sites, and SCF super({beta}TrCP) target lysines that are essential for processing. Our results support a simple model whereby PKA triggers a cascade of Gli3 phosphorylation by GSK3{beta} and CK1 that leads to direct {beta}TrCP binding and ubiquitination by SCF super({beta}TrCP). Binding of {beta}TrCP to Gli3 N- and C-terminal domains lacking DSGX sub(2) sub(-) sub(4)S-related motifs was also observed, which could reflect indirect interaction via other components of Hedgehog signaling, such as the tumor suppressor Sufu. Gli3 therefore joins a small set of transcription factors whose processing is regulated by the ubiquitin-proteasome pathway. Our study sheds light on the role of PKA phosphorylation in Gli3 processing and will help to analyze how dose-dependent tuning of Gli3 processing is achieved by Hedgehog signaling.