Deubiquitination Of Ci/Gli By Usp7/HAUSP Regulates Hedgehog Signaling

Hedgehog (Hh) was first identified in Drosophila through EMS-mediated gene mutation screening. The Hh signaling plays key roles in controlling pattern formation, embryonic development and adult tissue homeostasis in species ranging from insects to human. Malfunction of Hh pathway has been implicated in numerous human diseases, including birth defects and several types of cancer.Hh signaling transduction is achieved through the transcription factor Ci/Gli. In Drosophila, Ci is regulated by dual ubiquitin pathway. In the absence of Hh, Ci is ubiquitinated by Slimb-Cull E3 ligase, which leads to Ci partial degradation. In the presence of Hh, Ci is ubiquitinated to total degradation by Hib-Cul3 E3 ligase.Ubiquitination is an enzymatic process by which proteins are modified with ubiquitin chains. A major aim of ubiquitination is to target proteins for degradation by the proteasome or lysosome. Like other protein modification, the process of ubiquitination is reversible due to the action of deubiquitinases, which remove ubiquitin chains from target proteins.Regulation of the ubiquitination-mediated proteolysis of Ci transcription factor is central to Hh signaling, but whether deubiquitinase is involved in this process remains unknown. In this study, via RNAi-mediated screening, we find a ubiquitin-specific protease Usp7 could positively regulate Hh pathway through inhibiting Ci ubiquitination mediated by both Slimb-Cull and Hib-Cul3 E3 ligases. The protective effect of Usp7 upon Ci is stimulated by Hh activity. In addition, we demonstrate that Usp7 forms a complex with GMP-synthetase (GMPS) to promote Hh pathway activity. Finally, we show that the counterparts of Usp7 positively regulate Hh signaling in mammalian cells and zebrafish, indicating that Usp7 plays an evolutionarily conserved role for modulating Hh pathway.In conclusion, we provide evidence that Hh pathway could be regulated by direct deubiquitinating the transcription factor Ci/Gli. Our findings reveal a conserved mechanism by which Ci/Gli is stabilized by a deubiquitination enzyme and identify Usp7/HUASP as a critical regulator of Hh signaling and potential therapeutic target for Hh-related cancers.