Roadkill attenuates Hedgehog responses through degradation of Cubitus interruptus

Abstract

The final step in Hedgehog (Hh) signal transduction is post-translational regulation of the transcription factor, Cubitus interruptus (Ci). Ci resides in the cytoplasm in a latent form, where Hh regulates its processing into a transcriptional repressor or its nuclear access as a transcriptional activator. Levels of latent Ci are controlled by degradation, with different pathways activated in response to different levels of Hh. Here, we describe the roadkill (rdx) gene, which is expressed in response to Hh. The Rdx protein belongs to a conserved family of proteins that serve as substrate adaptors for Cullin3-mediated ubiquitylation. Overexpression of rdx reduced Ci levels and decreased both transcriptional activation and repression mediated by Ci. Loss of rdx allowed excessive accumulation of Ci. rdx manipulation in the eye revealed a novel role for Hh in the organization and survival of pigment and cone cells. These studies identify rdx as a limiting factor in a feedback loop that attenuates Hh responses through reducing levels of Ci. The existence of human orthologs for Rdx raises the possibility that this novel feedback loop also modulates Hh responses in humans.

Higher‐order oligomerization promotes localization of SPOP to liquid nuclear speckles

“…SPOP is known to regulate Hedgehog (Hh) pathway signaling through ubiquitination of GLI transcription factors (Kent et al , 2006; Hatayama & Aruga, 2012). We therefore chose to test the importance of SPOP oligomerization in vivo by monitoring Hh‐dependent wing patterning using the Drosophila melanogaster model system.…”

“…SPOP is a substrate adaptor of a cullin‐3‐RING ubiquitin ligase (CRL3) and serves to recruit substrates to the CRL3 (Zhuang et al , 2009) for subsequent ubiquitination and degradation (Hernández‐Muñoz et al , 2005; Kent et al , 2006; Kwon et al , 2006; Zhang et al , 2006; Li  et al , 2008). The Drosophila melanogaster homolog of SPOP, Roadkill/HIB, is essential for early development (Kent et al , 2006).…”

“…The Drosophila melanogaster homolog of SPOP, Roadkill/HIB, is essential for early development (Kent et al , 2006). Recent efforts to sequence the cancer genome have identified many mutations in SPOP that are associated with cancers (Lawrence et al , 2014), notably prostate (Kim et al , 2013), breast (Kim et al , 2011), endometrial (Le Gallo et al , 2012), and gastric (Kim et al , 2013) cancers [Appendix Fig S1 and www.cbioportal.org (Cerami et al , 2012; Gao et al , 2013)].…”

Hedgehog-induced phosphorylation by CK1 sustains the activity of Ci/Gli activator

“…Ci A is unstable and is degraded by the ubiquitin/proteasome pathway mediated by the MATH-and BTB-domain containing protein HIB (also called "Rdx") (8,31,32). Interestingly, HIB is up-regulated in response to Hh in both embryos and imaginal discs (31,32), and HIB also down-regulates Sufu through Crn (33), thus forming feedback loops to fine-tune Ci A activity.…”

“…Interestingly, HIB is up-regulated in response to Hh in both embryos and imaginal discs (31,32), and HIB also down-regulates Sufu through Crn (33), thus forming feedback loops to fine-tune Ci A activity. However, it is not clear how HIB-mediated degradation of Ci A is kept in check to prevent premature loss of Hh signaling activity.…”