Ubiquitin links smoothened to intraflagellar transport to regulate Hedgehog signaling

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The Hedgehog signaling pathway is crucial for development and disease.
• Patched-1 (Ptch1) and smoothened (Smo) are key receptors in this pathway.
• Regulation of Smo localization to cilia is critical for pathway activation.

Purpose of the Study:

• To elucidate the mechanisms controlling Smo's dynamic movement and localization within cilia.
• To investigate the role of ubiquitination in Smo regulation during Hedgehog signaling.
• To understand how intraflagellar transport components influence Smo ciliary levels.

Main Methods:

• Investigated Smo ubiquitination and ciliary removal in the absence and presence of Hedgehog ligand.
• Utilized E1 ligase inhibitors and site-directed mutagenesis to block Smo ubiquitination.
• Examined the dependence of Smo regulation on intraflagellar transport (IFT) components like Ift27 and the BBSome.

Main Results:

• Smo is ubiquitinated and removed from cilia in the absence of Hedgehog ligand, dependent on Ift27 and BBSome.
• Hedgehog pathway activation reduces Smo ubiquitination and promotes its ciliary accumulation.
• Inhibition of Smo ubiquitination leads to aberrant ciliary accumulation, uncoupled from pathway activation.

Conclusions:

• Smo ubiquitination state is a key regulator of its ciliary levels and Hedgehog pathway activation.
• Ubiquitination-dependent removal of Smo from cilia prevents pathway activation in the absence of ligand.
• These findings reveal a novel mechanism controlling Smo receptor dynamics via post-translational modification.