Multisite interaction with Sufu regulates Ci/Gli activity through distinct mechanisms in Hh signal transduction

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The tumor suppressor protein Suppressor of fused (Sufu) is crucial for regulating the Hedgehog (Hh) signaling pathway.
• Sufu inhibits transcription factors Cubitus interruptus (Ci)/Glioma-associated oncogene homolog (Gli), but the precise mechanism is unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms by which Sufu inhibits Ci/Gli activity.
• To identify novel Sufu-binding sites and their roles in regulating Ci/Gli function.

Main Methods:

• Co-immunoprecipitation assays to detect protein-protein interactions.
• Cellular localization studies to track Ci/Gli and Sufu.
• Functional assays to assess transcriptional activity and coactivator recruitment.

Main Results:

• Sufu binds Ci/Gli through both a previously known N-terminal site (SIN) and a newly identified C-terminal site (SIC).
• Both SIN and SIC are essential for Sufu's optimal inhibition of Ci/Gli.
• Sufu sequesters Ci/Gli in the cytoplasm via SIN, while SIC mediates nuclear inhibition by blocking CBP coactivator recruitment.
• A novel Sufu-binding motif was identified in the C-terminal region of Ci/Gli.

Conclusions:

• Sufu employs a dual-site binding mechanism (SIN and SIC) to regulate Ci/Gli activity.
• Sufu's inhibition involves cytoplasmic sequestration and nuclear interference with transcriptional coactivator binding.
• This provides key mechanistic insights into Sufu-mediated regulation of the Hedgehog pathway.