Hedgehog signaling is controlled by Rac1 activity

Area of Science:

• Molecular Biology
• Cell Signaling
• Developmental Biology

Background:

• Nuclear translocation of the Gli transcription factor is essential for Hedgehog (Hh) signaling.
• Dysregulation of Hh signaling is implicated in cancer progression.
• Mechanisms controlling Gli nuclear translocation remain incompletely understood.

Purpose of the Study:

• To elucidate the role of Rac1 activation in Hh signaling-induced Gli nuclear translocation.
• To investigate the molecular mechanisms linking Hh pathway activation to Rac1 activity.
• To examine the role of Rac1 in embryonic development and medulloblastoma.

Main Methods:

• Utilized C3H10T1/2 cell lines and mouse embryonic fibroblasts to study Rac1 regulation of Hh signaling.
• Employed transgenic mouse models and human medulloblastoma tissues to assess Rac1 function.
• Investigated protein-protein interactions and phosphorylation events in the Hh pathway.

Main Results:

• Hh binding to Patched1 (Ptch1) leads to Smoothened (Smo) dissociation and Vav2 binding, activating Rac1 via Vav2 phosphorylation at Y172.
• Rac1 regulates KIF3A phosphorylation at S689 and T694, impacting IFT88 stability and SuFu-Gli complex dissociation.
• Gli nuclear translocation is promoted by Rac1 activation, as evidenced by increased Vav2 phospho-Y172 in mouse and human cancers and impaired Hh signaling in Rac1-deficient embryos.

Conclusions:

• Rac1 activation is a critical, previously unrecognized mechanism controlling Hh signaling through Gli nuclear translocation.
• This pathway is vital for Hh-directed limb bud development and medulloblastoma progression.
• The Rac1-Vav2-Gli axis presents a potential therapeutic target for Hh pathway-driven diseases.