MAST4 promotes primary ciliary resorption through phosphorylation of Tctex-1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Primary cilia are crucial for cellular function and their dysregulation causes ciliopathies.
• Phosphorylated Tctex-1 at Thr94 (p-Tctex-1) at the ciliary base is known to regulate ciliary resorption.
• Defects in ciliary dynamics are linked to various human diseases.

Purpose of the Study:

• To investigate the role of microtubule-associated serine/threonine kinase family member 4 (MAST4) in primary cilium resorption.
• To elucidate the mechanism by which MAST4 regulates ciliary resorption and its relationship with Tctex-1.

Main Methods:

• Utilized cell-based assays to study primary cilium dynamics.
• Performed MAST4 knockdown and overexpression experiments.
• Investigated protein-protein interactions between MAST4 and Tctex-1 using biochemical methods.
• Analyzed the localization of p-Tctex-1 and MAST4 in primary cilia.
• Assessed the role of MAST4 in Cdc42 activation and Rab5-mediated endocytosis.

Main Results:

• MAST4 localizes to the primary cilium and regulates its resorption.
• MAST4 depletion blocks serum-induced ciliary resorption, while its overexpression accelerates it.
• Tctex-1 binds to the kinase domain of MAST4, with specific residues R503 and D504 being critical.
• MAST4 is essential for the ciliary base localization of p-Tctex-1 and for Cdc42 activation and Rab5-mediated endocytosis during resorption.
• Catalytic-inactive MAST4 mutants and MAST4 knockdown inhibit ciliary resorption and p-Tctex-1 localization.

Conclusions:

• MAST4 is a novel kinase that controls primary cilium resorption.
• MAST4 regulates ciliary resorption by modulating the ciliary base localization of p-Tctex-1.
• MAST4 is a potential therapeutic target for ciliopathies associated with ciliary resorption defects.