MAST4 promotes primary ciliary resorption through phosphorylation of Tctex-1

• DOI: 10.26508/lsa.202301947
• Publication Date: 2023-09-19T14:05:25Z
• Authors: Kensuke Sakaji; Sara Ebrahimiazar; Yasuhiro Harigae; Kenichi Ishibashi; Takeya Sato; Takeo Yoshikawa; Gen-ichi Atsumi; Ching-Hwa Sung; Masaki Saito
• Keywords: Humans; Phosphorylation; Protein Serine-Threonine Kinases; Microtubules; Microtubule-Associated Proteins; Research Articles; Actins; Ciliopathies

The primary cilium undergoes cell cycle–dependent assembly and disassembly. Dysregulated ciliary dynamics are associated with several pathological conditions called ciliopathies. Previous studies showed that the localization of phosphorylated Tctex-1 at Thr94 (T94) at the ciliary base critically regulates ciliary resorption by accelerating actin remodeling and ciliary pocket membrane endocytosis. Here, we show that microtubule-associated serine/threonine kinase family member 4 (MAST4) is localized at the primary cilium. Suppressing MAST4 blocks serum-induced ciliary resorption, and overexpressing MAST4 accelerates ciliary resorption. Tctex-1 binds to the kinase domain of MAST4, in which the R503 and D504 residues are key to MAST4-mediated ciliary resorption. The ciliary resorption and the ciliary base localization of phospho-(T94)Tctex-1 are blocked by the knockdown of MAST4 or the expression of the catalytic-inactive site-directed MAST4 mutants. Moreover, MAST4 is required for Cdc42 activation and Rab5-mediated periciliary membrane endocytosis during ciliary resorption. These results support that MAST4 is a novel kinase that regulates ciliary resorption by modulating the ciliary base localization of phospho-(T94)Tctex-1. MAST4 is a potential new target for treating ciliopathies causally by ciliary resorption defects.