ATAT1‑dependent α-tubulin acetylation controls chromosome segregation and ciliogenesis and contributes to maintaining α-tubulin tyrosination/detyrosination homeostasis

Microtubules (MTs) assemble specialized structures such as mitotic spindles and cilia axonemes. The fine regulation of MT functions by tubulin post-translational modifications (PTMs) is essential for the assembly and activity of these structures. Nowadays, the precise contribution of the different PTMs to the mitotic process and to ciliogenesis is still to be clarified. Alpha-tubulin N-acetyltransferase 1 (ATAT1) is the enzyme responsible for α-tubulin K40 acetylation a major tubulin PTM. To dissect the contribution of K40 tubulin acetylation and ATAT1 activity in the mitotic chromosome segregation fidelity and ciliogenesis of human cells, ATAT1 depleted cells were used. Microtubule dynamics, mitotic chromosome segregation, primary cilium assembly and tubulin PTMs were analysed by combining protein studies and state of the art microscopy. Cells expressing either wild-type α-tubulin or a non-acetylatable α-tubulin mutant and ectopic re-expression of catalytic active or inactive ATAT1 were used to discriminate the role of K40 tubulin acetylation and ATAT1 activity in these pathways. We demonstrated that ATAT1-mediated K40 tubulin acetylation controls chromosome alignment and segregation defects by impairing kinetochore-microtubule (KT-MT) error correction. A defective MCAK recruitment at KTs may be responsible for the impaired KT-MT error correction and the consequent chromosome segregation defects. ATAT1 silencing also impairs ciliogenesis and alters axonemal morphology. Analysis of tubulin PTMs revealed that lack of K40 acetylation was associated with decreased tubulin tyrosination and detyrosination in the MTs from mitotic spindles and cilia. We conclude that defects observed in ATAT1-silenced cells are linked to the reduction of acetylated tubulin induced by the silencing of the acetyltransferase. Reduction of acetylated tubulin by ATAT1 downregulation, in turn, leads to a defective α-tubulin detyrosination/tyrosination balance, which may be responsible for part of the observed phenotypes. Our findings demonstrate that tubulin PTMs are modulated by homeostatic pathways so that acetylation and the tyrosination/detyrosination cycle are interdependent.