α-Tubulin K40 acetylation is required for contact inhibition of proliferation and cell-substrate adhesion

Acetylation of alpha-tubulin on lysine 40 marks long-lived microtubules in structures such as axons and cilia, and yet the physiological role of alpha-tubulin K40 acetylation is elusive. Although genetic ablation of the alpha-tubulin K40 acetyltransferase alpha Tat1 in mice did not lead to detectable phenotypes in the developing animals, contact inhibition of proliferation and cell-substrate adhesion were significantly compromised in cultured alpha Tat1(-/-) fibroblasts. First, alpha Tat1(-/-) fibroblasts kept proliferating beyond the confluent monolayer stage. Congruently, alpha Tat1(-/-) cells failed to activate Hippo signaling in response to increased cell density, and the microtubule association of the Hippo regulator Merlin was disrupted. Second, alpha Tat1(-/-) cells contained very few focal adhesions, and their ability to adhere to growth surfaces was greatly impaired. Whereas the catalytic activity of alpha TAT1 was dispensable for monolayer formation, it was necessary for cell adhesion and restrained cell proliferation and activation of the Hippo pathway at elevated cell density. Because alpha-tubulin K40 acetylation is largely eliminated by deletion of alpha TAT1, we propose that acetylated microtubules regulate contact inhibition of proliferation through the Hippo pathway.