Microtubule Hyperacetylation Enhances KL1-Dependent Micronucleation under a Tau Deficiency in Mammary Epithelial Cells.

Haruka Sudo

doi:10.3390/ijms19092488

Abstract

Enhanced microtubule acetylation has been identified as a negative prognostic indicator in breast cancer. We reported previously that primary cultured human mammary epithelial cells manifest breast cancer-related aneuploidization via the activation of severing protein katanin-like (KL)1 when tau is deficient. To address in this current study whether microtubule hyperacetylation is involved in breast carcinogenesis through mitosis, the effects of tubacin on human mammary epithelial cells were tested using immunofluorescence techniques. Tau-knockdown cells showed enhancement of KL1-dependent events, chromosome-bridging and micronucleation in response to tubacin. These enhancements were suppressed by further expression of an acetylation-deficient tubulin mutant. Consistently, using a rat fibroblast-based microtubule sensitivity test, it was confirmed that KL1 also shows enhanced activity in response to microtubule hyperacetylation as well as katanin. It was further observed in rat fibroblasts that exogenously expressed KL1 results in more micronucleation under microtubule hyperacetylation conditions. These data suggest that microtubule acetylation upregulates KL1 and induces more aneuploidy if tau is deficient. It is thus plausible that microtubule hyperacetylation promotes tumor progression by enhancing microtubule sensitivity to KL1, thereby disrupting spindle microtubules and this process could be reversed by the microtubule-binding and microtubule protective octapeptide NAPVSIPQ (NAP) which recruits tau to the microtubules.

Highlights

Acetylation is one of the posttranslational modifications of microtubules
To investigate the effects of enhanced microtubule acetylation on microtubule severing, previously characterized tools were employed such as tubacin (10 μM), an inhibitor of the principal tubulin deacetylase in vertebrate cells, HDAC6 [21]
An increase was observed in tubulin acetylation in the tubacin-treated cells as assessed by immunofluorescence (Figure 1A, Ctrl vs. Tuba; Figure 1A graph, ratio of acetylated to total tubulin)

Summary

Introduction

Acetylation is one of the posttranslational modifications of microtubules. It occurs on α-tubulin and is unique among the various microtubule modification processes in that it occurs on the luminal face of the microtubule (for review, see [1,2,3]). Microtubule acetylation occurs on lysine 40 (K40), which is embedded within the tubulin subunit. Two different enzymes have been identified that can remove this acetyl group, namely histone deacetylase (HDAC) and sirtuin (Sirt). K40 acetylation has so far been linked to cell migration [5,6], touch sensation [7], intracellular trafficking [8,9], and cell adhesion [10]

Methods

Results

Conclusion