Acetylation of Microtubules Influences Their Sensitivity to Severing by Katanin in Neurons and Fibroblasts

Abstract

Here we investigated whether the sensitivity of microtubules to severing by katanin is regulated by acetylation of the microtubules. During interphase, fibroblasts display long microtubules with discrete regions rich in acetylated tubulin. Overexpression of katanin for short periods of time produced breaks preferentially in these regions. In fibroblasts with experimentally enhanced or diminished microtubule acetylation, the sensitivity of the microtubules to severing by katanin was increased or decreased, respectively. In neurons, microtubules are notably more acetylated in axons than in dendrites. Experimental manipulation of microtubule acetylation in neurons yielded similar results on dendrites as observed on fibroblasts. However, under these experimental conditions, axonal microtubules were not appreciably altered with regard to their sensitivity to katanin. We hypothesized that this may be attributable to the effects of tau on the axonal microtubules, and this was validated by studies in which overexpression of tau caused microtubules in dendrites and fibroblasts to be more resistant to severing by katanin in a manner that was not dependent on the acetylation state of the microtubules. Interestingly, none of these various findings apply to spastin, because the severing of microtubules by spastin does not appear to be strongly influenced by either the acetylation state of the microtubules or tau. We conclude that sensitivity to microtubule severing by katanin is regulated by a balance of factors, including the acetylation state of the microtubules and the binding of tau to the microtubules. In the neuron, this contributes to regional differences in the microtubule arrays of axons and dendrites.

A novel family of katanin-like 2 protein isoforms (KATNAL2), interacting with nucleotide-binding proteins Nubp1 and Nubp2, are key regulators of different MT-based processes in mammalian cells

“…The battery of phenotypes documented in Katnal2-silenced cells indicate an impressive multitasking functionality of KATNAL2s, affecting different MT-based processes in these intracellular locations: downregulation was characterized by centriole amplification throughout the cell cycle, the consequent formation of aberrant multipolar spindles in mitosis, absence, deficiency or inequality of cytokinesis with a concomitant significant number of binucleated cells, a strikingly enlarged cellular and nuclear size likely accompanied by polyploidy and occasionally by abnormal nuclear shape, a disturbed cell cycle profile with increased accumulation in G2, an altered mitotic profile combining reduced mitotic index and some stalling at prophase, and a seemingly normal organization of the MT network at interphase, albeit with indications of enhanced acetylation. Acetylation at K40, a major post-translational modification of a-tubulin, is a molecular hallmark of older MTs that are hotspots of katanin binding and severing activity [14,53] and its increase in silenced clone 2.43 was not only consistent with the downregulation of KATNAL2 but could be at the basis of several of the observed phenotypes. For instance, depletion or reduction of KATNAL2 would hinder efficient resolution of a highly acetylated and particularly stable bundle of long midbody MTs to allow cytokinesis progression, thus contributing to inability of or unequal daughter cell segregation and consequent anomalies in cellular and nuclear size and ploidy and the acquisition of multiple nuclei.…”

αTAT1 is the major α-tubulin acetyltransferase in mice

“…It is perhaps surprising that Atat1 knockout mice displayed only minor differences in neurological behaviour. a-tubulin acetylation has been suggested to influence kinesin-mediated transport 10 , and increase sensitivity of microtubules to severing in neuronal axons 43 , although these effects may be more dependent upon other tubulin modifications such as tyrosination 44,45 and polyglutamylation 46 . Migration and maturation of cortical neurons during development have also been reported to be dependent upon tubulin acetylation 14,47 , and depletion of mec17 in zebrafish leads to substantial neurological deficits 17 .…”

Inhibition of HDAC6 Deacetylase Activity Increases Its Binding with Microtubules and Suppresses Microtubule Dynamic Instability in MCF-7 Cells

“…The functional significance of microtubule acetylation has remained largely unknown. Tubulin acetylation, most likely, acts as guidance cues for the recruitment of proteins such as kinesins (12,13), Hsp90 (14) (which in turn, increases the binding and activity of two of its client proteins namely the kinase Akt/PKB and the transcription factor p53 to microtubules) or microtubule-severing enzymes (15). Tubulin acetylation may also have an important role in maintaining the microtubule protofilament number in cells (16).…”