A redox-mediated conformational change in NQO1 controls binding to microtubules and α-tubulin acetylation

The localization of NQO1 near acetylated microtubules has led to the hypothesis that NQO1 may work in concert with the NAD(+)-dependent deacetylase SIRT2 to regulate acetyl alpha-tubulin (K-40) levels on microtubules. NQO1 catalyzes the oxidation of NADH to NAD + and may supplement levels of NAD(+) near microtubules to aid SIRT2 deacetylase activity. While HDAC6 has been shown to regulate the majority of microtubule acetylation at K-40, SIRT2 is also known to modulate microtubule acetylation (K-40) in the perinuclear region. In this study we examined the potential roles NQO1 may play in modulating acetyl alpha-tubulin levels. Knock-out or knock-down of NQO1 or SIRT2 did not change the levels of acetyl alpha-tubulin in 16HBE human bronchial epithelial cells and 3T3-L1 fibroblasts; however, treatment with a mechanism-based inhibitor of NQO1 (MI2321) led to a short-lived temporal increase in acetyl alpha-tubulin levels in both cell lines without impacting the intracellular pools of NADH or NAD(+). Inactivation of NQO1 by MI2321 resulted in lower levels of NQO1 immunostaining on microtubules, consistent with redox-dependent changes in NQO1 conformation as evidenced by the use of redox-specific, anti-NQO1 antibodies in immunoprecipitation studies. Given the highly dynamic nature of acetylation-deacetylation reactions at alpha-tubulin K-40 and the crowded protein environment surrounding this site, disruption in the binding of NQO1 to microtubules may temporally disturb the physical interactions of enzymes responsible for maintaining the microtubule acetylome.

Automated summary

The localization of NQO1 near acetylated microtubules suggests its potential synergy with the NAD(+)-dependent deacetylase SIRT2 in regulating acetyl alpha-tubulin levels. While knock-down or knock-out of NQO1 or SIRT2 did not change acetyl alpha-tubulin levels, treatment with a mechanism-based inhibitor of NQO1 led to a temporary increase in acetyl alpha-tubulin levels. The disruption in NQO1 binding to microtubules may disturb the interactions of enzymes maintaining microtubule acetylation temporarily.