Actin polymerization and cell motility are affected by NAA80-mediated posttranslational N-terminal acetylation of actin

Abstract

Actin is the most abundant protein in our cells, and also one of the most studied. Nevertheless, an important modifier of actin, the N-terminal acetyltransferase (NAT) for actin, remained unknown until now. The recent identification of the enzyme that catalyzes actin acetylation, has opened up for functional studies of unacetylated actin using knockout cells. This enzyme, called NAA80 (Nα-acetyltransferase 80) or NatH, belongs to the NAT family of enzymes, which together provides N-terminal acetylation for around 80 % of the human proteome. In many cases, N-terminal acetylation is essential. In the case of actin, the acetyl group that NAA80 attaches to actin plays an important role in actin's polymerization properties as well as in actin's function in cell migration.

Keywords: Acetyltransferase; N-terminal acetylation; NAA80; NatH; actin; cell motility; cytoskeleton.

Figure 1.

NAA80 KO cells have increased migration speed. HAP1 CTRL and NAA80 KO cells were subjected to live-cell holographic imaging with image acquisition every 15 minutes for 24 hours. A) Rose plot of single-cell trajectories for CTRL and NAA80 KO. B) Migration speed per hour for CTRL (n = 9) and NAA80 KO (n = 9). Error bars show SEM, **P ≤ 0.05, two-sided Student’s t test. C) Example images showing single-cell migration of one representative cell. Migration speed for shown cell (over 24 h): CTRL, 11.8 μm/h; NAA80 KO, 43.5 μm/h. Scale bar, 25 μm.

Figure 2.

In vitro polymerized actin isolated from CTRL and NAA80 KO cells. A mixture of endogenous β/γ-actin was purified from HAP1 control (Ac-actin) and NAA80 knockout (non-Ac-actin) cells and allowed to polymerize for 1 or 2 hours. F-actin was stained with phalloidin-488 and imaged. Scale bar, 10 μm.

Figure 3.

Effects of Nt-acetylation of actin. Nt-acetylation of β/γ-actin is mediated by the animal-specific NAT, NAA80 (left side). The lack of the acetyl group results in altered actin filament dynamics. Polymerization rates are reduced in non-Ac-actin, however, filament stability is increased, leading to elevated formation of filopodia and lamellipodia in NAA80 KO cells (right side). Nt-acetylation of actin acts like a break by keeping cell motility in check in wildtype cells, whereas NAA80 KO cells move faster (bottom).