Figure 7. NDV entry into DF-1 cells involves Rac1 activation and Pak1 phosphorylation.

(A) Activation of Rac1 during NDV entry. DF-1 cells were infected with 5 MOI NDV, and Rac1 activation was measured using GST-Pak1-PBD pull-down assays. (B) Rac1 inhibition prevented NDV entry. Pretreated cells (100 μM Rac1 inhibitor) were infected for 4 h at 37°C and observed using CLSM: Actin filaments (red), NP (green), and cell nucleus (blue). (C) Western blots showing that treatment with a Rac1 inhibitor for 4 h before or after infection inhibited NDV entry into DF-1 cells. (D) NDV titers of supernatants of Mock- or Rac1 inhibitor-treated cells were determined by using TCID₅₀ assays. The results are presented as the mean ± SD. *P < 0.05. (E) NDV infection led to Pak1 phosphorylation early after infection. Cells were infected (5 MOI), after which levels of phosphorylated Pak1 (Ser144) and total Pak1 at the indicated times were determined using western blotting. (F) CLSM imaging showing the distribution of p-Pak1 in DF-1 cells at the indicated after infection with 5 MOI NDV. Scale bar = 20 μm.