Stimulation of MAPK pathway enhances nuclear RNP export of A/HK/218847/06 (H1N1) influenza virus. MDCK cells were infected with H1N1 ± TPA at m.o.i. = 1. RNPs were stained with anti-NP mAb and Alexa488-coupled goat anti-mouse Abs (green). The nucleus was counterstained with TO-PRO-3 (blue). Intracellular RNP localization was analyzed at indicated time points p.i. by multiphoton laser scanning microscopy. The merger of both channels is shown.