Immunofluorescence analysis was performed as previously described 30 (link). Briefly, NP cells or tissues attached to slides were fixed with 4% paraformaldehyde, then permeabilized with 0.2% Triton X-100 in PBS. The slides were washed in PBS and blocked with 2% bovine serum albumin (BSA) in PBS for 2 h at 37 °C, and then incubated with primary antibodies against: GRP78 (1:50), GRP94 (1:50), CHOP (1:100), caspase-3 (1:50), or caspase-12 (1:100) (Proteintech). After washed twice, the slides were subsequently treated with secondary goat anti-rabbit antibody (Boster) at 37 °C for 2 h. Nuclei were co-stained for 5 min with 0.1 g/mL DAPI (Beyotime, Nantong, China), and images were captured under a microscope (Olympus, BX53; Melville, NY, USA).