Activator protein 1 (API) is a complex of Fos and Jun, and it regulate
s the transcription of genes possessing the AP1-binding sequence. The
purpose of this study was to detect living cells that express AP1 afte
r stimulation with a tumor promoter, The Fos and Jun components of AP1
were induced rapidly and transiently in PC12 cells following the addi
tion of phorbol ester (phorbol 12-myristate 13-acetate, PMA). The DNA
fragment containing the AP1-binding sequence was combined with ethidiu
m bromide, which was used as a fluorescent probe, The probe was transf
ected into the cells using cationic liposomes. Fluorescence in the tra
nsfected cells was observed using a fluorescence microscope. The nucle
i of transfected cells emitted strong fluorescence in the presence of
PMA, whereas weak fluorescence was retained in the cytoplasm in its ab
sence, The former phenomenon is evidence that AP1 combined with the fl
uorescent probe was transported into the nuclei. This study suggests t
hat such a fluorolabeling method is feasible to detect living AP1-expr
essed neurons.