Protoporphyrin IX (PIX) decreases frataxin protein levels in uninduced Friend 707 cells, and LMTK⁻ fibroblasts and SK-N-MC neuroepithelioma cells.

(A) Friend cells were incubated in the presence (+) or absence (−) of 1.5% DMSO for 96 hours at 37°C. After this, the incubation was continued for a further 20 hours at 37°C in the presence (+) or absence (−) of 1.5% DMSO alone (controls) or in these media containing either DFO (100 μM), FAC (100 μg/mL), PIH (50 μM), hemin (50 μM), PIX (50 μM), or SA (2 mM). (B) The SK-N-MC and LMTK⁻ cell lines were incubated for 20 hours at 37°C with PIX (50 μM). These results are compared with induced and uninduced Friend cells incubated with (+) or without (−) 1.5% DMSO for 96 hours and then exposed to PIX (50 μM) for 20 hours at 37°C. Western blot analysis was performed as described in “Materials and methods.” The result illustrated in panel A is typical of 8 experiments performed, and that in panel B is typical of 4 experiments.