Endocytosis and retrograde transport of pertussis toxin to the Golgi complex as a prerequisite for cellular intoxication.

The uptake mechanism of pertussis toxin (PT) in CHO and insulin-producing HIT-T15 cells was studied. By electron microscopy after direct labeling of the toxin with gold particles, PT was found to be taken up by receptor-mediated endocytosis. The presence of active pertussis toxin in the Golgi complex was shown by subcellular fractionation. The importance of the Golgi localization of pertussis toxin for the S1-dependent ADP-ribosylation of G-proteins was investigated employing Brefeldin A (BFA) treatment to disrupt Golgi structures. Treatment with Brefeldin A completely blocked the pertussis toxin mediated ADP-ribosylation of cellular G-proteins in CHO and HIT-T15 cells, whereas the BFA-resistant MDCK cells were not protected. A mutant CHO cell line (V24.1) exhibiting a temperature-sensitive Golgi complex could be protected when grown at restrictive conditions. These results strongly indicate that retrograde transport to the Golgi network is a necessary prerequisite for pertussis toxin mediated ADP-ribosylation of G-proteins and thus also for cellular intoxication.