Protein kinase C delta is activated by Shiga toxin and regulates its transport

Protein kinase C (PKC) isozymes regulate different vesicular trafficking steps in the recycling or degradative pathways. However, a possible role of these kinases in the retrograde pathway from endosomes to the Golgi complex has previously not been investigated. We report here the involvement of a specific PKC isozyme, PKC delta, in the intracellular transport of the glycolipid-binding Shiga toxin (Stx), which utilizes the retrograde pathway to intoxicate cells. Upon binding to cells, Stx was shown to specifically activate PKC delta and not PKC alpha. The involvement of PKC delta and PKC alpha in the retrograde transport of Stx was then monitored biochemically and by immunofluorescence after inhibition or depletion of the isozymes. PKC delta, but not PKC alpha, was shown to selectively regulate the endosome-to-Golgi transport of StxB. Upon inhibition or knockdown of PKC delta, StxB molecules colocalized less with giantin and more with EEA1, indicating that the molecules were accumulated in endosomes, unable to reach the Golgi complex. The inhibition of Golgi transport of Stx was reflected by a strong reduction in the toxic effect, demonstrating that transport of Stx to the cytosol is dependent on PKC delta activity. These results are in agreement with our previous data, which show that Stx is able to stimulate its own transport.