Sorting nexin 8 regulates endosome-to-Golgi transport.

Sorting nexin 8 (SNX8) belongs to the sorting nexin protein family, whose members are involved in endocytosis and endosomal sorting and signaling. The function of SNX8 has so far been unknown. Here, we have investigated the role of SNX8 in intracellular transport of the bacterial toxin Shiga toxin (Stx) and the plant toxin ricin. After being endocytosed, these toxins are transported retrogradely from endosomes, via the Golgi apparatus and the endoplasmic reticulum (ER), into the cytosol, where they exert their toxic effect. Interestingly, our experiments show that SNX8 regulates the transport of Stx and ricin differently; siRNA-mediated knockdown of SNX8 significantly increased the Stx transport to the trans-Golgi network (TGN), whereas ricin transport was slightly inhibited. We also found that SNX8 colocalizes with early endosome antigen 1 (EEA1) and with retromer components, suggesting an endosomal localization of SNX8 and supporting our finding that SNX8 is involved in endosomal sorting.