The Role of SNX8 in Retrograde Transport of Shiga Toxin : SNX8 facilitated transport of Shiga toxin is regulated by PKCdelta and p38alfa

Abstract

Sorting nexin 8 (SNX8) belongs to the sorting nexin protein family. Members of this family are known to be involved in endocytosis and endosomal sorting. It was recently reported that SNX8 regulates retrograde transport of protein Shiga toxin (Stx) and colocalizes with the early endosome marker EEA1 and the retromer components SNX1 and SNX2. Furthermore, intracellular transport of Stx is controlled by mitogen-activated protein kinase (MAPK) p38alfaand protein kinase C delta (PKCdelta) signaling. The results of the present work expand our knowledge about the role of SNX8 in intracellular transport. First, sulfation experiments confirm the previously published data where the depletion of SNX8 by RNA interference leads to more than a 2-fold increase in the transport of Stx B subunit (StxB) to the trans-Golgi network (TGN) in HeLa cells. The observed effect on StxB transport following SNX8 knockdown in combination with kinase specific pharmacological drugs, indicates that both MAPK p38alfa and PKCdelta are linked to SNX8 function. In addition, the role of Vps24, a protein belonging to the ESCRT-III complex, found at maturating endosomes/MVB, was also studied. Vps24 does not appear to play a role in the retrograde transport of Shiga toxin. The importance of SNX8 was further investigated by studying its function in relation to the location of the cation independent-mannose 6 phosphate receptor (CI-M6PR). Depletion of SNX8 did not affect the cellular distribution of CI-M6PR relatively to Golgi, early endosome and retromer selective markers in HeLa cells. Furthermore, preliminary studies of SNX8 relative mRNA expression in various cell lines suggest that SNX8 is expressed differently in breast, cervix and colon cancer cells.