Fig. 8. SKD1 functions in mammalian endosomal/lysosomal systems at multiple steps in membrane transport. A schematic diagram represents the stages of membrane transport that are inhibited by the overexpression of SKD1(E235Q). (A) SKD1(E235Q)-expression inhibits the early endosomal recycling of TfR, LDLR and ASGPR to the PM as well as of TGN38 and MPR to the TGN. EGFR downregulation was suppressed by the inhibition of either the vesicle transport from early to late endosomes or the maturation (multivesicular formation?) of the early endosome into a late endosome. (B) SKD1(E235Q)-expression may inhibit the reformation of lysosomes from the hybrid organelles. This defect leads to the accumulation of hybrid organelles.