Figure 1

Schematic simplified representation of potential routes for active uptake of in non-phagocytic cells. Mechanisms of endocytosis include clathrin-dependent and clathrin-independent routes. Clathrin-dependent uptake occurs via clathrin-coated pits (CC). Clathrin-independent routes include ingestion by macropinocytosis and circular dorsal ruffles via macropinosomes (MP), caveolae-mediated endocytosis via caveosomes (Cav) and various non-clathrin non-caveolae mediated processes. The later can be subdivided into RhoA/IL2β pathway, Arf1/Cdc42, flotillin and Arf6 endocytosis. Whereas RhoA/IL2β receptor uptake involves specific tubulovesicular endosomes, the content of Arf1/Cdc42, flotillin and Arf6 endocytotic vesicles is delivered to glycophosphatidylinositol-anchored protein-enriched compartments (GEEC). Caveosomes may deliver their content to the endoplasmatic reticulum (ER) and to early endosomes (EE). The other routes transport the ingested material via endosomes (EE) and late endocytotic vesicles (LE) to lysosomes (L). Late endocytotic vesicles may also contact the endoplasmic reticulum. Recycling of membranes occurs via recycling endosomes (RE).