Preferred sites of endocytosis have been observed in various cell types, but whether they occur randomly or are linked to cellular cues is debated. Here, we quantified the sites of endocytosis of transferrin (Tfn) and epidermal growth factor (EGF) in cells whose adhesion geometry was defined by micropatterns. 3D probabilistic density maps revealed that Tfn was enriched in adhesive sites during uptake, whereas EGF endocytosis was restricted to the dorsal cellular surface. This spatial separation was not due to distributions of corresponding receptors but was regulated by uptake mechanisms. Asymmetric uptake of Tfn resulted from the enrichment of clathrin and adaptor protein 2 at adhesive areas. Asymmetry in EGF uptake was strongly dependent on the actin cytoskeleton and led to asymmetry in EGF receptor activation. Mild alteration of actin dynamics abolished asymmetry in EGF uptake and decreased EGF-induced downstream signaling, suggesting that cellular adhesion cues influence signal propagation. We propose that restriction of endocytosis at distinct sites allows cells to sense their environment in an “outside-in” mechanism.
Cells on micropatterned surfaces show asymmetric uptake of transferrin at adhesive areas that is dependent on the enrichment of clathrin and adaptor protein 2, and EGF at the dorsal side regulated by the actin cytoskeleton.
- Spatial analysis of endocytic sites reveals dorsal/ventral asymmetry in both clathrin-dependent and clathrin-independent endocytosis.
- Presence of receptors at the plasma membrane is not sufficient to initiate endocytosis after cargo binding.
- Tfn, and by extension, clathrin-dependent endocytosis is enriched at cell-ECM adhesions.
- Restriction of EGF endocytosis to the dorsal side is accompanied by spatial restriction of EGF receptor activation.
- The actin network integrates the cell with its extracellular environment using a delicate balance between restriction and propagation of endocytosis.