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Figure 3. Schematic figure of PtdIns[4,5]P2 involvement in transferrin and membrane recycling pathways. Transferrin recycles through a series of endosomal compartments. It is rapidly delivered to a sorting endosome and subsequently sorted to a recycling compartment, from which it returns to the plasma membrane. PtdIns[4,5]P2 can affect not only initial transferrin endocytic processes but also recycling of internalized transferrin back to cell surface. Lipids and other membrane constituents also recycle between plasma membrane and intracellular endocytic compartments. Fast recycling pathway involves vesicular transport from sorting endosome to plasma membrane, whereas slow pathway involves transport from recycling endosome. PtdIns[4,5]P2 plays a critical role after membrane internalization in one or multiple steps of a membrane recycling pathway. The involvement of PtdIns[4,5]P2 in exocytosis is still unclear.
