Abstract
Uptake of large volumes of extracellular fluid by actin-dependent macropinocytosis has an important role in infection, immunity and cancer development. A key question is how actin assembly and disassembly are coordinated around macropinosomes to allow them to form and subsequently pass through the dense actin network underlying the plasma membrane to move towards the cell center for maturation. Here we show that the PH and FYVE domain protein Phafin2 is recruited transiently to newly-formed macropinosomes by a mechanism that involves coincidence detection of PtdIns3P and PtdIns4P. Phafin2 also interacts with actin via its PH domain, and recruitment of Phafin2 coincides with actin reorganization around nascent macropinosomes. Moreover, forced relocalization of Phafin2 to the plasma membrane causes rearrangement of the subcortical actin cytoskeleton. Depletion of Phafin2 inhibits macropinosome internalization and maturation and prevents KRAS-transformed cancer cells from utilizing extracellular protein as an amino acid source. We conclude that Phafin2 promotes macropinocytosis by controlling timely delamination of actin from nascent macropinosomes for their navigation through the dense subcortical actin network.
Highlights
Uptake of large volumes of extracellular fluid by actin-dependent macropinocytosis has an important role in infection, immunity and cancer development
Macropinocytosis is an actin-dependent endocytosis mechanism that allows cells to take up extracellular fluids and soluble macromolecules by the formation of membrane ruffles that collapse into large vacuoles[1]
We demonstrate that the PH and FYVE domain-containing protein Phafin[2] plays a critical role during this process by a mechanism that involves coincidence detection of phosphoinositide pools and direct control of subcortical actin dynamics
Summary
Uptake of large volumes of extracellular fluid by actin-dependent macropinocytosis has an important role in infection, immunity and cancer development. Macropinocytosis is an actin-dependent endocytosis mechanism that allows cells to take up extracellular fluids and soluble macromolecules by the formation of membrane ruffles that collapse into large vacuoles[1]. We report a maturation stage of macropinosomes immediately after their scission from the plasma membrane and prior to their acquisition of endocytic markers Their limiting membrane is densely coated with actin, which is stripped from the vesicle, allowing the macropinosome to escape the actin cytoskeleton and acquire an endosomal identity. We demonstrate that the PH and FYVE domain-containing protein Phafin[2] plays a critical role during this process by a mechanism that involves coincidence detection of phosphoinositide pools and direct control of subcortical actin dynamics
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