WASH drives early recycling from macropinosomes and phagosomes to maintain surface phagocytic receptors

Abstract

Macropinocytosis is an ancient mechanism that allows cells to harvest nutrients from extracellular media, which also allows immune cells to sample antigens from their surroundings. During macropinosome formation, bulk plasma membrane is internalized with all its integral proteins. It is vital for cells to salvage these proteins before degradation, but the mechanisms for sorting them are not known. Here we describe the evolutionarily conserved recruitment of the WASH (WASP and SCAR homolog) complex to both macropinosomes and phagosomes within a minute of internalization. Using Dictyostelium, we demonstrate that WASH drives protein sorting and recycling from macropinosomes and is thus essential to maintain surface receptor levels and sustain phagocytosis. WASH functionally interacts with the retromer complex at both early and late phases of macropinosome maturation, but mediates recycling via retromer-dependent and -independent pathways. WASH mutants consequently have decreased membrane levels of integrins and other surface proteins. This study reveals an important pathway enabling cells to sustain macropinocytosis without bulk degradation of plasma membrane components.phagocytosis | macropinocytosis | WASH | Dictyostelium | trafficking

Retriever is a multiprotein complex for retromer-independent endosomal cargo recycling

“…We have shown however that in a VPS35 KO cell line a significant proportion of FAM21 remains associated with the endosomal network. This clearly establishes that in human cells the endosomal association of FAM21 and WASH is mediated through both retromer-dependent and retromer-independent mechanisms, a conclusion that is in agreement with work in Dictyostelium describing the retromer-independent recruitment of the WASH complex 56 . While the mechanism for retromer-independent association of the WASH complex to endosomes remains to be established it is perhaps worth noting that the WASH complex has an inherent ability to bind to phospholipids 21, 23 .…”

“…We have established that the WASH-FAM21-CCC axis is essential for the localisation of retriever to endosomes, an observation that is consistent with these complexes having co-evolved. Importantly, the identification of the WASH-FAM21-CCC-retriever-SNX17 pathway provides a mechanism to account for several studies that have shown a role for the WASH complex in α 5 β 1 -integrin recycling even though the sorting of this cargo is known to be retromer-independent 26, 56–58 . WASH dependent α 5 β 1 -integrin recycling requires retriever in order to couple sequence-dependent cargo recognition through SNX17 with actin polymerisation necessary for subsequent recycling.…”

Cellular functions of WASP family proteins at a glance

“…A similar role for WASH in the recycling of integrins has been seen in mammalian cells . Moreover, WASH regulates the retrieval of the vacuolar (V)-ATPase from post-lysosomal compartments, and the recycling of plasma membrane components from early macropinosomes and phagosomes in Dictyostelium (Buckley et al, 2016;Carnell et al, 2011). Thus, the ability of WASH to regulate receptor recycling and lysosome neutralization has been highly conserved throughout evolution.…”

Resolution of macropinosomes, phagosomes and autolysosomes: Osmotically driven shrinkage enables tubulation and vesiculation

“…Like macropinosomes, phago‐ and autolysosomes eventually resolve and this occurs via tubulation and vesiculation that entail gross changes in surface‐to‐volume ratio. In fact, the tubulation is not only required to eliminate the original compartment, but has well delineated roles: recycling of phagocytic receptors, delivery of p‐MHC to the plasma membrane and restoration of the normal complement of lysosomes . Unlike macropinosomes, however, we believe that phagosomes and autolysosomes accomplish shrinkage by exporting the organic osmolytes generated during target degradation.…”

“…Rather than degrading valuable plasmalemmal components, the cell promptly redirects them to the surface. Indeed, recycling of receptors internalized during macropinocytosis is essential for cells to maintain normal responsiveness . Extraction of components from macropinosomes is also necessary for delivery of major histocompatibility complex (MHC) class II loaded with luminal antigens to the cell surface for presentation to T cells .…”