Macropinosome

Macropinosomes are a type of cellular compartment that form as a result of macropinocytosis. Macropinosomes are a type of cellular compartment that form as a result of macropinocytosis. Macropinosomes have been described to form via a wave-like mechanism or via a tent-pole formation both of which processes require rapid polymerisation of actin-rich structures that rise up from the cell surface before collapsing back down into a macropinosome. Macropinosomes serve primarily in the uptake of solutes from the extracellular fluid. Once inside the cell, macropinosomes undergo a process of maturation characterized by increasing expression of Rab7 as they progress through the endocytic pathway, until they fuse with lysosomes where the contents of the macropinosome are degraded. PI3K and phosphoinositide phospholipase C activation have been shown to be necessary for macropinosome formation in fibroblasts. Members of the SNX family have also been shown to be important in macropinosome formation. Conversely, cyclic AMP has been shown to promote regurgitation from macropinosomes. Because the process of macropinocytosis is non-specific, many pathogens take advantage of macropinosomes to infect their target cells. One example is ebola, responsible for the devastating eponymous disease, which stimulates macropinosome formation upon binding to the target cell surface. Shiga toxin produced by enterohemorrhagic E. coli has been shown to enter target cells via macropinocytosis, causing gastrointestinal tract complications. Other pathogens that have been shown to utilize this mechanism are Kaposi's sarcoma-associated herpesvirus and Salmonella.