Macropinosome

Formation

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.

Function

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.

Regulation

PI3K and phosphoinositide phospholipase C activation have been shown to be necessary for macropinosome formation in fibroblasts.{{Cite journal | editor1-last = Caplan | editor1-first = Steve H. | article-number = e13763 | doi-access = free

Role in pathogenesis

Because the process of macropinocytosis is non-specific, many pathogens take advantage of macropinosomes to infect their target cells. In this way, pathogens internalized in macropinosomes avoid barriers and obstructions that the plasma membrane, cytoplasmic crowding and cortical cytoskeleton pose when moving deeper into the cytoplasm. One example is Zaire ebolavirus, responsible for the devastating ebola virus disease, which stimulates macropinosome formation upon binding to the target cell surface.{{Cite journal | editor1-last = Basler | editor1-first = Christopher F. | article-number = e1001110 | doi-access = free | editor1-last = Früh | editor1-first = Klaus | article-number = e1001238 | doi-access = free

References

References

1. (2009). "Virus entry by macropinocytosis". Nature Cell Biology.
2. (2018-08-27). "Macropinosome formation by tent pole ruffling in macrophages". J Cell Biol.
3. (1992). "M-CSF-induced macropinocytosis increases solute endocytosis but not receptor-mediated endocytosis in mouse macrophages". Journal of Cell Science.
4. (1997). "Fluid-phase uptake by macropinocytosis in Dictyostelium". Journal of Cell Science.
5. (1993). "Macropinosome maturation and fusion with tubular lysosomes in macrophages". The Journal of Cell Biology.
6. (August 2015). "Vaccinia Virus Infection Requires Maturation of Macropinosomes". Traffic.