The ability of eukaryotic cells to engulf and degrade both intracellular and extracellular material is vital to the development and maintenance of healthy cells and organisms. These engulfment pathways underpin fundamental processes such as the generation of nutrients, clearance of damaged proteins and organelles, elimination of pathogens, antigen presentation, and the regulation of the immune response.
Conversely, dysregulation of these engulfment and degradative pathways are associated with a number of pathologies, including those associated with the ageing process, and diseases including cancer.
Autophagy is an important intracellular degradation pathway where parts of a cell are engulfed and sequestered in double-membrane compartments called autophagosomes, which then fuse to lysosomes where the contents are degraded and recycled.
Phagocytosis and macropinocytosis are examples of macro-scale endocytic processes where extracellular material is internalised into specialised single-membrane compartments (phagosomes, macropinosomes) that mature and fuse with lysosomes upon which their contents are degraded.
The lab also studies an unusual cannibalistic engulfment process called ‘entosis’ (Overholtzer et al, Cell, 2007). Unlike the engulfment of dead cells via phagocytosis, entosis involves the engulfment of viable live cells generating so called ‘cell-in-cell’ structures. Such cellular structures are often seen in human cancers and understanding their formation and role in tumor biology is one of the main areas of research in the lab.
Time-lapse of entosis and cell-in-cell formation by MCF10A cells in suspension - note the internalised cell undergoes cell division, demonstrating the viable nature of the cell.
Recently, we identified an interplay between components of the autophagy pathway and macroendocytic processes (Florey et al, Nat Cell Bio, 2011; Florey et al, Trends Cell Biol, 2012). Using a range of cell culture and in vivo based systems, time–lapse fluorescent microscopy and biochemical techniques, we have shown how autophagy proteins, such as microtubule-associated protein 1light chain 3 (LC3) are targeted to macro-endocytic vacuoles during phagocytosis, macropinocytosis and entosis. The lab is now focused on determining the molecular mechanisms regulating this non-canonical autophagy pathway and establishing what function it performs in both normal physiology and disease settings.
Confocal time-lapse movie of cell-in-cell structure in cells expressing GFP-LC3 and H2B-mCherry. Note the rapid and transient recruitment of GFP-LC3 to the entotic vacuole prior to death of inner cell.