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Phagocytosis and Autophagy Cellular Pathways Linked

Toll-like receptor signaling during phagocytosis triggers autophagy pathway

THURSDAY, Jan. 3 (HealthDay News) -- The cellular processes of phagocytosis, in which a macrophage engulfs extracellular organisms, and autophagy, in which a cell destroys intracellular organisms or unwanted cellular debris, appear to be linked, according to an article published in Nature in December.

Miguel A. Sanjuan, of St. Jude Children's Research Institute in Memphis, Tenn., and colleagues used fluorescent-labeled proteins and electron microscopy to visualize cellular processes in mouse macrophages.

The researchers showed that a foreign particle's engagement with a toll-like receptor on a macrophage as it is being phagocytosed triggers recruitment of an autophagosome marker LC3 to the phagosome and involves several proteins known to be part of the autophagy pathway. Translocation of BECN1 and LC3 led to phagosome fusion with lysosomes, resulting in rapid acidification and destruction of an engulfed organism.

The authors conclude that "toll-like receptor signaling during phagocytosis of an extracellular organism usurps the autophagy pathway to associate LC3 rapidly with the phagosome, apparently without the formation of conventional autophagosomes in this time period." In addition, "the extremely rapid association of the phagosome with BECN1 (approximately 1 min)…followed by association with LC3 only a few minutes later, suggests the possibility that elements of the classical autophagy pathway are effectively and efficiently recruited to the phagosome on toll-like receptor signaling."

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