Subcompartments of the macrophage recycling endosome direct the differential secretion of IL-6 and TNFα

Abstract

Activated macrophages secrete an array of proinflammatory cytokines, including tumor necrosis factor-α (TNFα) and interleukin 6 (IL-6), that are temporally secreted for sequential roles in inflammation. We have previously characterized aspects of the intracellular trafficking of membrane-bound TNFα and its delivery to the cell surface at the site of phagocytic cups for secretion (Murray, R.Z., J.G. Kay, D.G. Sangermani, and J.L. Stow. 2005. Science. 310:1492–1495). The trafficking pathway and surface delivery of IL-6, a soluble cytokine, were studied here using approaches such as live cell imaging of fluorescently tagged IL-6 and immunoelectron microscopy. Newly synthesized IL-6 accumulates in the Golgi complex and exits in tubulovesicular carriers either as the sole labeled cargo or together with TNFα, utilizing specific soluble NSF attachment protein receptor (SNARE) proteins to fuse with the recycling endosome. Within recycling endosomes, we demonstrate the compartmentalization of cargo proteins, wherein IL-6 is dynamically segregated from TNFα and from surface recycling transferrin. Thereafter, these cytokines are independently secreted, with TNFα delivered to phagocytic cups but not IL-6. Therefore, the recycling endosome has a central role in orchestrating the differential secretion of cytokines during inflammation.

Active Rab11 and functional recycling endosome are required for E-cadherin trafficking and lumen formation during epithelial morphogenesis

“…Our findings support the growing concept of the RE as an important compartment for exocytosis of multiple proteins; the RE is often associated with the polarized delivery of proteins to cell surface domains in epithelial cells and in macrophages (2,25,29). In MDCK cells, the RE mediates the exocytic delivery of other basolateral proteins, VSV-G and TfR (2,6,17), although Gravotta et al (17) showed TfR bypassing the RE on its direct journey to the cell surface in fully polarized epithelia.…”

“…The RE compartment was initially designated for recycling proteins, such as transferrin-loaded transferrin receptor (TfR), back to the cell surface following endocytosis (31,42). More recently, the RE has been increasingly recognized as a way station for post-Golgi exocytosis and sorting of membrane and soluble cargo proteins destined for the cell surface (2,6,12,17,25,29). In nonpolarized or early-polarized cells, basolateral proteins travel from the Golgi complex to the cell surface via the RE (2,24), where, according to recent studies, these proteins are also sorted (12).…”

Synaptotagmin XI Regulates Phagocytosis and Cytokine Secretion in Macrophages

“…From recycling endosomes, VAMP3-bearing vesicles are delivered to the plasma or phagosome membrane where Syntaxin-4-a cognate SNARE of VAMP3-is present. Although TNF is delivered to forming phagosomes, IL-6 is not (16). Failure to regulate cytokine secretion results in pathologies in which excess TNF and IL-6 leads to chronic inflammation (17,18).…”

Automated organelle‐based colocalization in whole‐cell imaging

“…Our own research interests focus on recycling endosomes, which are highly dynamic, multifaceted, and multifunctional organelles, found in most cells (6). As with other endosomes, each type of recycling endosome is characterized by various resident membrane proteins, by the more transient populations of membrane-associated proteins, and by cohorts of cargo proteins that pass dynamically through these organelles (7).…”

“…As with other endosomes, each type of recycling endosome is characterized by various resident membrane proteins, by the more transient populations of membrane-associated proteins, and by cohorts of cargo proteins that pass dynamically through these organelles (7). While endosomes are best known for handling protein cargo being internalized from and recycled back to the cell surface-such as transferrin-these endosomes are now also recognized as stations for exocytic cargo moving to the cell surface in secretory pathways (6)(7)(8)(9). The multiple trafficking pathways feeding into endosomes and the selective egress of proteins leaving endosomes require sophisticated mechanisms for protein sorting and handling.…”