The C-terminal acidic tail is responsible for the inhibitory effects of HMGB1 on efferocytosis.
HMGB1 was described originally as a nuclear protein involved in DNA binding and transcriptional regulation. However, HMGB1 also has an extracellular role as a potent mediator of inflammation and can diminish the uptake of apoptotic cells by phagocytes, a process called efferocytosis. To explore the mechanism responsible for the ability of HMGB1 to inhibit efferocytosis, we examined the role of the C-terminal acidic tail, a region of HMGB1 that has been shown to participate in specific intramolecular interactions. Deletion of the C-terminal tail abrogated the ability of HMGB1 to decrease murine macrophage ingestion of apoptotic neutrophils and to diminish phagocytosis-induced activation of Erk and Rac-1 in macrophages. We found that RAGE plays a major role in efferocytosis, and deletion of the C-terminal tail of HMGB1 prevented binding of HMGB1 to RAGE but not to other macrophage receptors involved in efferocytosis, such as the α(V)β(3) integrin. Whereas HMGB1 decreased ingestion of apoptotic neutrophils significantly by alveolar macrophages under in vivo conditions in the lungs of mice, this effect was lost when the C-terminal acidic tail was absent from HMGB1. These results demonstrate that the HMGB1 C-terminal tail is responsible for the inhibitory effects of HMGB1 on phagocytosis of apoptotic neutrophils under in vitro and in vivo conditions.
Banerjee
Sami
S
University of Alabama at Birmingham, School of Medicine, 1808 7th Ave., S., Birmingham, AL 35294, USA.
Friggeri
Arnaud
A
Liu
Gang
G
Abraham
Edward
E
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D024243:HMGB1 Protein / Q000235:genetics* / Q000502:physiology; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000172:deficiency / Q000378:metabolism; D009504:Neutrophils / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology; D010957:Plasmids
D024243:HMGB1 Protein; D039302:Integrin alphaVbeta3; D010446:Peptide Fragments; C498977:Mok protein, mouse; D020928:Mitogen-Activated Protein Kinases