Poly(ADP-ribosyl)ation of high mobility group box 1 (HMGB1) protein enhances inhibition of efferocytosis.
Phagocytosis of apoptotic cells by macrophages, known as efferocytosis, is a critical process in the resolution of inflammation. High mobility group box 1 (HMGB1) protein was first described as a nuclear nonhistone DNA-binding protein, but is now known to be secreted by activated cells during inflammatory processes, where it participates in diminishing efferocytosis. Although HMGB1 is known to undergo modification when secreted, the effect of such modifications on the inhibitory actions of HMGB1 during efferocytosis have not been reported. In the present studies, we found that HMGB1 secreted by Toll-like receptor 4 (TLR4) stimulated cells is highly poly(ADP-ribosyl)ated (PARylated). Gene deletion of poly(ADP)-ribose polymerase (PARP)-1 or pharmacological inhibition of PARP-1 decreased the release of HMGB1 from the nucleus to the extracellular milieu after TLR4 engagement. Preincubation of macrophages or apoptotic cells with HMGB1 diminished efferocytosis through mechanisms involving binding of HMGB1 to phosphatidylserine on apoptotic cells and to the receptor for advanced glycation end products (RAGE) on macrophages. Preincubation of either macrophages or apoptotic cells with PARylated HMGB1 inhibited efferocytosis to a greater degree than exposure to unmodified HMGB1, and PARylated HMGB1 demonstrated higher affinity for phosphatidylserine and RAGE than unmodified HMGB1. PARylated HMGB1 had a greater inhibitory effect on Ras-related C3 botulinum toxin substrate 1 (Rac-1) activation in macrophages during the uptake of apoptotic cells than unmodified HMGB1. The present results, showing that PARylation of HMGB1 enhances its ability to inhibit efferocytosis, provide a novel mechanism by which PARP-1 may promote inflammation.
Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-0006, USA.
Kasey
K
Davis
Sami
S
Banerjee
Arnaud
A
Friggeri
Celeste
C
Bell
Edward
E
Abraham
Mourad
M
Zerfaoui
D000818:Animals; D002460:Cell Line; D024243:HMGB1 Protein / Q000235:genetics / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009479:Neuropeptides / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism*; D000067759:Receptor for Advanced Glycation End Products; D011971:Receptors, Immunologic / Q000378:metabolism; D060168:Thymocytes / Q000502:physiology; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020830:rac1 GTP-Binding Protein
D024243:HMGB1 Protein; D009479:Neuropeptides; C484602:Rac1 protein, mouse; D000067759:Receptor for Advanced Glycation End Products; D011971:Receptors, Immunologic; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; C499321:Parp1 protein, mouse; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein