EPCR-dependent PAR2 activation by the blood coagulation initiation complex regulates LPS-triggered interferon responses in mice

Abstract

Infection and inflammation are invariably associated with activation of the blood coagulation mechanism, secondary to the inflammation-induced expression of the coagulation initiator tissue factor (TF) on innate immune cells. By investigating the role of cell-surface receptors for coagulation factors in mouse endotoxemia, we found that the protein C receptor (ProcR; EPCR) was required for the normal in vivo and in vitro induction of lipopolysaccharide (LPS)-regulated gene expression. In cultured bone marrowderived myeloid cells and in monocytic RAW264.7 cells, the LPS-induced expression of functionally active TF, assembly of the ternary TF-VIIa-Xa initiation complex of blood coagulation, and the EPCR-dependent activation of protease-activated receptor 2 (PAR2) by the ternary TF-VIIa-Xa complex were required for the normal LPS induction of messenger RNAs encoding the TLR3/4 signaling adaptor protein Pellino-1 and the transcription factor interferon regulatory factor 8. In response to in vivo challenge with LPS, mice lacking EPCR or PAR2 failed to fully initiate an interferon-regulated gene expression program that included the Irf8 target genes Lif, Iigp1, Gbp2, Gbp3, and Gbp6. The inflammation-induced expression of TF and crosstalk with EPCR, PAR2, and TLR4 therefore appear necessary for the normal evolution of interferon-regulated host responses. (Blood. 2015;125(18):2845-2854

Coagulation factor V mediates inhibition of tissue factor signaling by activated protein C in mice

“…on May 12, 2018. by guest www.bloodjournal.org From this aPC-and fV-dependent gene signature was congruent with the LPS-induced transcriptional program that is mediated by the EPCRdependent activation of PAR2 by the ternary TF-fVIIa-fXa complex. 27 This finding indicated that the fV-sensitive aPC mechanism involved the suppression of EPCR-dependent inflammatory TF signaling. Quantitative real-time polymerase chain reaction analysis confirmed that 5A-aPC suppressed the LPS-induced expression of Peli1, Ccl22, Malt1, and Irf8 in BMDCs to the same extent as function-blocking anti-mouse TF antibodies ( Figure 3B).…”

“…To each well, 3 mL of medium containing various reagents was added exactly as described earlier. 27 All culture media contained hirudin (2 U/mL) to inhibit potential thrombin activity.…”

“…27 Image data were analyzed with Affymetrix GeneChip Operating Software and normalized with Robust Multichip Analysis (www. bioconductor.org).…”

Factor V: an active player in inflammation

“…Analysis of the gene expression signature suggested that aPC and fV mediated this LPS-induced transcription program through the endothelial protein C receptor (EPCR)-dependent activation of protease-activated receptor 2 (PAR2) by the ternary tissue factor (TF)-VIIaXa complex. 7 Stabilizing the TF-VIIa-Xa complex with nematode anticoagulant protein C2 (NapC2) abolished aPC's inhibitory activity against gene expression, suggesting that aPC inhibits TF-EPCR-PAR2 by destabilizing the TF-VIIa-Xa complex. By testing several function-selective aPC variants and recombinant fV mutants, Liang et al found that inhibition of TF-EPCR-PAR2 signaling by aPC required protein S, the fV B domain, and the intact R506 cleavage site.…”

“…They elegantly showed that ATF4 regulates the expression and secretion of angiopoietin-like 3 (Angptl3) in endothelial and stroma cells, which plays pivotal roles in supporting stemness in LT-HSCs. 7,8 LT-…”