C5L2, a Nonsignaling C5A Binding Protein

Abstract

C5a anaphylatoxin, a potent inflammatory mediator, is known to act through a specific G protein coupled receptor. However, some of the complex effects of C5a in vivo may not be explained solely by the deletion of the known receptor. Here, we show that an orphan receptor, identified as C5L2, is a high affinity C5a binding protein. Unlike the previously described C5aR, C5L2 is obligately uncoupled from heterotrimeric G proteins, in part by virtue of an amino acid alteration in the so-called DRY sequence at the end of the third transmembrane segment. Both human and murine C5L2 bear a leucine for arginine replacement at this site. C5L2, when transfected into several cell types, is weakly phosphorylated in transfected cells following binding of C5a but does not induce significant activation of MAP kinases, mediate calcium flux, or stimulate chemotaxis. Bone marrow cells from wild type respond robustly to C5a with induction and suppression of a number of inflammation related genes. In contrast, C5a receptor deficient mice, which bear C5L2 alone, do not respond to C5a with changes in gene transcription by microarray analyses. Biophysical properties of the C5L2, including slow ligand on and off rates, absence of internalization, and relatively high affinity for the C5a des Arg metabolite, suggest that this receptor may serve to modulate C5a biological functions in vivo. Finally, in contrast to previous reports, we find absolutely no interaction of C5L2 with other anaphylatoxins C3a and C4a.

Inflammatory Responses Induced by Lipopolysaccharide Are Amplified in Primary Human Monocytes but Suppressed in Macrophages by Complement Protein C5a

“…This suggests that the regulatory effects of C5aR on TLR4 depend on cellular context, for example differentiation status. Although C5aR mediates C5a-dependent responses, a second C5a receptor, C5L2, has also been reported to exhibit anti-inflammatory functions (3,28). However, FIGURE 2.…”

“…Elevated plasma levels of C5a or its receptor are associated with inflammatory diseases such as rheumatoid arthritis, inflammatory bowel diseases, respiratory distress syndrome, ischemiareperfusion injury, and sepsis (1). C5a binds to and signals through the receptor C5aR (CD88), a class A G protein-coupled rhodopsinlike receptor (2), and to a second receptor C5L2, which does not couple G proteins and may be nonsignaling, but may also modulate C5aR (3,4). C5aR couples to the pertussis toxin (PTX)-sensitive G ai and in some cells such as monocytes to the PTX-insensitive G a16 , and it recruits b-arrestins-1,2 to the plasma membrane (1,5).…”

C3a and C5a Are Chemotactic Factors for Human Mesenchymal Stem Cells, Which Cause Prolonged ERK1/2 Phosphorylation

“…There is a third anaphylatoxin receptor, C5L2, which binds C5a, but according to most reports its activation does not cause any cell stimulation (20), suggesting that this may be a scavenger receptor for C5a (21).…”

Complement 5a receptor-mediated neutrophil dysfunction is associated with a poor outcome in sepsis

“…Generally, C5aR and C5L2 are independent, and the putative 'default' receptor, C5L2, has an important role in balancing the biological effects of C5a. 6 However, the role of C5L2 in inflammatory responses is controversial, 7,8 its elucidation will require further investigation. In sepsis, it has been reported that excessive systemic C5a levels were associated with exhaustion of the granulocytic response.…”