Ligand specificity of the anaphylatoxin C5L2 receptor and its regulation on myeloid and epithelial cell lines.
During complement activation the pro-inflammatory anaphylatoxins C3a and C5a are generated, which interact with the C3a receptor and C5a receptor (CD88), respectively. C5a and its degradation product C5a-des-Arg(74) also bind to the C5a receptor-like 2 (C5L2). C3a and C3a-des-Arg(77), also called acylation-stimulating protein, augment triglyceride synthesis and glucose uptake in adipocytes and skin fibroblasts. Based on data obtained using transfected HEK293 and RBL cells, C5L2 is additionally proposed as a functional receptor for C3a and C3a-des-Arg(77). Here we use (125)I-ligand binding assays and flow cytometry with fluorescently labeled ligands to demonstrate that neither C3a nor C3a-des-Arg(77) binds to C5L2. C5L2 expression and its regulation are investigated on various cell lines by a novel C5L2-restricted binding assay and quantitative real time PCR. Dibutyryl cAMP and interferon-gamma induce up-regulation of this receptor on myeloblastic cell lines (U937 and HL-60), whereas tumor necrosis factor-alpha (TNF-alpha) has no effect. In contrast, epithelial HeLa cells are found to constitutively express C5L2 but not the C5a receptor. In HeLa cells, interferon-gamma and TNF-alpha drastically reduce C5L2 expression. No C5a-dependent Ca(2+) signaling is observed even in these cells endogenously expressing C5L2. Taken together, C5L2 is not a receptor for C3a or C3a-des-Arg(77). Thus, this receptor is unlikely to be directly involved in lipid metabolism. Instead, the identification of stimuli modifying C5L2 expression indicates that C5L2 is a highly regulated scavenger receptor for C5a and C5a-des-Arg(74).
Johswich
Kay
K
Department of Medical Microbiology, Medical School Hannover, Carl-Neuberg-Strasse 1, D-30625 Hannover, Germany.
Martin
Myriam
M
Thalmann
Jessica
J
Rheinheimer
Claudia
C
Monk
Peter N
PN
Klos
Andreas
A
D000706:Anaphylatoxins / Q000737:chemistry; D000818:Animals; D015926:Complement C3a / Q000737:chemistry; D015936:Complement C5a / Q000737:chemistry; D004847:Epithelial Cells / Q000166:cytology*; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D008055:Lipids / Q000737:chemistry; D022423:Myeloid Cells / Q000378:metabolism*; D051381:Rats; D044087:Receptor, Anaphylatoxin C5a; D019707:Receptors, Chemokine / Q000737:chemistry / Q000502:physiology*; D014162:Transfection; D020298:U937 Cells
D000706:Anaphylatoxins; C417003:C5aR2 protein, human; D008024:Ligands; D008055:Lipids; D044087:Receptor, Anaphylatoxin C5a; D019707:Receptors, Chemokine; D015926:Complement C3a; D015936:Complement C5a