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Department of Internal Medicine, Division of Nephrology, and
Department of Microbiology and Medical Biochemistry, The Ohio State University, Columbus, OH 43210; and
The Scripps Research Institute, La Jolla, CA 92037
In these studies, we determined whether there are receptors for the
anaphylatoxin C5a (C5aR, CD88) on human mesangial cells (HMC). To
prepare Abs to C5aR, we first synthesized an immunogenic peptide
spanning residues 832 of the molecule, and this peptide was used to
immunize rabbits. Anti-C5aR antiserum, but not preimmune serum, stained
fixed and unfixed HMC in culture. By Western blotting anti-C5aR,
Abs identified a 49.6-kDa protein in HMC. By reverse-transcription PCR,
a cDNA product of 558 bp was amplified corresponding to the expected
size of C5aR cDNA. A cDNA of the same size was amplified simultaneously
from human PBL. Restriction mapping of the products amplified from HMC
and from PBL gave restriction fragments of the same size. Incubation of
HMC with increasing doses of C5a caused a progressive increase in the
levels of the transcription factors activator protein-1 (AP-1) and cAMP
response element binding protein (CREB), but C5a had no effect on the
level of nuclear factor-
B (NF-
B). The effects of C5a on AP-1 were
concentration and time dependent and peaked after 60 min. In contrast,
the C5a metabolite C5adesArg had no significant effect on AP-1 levels.
Preincubation of HMC with rabbit anti-C5aR antiserum inhibited
partially the effect of C5a on AP-1. However, anti-C5aR Abs alone
had no appreciable effects on AP-1. C5a caused a significant
up-regulation of mRNA for the early response genes c-jun
and c-fos on HMC. These results provide evidence for the
presence of C5aR in adult HMC in culture and indicate that, after
binding to C5aR, the anaphylatoxin C5a causes significant up-regulation
of certain transcription factors and early response genes.
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