The transcription factors AP-1 and Ets are regulators of C3a receptor expression.
The anaphylatoxin C3a is a proinflammatory mediator generated during complement activation. The tight control of C3a receptor (C3aR) expression is crucial for the regulation of anaphylatoxin-mediated effects. Key factors regulating constitutive expression of the C3aR in the mast cell line HMC-1 and receptor induction by dibutyryl-cAMP in monomyeloblastic U937 cells were determined by functional characterization of the C3aR promoter. Nucleotides -18 to -285 upstream of the translational start site proved to be critical for promoter activity in HMC-1 cells. Binding sites for the transcription factors AP-1 and Ets could be located. Overexpressed c-Jun/c-Fos (AP-1) and Ets-1 led synergistically to increased promoter activity that was substantially reduced by site-directed mutagenesis of the corresponding elements within the C3aR promoter. In HMC-1 cells, Ets interacted directly with the predicted binding motif of the C3aR promoter as determined by electromobility shift assays. AP-1 binding to the C3aR promoter was augmented during C3aR induction in U937 cells. A retroviral gene transfer system was used to express a dominant negative mutant of Ets-1 in these cells. The resulting cells failed to up-regulate the C3aR after stimulation with dibutyryl-cAMP and showed decreased AP-1 binding, suggesting that Ets acts here indirectly. Thus, it was established that Ets and the AP-1 element mediates dibutyryl-cAMP induction of C3aR promoter activity, hence providing a mechanistic explanation of dibutyryl-cAMP-dependent up-regulation of C3aR expression. In conclusion, this study demonstrates an important role of AP-1 and a member of the Ets family in the transcriptional regulation of C3aR expression, a prerequisite for the ability of C3a to participate in immunomodulation and inflammation.
Schaefer
Myriam
M
Department of Medical Microbiology, Medical School Hannover (MHH), Carl-Neubergstrasse 1, D-30625 Hannover, Germany.
Konrad
Stephanie
S
Thalmann
Jessica
J
Rheinheimer
Claudia
C
Johswich
Kay
K
Sohns
Bettina
B
Klos
Andreas
A
D020121:5' Untranslated Regions; D001483:Base Sequence; D002460:Cell Line; D015926:Complement C3a / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D011401:Promoter Regions, Genetic; D050784:Proto-Oncogene Protein c-ets-1 / Q000502:physiology*; D011951:Receptors, Complement / Q000235:genetics / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D018808:Transcription Factor AP-1 / Q000502:physiology*
D020121:5' Untranslated Regions; D017931:DNA Primers; D050784:Proto-Oncogene Protein c-ets-1; D011951:Receptors, Complement; D018808:Transcription Factor AP-1; D015926:Complement C3a