The Transcription Factors AP-1 and Ets Are Regulators of C3a Receptor Expression

• Published in: The Journal of biological chemistry Vol. 280; no. 51; pp. 42113 - 42123
• Main Authors: Schaefer, Myriam, Konrad, Stephanie, Thalmann, Jessica, Rheinheimer, Claudia, Johswich, Kay, Sohns, Bettina, Klos, Andreas
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 23.12.2005; American Society for Biochemistry and Molecular Biology
• Subjects: 5' Untranslated Regions; Base Sequence; Cell Line; Complement C3a - metabolism; DNA Primers; Humans; Promoter Regions, Genetic; Proto-Oncogene Protein c-ets-1 - physiology; Receptors, Complement - genetics; Receptors, Complement - metabolism; Regulatory Sequences, Nucleic Acid; Transcription Factor AP-1 - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M508146200

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.