Transcriptional control of the C3a receptor gene in glial cells: Dependence upon AP-1 but not Ets.

The C3a anaphylatoxin has been implicated in several autoimmune states including arthritis and multiple sclerosis. The expression pattern of the C3a receptor (C3aR) is critically important in C3a biology, yet very little is known about the transcriptional control of the C3aR gene. Since C3a is hypothesized to play a role in neuroinflammation, we investigated the molecular mechanisms governing C3aR expression in astrocytes and microglia. In the current study, we demonstrate that C3aR transcription in microglia mirrors that in other macrophages, with strong transcription factor binding at the AP-1 and Ets sites. In transformed astrocytes there is evidence for AP-1 and Ets binding in the C3aR promoter region, while in primary astrocytes these sites do not apparently bind strongly to these transcription factors. Primary astrocytes lack a strong complex at the C3aR AP-1 site and reporter gene assays indicate a much smaller contribution of this site to transcriptional activity. Although EMSA analyses using astrocyte extracts show strong complexes exist at the Ets site, this sequence has a minimal activity in reporter assays. Finally, in vivo footprinting demonstrates much stronger DNA binding activity at both the AP-1 and Ets sites in microglia when compared to astrocytes. Collectively, our data demonstrate that transcriptional control of C3aR expression in astrocytes is fundamentally different than that in myeloid cells.