Roles of promoter and 3′ untranslated motifs in expression of the human C5a receptor

The C5a receptor (C5aR) is a 7 transmembrane G-protein coupled receptor (GPCR) that mediates the powerful pro-inflammatory effect of the complement activation product C5a. Excess C5a generated under pathological conditions has been implicated in a variety of conditions including sepsis, asthma and rheumatoid arthritis, but very little is known about the regulation of expression of the C5aR. The 5′ promoter region and 3′ untranslated region (UTR) of the C5aR mRNA were cloned, generating enhanced green fluorescent protein (EGFP)-reporter plasmids, which were transfected into the monocytic cell line U937. Most of the cloned 2 kb 5′ region was dispensable for the expression of the reporter constructs and the majority of regulatory sequences are in the first 200 bp. Three motifs, a NFκB, a CCAAT and a NFAT site, were identified to be of importance by site directed mutagenesis for basal expression. Analysis of the 3′UTR of the C5aR mRNA showed that it contained two AU-rich elements (AREs), however site directed mutagenesis showed that these had no effect on basal expression. While the phorbol ester PMA and dibutyryl cAMP increased C5aR protein expression, these agents had no effect on the regulation of expression via the promoter or the 3′UTR. This is the first study to investigate the role of both the promoter and 3′UTR in regulating C5aR expression and our results show that regulation of the human C5aR is similar but not identical to that of the mouse C5aR.

► We investigated the roles of motifs in the 2 kb promoter region and the 3′UTR of the C5aR.
► The majority of the regulatory sequences are in the first 200 bp of the promoter region.
► Strong regulatory activity was found in a NFAT motif and a CCAAT motif, while some regulatory activity was found in an NFκB motif.
► Two AU-rich regions were found in the 3′UTR, however, these did not have any regulatory activities.
► PMA and dibutyryl cAMP, while increasing the expression of the C5aR protein, did not affect the 2 kb promoter construct expression, suggesting that regulatory sequences do exists outside the regions investigated.