A Novel Intronic cAMP Response Element Modulator (CREM) Promoter Is Regulated by Activator Protein-1 (AP-1) and Accounts for Altered Activation-induced CREM Expression in T Cells from Patients with Systemic Lupus Erythematosus

Abstract

The transcriptional repressor cAMP response element modulator (CREM) ␣ has important roles in normal T cell physiology and contributes to aberrant T cell function in patients with systemic lupus erythematosus (SLE). Recently, we characterized a specificity protein-1-dependent promoter located upstream of the CREM gene that accounts for increased basal CREM expression in SLE T cells and reflects disease activity. Here, we identify a novel intronic CREM promoter (denoted P2) in front of the second exon of the CREM gene that harbors putative binding sites for TATA-binding proteins and the transcriptional activator AP-1. DNA binding studies, chromatin immunoprecipitation, and reporter assays confirmed the functional relevance of these sites, and T cell activation through CD3/CD28 stimulation or phorbol 12-myristate 13-acetate/ionomycin treatment enhances P2 promoter activity. Although the basal CREM levels are increased in T cells from SLE patients compared with healthy controls, there are remarkable differences in the regulation of CREM expression in response to T cell activation. Whereas T cells from healthy individuals display increased CREM expression after T cell activation, most likely through AP-1-dependent up-regulation of the P2 promoter, SLE T cells fail to further increase their basal CREM levels upon T cell activation due to a decreased content of the AP-1 family member c-Fos. Because CREM trans-represses c-fos transcription in SLE T cells, we propose an autoregulatory feedback mechanism between CREM and AP-1. Our findings extend the understanding of CREM gene regulation in the context of T cell activation and disclose another difference in the transcriptional machinery in SLE T cells.The cAMP response element modulator (CREM) 3 belongs to a superfamily of transcription factors, including cAMP response element (CRE)-binding protein, CREM, the inducible CRE repressor, and activating transcription factors, which are involved in numerous biologic processes, including immune cell homeostasis, steroid metabolism, and spermatogenesis (1-3). The cAMP-mediated signaling cascade is an evolutionarily conserved pathway that comprises stimulus-dependent cAMP production, cAMP binding to the regulatory subunits of protein kinases, nuclear translocation of the regulatory units of these kinases, and phosphorylation of the CRE-binding protein/CREM/activating transcription factors. All CREM proteins are characterized by basic domain/leucine zipper motifs; however, the multiexonic character of the CREM gene, the usage of an inducible intronic promoter or alternative initiation codons, and differential splicing mechanisms account for the presence of multiple CREM isoforms that are expressed in a cell-and development-specific fashion (4 -6). Based on the specific exon composition, CREM exerts trans-activating or trans-repressive effects on target gene expression by direct binding to CREs (TGACGTCA) or the CRE 5Ј-half-site in cisregulatory regions (6). CREs are highly conserved within numerous promoters of eukaryotic genes. T...

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cAMP responsive element modulator: a critical regulator of cytokine production

“…Given that SP-1 expression is significantly enhanced in response to estrogen receptor engagement, this mechanism may contribute to the female predominance in SLE [31]. In contrast to P1, the intronic CREM promoter P2 is under the tight transcriptional control of activating protein (AP)-1 in response to T cell activation mediated through stimulation with anti-CD3/anti-CD28 or phorbol myristate acetate (PMA)/ionomycine [32]. In T cells from healthy individuals, T cell activation increases AP-1 recruitment to P2 with subsequent promoter activation and enforced CREMα transcription.…”