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) α 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.