Transcriptional Activation of the cAMP-responsive Modulator Promoter in Human T Cells Is Regulated by Protein Phosphatase 2A-mediated Dephosphorylation of SP-1 and Reflects Disease Activity in Patients with Systemic Lupus Erythematosus

Abstract

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with numerous abnormalities recorded at the cellular, molecular, and genetic level. Expression of the basic leucine zipper transcription factor cAMP-responsive element modulator (CREM)␣ was reported to be abnormally increased in T cells from SLE patients. CREM␣ suppresses IL-2 and T cell receptor chain gene transcription by direct binding to the respective promoters. Here, we show that increased CREM expression is the result of enhanced promoter activity. DNA binding analyses reveal direct binding of transcription factor specificity protein-1 (SP-1) to the CREM promoter resulting in enhanced transcriptional activity and increased CREM expression. Protein phosphatase 2A is known to activate SP-1 through dephosphorylation at its serine residue 59. Our results show that nuclei from SLE T cells contain lower levels of Ser 59 -phosphorylated SP-1 protein and a stronger SP-1 binding to the CREM promoter. We conclude that protein phosphatase 2A accounts for enhanced SP-1 dephosphorylation at Ser 59 in SLE T cells. More importantly, CREM promoter activity mirrors reliably disease activity in SLE patients, underscoring its potential role as a biomarker for the prediction of flares in SLE patients. Systemic lupus erythematosus (SLE)3 is a chronic inflammatory disease characterized by an autoimmune process affecting every organ, including joints, kidneys, skin, and the central nervous system (1). T cells have been demonstrated to be important in the pathogenesis of SLE (2). Functional abnormalities in SLE T cells are largely underwritten by altered gene transcription, and recent studies have revealed a vast number of transcription factors in SLE T cells displaying changes in their expression levels and function. Among them, the ␣-isoform of the transcriptional regulator cAMP-responsive element modulator (CREM) has emerged as a potent regulator of target genes that are crucially involved in T cell physiology, e.g. interleukin (IL)-2, T cell receptor chain, and transcription factor c-fos (3-5).The CREM protein family constitutes a group of transcription factors that belong to the superfamily of basic domain/ leucine zipper domain proteins such as cAMP-responsive element-binding protein (CREB) and activating transcription factors. All of them share high structural similarities and possess the ability to bind specifically cis-regulatory DNA sequences as homo-or heterodimers. The target motifs are palindromic DNA sequences denoted cAMP response elements (CRE, TGACGTCA) as well as the 5Ј-TGAC half-sites of this palindrome, both of which are highly conserved within numerous promoters of eukaryotic genes (6). Increased intracellular cAMP levels stimulate a multitude of kinases, e.g. calmodulin kinase IV, that subsequently phosphorylate and thereby activate CREM (7).Previous studies from our group have provided evidence that CREM␣ expression is increased in T cells from SLE patients (8). We have shown that CREM␣ binds to the Ϫ180 site of the IL-2 promoter in SLE T c...

A novel isoform of the orphan receptor RORγt suppresses IL-17 production in human T cells

“…Peripheral venous blood was collected and primary T cells were purified and cultured as described previously. 19 HEK293T cells were cultured in Dulbecco's modified Eagle medium with 10% fetal bovine serum and 1% penicillin/ streptomycin.…”

“…19 Polyclonal anti-RORg(t) (Santa Cruz, Santa Cruz, CA, USA) and secondary HRPlinked anti-rabbit Ab (Santa Cruz) were used for protein detection. For …”

cAMP response element modulator α controls IL2 and IL17A expression during CD4 lineage commitment and subset distribution in lupus

“…CREMα has been linked to reduced IL-2 and increased IL-17A expression through diametric trans-regulatory effects on the IL2 and IL17A genes (8,(15)(16)(17). CREMα expression is controlled by trans-activation and trans-repression of the CREM promoter P1 (9,10). In SLE patients, dephosphorylated Sp-1 trans-activates CREM P1 in a disease activity-dependent manner (10,12).…”

“…Together with the cAMP response element binding protein (CREB), CREM is a member of the ATF superfamily of transcription factors. This family is involved in numerous physiological processes, including immune homeostasis, steroid metabolism, and spermatogenesis (9,10). As a result of its specific exon composition, CREM exerts both trans-activating and trans-repressing effects on target genes.…”

“…CREMα expression is controlled by trans-activation and trans-repression of the CREM promoter P1 (9,10). In SLE patients, dephosphorylated Sp-1 trans-activates CREM P1 in a disease activity-dependent manner (10,12).…”