Analysis of Il36a induction by C/EBPβ via a half-CRE•C/EBP element in murine macrophages in dependence of its CpG methylation level

Interleukin-36α is a novel member of the IL-1 cytokine family that is highly expressed in epithelial tissues and several myeloid-derived cell types after induction. The transcription factor (TF) C/EBPβ binds specifically to an essential half-CRE•C/EBP motif in the Il36a promoter to induce Il36a expression upon LPS stimulation. C/EBPs regulate gene expression by binding to recognition sequences that can contain 5′-cytosine-phosphate-guanine-3′ dinucleotides (CpG), whose methylation can influence TF binding and gene expression. Herein we show that the half-CRE•C/EBP element in the Il36a promoter is differentially methylated in the murine RAW264.7 macrophage cell line and in primary murine macrophages. We demonstrate that C/EBPβ binding to the half-CRE•C/EBP element in the Il36a promoter following LPS stimulation is insensitive to CpG methylation and that methylation of the CpG in the half-CRE•C/EBP element does not alter LPS-induced Il36a promoter activity which correlated with similar Il36a mRNA copy numbers and pro-IL-36α protein amount in both cell types. Taken together, our data indicate that C/EBPβ binding to the half-CRE•C/EBP element and subsequent gene activation occurs independently of the CpG methylation status of the half-CRE•C/EBP motif and underlines the potential of C/EBPs to recognize methylated as well as unmethylated motifs.