Mechanism of interleukin-1α transcriptional regulation of S100A9 in a human epidermal keratinocyte cell line

S100A9 is a calcium-binding protein and subunit of antimicrobial calprotectin complex (S100A8/A9). Produced by neutrophils, monocytes/macrophages and keratinocytes, S100A9 expression increases in response to inflammation. For example, IL-1 alpha produced by epithelial cells acts autonomously on the same cells to induce the expression of S100A8/A9 and cellular differentiation. Whereas it is well known that IL-1 alpha and members of the IL-10 family of cytokines upregulate S100A8 and S100A9 in several cell lineages, the pathway and mechanism of IL-1 alpha-dependent transcriptional control of S100A9 in epithelial cells are not established. Modeled using human epidermal keratinocytes (HaCaT cells), IL-1 alpha stimulated the phosphorylation of p38 MAPK and induced S100A9 expression, which was blocked by IL-1 receptor antagonist, RNAi suppression of p38, or a p38 MAPK inhibitor. Transcription of S100A9 in HaCaT cells depended on nucleotides -94 to -53 in the upstream promoter region, based upon the use of deletion constructs and luciferase reporter activity. Within the responsive promoter region, IL-1 alpha increased the binding activity of CCAAT/enhancer binding protein beta (C/EBP beta). Mutated C/EBP beta binding sequences or C/EBP beta-specific siRNA inhibited the S100A9 transcriptional response. Hence, IL-1 alpha is strongly suggested to increase S100A9 expression in a human epidermal keratinocyte cell line by signaling through the IL-1 receptor and p38 MAPK, increasing C/EBP beta-dependent transcriptional activity. (c) 2013 Elsevier B.V. All rights reserved.