Haplotype-Independent Costimulation of IL-10 Secretion by SDF-1/CXCL12 Proceeds via AP-1 Binding to the Human IL-10 Promoter

Abstract

Costimulation by the chemokine, stromal cell-derived factor-1 (SDF-1)/CXCL12, has been shown to increase the amount of IL-10 secreted by TCR-stimulated human T cells; however, the molecular mechanisms of this response are unknown. Knowledge of this signaling pathway may be useful because extensive evidence indicates that deficient IL-10 secretion promotes autoimmunity. The human IL-10 locus is highly polymorphic. We report in this study that SDF-1 costimulates IL-10 secretion from T cells containing all three of the most common human IL-10 promoter haplotypes that are identified by single-nucleotide polymorphisms at -1082, -819, and -592 bp (numbering is relative to the transcription start site). We further show that SDF-1 primarily costimulates IL-10 secretion by a diverse population of CD45RA(-) ("memory") phenotype T cells that includes cells expressing the presumed regulatory T cell marker, Foxp3. To address the molecular mechanisms of this response, we showed that SDF-1 costimulates the transcriptional activities in normal human T cells of reporter plasmids containing 1.1 kb of all three of the common IL-10 promoter haplotypes. IL-10 promoter activity was ablated by mutating two nonpolymorphic binding sites for the AP-1 transcription factor, and chromatin immunoprecipitation assays of primary human T cells revealed that SDF-1 costimulation enhances AP-1 binding to both of these sites. Together, these results delineate the molecular mechanisms responsible for SDF-1 costimulation of T cell IL-10 secretion. Because it is preserved among several human haplotypes and in diverse T cell populations including Foxp3(+) T cells, this pathway of IL-10 regulation may represent a key mechanism for modulating expression of this important immunoregulatory cytokine.