We next examined the effect of proximal promoter deletion on ST2 expression in fibroblasts. First, we quantitated total ST2 expression using a qPCR assay that measures both ST2L and sST2. ST2 expression was abolished in promoter deficient find more fibroblasts compared with the high amounts of total ST2 expression seen in wild-type fibroblasts (Fig. 2A). In contrast, BMMCs from both wild type and knockout mice expressed similar amounts of ST2, consistent with the results shown in Fig. 1. We treated fibroblasts
with either PMA or PDGF, which have previously been shown to increase sST2 expression , however these agents induced minimal sST2 expression in the promoter-deficient fibroblasts compared with wild-type cells. These results imply that the large majority of ST2 expression in fibroblasts, even following activation, is dependent on the proximal promoter and enhancer element. Next, a series of PCR assays were performed to measure sST2 or ST2L transcripts initiated from either the distal or proximal promoter (primer locations indicated in Fig. 1A). The majority Selleck Gefitinib of ST2
expression in BMMCs was linked to exon 1a of the distal promoter (both sST2 and ST2L); however, some ST2L expression was associated with the proximal promoter (Fig. 2B). In contrast, both sST2 and ST2L expression in fibroblasts were linked to the proximal promoter, either in untreated cells or following activation with serum, PMA, PDGF, or a combination of IL-17 and TNF. This was true for both primary tail-derived fibroblasts and 3T3 fibroblasts. No fibroblast expression was associated with the distal promoter, even though very low amounts of sST2 transcript could be detected in stimulated knockout fibroblasts samples (Fig. 2A and other data not shown),
suggesting there may be additional sites of ST2 RNA initiation. Interestingly, Urease wild-type fibroblasts expressed both sST2 and ST2L (Fig. 2B). In order to determine if fibroblasts were responsive to IL-33, we measured the gene expression of a panel of inflammatory mediators following IL-33 treatment. As shown in Fig. 2C, IL-33 stimulation for 4 h resulted in induced expression of a selective set of chemokines and cytokines in wild type, but not promoter knockout tail fibroblasts (induction of CXCL1, CXCL10, and CCL2, but not CCL27, TGF-β1, or IL-18). This observation is consistent with another report describing IL-33 activity on fibroblasts  and, moreover, suggests that fibroblasts are a potential source of the neutrophil-attracting chemokine CXCL1, which is induced by IL-33 in vivo . We next measured the production of sST2 protein from fibroblasts. Wild-type tail fibroblasts and 3T3 fibroblasts both secreted sST2 protein in response to stimulation with either serum, PMA or IL-33 (Fig. 2D and data not shown). In contrast, knockout fibroblasts produced no sST2 protein under any of the stimulation conditions tested. The proximal promoter is thus essential for sST2 protein secretion from fibroblasts.