Regulation of S100A8 by glucocorticoids.

S100A8 (A8) has roles in inflammation, differentiation and development and is associated with oxidative defense. Murine A8 (mA8) is up-regulated in macrophages, fibroblasts, and microvascular endothelial cells by LPS. Glucocorticoids (GCs) amplified LPS-induced mA8 in these cells. Relative to stimulation by LPS, GCs increased mA8 gene transcription and mRNA half-life. Enhancement required new protein synthesis, IL-10 and products of the cyclooxygenase-2 pathway, and both ERK1/2 and p38 MAPK. Protein kinase A positively and protein kinase C negatively regulated this process. Promoter analysis indicated element(s) essential for LPS and dexamethasone enhancement colocated within the region -178 to 0 bp. In the absence of glucocorticoid response elements, NF1 motif at -58 is a candidate for mediation of enhancement. Gel shift analysis detected no differences between LPS- and LPS/dexamethasone-treated complexes within this region. GCs increased constitutive levels of A8 and S100A9 (A9) mRNA in human monocytes. The synovial membrane of rheumatoid patients treated with high dose i.v. methylprednisolone contained higher numbers of A8/A9-positive macrophages than pre- or posttreatment samples. Results support the proposal that A8 has anti-inflammatory properties that may be independent of hetero-complex formation with A9 and may also enable localized defense in the absence of overriding deleterious host responses.

Mechanism of prostaglandin (PG)E2-induced prolactin expression in human T cells: cooperation of two PGE2 receptor subtypes, E-prostanoid (EP) 3 and EP4, via calcium- and cyclic adenosine 5'-monophosphate-mediated signaling pathways.

We previously reported that prolactin gene expression in the T-leukemic cell line Jurkat is stimulated by PGE(2) and that cAMP acts synergistically with Ca(2+) or protein kinase C on the activation of the upstream prolactin promoter. Using the transcription inhibitor actinomycin D, we now show that PGE(2)-induced prolactin expression requires de novo prolactin mRNA synthesis and that PGE(2) does not influence prolactin mRNA stability. Furthermore, PGE(2)-induced prolactin expression was inhibited by protein kinase inhibitor fragment 14-22 and BAPTA-AM, which respectively, inhibit protein kinase A- and Ca(2+)-mediated signaling cascades. Using specific PGE(2) receptor agonists and antagonists, we show that PGE(2) induces prolactin expression through engagement of E-prostanoid (EP) 3 and EP4 receptors. We also found that PGE(2) induces an increase in intracellular cAMP concentration as well as intracellular calcium concentration via EP4 and EP3 receptors, respectively. In transient transfections, 3000 bp flanking the leukocyte prolactin promoter conferred a weak induction of the luciferase reporter gene by PGE(2) and cAMP, whereas cAMP in synergy with ionomycin strongly activated the promoter. Mutation of a C/EBP responsive element at -214 partially abolished the response of the leukocyte prolactin promoter to PGE(2), cAMP, and ionomycin plus cAMP.