Modulation of prolactin expression in human T lymphocytes by cytokines.

Besides its pivotal role in reproduction, the polypeptide hormone prolactin (PRL) has immunomodulatory properties. Whereas the bulk of circulating PRL is produced by the pituitary, PRL is also produced by the decidua, the myometrium, the mammary gland and leukocytes. Extrapituitary PRL expression is regulated differently from that in the pituitary, due to the use of an alternative promoter. Here we show for the first time that in T lymphocytes PRL expression is subject to regulation by cytokines. We established that both IL-2 and IL-4 reduced PRL mRNA levels in T lymphocytes to 25 and 28% of control values, respectively. PRL mRNA expression was inhibited to a lesser extent by IL-1beta, which decreased PRL mRNA levels to 58% of control values.

Multiple, PKA-dependent and PKA-independent, signals are involved in cAMP-induced PRL expression in the eosinophilic cell line Eol-1.

Besides its pivotal role in reproduction, the polypeptide hormone prolactin (PRL) has been attributed an immunomodulatory function. Extrapituitary PRL expression is regulated differently from that in the pituitary, due to the use of an alternative promoter. In leukocytes, cAMP is an important regulator of PRL expression. We report that in the human eosinophilic cell line Eol-1, cAMP-induced PRL expression is partially abrogated by two protein kinase A (PKA) inhibitors (H89, PKI) and by the p38 inhibitor SB203580. Phosphorylation of p38 was PKA-independent and could be stimulated by a methylated cAMP analogue, which specifically activates the exchange factor directly activated by cAMP (EPAC). Furthermore, cAMP induced a PKA-dependent phosphorylation of cAMP-responsive element binding protein (CREB). We postulate that cAMP induces PRL expression via two different signalling pathways: a PKA-dependent pathway leading to the phosphorylation of CREB, and a PKA-independent pathway leading to the phosphorylation of p38.

Suppressor of cytokine signaling 7 inhibits prolactin, growth hormone, and leptin signaling by interacting with STAT5 or STAT3 and attenuating their nuclear translocation.

We report here the role of one of the less studied members of the family of suppressors of cytokine signaling (SOCS), namely SOCS-7, in cytokine signaling. We demonstrate that SOCS-7 inhibits prolactin (PRL), growth hormone (GH), or leptin (LEP) signaling mediated through STAT3 and STAT5 in a dose-dependent manner. SOCS-7 also attenuated STAT3 and STAT5 signaling induced by overexpression of JH1, the catalytic subdomain of JAK2. Since SOCS-7 interacted with phosphorylated STAT3 or STAT5, we assumed that SOCS-7 acts at the level of STAT proteins. Indeed, we showed that SOCS-7 inhibits PRL- and leptin-induced STAT5 and STAT3 phosphorylation and prevented the nuclear translocation of activated STAT3. Taken together, our results indicate that SOCS-7 is a physiological dysregulator of PRL, leptin, and probably also GH signaling and that its mode of action is a novel variation of SOCS protein inhibition of cytokine-inducible STAT-mediated signal transduction.

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.

Limited effect of selected organic pollutants on cytokine production by peripheral blood leukocytes.

To test the hypothesis that some persistent organic pollutants contribute to the increased prevalence of allergic disease, the effects of selected compounds on cytokine production by PBMC from control and allergic donors were evaluated. Cells were cultured for six days in the presence of a xenobiotic (PCB 153, hexachlorobenzene, pentachlorobenzene, pentachlorophenol, lindane, atrazine or DMSO vehicle) with phytohemagglutinin (PHA) or Dermatophagoides pteronyssinus extract, then for one day in the presence of PHA + phorbol 12-myristate 13-acetate. PCB 153 reduced the levels of IL-10, IFN-gamma and TNF-alpha. Hexachlorobenzene reduced the levels of IL-5, IL-10 and IFN-gamma. Pentachlorobenzene reduced IL-6 levels. Pentachlorophenol reduced IL-5 levels. Lindane and atrazine reduced both IL-5 and IFN-gamma. In addition, lindane reduced TNF-alpha levels. As these compounds had similar effects on cells from allergic and non-allergic donors, and as these effects were, in all cases, very limited indeed, the potential deleterious impact of the xenobiotics tested on the allergic response seems unlikely.

The suppressor of cytokine signaling (SOCS)-7 interacts with the actin cytoskeleton through vinexin.

To understand the function of the suppressor of cytokine signaling (SOCS)-7, we have looked for proteins interacting with SOCS-7 in a stringent yeast two-hybrid screen of a human leukocyte cDNA-library. We identified the cytoskeletal molecule vinexin as a partner interacting with SOCS-7. Tests with deletion mutants of SOCS-7 demonstrated that a central region of the molecule containing several proline-rich regions, N-terminal to the SH2 domain, was responsible for the binding to vinexin. It is thus likely that one of the SH3 domains of vinexin interacts with a poly-proline region of SOCS-7. The interaction with vinexin was confirmed biochemically as vinexin-alpha was co-precipitated with SOCS-7. Confocal laser-scanning microscopy in HEK293T, MCF-7, and 3T3-L1 cells showed that part of the transfected SOCS-7-green fluorescent protein (GFP) molecules merged with vinexin and with actin. Taken together, our data indicate that SOCS-7 interacts with vinexin and the actin cytoskeleton.

Inhibition of cytokine production by the herbicide atrazine. Search for nuclear receptor targets.

The hematological toxicity of the commonly used triazine herbicides is a cause for concern. In a search for molecular targets of these compounds, as their effects paralleled those seen with dexamethasone (DEX), we first looked for interaction with the glucocorticoid receptor. In contrast to the effects on proliferation and cytokine production of DEX, those induced by atrazine were not prevented by the glucocorticoid antagonist RU486. Also, whereas DEX was able to inhibit the promoter activity of genes regulated by NF-kappaB, atrazine failed to do so. We next looked for interaction with members of the peroxisome proliferator-activated receptor (PPAR) family. No peroxisome proliferation was observed in the liver or kidneys of mice treated with atrazine. Moreover, no PPAR-mediated induction of promoter activity was seen on targets of PPARalpha, PPARgamma, or PPARdelta. Similarly, neither atrazine nor simazine were able to stimulate RORalpha-mediated promoter activity. Finally, no binding of atrazine to the AR was observed. In conclusion, the effects of atrazine-type herbicides most probably do not result from interaction with the above-mentioned nuclear receptors.