Regulation of expression of the rat serine protease inhibitor 2.3 gene by glucocorticoids and interleukin-6. A complex and unusual interplay between positive and negative cis-acting elements

Regulation of expression of the rat SOCS-3 gene in hepatocytes by growth hormone, interleukin-6 and glucocorticoids mRNA analysis and promoter characterization

Suppressors of cytokine signalling (SOCS) represent a newly discovered family of molecules that seem to play an important role in the shutting off of cytokine and possibly peptide hormone action. Thus, understanding the mechanisms controlling their expression is of cardinal importance. In the present study, we have cloned the rat SOCS-3 gene and analyzed its expression and the functioning of its promoter in hepatocytes. Expression of SOCS-3 mRNA, which is very weak in freshly isolated cells, tended to increase when hepatocytes were incubated without hormones. Growth hormone (GH) and, to a much larger extent, interleukin-6 (IL-6) rapidly activated mRNA synthesis whereas glucocorticoids (GC) strongly inhibited both basal and hormone-dependent expressions. A short promoter fragment (-137/+35) responded maximally to GH and IL-6 (a threefold stimulation for each effector) and to GC (a 70-80% inhibition), whereas longer promoter sequences supported higher basal activity and lower positive hormonal responses. Deletion and mutation analyses indicated that all hormonal responses were dependent on two cis-acting sequences termed the G-rich and the A/T-rich elements. Only the A/T-rich element was active in a heterologous context, thus behaving as a typical enhancer. Unexpectedly, the two signal transducer and activator of transcription (STAT) binding sites found immediately upstream of the G-rich motif didn't seem to participate in either GH or IL-6 effect, despite the fact that one of them strongly responded to IL-6 when placed in front of a heterologous promoter. Finally, the negative regulation of SOCS-3 promoter by GC that may contribute to gene silencing in vivo, appeared to involve interactions of the GC receptor with other transcription factors and not direct binding to DNA, as no GC-response element was found in the sequence.

Molecular cloning and expression studies of a prolactin receptor in goldfish (Carassius auratus)

A full-length cDNA clone, of a size of 4.6 kb, for the goldfish prolactin receptor has been isolated. This cDNA clone encodes a protein of 600 amino acids homologous to prolactin receptors of other species. A Kyte-Doolittle hydropathy analysis of the receptor indicates that the translated protein consists of a signal peptide of 22 amino acids, an extracellular domain of 228 amino acids, a single transmembrane domain of 24 amino acids, and an intracellular domain of 346 amino acids. Several characteristic landmarks of prolactin receptor could be identified in this clone. These include the four conserved cysteine residues and the WS motif within the extracellular domain, and the box 1 and box 2 regions of the intracellular domain. Among all the prolactin receptor sequences known to date, this clone bears the closest resemblance to the tilapia prolactin receptor, although homology between these two fish prolactin receptors is rather low. There are only 57.4% of nucleotide and 48.3% of amino acid sequence identities between these two fish receptors. This receptor cDNA was transfected into CHO-K1 cells for functional analysis. RT-PCR analysis with a pair of gene specific primers indicate that the receptor was transcribed in the transfected cells. Using a cell proliferation assay based on the reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, the receptor transfected CHO-K1 cells can be stimulated to proliferate upon the addition of ovine prolactin in the culture medium. The tissue distribution of the prolactin receptor in goldfish was studied by RT-PCR/Southern analysis and by Northern analysis. The results indicated that the receptor is expressed mostly in the kidney, the gill and the intestine of goldfish, corroborating with the osmoregulatory role of prolactin in fish. In addition, an appreciable level of the receptor is also found in the brain and gonads of goldfish. Northern analysis showed that there are two transcript sizes, a major 4.6 kb and a minor 3.5 kb mRNAs, in the kidney, gill and intestine.

Growth hormone-mediated transcriptional activation of the rat serine protease inhibitor 2.1 gene involves both interleukin-1 beta-sensitive and -insensitive pathways

Growth hormone (GH)-dependent activation of the rat serine protease inhibitor 2.1 (spi 2.1) gene in vivo requires both a modification of the chromatin structure and the activation of transcription factors mediated by the tyrosine protein Janus kinase JAK2. To address the question of the relationship between those two GH effects, we used interleukin 1 beta (Il-1 beta) that was previously shown to inhibit spi 2.1 gene expression. In cultured hepatocytes from normal rats, Il-1 beta did not antagonize GH-dependent stimulation of promoter activity (i.e., in episomal constructs) mediated by transcription factors activated by JAK2. In hepatocytes from inflamed rats, GH triggered JAK2-dependent activation of transcription factors as in control cells but failed to stimulate genomic spi 2.1 gene expression. It thus appears that the Il-1 beta-insensitive activation of transcription factors by GH is independent of its action on the nucleosomal structure of the spi 2.1 gene which, in contrast, is sensitive to this cytokine.

Transcription of the rat serine protease inhibitor 2.1 gene in vivo: correlation with GAGA box promoter occupancy and mechanism of cytokine-mediated down-regulation

Two GH-response elements (GHREs) and a single glucocorticoid (GC)-response element were found to regulate activity of the rat serine protease inhibitor 2.1 gene (spi 2.1) promoter in vitro. To assess the physiological relevance of these observations, we have investigated the relationship existing between the level of spi 2.1 gene transcription, structural modifications of the chromatin, and in vivo nuclear protein-promoter interactions monitored by genomic footprinting, in control, hypophysectomized, and inflamed rats. We also addressed the mechanism of inflammation-mediated gene down-regulation. We found that a high level of spi 2.1 gene transcription correlates with hypersensitivity of the promoter to deoxyribonuclease I (DNase I) and maximal occupancy of the GAGA box (GHRE-I). The failure of GAGA-box binding proteins (GAGA-BPs) to interact with the GAGA box appears to result from an impairment in GH action due to its absence (i.e. hypophysectomized animals) or to the appearance of a cytokine-mediated GH-resistant state (i.e. inflamed rats) in liver. Unlike the GAGA box, signal transducer and activator of transcription (STAT) factor-binding sites included in the GHRE-II were never found to be protected against DNase I attack but displayed a differential DNase I reactivity depending on the level of gene transcription. Alterations in DNase I reactivity of the GC-response element region suggest that GC receptor-GC complexes may associate, in a transient manner, with the promoter in the actively transcribing control state. Taken together, our studies suggest a mechanism of spi 2.1 gene activation in vivo whereby the GH-dependent chromatin remodeling caused by or concomitant to the recruitment of GAGA-box binding proteins is the first compulsory and presumably predominant step.