Interleukin 2 (IL-2) has an important role in the regulation of the expression of IL-2 receptors and the synthesis of gamma interferon (IFN-gamma) by T lymphocytes. IL-2 is required for the optimum expression of IL-2 receptors on activated T lymphocytes and for maximum synthesis of IFN-gamma in vitro. Dexamethasone, an immunosuppressant drug that inhibits IL-2 synthesis, diminished the expression of IL-2 receptors and the synthesis of IFN-gamma. Anti-Tac, a monoclonal antibody known to prevent the binding of IL-2 to its receptor without inhibiting IL-2 synthesis, down-regulated the expression of the receptor and partially inhibited synthesis of IFN-gamma. In a population of T lymphocytes prevented from synthesizing IL-2 by dexamethasone and incapable of using IL-2 as a result of blockage of IL-2 receptors by anti-Tac, the number of receptor-bearing cells and receptor density were diminished. Anti-Tac in combination with dexamethasone also exerted a synergistic effect on IFN-gamma synthesis, inhibiting it almost completely. The inhibitory effect of dexamethasone IFN-gamma synthesis may be of clinical importance, since IFN-gamma activates macrophages and thereby triggers one of the defense mechanisms against bacterial infections.

Nopp140 is thought to shuttle between nucleolus and cytoplasm. However, the predominant nucleolar localization of Nopp140 homologues from different species suggests that Nopp140 is also involved in events occurring within the nucleolus. In this study, we demonstrated that the largest subunit of RNA polymerase I, RPA194, was coimmunoprecipitated with the human Nopp140 (hNopp140). Such an interaction is mediated through amino acids 204 to 382 of hNopp140. By double immunofluorescence, hNopp140 was colocalized with RNA polymerase I at the rDNA (rRNA genes) transcription active foci in the nucleolus. These results suggest that Nopp140 can interact with RNA polymerase I in vivo. Transfected cells expressing the amino-terminal half of hNopp140, hNopp140N382 (amino acids 1 to 382), displayed altered nucleoli with crescent-shaped structures. This phenotype is reminiscent of the segregated nucleoli induced by actinomycin D treatment, which is known to inhibit rRNA synthesis. Consistently, the hNopp140N382 protein mislocalized the endogenous RNA polymerase I and shut off cellular rRNA gene transcription as revealed by an in situ run-on assay. These dominant negative effects of the mutant hNopp140N382 suggest that Nopp140 plays an essential role in rDNA transcription. Interestingly, ectopic expression of hNopp140 to a very high level caused the formation of a transcriptionally inactive spherical structure occupying the entire nucleolar area which trapped the RNA polymerase I, fibrillarin, and hNopp140 but excluded the nucleolin. The mislocalizations of these nucleolar proteins after hNopp140 overexpression imply that Nopp140 may also play roles in maintenance of nucleolar integrity.The nucleolus in eukaryotic cells carries out most of the important reactions in ribosome biogenesis, including rDNA (rRNA genes) transcription, rRNA processing, and preribosome assembly (34,47,49,50). Elements of nucleolar architecture mediate a tight temporal and topological orchestration of these processes. In higher eukaryotic cells, nucleoli exhibit a common organization consisting of three ultrastructurally distinct regions, the fibrillar center (FC), the dense fibrillar component (DFC), and the granular component (GC). The main body of the nucleolus is made up of the GC, embedded in this granular mass are several islets of rounded structures, FCs, each surrounded by a compact layer of the DFC. Tandemly repeated rRNA genes are clustered mostly in the FCs (42, 57), with transcription occurring largely at the boundary between the FC and the DFC (13,20,42,58). Nascent rRNA transcripts are processed in the DFC (25,38,59). Some processing steps may also occur in the GC, together with the assembly of the mature rRNA and ribosomal proteins into preribosomal subunits (42,47). In addition to rDNA, rRNA, and ribosomal proteins, the nucleolus harbors a large number of nonribosomal proteins and small nucleolar RNAs, which mediate the transcriptional and posttranscriptional reactions of ribosome biogenesis (49, 54). Many nucleolar proteins locate in pa...

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Expression of the acute-phase response genes, such as that for alpha-i acid glycoprotein (AGP), involves both positive and negative transcription factors. A positive transcription factor, AGP/EBP, and a negative transcription factor, factor B, have been identified as the two most important factors responsible for the induction of the AGP gene. In this paper we report the purification, characterization, and identification of a B-motif-binding factor from the mouse hepatoma cell line 129p. The purified factor has been identified as nucleolin by amino acid sequence analysis. Biochemical and functional studies further established that nucleolin is a transcription repressor for regulation of AGP and possibly other acute-phase response genes. Thus, in addition to the many known functions of nucleolin, such as rRNA transcription, processing, ribosome biogenesis, and the shuttling of proteins between the cytoplasmic and nuclear compartments, it may also function as a transcriptional repressor.The initiation of transcription in eukaryotes is an intricately controlled process. Short sequence motifs in the promoter regions of genes interact in a specific manner with DNAbinding transcription factors. These bound factors interact with general transcription factors and thereby result in gene transcription. Not only transcriptional activators but also repressors are important in the controlled regulation of gene expression. For a given gene, the combinations of cis elements and the trans-acting factors are major determinants of transcriptional activity. Protein-protein interactions and posttranslational modifications are important for regulating the activities of these factors. An array of transcriptional activators and repressors have been identified and characterized (9,12,14,15,18,24,35,37).Tissue injury and infection produce significant alterations of the host metabolic and immune homeostasis (19). It has become increasingly clear that many of these changes result from a complex cascade of mononuclear phagocyte-derived endogenous mediators, in particular, cytokines. Injection of purified lipopolysaccharide (LPS) into laboratory animals leads to the development of many biological activities with similarities to those that follow tissue injury and infection. These can range from an acute-phase response to shock with lethal outcome. The well-studied biological activities of LPSinduced liver gene expression are mediated by multiple cytokines, including interleukins 1, 6, and 11, leukemia inhibitory factor, and tumor necrosis factor alpha (13,19,30,31). We used LPS-induced transcription of the alpha-1 acid glycoprotein (AGP) gene as a model for studying the regulation of gene expression during the acute-phase response (9, 24). Transcription of the AGP gene in response to LPS treatment is regulated by both a positive factor, AGP/EBP (C/EBP-P), and a negative factor, factor B (24). During the acute-phase * Corresponding author. Mailing address: Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taip...