Suppression of Smad-1 mRNA expression level by Smad-2 likely control dichotomy of NF-κB and Smads mediated activation

The aim of this study was to find out how NF-κB and Smad-mediated signaling influenced the expression of astrogliogenic versus neurogenic markers of brain development in U4C cells which were either enriched (Tg Jak-1) or deprived in Jak-1 molecule (Jak-1 KO). Genetically modified U4C cells were transfected with NF-kB reporter plasmid in order to follow its activation when cells were cotransfected with different combinations of Smads constructs. In wild type cells no significant activation of NF-κB was observed while genetically modified cells exhibited somewhat different pattern of NF-κB activation depending on the Smad constructs combination used. The absence of NF-κB activation in Jak-1 transgenic cells transfected with Smad-1 plus Smad-3 was accompanied by the appearance of apoptotic cells as revealed by DAPI staining. Smad-1 expression was undetectable in Jak-1 transgenic cells and was downregulated in wild type cells upon transfection with Smad-2. The absence of p65 nuclear translocation in Smad-2 transfected cells and the presence of Smad-4 in nucleus of the same cells indicates dichotomy in NF-κB and Smads mediated signaling pathways. The significance of this study is that helps to elucidate the point of collaboration among three different signaling pathways - Jak-1 mediated cytokine signaling, NF-κB and Smads mediated pathways.

Resolving the role of topoisomerase II in chromatin structure and function

The catalytic activities of topoisomerase II are responsible primarily for solving the complex topological problems that arise from cellular processes such as DNA replication, transcription and chromosome segregation; however, topoisomerase II may also play a crucial structural role in the chromosome scaffold. Cell-cycle-regulated phosphorylation might be the key to these diverse functions. Phosphorylation of topoisomerase II might trigger the enzymatic activities essential for mitosis and promote interactions with specialized DNA sequences and other protein components of the eukaryotic chromosome to ensure the proper establishment and maintenance of chromatin architecture and function.

Only centromeres can supply the partition system required for ARS function in the yeast Yarrowia lipolytica

Autonomously replicating sequences (ARSs) in the yeast Yarrowia lipolytica require two components: an origin of replication (ORI) and centromere (CEN) DNA, both of which are necessary for extrachromosomal maintenance. To investigate this cooperation in more detail, we performed a screen for genomic sequences able to confer high frequency of transformation to a plasmid-borne ORI. Our results confirm a cooperation between ORI and CEN sequences to form an ARS, since all sequences identified in this screen displayed features of centromeric DNA and included the previously characterized CEN1-1, CEN3-1 and CEN5-1 fragments. Two new centromeric DNAs were identified as they are unique, map to different chromosomes (II and IV) and induce chromosome breakage after genomic integration. A third sequence, which is adjacent to, but distinct from the previously characterized CEN1-1 region was isolated from chromosome I. Although these CEN sequences do not share significant sequence similarities, they display a complex pattern of short repeats, including conserved blocks of 9 to 14 bp and regions of dyad symmetry. Consistent with their A+T-richness and strong negative roll angle, Y. lipolytica CEN-derived sequences, but not ORIs, were capable of binding isolated Drosophila nuclear scaffolds. However, a Drosophila scaffold attachment region that functions as an ARS in other yeasts was unable to confer autonomous replication to an ORI-containing plasmid. Deletion analysis of CEN1-1 showed that the sequences responsible for the induction of chromosome breakage could be eliminated without compromising extrachromosomal maintenance. We propose that, while Y. lipolytica CEN DNA is essential for plasmid maintenance, this function can be supplied by several sub-fragments which, together, form the active chromosomal centromere. This complex organization of Y. lipolytica centromeres is reminiscent of the regional structures described in the yeast Schizosaccharomyces pombe or in multicellular eukaryotes.

Distinct activities of p52/NF-kappa B required for proper secondary lymphoid organ microarchitecture: functions enhanced by Bcl-3

Mice rendered deficient in p52, a subunit of NF-kappa B, or in Bcl-3, an I kappa B-related regulator that associates with p52 homodimers, share defects in the microarchitecture of secondary lymphoid organs. The mutant mice are impaired in formation of B cell follicles and are unable to form proper follicular dendritic cell (FDC) networks upon antigenic challenge. The defects in formation of B cell follicles may be attributed, at least in part, to impaired production of the B lymphocyte chemoattractant (BLC) chemokine, possibly a result of defective FDCs. The p52- and Bcl-3-deficient mice exhibit additional defects within the splenic marginal zone, including reduced numbers of metallophilic macrophages, reduced deposition of the laminin-beta 2 chain and impaired expression of a mucosal addressin marker on sinus-lining cells. Whereas p52-deficient mice are severely defective in all of these aspects, Bcl-3-deficient mice are only partially defective. We determined that FDCs or other non-hemopoietic cells that underlie FDCs are intrinsically impaired in p52-deficient mice. Adoptive transfers of wild-type bone marrow into p52-deficient mice failed to restore FDC networks or follicles. The transfers did restore metallophilic macrophages to the marginal zone, however. Together, the results suggest that p52 carries out functions essential for a proper splenic microarchitecture in both hemopoietic and non-hemopoietic cells and that Bcl-3 is important in enhancing these essential activities of p52.

Mice deficient in nuclear factor (NF)-kappa B/p52 present with defects in humoral responses, germinal center reactions, and splenic microarchitecture

p52 is a subunit of nuclear factor (NF)-kappa B transcription factors, most closely related to p50. Previously, we have shown that p52, but not p50 homodimers can form transactivating complexes when associated with Bcl-3, an unusual member of the I kappa B family. To determine nonredundant physiologic roles of p52, we generated mice deficient in p52. Null mutant mice were impaired in their ability to generate antibodies to T-dependent antigens, consistent with an absence of B cell follicles and follicular dendritic cell networks in secondary lymphoid organs, and an inability to form germinal centers. Furthermore, the splenic marginal zone was disrupted. These phenotypes are largely overlapping with those observed in Bcl-3 knockout animals, but distinct from those of p50 knockouts, supporting the notion of a physiologically relevant complex of p52 homodimers and Bcl-3. Adoptive transfer experiments further suggest that such a complex may be critical in accessory cell functions during antigen-specific immune reactions. Possible roles of p52 and Bcl-3 are discussed that may underlie the oncogenic potential of these proteins, as evidenced by recurrent chromosomal translocations of their genes in lymphoid tumors.

Requirement for NF-kappaB in osteoclast and B-cell development

NF-kappaB is a family of related, dimeric transcription factors that are readily activated in cells by signals associated with stress or pathogens. These factors are critical to host defense, as demonstrated previously with mice deficient in individual subunits of NF-kappaB. We have generated mice deficient in both the p50 and p52 subunits of NF-kappaB to reveal critical functions that may be shared by these two highly homologous proteins. We now demonstrate that unlike the respective single knockout mice, the p50/p52 double knockout mice fail to generate mature osteoclasts and B cells, apparently because of defects that track with these lineages in adoptive transfer experiments. Furthermore, these mice present markedly impaired thymic and splenic architectures and impaired macrophage functions. The blocks in osteoclast and B-cell maturation were unexpected. Lack of mature osteoclasts caused severe osteopetrosis, a family of diseases characterized by impaired osteoclastic bone resorption. These findings now establish critical roles for NF-kappaB in development and expand its repertoire of roles in the physiology of differentiated hematopoietic cells.

Human immunodeficiency virus type 1 nucleocapsid protein specifically stimulates Mg2+-dependent DNA integration in vitro

The integrase (IN) protein of the human immunodeficiency virus mediates integration of the viral DNA into the cellular genome. In vitro, this reaction can be mimicked by using purified recombinant IN and model DNA substrates. IN mediates two reactions: an endonucleolytic cleavage at each 3' end of the proviral DNA (terminal cleavage) and the joining of the linear viral DNA to 5' phosphates in the target DNA (strand transfer). Previous investigators have shown that purified IN requires Mn2+ or Mg2+ to promote strand transfer in vitro, although Mg2+ is the likely metal cofactor in vivo. IN activity in the presence of Mg2+ in vitro requires high IN concentrations and low concentrations of salt. Here, we show that the viral nucleocapsid protein NCp7 allows efficient IN-mediated strand transfer in the presence of Mg2+ at low enzyme concentrations. This potentiating effect appears to be unique to NCp7, as other small DNA-binding proteins, while capable of stimulating integration in the presence of Mn2+, all failed to stimulate strand transfer in the presence of Mg2+.

Leu-enkephalin enhances interferon secretion in mice

This work has explored the possibility that alterations of NK activity induced by the opioid pentapeptide leu-enkephalin (LENK) may reflect the alterations in secretion of IFN, an important regulator of NK activity. The NK activity in the spleen of mice was determined in parallel with the plasma IFN level 24 and 48 h after an i.p. injection of LENK (10 mg/kg). A known inducer of IFN secretion, polyinosinic-polycytidylic acid (poly-IC), was also used. LENK injection significantly increased basal IFN secretion 24 and 48 h later. The level was comparable to that induced by poly-IC. However, LENK was not able to augment the poly-IC-increased IFN level. The increase of IFN at 48 h coincided with a mild enhancement of NK activity in the spleens, but 24 h after LENK injection, the increased IFN level in plasma was associated with a significant drop of splenic NK activity. LENK did not affect the NK activity stimulated with poly-IC. Naloxone (20 mg/kg), an opioid receptor-blocking agent, only partly diminished the LENK-induced IFN secretion. However, naloxone itself increased the plasma IFN level. These data indicate that the immunomodulatory effects of the opioid peptide LENK in vivo are associated with alterations of IFN secretion.

SARs stimulate but do not confer position independent gene expression

Two minimal scaffold-associated regions (SARs) from Drosophila were tested in stably transformed cells for their effects on the expression of reporter genes. The expression of genes bounded by two SARs is consistently stimulated by about 20- to 40-fold, if the average of a pool of cell transformants is analyzed. However, analysis of individual, stable cell transformants demonstrates that flanking SAR elements do not confer position-independent expression on the reporter gene and that the extent of position-dependent variegation is similarly large with or without the flanking SAR elements. The SAR stimulation of expression is observed in stable but not in transiently transfected cell lines. The Drosophila scs and scs' boundary elements, which do not bind to the nuclear matrix in vitro, are only about one-tenth as active as SARs in stimulating expression in stable transformants. Interestingly, the SAR stimulatory effect can be blocked by a fragment containing CpG islands (approximately 70% GC), if positioned between the SAR and the enhancer. In contrast, when inserted in the same position, control fragments, such as the scs/scs' elements, do not interfere with SAR function.

p185neu is expressed in yolk sac during rat postimplantation development

We have shown that the neu oncogene product (p185neu) is not present in the rat embryo before organogenesis. However, coincident with the onset of organogenesis, p185neu was detected in neural and connective tissue as well as in the secretory epithelium as was described by Kokai et al. (1987). In addition, p185neu is also expressed in the rat visceral yolk sac (VYS) endodermal cells but not in the mesenchymal and mesothelial layers of the same structure nor in the amnion. The first detectable sign of p185neu expression in VYS was found at d 11 of gestation and the levels of protein increased towards the end of pregnancy. In the yolk sac carcinoma (YSC), which is considered to be the malignant counterpart of the rat yolk sac, p185neu was observed only within columnar epithelial cells (the visceral component of the neoplasm) while parietal endoderm-like cells were devoid of detectable protein. From d 9 of pregnancy up to delivery some of the trophoblastic giant cells also showed a faint to moderate immunoreactivity. Results are presented which would indicate a possible role of p185neu in rat embryogenesis.

A model for chromatin opening: stimulation of topoisomerase II and restriction enzyme cleavage of chromatin by distamycin

Histone H1 preferentially and cooperatively binds scaffold-associated regions (SARs) in vitro via specific interactions with the numerous short A + T-rich tracts (A-tracts) contained in these sequences. Selective titration of A-tracts by the oligopeptide distamycin abolishes this interaction and results in a redistribution of H1. Similarly, treatment of intact cells and isolated nuclei with distamycin specifically enhances cleavage of internucleosomal linkers of SARs by topoisomerase II and restriction enzymes. The increased accessibility of these linkers is thought to result from the unfolding (or opening) of the chromatin fiber and to be due to a reduced occupancy by histone H1. Chromatin extraction and H1 assembly experiments support this view. We discuss a model whereby open, H1-depleted chromatin regions may be generated by titration of A-tracts by putative distamycin analogues; this local opening may spread to adjacent regions assuming highly cooperative H1-H1 interactions in chromatin.

Scaffold-associated regions: cis-acting determinants of chromatin structural loops and functional domains

It has been proposed that scaffold-associated regions are DNA elements that form the bases of chromatin loops in eukaryotic cells. Recent evidence supports a role for these elements as cis-acting 'handlers' of both structural and functional chromatin domains.