NF-kappaB2 is a putative target gene of activated Notch-1 via RBP-Jkappa

Transcriptional regulatory effects of lymphoma-associated NFKB2/lyt10 protooncogenes

C-terminal truncations of the NFKB2 p100 gene product have been observed in a number of cases of human cutaneous T cell lymphomas, as well as human B-cell lymphomas and myelomas. The contribution of these alterations to lymphomagenesis is not understood; however, truncation at amino acid 666 to generate 80 - 85 kD proteins in the HUT78 cell line is associated with addition of a short (serine-alanine-serine) fusion at the 3' end of p80HT, as well as with increased expression of NFKB2 mRNA. We therefore examined the effects of p80HT on the regulation of NFKB2 expression, as well as the properties of a series of other tumor-associated, and site directed mutations of NFKB2. While p80HT had not itself acquired novel transcriptional activation properties with respect to the NFKB2 P1 or P2 promoters or the IL-6 kappaB promoter, p80HT had lost the potent inhibitory (IkappaB-like) activity associated with the wild-type, p100 gene product. Loss of the inhibitory property depended on the SAS residues in the fusion protein, direct truncation at aa666 was fully inhibitory, as was a substitution of three alanines for the SAS residues. The presence of as few as two C-terminal ankyrin motifs was sufficient for inhibition of NF-kappaB-mediated transcriptional activation. Assays of a series of additional lymphoma-associated NF-kappaB-2 truncation suggested that the C-terminal truncation associated with these proteins was also associated with a loss of the IkappaB-like activities of p100 NF-kappaB-2, for at least some NF-kappaB target promoters. Thus, the loss of IkappaB-like activity of lymphoma-associated NFKB2 mutations may play an important role in the genesis of a subset of human lymphomas.

Inhibition of nuclear factor kappa B and induction of apoptosis in T-lymphocytes by sulfasalazine

1. Chronic inflammatory diseases have been shown to be associated with NF-kappaB activation and impaired apoptosis of immune cells. The aim of the present study was to investigate if sulfasalazine and its colonic metabolites 5-aminosalicylic acid (5ASA) and sulfapyridine affect NF-kappaB/Rel activation and viability of T-lymphocytes. 2. Sulfasalazine inhibits NF-kappaB/Rel activation in the murine T-lymphocyte cell line RBL5 using electrophoretic mobility shift assays. In transfection assays sulfasalazine treatment for 4 h inhibits kappaB-dependent transcription with an IC50 value of approximately 0.625 mM. 3. Higher doses or prolonged treatment result in cell death of T-lymphocytes in a dose- and time-dependent manner. Cell death is caused by apoptosis as judged by DNA fragmentation, annexin V and Apo 2.7 staining. Induction of apoptosis is a fast event with 50% apoptotic cells after a 4 h incubation with 2.5 mM sulfasalazine. The ED50 value for apoptosis induction after 24 h treatment was approximately 0.625 mM. 4. In contrast, 5ASA and sulfapyridine neither inhibit NF-kappaB/Rel activation nor induce apoptosis in T-lymphocytes at doses up to 5.0 mM. 5. These results demonstrate that sulfasalazine, but not 5ASA or sulfapyridine, strongly inhibits NF-kappaB activation and potently induces apoptosis in T-lymphocytes. Inhibition of NF-kappaB/Rel activation and subsequent clearance of activated T-lymphocytes by apoptosis might thus explain the beneficial effects of sulfasalazine in the treatment of chronic inflammatory disorders.

Arbiter of differentiation and death: Notch signaling meets apoptosis

Notch-ligand interactions are a highly conserved mechanism that regulates cell fate decisions. Over the past few years, numerous observations have shown that this mechanism operates to regulate cell differentiation in an enormous variety of developmental and cell maturation processes. Recent studies indicate that in addition to cell differentiation, Notch signaling has direct effects on proliferation and programmed cell death. The picture emerging from these findings suggests that, depending on cellular and developmental context, Notch signaling may function as a general "arbiter" of cell fate, regulating differentiation potential, rate of proliferation, and apoptotic cell death. In this review, we briefly summarize the current knowledge of the structure and function of Notch receptors and discuss the recent evidence that Notch signaling regulates apoptotic cell death. The possible mechanisms of this effect and its potential implications for developmental biology, immunobiology, neuropathology, and tumor biology are discussed.

Lineage-specific differences among CD8+ T cells in their dependence of NF-kappa B/Rel signaling

Whereas most CD8+ T cells in lymph nodes and spleen express the CD8alpha beta heterodimer and depend absolutely on thymic competence for their development, a substantial population of T cells expressing CD8alpha alpha matures extrathymically. Although the existence of these CD8 sublineages is well established, relatively little is known about differences that might exist among CD8 cells in their requirement for particular transcriptional pathways during the development and maintenance of normal populations. Transgenic mice whose T lineage expresses an IkappaBalpha mutant exhibited decreased NF-kappaB signaling and a diminution in mature CD8 T cells. We now have determined that although TCR-dependent CD69 induction by CD8alpha alpha and CD8alpha beta T cells was unaffected by inhibition of NF-kappaB, TCRalpha beta CD8alpha beta T cells were preferentially reduced compared to their TCRalpha beta CD8alpha alpha or TCRgamma delta counterparts. This finding was most prominent in spleen, but was also apparent in Peyer's patches of transgenic mice. In addition, diminished antiviral cytotoxic responses of CD8alpha beta intraepithelial lymphocytes were observed after enteric reovirus infection. Taken together, these results indicate that NF-kappaB signaling is more important for the thymus-dependent TCRalpha beta CD8alpha beta population than for other CD8 lineages, and thus regulates the number, function, and normal balance of CD8 subsets in the periphery.

Murine leukemia provirus-mediated activation of the Notch1 gene leads to induction of HES-1 in a mouse T lymphoma cell line, DL-3

Constitutive activation of Notch signaling is known to be associated with tumorigenesis. In a mouse T lymphoma cell line, DL-3, we found that a murine leukemia provirus was inserted in the Notch1 locus, which led to marked expression of a virus-Notch1 fusion mRNA encoding an intracellular portion of the Notch1 protein. Furthermore, expression and nuclear localization of this constitutively active form of Notch1 protein were confirmed. Corresponding to this finding, the transcription of the hairy/enhancer of split (HES-1) gene, a known target of Notch1 signaling, was elevated in this cell line. A potential role for overexpressed HES-1 in the development of the lymphoma was discussed.

Notch-1 inhibits apoptosis in murine erythroleukemia cells and is necessary for differentiation induced by hybrid polar compounds

Strikingly increased expression of notch-1 has been demonstrated in several human malignancies and pre-neoplastic lesions. However, the functional consequences of notch-1 overexpression in transformed cells remain unclear. We investigated whether endogenously expressed notch-1 controls cell fate determination in mouse erythroleukemia (MEL) cells during pharmacologically induced differentiation. We found that notch-1 expression is modulated during MEL cell differentiation. Premature downregulation of notch-1 during differentiation, by antisense S-oligonucleotides or by enforced expression of antisense notch-1 mRNA, causes MEL cells to abort the differentiation program and undergo apoptosis. Downregulation of notch-1 expression in the absence of differentiation inducer increases the likelihood of spontaneous apoptosis. We conclude that in MEL cells, endogenous notch-1 expression controls the apoptotic threshold during differentiation and growth. In these cells, notch-1 allows differentiation by preventing apoptosis of pre-committed cells. This novel function of notch-1 may play a role in regulating apoptosis susceptibility in notch-1 expressing tumor cells.

Regulation of NF-kappaB activity by I kappaB-related proteins in adenocarcinoma cells

Constitutive NF-kappaB activity varies widely among cancer cell lines. In this report, we studied the expression and the role of different I kappaB inhibitors in adenocarcinoma cell lines. High constitutive NF-kappaB activity and low I kappaB-alpha expression was found in a number of these cell lines. Moreover, some of these cells showed a high p100 expression, responsible for the cytoplasmic sequestration of most of p65 complexes. Treatment of these cells with TNF-alpha or other NF-kappaB activating agents induced only weakly nuclear NF-kappaB activity without significant p100 processing and led to a very weak transcription of NF-kappaB-dependent reporter gene. Induction of NF-kappaB activity can be restored by expression of the Tax protein or by treatment with antisense p100 oligonucleotides. In MCF7 A/Z cells stably transfected with a p100 expression vector, p65 complexes were sequestered in the cytoplasm by p100. These cells showed a reduced nuclear NF-kappaB induction and NF-kappaB-dependent gene transcription following TNF-alpha stimulation. As a consequence of a competition between I kappaB-alpha and p100, cells expressing high levels of p100 respond poorly to NF-kappaB activating stimuli as TNF-alpha.

The mammalian transcriptional repressor RBP (CBF1) targets TFIID and TFIIA to prevent activated transcription

RBP is a cellular protein that functions as a transcriptional repressor in mammalian cells. RBP has elicited great interest lately because of its established roles in regulating gene expression, in Drosophila and mouse development, and as a component of the Notch signal transduction pathway. This report focuses on the mechanism by which RBP represses transcription and thereby regulates expression of a relatively simple, but natural, promoter. The results show that, irrespective of the close proximity between RBP and other transcription factors bound to the promoter, RBP does not occlude binding by these other transcription factors. Instead, RBP interacts with two transcriptional coactivators: dTAFII110, a subunit of TFIID, and TFIIA to repress transcription. The domain of dTAFII110 targeted by RBP is the same domain that interacts with TFIIA, but is disparate from the domain that interacts with Sp1. Repression can be thwarted when stable transcription preinitiation complexes are formed before RBP addition, suggesting that RBP interaction with TFIIA and TFIID perturbs optimal interactions between these coactivators. Consistent with this, interaction between RBP and TFIIA precludes interaction with dTAFII110. This is the first report of a repressor specifically targeting these two coactivators to subvert activated transcription.