Induction of kappa transcription by interferon-gamma without activation of NF-kappa B

A gamma interferon-unresponsive variant of cell line 70Z/3, IFN-4, can be partially rescued by phorbol myristate acetate

Lipopolysaccharide (LPS) and gamma interferon (IFN-gamma) induce kappa transcription in 70Z/3 cells by different mechanisms; LPS treatment induces both NF-kappa B and OTF-2 transcription factors, but IFN-gamma treatment does not. We have dissected these two activation pathways by selecting and analyzing an LPS+ IFN- variant of 70Z/3.

Lipopolysaccharide-unresponsive mutant pre-B-cell lines blocked in NF-kappa B activation

NF-kappa B activation is a crucial late step in the induction of immunoglobulin kappa light-chain gene expression in pre-B cells by lipopolysaccharide (LPS). We have analyzed NF-kappa B activation in three independent mutant lines of 70Z/3 pre-B cells which are unresponsive to LPS. All three variant cell lines failed to activate NF-kappa B when induced with LPS or the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. However, all three cell lines contained functional NF-kappa B, as revealed by detergent treatment of cytoplasmic extracts. Moreover, cycloheximide induced limited activation of NF-kappa B comparable to that in wild-type 70Z/3 pre-B cells in two of the three variant lines. These results indicate that the mutations blocking kappa gene induction in these variant 70Z/3 pre-B-cell lines affect NF-kappa B activation.

Regulation of the immunoglobulin gene transcription

The transcription of the immunoglobulin heavy (IGH), kappa (IGK) and lambda (IGL) chain genes is coordinate and B lymphocyte specific. This expression of the immunoglobulin genes is under the control of regulatory elements: the promoters located 5' of each variable (V) gene and the enhancers located between the joining and constant genes in the IGH and IGK locus and downstream on the C kappa gene. These sequences represent sites for the binding of transcription factors. A 90-100 kDa ubiquitous proteins (NF-A1) as well as two specific B cell proteins (NF-A2, OTF-2B) bind to the octamer site of the V promoter and IGH enhancer. The NF-kB protein binds to the kB site in the intron kappa enhancer, but also to kB-like sites found in the promoter regions of other genes. This paper reviews the recent data on these factors and other transcription factors which bind to the promoters and enhancers of the immunoglobulin genes and control their expression.

Regulation of IgG production by suppressor Fc gamma RII+ T hybridomas

In this work, we analyzed the immunoglobulin heavy (H) and light (L) chain production by two variant B hybridomas, UN2.C3 and UN2.C17.K1 co-cultured with cells from a Fc gamma RII+, IgG-binding factor (IgG-BF)-producer T hybridoma (T2D4.C1) or with cells of a Fc gamma RII-, IgG-BF-nonproducer variant (D10C5). We showed that only the Fc gamma RII+ hybridoma directly inhibits the IgG secretion by UN2.C3 through a soluble mediator. This inhibition affects the H and L chain synthesis as well as the H and L chain-encoding mRNA steady state. No apparent cytotoxic effect could be detected. In contrast, the production of kappa chain by an H chain-negative variant (UN2.C17.K1) was unaffected. This indicates that a complete IgG molecule is required to observe the inhibitory effect induced by T2D4.C1. The pattern of effector/target cell interactions observed in our work suggests that the soluble factor involved in the suppression of IgG production is IgG-BF, able to transiently modify the IgG gene expression in target cells.

Slow response variant of the B lymphoma 70Z/3 defective in LPS activation of NF-kappa B

The mouse B cell lymphoma 70Z/3 is membrane immunoglobulin M (mIgM) negative, but treatment of the cells with bacterial lipopolysaccharide (LPS) induces the expression of kappa (kappa) light chain synthesis, and the cells become mIgM+. In wild type cells, this reaction is maximal after 24 h; we have isolated a variant, 1B8, which becomes mIgM+ only after a more prolonged incubation with LPS. This delayed response results from a reduced rate of accumulation of (kappa) mRNA and protein. The transcription factor, NF-kappa B is present in the cytoplasm of both the wild type and the variant cells in its inactive form. The delay in kappa expression is correlated with the failure of NF-kappa B to be activated and translocated to the nucleus. Although NF-kappa B cannot be activated by LPS, it can be activated by treatment with phorbol ester (PMA). In contrast to the clear defect in NF-kappa B, LPS treatment of 1B8 cells causes the octamer-binding factor OTF-2 to increase normally. We conclude that the defect in 1B8 cells is in an early part of the LPS activation pathway, prior to the activation of NF-kappa B, but after the signal for OTF-2 induction. The phenotype of 1B8 demonstrates that an increase in OTF-2 alone is sufficient to cause a large increase in kappa transcription in 70Z/3 cells, but that without NF-kappa B, the response is slow to develop. In this view, NF-kappa B functions to facilitate kappa transcription and to speed its rate of increase, but is not required for the long-term response of 70Z/3 cells to LPS.

Lipopolysaccharide-unresponsive mutant pre-B-cell lines blocked in NF-kappa B activation

NF-kappa B activation is a crucial late step in the induction of immunoglobulin kappa light-chain gene expression in pre-B cells by lipopolysaccharide (LPS). We have analyzed NF-kappa B activation in three independent mutant lines of 70Z/3 pre-B cells which are unresponsive to LPS. All three variant cell lines failed to activate NF-kappa B when induced with LPS or the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. However, all three cell lines contained functional NF-kappa B, as revealed by detergent treatment of cytoplasmic extracts. Moreover, cycloheximide induced limited activation of NF-kappa B comparable to that in wild-type 70Z/3 pre-B cells in two of the three variant lines. These results indicate that the mutations blocking kappa gene induction in these variant 70Z/3 pre-B-cell lines affect NF-kappa B activation.

1.3E2, a variant of the B lymphoma 70Z/3, defective in activation of NF-kappa B and OTF-2

The mouse B-cell cell lymphoma 70Z/3 is a convenient model system in which to study the regulation of immunoglobulin synthesis. Three transcriptional activators of kappa (kappa) light chain synthesis have been identified for these cells: bacterial lipopolysaccharide (LPS), interferon-gamma (IFN), and interleukin-1 (IL-1). The response of the kappa gene in 70Z/3 cells to LPS is mediated by increases in two transcription factors: NF-kappa B and OTF-2. In contrast, IFN has no effect on either of these factors in 70Z/3 cells. We have isolated by immunoselection an LPS- IFN+ variant of 70Z/3 called 1.3E2. We show here that LPS treatment of these cells causes no increase in nuclear localization of either NF-kappa B or OTF-2. Although they have normal levels of cytoplasmic NF-kappa B, it cannot be activated by LPS or by phorbol 12-myristate 13-acetate (PMA) treatment of the cells. These experiments expand the genetic dissection of the molecular pathways of activation of kappa transcription in 70Z/3 cells.

Immunoglobulin gene transcription: molecular mechanisms

Recently, many of the proteins involved in transcriptional regulation of immunoglobulin genes have been identified, purified and their cDNAs cloned. This detailed molecular information has revealed fascinating similarities among different classes of DNA-binding proteins and has dramatically expanded the number of potential mechanisms for achieving precise tissue- and developmental stage-specific immunoglobulin transcription.

A gamma interferon-unresponsive variant of cell line 70Z/3, IFN-4, can be partially rescued by phorbol myristate acetate

Lipopolysaccharide (LPS) and gamma interferon (IFN-gamma) induce kappa transcription in 70Z/3 cells by different mechanisms; LPS treatment induces both NF-kappa B and OTF-2 transcription factors, but IFN-gamma treatment does not. We have dissected these two activation pathways by selecting and analyzing an LPS+ IFN- variant of 70Z/3.

Interleukin 6 induces secretion of IgG1 by coordinated transcriptional activation and differential mRNA accumulation

The molecular mechanism by which interleukin 6 (IL-6) induces terminal differentiation of B cells was investigated in a subpopulation of the clonal human B-lymphoblastoid cell line CESS selected for high density of cell surface IgG1. Induction of CESS cells with IL-6 resulted in a 15-fold preferential accumulation of secreted-specific gamma 1 (gamma 1s) mRNA but not of the alternatively processed membrane-specific gamma 1 (gamma 1m) mRNA. Similarly, microseconds mRNA but not the microns mRNA of the nonproductively rearranged mu heavy-chain allele was also increased. Accompanying the differential accumulation of gamma 1s mRNA was a 4.5-fold increase in lambda light-chain mRNA, leading to secretion of IgG1. Analyses of transcription in isolated nuclei demonstrated that transcriptional activation was the primary mechanism for quantitative increase of immunoglobulin mRNAs (5.5-fold for gamma 1 and mu and at least 2-fold for lambda). Since polymerase loading is diminished by 75% before reaching the downstream gamma 1m polyadenylylation site in CESS cells, irrespective of IL-6 induction, transcriptional pausing/termination appears intrinsic and contributes to the selection of gamma 1s and gamma 1m polyadenylylation sites in activated B cells. Furthermore, differential mRNA stabilization is likely to contribute to the alteration of the gamma 1s/gamma 1m mRNA ratio at IL-6 induction.

Partial purification of an immunosuppressive protein from a human tumor cell line and analysis of its relationship to transforming growth factor beta

The A673 human rhabdomyosarcoma cell line constitutively produces an acid-soluble, potent immunosuppressive factor (ISF), which inhibits T-cell proliferation. We have partially purified this factor from the culture supernatant of A673 cells by a sequence of acid extraction, gel filtration, cation exchange chromatography, and reverse-phase HPLC. Characterization studies indicate that ISF is similar or identical to transforming growth factor beta (TGF beta). ISF exhibits a molecular weight of 25 kDa in sodium dodecyl sulfate-polyacrylamide gels. ISF, like TGF beta, is a very basic protein (pI = 9.5) that is sensitive to reduction. Anti-TGF beta 1 antibodies completely block ISF activity in the thymocyte assay. Furthermore, ISF, like TGF beta, stimulated the anchorage-independent growth of normal rat kidney fibroblasts in soft agar.