Functional characterization of the developmentally controlled immunoglobulin kappa 3' enhancer: regulation by Id, a repressor of helix-loop-helix transcription factors

Negative regulation of transcription in eukaryotes

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Abnormal kappa B-binding protein in the cytoplasm of a plasmacytoma cell line that lacks nuclear expression of NF-kappa B

The transcription factor NF-kappa B appears to play an important role in immunoglobulin gene expression and lymphokine production, and may play a role in primary B cell activation. Constitutive nuclear expression of NF-kappa B has been found in all mature B cell lines with the notable exception of the murine plasmacytoma, S107. We report herein that S107 cells express cytoplasmic kappa B-binding material detected by electrophoretic mobility shift assay that by several criteria represents authentic NF-kappa B. Despite the presence of cytoplasmic NF-kappa B, several stimuli known to induce nuclear translocation of NF-kappa B failed to do so in S107 cells, including: the PKC agonist, PMA; the protein synthesis inhibitor, cycloheximide; and LPS. Transfection of S107 cells with a kappa B-CAT reporter gene construct confirmed the absence of functional activity. Importantly, a global failure of nuclear transcription factor expression was ruled out by the ability of PMA to induce nuclear expression of another trans-acting factor, AP-1. Thus, rather than lacking NF-kappa B altogether, S107 cells manifest disordered regulation of NF-kappa B in which cytoplasmic material is incapable of translocation to the nucleus. While Northern analysis failed to reveal a gross defect in the mRNA coding for the DNA binding subunit of NF-kappa B, UV-photo-cross-linking followed by denaturing gel electrophoresis demonstrated the presence of a cytoplasmic kappa B-binding protein of abnormally elevated molecular size. This finding suggests that the abnormal regulation of NF-kappa B in S107 cells is associated with the appearance of an unusual kappa B-binding molecule.

Id expression during mouse development: a role in morphogenesis

We have characterized the spatial and temporal pattern of Id transcription during mouse embryogenesis. The Id gene encodes a helix-loop-helix (HLH) protein which can heterodimerize with the ubiquitously expressed HLH protein products of the E2A gene, and prevent them from binding DNA either alone or as a heterodimer with tissue specific HLH transcription factors such as the muscle determination gene, MyoD1 (Benezra et al., 1990: Cell 61:49-59). Since Id has been shown to be down-regulated during induced differentiation in several cell lines, it has been postulated that Id plays a general inhibitory role in cell differentiation (Benezra et al., 1990). In situ analysis of Id mRNA expression in the mouse embryo was performed in order to determine whether the pattern of Id expression is consistent with this postulate. A detailed study throughout the entirety of mouse postimplantation development reveals that Id is expressed upon gastrulation at very high levels in almost all regions of the mouse embryo and expression declines as embryogenesis proceeds. In skeletal muscle, in which the inhibitory action of Id has been established in tissue culture models (Benezra et al., 1990), Id and the HLH myogenic factors are expressed in a mutually exclusive manner suggesting that myogenic precursors do not express both types of HLH gene products. In addition, Id colocalizes both spatially and temporally with Hox-7.1, a murine homeobox gene which is associated with regions of high cell proliferation and positional fate assignment.

Translocation (2;9)(p12;p23) in a case of acute leukemia with t(4;11)(q21;q23). Lack of rearrangement of the kappa and interferon gene loci

A case is reported of an adult male patient with acute leukemia characterized by the presence of the novel cytogenetic abnormality, t(2;9)(p12;p23), in addition to a t(4;11)(q21;q23). The immunophenotype of the blast cell population was consistent with immature early pre-B cell acute lymphoblastic leukemia (ALL) (TdT+,HLA-DR+,CD19+,CD24 +/-,CD10-) expressing myelo-monocytic antigens (CDw65,CD15). The genotype showed a clonal rearrangement of the immunoglobulin heavy chain locus. Because the immunoglobulin kappa (kappa) light chain gene is located on chromosome 2 at band p12 and interferon alpha (alpha) and beta (beta) map to chromosome 9p21-p22, rearrangements of these loci as a result of the t(2;9) were studied. There was no evidence for rearrangement of the region covering about 40 kilobases around the kappa locus when hybridized to C(kappa), the 3' kappa enhancer or the kappa deleting element. Only germline size restriction fragments were also found for the interferon alpha and beta genes. The patient's clinical features were typical for ALL associated with the t(4;11), including a high white blood cell count at presentation, hepatosplenomegaly, and a poor outcome. The potential significance of 2p and 9p abnormalities in addition to t(4;11) is discussed.

Regulation of immunoglobulin gene transcription

Analysis of the immunoglobulin gene suggests that their expression is controlled through the combinatorial action of tissue- and stage-specific factors (OTF-2, TF-microB, NF-kappa B), as well as more widely expressed E motif-binding factors such as E47/E12. Two basic issues cloud understanding of how these factors are involved in immunoglobulin gene regulation. First, cloning of these factors shows them to be members of families of proteins, all with similar DNA-binding specificities. OTF-2 is a member of the POU domain family, NF-kappa B is a related protein, and the microE5/kappa E2-binding factors are members of the bHLH family. Second, these binding sites and associated factors are involved in the regulation of many genes, not only the immunoglobulin genes, and in fact not only lymphoid-specific genes. These facts complicate understanding which member of a family is in fact responsible for interaction with, and activation of, a particular binding element in an enhancer/promoter. Recently, more detailed analysis of the interactions between such proteins and their related binding sites suggest that a certain level of specificity may in fact be encoded by the DNA element such that one family member of a protein is preferentially bound, or alternatively that the protein-DNA interactions that occur give subtle alterations in protein conformation that unmask an activation or protein-protein interactive domain. An additional level of regulation is imparted by combinatorial mechanisms such as adjacent DNA-binding elements and factors that may alter activity, as well as "cofactors" that, by forming a complex with the bound factor, affect its activation of a gene in a particular cell type. A third level of specificity may be obtained by factors such as NF-kappa B and the bHLH family due to their ability to create heterogeneous complexes, creating unique complexes in a tissue- or stage-specific manner. The multiple functions transcription factors such as NF-kappa B and OTF-2 play in the transcriptional regulation of multiple genes seems complex in contrast to a one factor, one gene regulation model. However, this type of organization may limit the number of factors lymphocytes would require if each lymphoid-specific gene were activated by a unique factor. Thus what appears to be complexity at the molecular level may reflect an economical organization at the cellular level. Investigation of the key factors controlling these genes suggests an ordered cascade of transcription factors becomes available in the cell during B cell differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

Helix-loop-helix proteins in the regulation of immunoglobulin gene transcription

Transcriptional control of the Ig heavy chain and kappa light chain is dominated by single enhancers located within the body of each gene. These enhancers bind distinct, yet overlapping, sets of cell-type-specific and ubiquitous nuclear proteins. This review focuses on one particular subclass of enhancer-binding protein, termed helix-loop-helix (HLH) proteins, describing their role in the establishment of cell-type-specific transcription and suggesting how they may be regulated during B-cell maturation.

Transforming growth factor-beta: an important mediator of immunoregulation

Transforming growth factor-beta (TGF-beta) is synthesized and secreted by a wide variety of cells, including cells of the immune system. Lymphocytes and monocytes possess high affinity TGF-beta receptors and the addition of TGF-beta to in vitro cell cultures results in significant modulation of immune function. TGF-beta inhibits the proliferation of thymocytes, T cells, B cells, and natural killer cells. Additionally, it inhibits certain differentiative functions of lymphocytes including a marked inhibition of immunoglobulin production by human B lymphocytes. TGF-beta has dichotomous actions on monocytes. It is a potent chemoattractant for monocytes and induces interleukin 1 mRNA expression while inhibiting generation of reactive oxygen intermediates and monocyte killing. Evidence is accumulating that TGF-beta regulates immune function in vivo and that overproduction of TGF-beta may be associated with immunosuppression.