Peptide-Induced Negative Selection of Thymocytes Activates Transcription of an NF-ΚB Inhibitor

Abstract

Negative selection eliminates thymocytes bearing autoreactive T cell receptors (TCR) via an apoptotic mechanism. We have cloned an inhibitor of NF-kappa B, I kappa BNS, which is rapidly expressed upon TCR-triggered but not dexamethasone- or gamma irradiation-stimulated thymocyte death. The predicted protein contains seven ankyrin repeats and is homologous to I kappa B family members. In class I and class II MHC-restricted TCR transgenic mice, transcription of I kappa BNS is stimulated by peptides that trigger negative selection but not by those inducing positive selection (i.e., survival) or nonselecting peptides. I kappa BNS blocks transcription from NF-kappa B reporters, alters NF-kappa B electrophoretic mobility shifts, and interacts with NF-kappa B proteins in thymic nuclear lysates following TCR stimulation. Retroviral transduction of I kappa BNS in fetal thymic organ culture enhances TCR-triggered cell death consistent with its function in selection.

The Nuclear Protein IκBζ Forms a Transcriptionally Active Complex with Nuclear Factor-κB (NF-κB) p50 and the Lcn2 Promoter via the N- and C-terminal Ankyrin Repeat Motifs

“…Nuclear IB proteins are also known to form a complex with NF-B p52, a protein homologous to p50 (7,12,37). As expected from the homology, in vitro complex formation with p52 was impaired by threonine substitution for the invariant aspartate in ANK1 of nuclear IBs: Asp-451 in IB, Asp-60 in IB NS , and Asp-127 in Bcl-3 ( Fig.…”

“…The ARD of IBs mediates the association with NF-B dimers via direct binding to the NF-B Rel homology region (23,33,34). Although the ARD of nuclear IBs displays a high sequence similarity to that of cytoplasmic IBs except for the additional seventh motif ANK7 (10,12,35,36), the preference for NF-B dimer species differs between the nuclear and cytoplasmic IBs, as described above (7-9, 12, 16, 37). Furthermore, there exists a difference in interaction with B DNA.…”

“…The primarily induced gene products include the atypical/ nuclear IB proteins Bcl-3 (7,8), IB (also known as MAIL or INAP) (9 -11), and IB NS (12), which are not expressed in resting cells. In contrast to the cytoplasmic IBs, which preferentially associate with NF-B dimers that possess at least one p65 or c-Rel subunit such as the p50-p65 heterodimer (13), the nuclear IBs prefer the p50 (or p52) homodimer as a partner to directly regulate the activation of secondary response genes for appropriate host defense responses (14 -19).…”

NF-κB and the regulation of hematopoiesis

“…This study was performed with a new IkB family member (IkBNS) which can be induced by TCR stimulation. 37 The authors showed that NF-kB could be blocked by overexpression of IkBNS, and that this increased anti-CD3e-induced apoptosis of FTOC. Further studies are however necessary to confirm the role of this new IkB protein.…”

The complicated role of NF-κB in T-cell selection

“…52 The authors found that a novel IkB-like NF-kB inhibitor, IkBNS, is upregulated by peptides that trigger negative selection but not by those inducing positive selection (i.e., survival) or nonselecting peptides. IkBNS blocks transcription from NF-kB reporters.…”