Proteolysis of NF-kappaB1 p105 is essential for T cell antigen receptor-induced proliferation

Development of Foxp3(+) regulatory t cells is driven by the c-Rel enhanceosome

Regulatory T (Treg) cells are essential for maintaining immune homeostasis. Although Foxp3 expression marks the commitment of progenitors to Treg cell lineage, how Treg cells are generated during lymphocyte development remains enigmatic. We report here that the c-Rel transcription factor controlled development of Treg cells by promoting the formation of a Foxp3-specific enhanceosome. This enhanceosome contained c-Rel, p65, NFAT, Smad, and CREB. Although Smad and CREB first bound to Foxp3 enhancers, they later moved to the promoter to form the c-Rel enhanceosome. c-Rel-deficient mice had up to 90% reductions of Treg cells compared to wild-type mice, and c-Rel-deficient T cells were compromised in Treg cell differentiation. Thus, Treg cell development is controlled by a c-Rel enhanceosome, and strategies targeting Rel-NF-kappaB can be effective for manipulating Treg cell function.

A mutation of Ikbkg causes immune deficiency without impairing degradation of IkappaB alpha

Null alleles of the gene encoding NEMO (NF-kappaB essential modulator) are lethal in hemizygous mice and men, whereas hypomorphic alleles typically cause a syndrome of immune deficiency and ectodermal dysplasia. Here we describe an allele of Ikbkg in mice that impaired Toll-like receptor signaling, lymph node formation, development of memory and regulatory T cells, and Ig production, but did not cause ectodermal dysplasia. Degradation of IkappaB alpha, which is considered a primary requirement for NEMO-mediated immune signaling, occurred normally in response to Toll-like receptor stimulation, yet ERK phosphorylation and NF-kappaB p65 nuclear translocation were severely impaired. This selective loss of function highlights the immunological importance of NEMO-regulated pathways beyond IkappaB alpha degradation, and offers a biochemical explanation for rare immune deficiencies in man.

PI3Ks in lymphocyte signaling and development

Lymphocyte development and function are regulated by tyrosine kinase and G-protein coupled receptors. Each of these classes of receptors activates phosphoinositide 3-kinase (PI3K). In this chapter, we summarize current understanding of how PI3K contributes to key aspects of the adaptive immune system.

Understanding the logic of IκB:NF-κB regulation in structural terms

NF-κB is an inducible transcription factor that controls expression of diverse stress response genes. The entire mammalian NF-κB family is generated from a small cadre of five gene products that assemble with one another in various combinations to form active homo- and heterodimers. The ability of NF-κB to alter target gene expression is regulated at many levels. Chief among these regulatory mechanisms is the noncovalent association in the cell cytoplasm of NF-κB dimers with IκB inhibitor proteins. Removal of IκB leads to accumulation of active NF-κB within the cell nucleus where it binds to specific DNA sequences contained within the promoter regions of target genes and initiates recruitment of general transcription factors and assembly of the basal transcription machinery. Here we provide a detailed description of these fundamental NF-κB regulatory events using as a basis macromolecular structures and experimental data derived from structure-based biochemistry.

Roles of the NF-kappaB pathway in lymphocyte development and function

This article focuses on the functions of NF-kappaB that vitally impact lymphocytes and thus adaptive immunity. NF-kappaB has long been known to be essential for many of the responses of mature lymphocytes to invading pathogens. In addition, NF-kappaB has important functions in shaping the immune system so it is able to generate adaptive responses to pathogens. In both contexts, NF-kappaB executes critical cell-autonomous functions within lymphocytes as well as within supportive cells, such as antigen-presenting cells or epithelial cells. It is these aspects of NF-kappaB's physiologic impact that we address in this article.

The Nfkb1 and Nfkb2 proteins p105 and p100 function as the core of high-molecular-weight heterogeneous complexes

Nfkb1 and Nfkb2 proteins p105 and p100 serve both as NF-kappaB precursors and inhibitors of NF-kappaB dimers. In a biochemical characterization of endogenous cytoplasmic and purified recombinant proteins, we found that p105 and p100 assemble into high-molecular-weight complexes that contribute to the regulation of all NF-kappaB isoforms. Unlike the classical inhibitors IkappaBalpha, -beta, and -epsilon, high-molecular-weight complexes of p105 and p100 proteins bind NF-kappaB subunits in two modes: through direct dimerization of Rel homology domain-containing NF-kappaB polypeptides and through interactions of the p105 and p100 ankyrin repeats with preformed NF-kappaB dimers, thereby mediating the bona fide IkappaB activities, IkappaBgamma and IkappaBdelta. Our biochemical evidence suggests an assembly pathway in which kinetic mechanisms control NF-kappaB dimer formation via processing and assembly of large complexes that contain IkappaB activities.

Control of regulatory T cell lineage commitment and maintenance

Foxp3-expressing regulatory T (Treg) cells suppress pathology mediated by immune responses against self and foreign antigens and commensal microorganisms. Sustained expression of the transcription factor Foxp3, a key distinguishing feature of Treg cells, is required for their differentiation and suppressor function. In addition, Foxp3 expression prevents deviation of Treg cells into effector T cell lineages and confers dependence of Treg cell survival and expansion on growth factors, foremost interleukin-2, provided by activated effector T cells. In this review we discuss Treg cell differentiation and maintenance with a particular emphasis on molecular regulation of Foxp3 expression, arguably a key to mechanistic understanding of biology of regulatory T cells.