NF-kappaB
NF-kappaB is the prototype of a family of dimeric transcription factors made from monomers that have approximately 300 amino-acid Rel regions which bind to DNA, interact with each other, and bind the IkappaB inhibitors. Activation of NF-kappa B to move into the nucleus is controlled by the targeted phosphorylation and subsequent degradation of I kappa B. There are multiple forms of I kappa B that appear to regulate NF-kappa B by distinct mechanisms. NF-kappa B can be activated by exposure of cells to LPS or inflammatory cytokines such as TNF or IL-1, viral infection or expression of certain viral gene products, UV irradiation, B or T cell activation, and by other physiological and nonphysiological stimuli. NF-kB activation has been implicated in many biological processes, including inflammation, immunoregulation, apoptosis, neuronal function, cell growth and transportation, and cell proliferation.
 

Function of Neuronal NF-kB
Mollie K. Meffert and David Baltimore

Long-lasting alterations of neuronal properties, such as those involved in plasticity and apoptosis, depend upon changes in gene expression. We have explored the neuronal function of a potent transcription factor, Nuclear Factor kappa B (NF-kB), which is critical to host defense and is found in almost all cells. We find that basal synaptic input in mature mouse hippocampal neurons activates the NF-kB transcription factor and induces kB DNA-binding activity consisting of p50:p65 and p50:p50 dimers (measured by EMSA). Experiments using synaptosomes (isolated nerve terminals) indicate that both p50 and p65, as well as IkBa and IkBb, are found at synapses. While both p50:50 and p50:p65 dimers occur in intact neurons, synapses contain only p65:p50. We have confirmed this interesting finding using a p65 knockout mouse made in our laboratory. While intact neurons from this p65 null mouse contain p50:p50 dimers, no NF-kB or IkB can be detected at synapses.
Ca2+-regulated gene transcription is essential to diverse physiological processes including the adaptive plasticity associated with learning. We have utilized TNFR-/-,p65-/- mice to address the possible functions of NF-kB in adaptive learning. Mice lacking p65 exhibited a selective learning deficit in a version of the radial arm maze requiring the use of spatial information, while learning in a cued-version of the maze did not differ from p65-wildtype sibling controls. These observations suggest that long-term changes to adult neuronal function caused by synaptic stimulation can be regulated by NF-kB nuclear translocation and gene activation.

The Role of NF-kB in Cell Growth and Transformation

Jeff Wiezorek and David Baltimore

Although the transforming ability of the v-REL oncoprotein was established many years ago, recent evidence suggests other human NF-kB family members may be important in oncogenesis. NF-kB DNA binding activity is constitutively increased in many lymphoid and epithelial tumors. The RAS, BCR-ABL, and HER2 oncogenes and transforming viruses can activate NF-kB. Furthermore, several genes thought to be essential to the cancer phenotype—those controlling angiogenesis, invasion, proliferation, and metastasis, contain kB binding sites. However, direct genetic evidence demonstrating the role of NF-kB in transformation and cancer progression is lacking.
Our lab has generated strains of knock out mice in which one or more of the NF-kB family members are deleted. 3T3 and primary fibroblasts of a specific genotype generated from these mice are powerful tools for dissecting NF-kB signaling pathways. These cells and mice are being used to study different aspects of cellular senescence, transformation, and cancer progression.
The direct role of the NF-kB proteins in transformation and oncogene-induced senescence is being investigated in primary mouse embryonic fibroblasts and immortalized fibroblasts. In vitro assays have identified differing requirements for NF-kB family members in transformation. RelA and c-Rel are most important, whereas p50 and p52 may inhibit transformation. Because this signaling pathway may be important in some breast cancers, the contribution of NF-kB to the cancer phenotype is being evaluated in vivo. We have identified RelB as necessary for alveolar proliferation during pregnancy in a knockout model. This signaling pathway and its role in mammary transformation is under investigation. Additionally, by crossing the MMTV-cNeu transgene into NF-kB knockout strains, the contribution of constitutive NF-kB activity to tumor initiation, hypoxic survival, invasion/metastasis, and angiogenesis is being directly studied.