Every day, our bodies are exposed to environmental toxins and invaded by bacteria, viruses, and other pathogens. Fortunately, we are equipped with powerful defense systems that usually neutralize these invaders. The inflammatory and immune responses are key elements of our defensive shield.

To work at their best, these systems are continually and carefully fine-tuned by a complex system of regulatory factors. Chief among these is the inducible NF-κB family of transcription factors. These “master regulators” orchestrate an array of host genes that, in turn, execute the inflammatory and immune responses.

Although NF-κB is key to maintaining good health, it can wreak havoc if it gets out of balance. Loss of regulation of NF-κB results in chronic inflammatory and autoimmune diseases, such as rheumatoid arthritis. Because NF-κB enhances cell growth and stops apoptosis—the “programmed” death of damaged cells—its uncontrolled expression can promote the development of cancer. NF-κB also functions abnormally in asthma, heart disease, inflammatory bowel disease, and neurodegenerative syndromes, including Alzheimer’s disease.

Only by understanding the intricacies of the biology of NF-κB can we devise therapies that blunt its adverse actions while preserving its essential normal functions. Gladstone research is leading the way in these areas, and the laboratory of Dr. Warner C. Greene in the Gladstone Institute of Virology and Immunology has been particularly prominent.

Turning NF-κB On

Because NF-κB is a potent and broadly active regulator, it is not surprising that it is tightly controlled. NF-κB is usually locked away in the cytoplasm through its assembly with a specific inhibitor protein termed IκB. Scientists in Dr. Greene’s laboratory were the first to describe how NF-κB escapes the grasp of IκB. Upon stimulation, IκB undergoes phosphorylation and is subsequently degraded, liberating the NF-κB complex, which moves rapidly into the nucleus. Once in the nucleus, NF-κB engages the control regions of diverse NF-κB target genes and recruits key cellular factors that act together to turn on the expression of these genes.

NF-κB is activated in response to a diverse array of stimuli, almost all of which converge on a common activation pathway that promotes the expression of key target genes. Among its many targets, nuclear NF-κB stimulates the expression of various cytokines and chemokines. These secreted cellular factors play essential roles in activating and orchestrating the protective immune and inflammatory responses.

The diversity of stimuli that can activate NF-κB is a major challenge to elucidating the unique upstream components of signaling pathways. By identifying such components, we might interdict a unique signaling pathway that shares NF-κB as a common downstream effector. Thus, it may be possible to produce anti–inflammatory drugs that are not simultaneously immunosuppressive. Scientists in the Gladstone Institute of Virology and Immunology have been successful in identifying many upstream signaling factors that participate exclusively in either the inflammatory or immune response.

Turning NF-κB Off

Turning off the NF-κB response is as important as turning it on. In the course of identifying the various genes activated by NF-κB, Dr. Shao-Cong Sun in the Greene laboratory made the startling discovery that NF-κB activates the gene encoding its own inhibitor, IκBa. These studies highlight a natural “feedback inhibitory loop” in which the action of NF-κB is tightly regulated through the induced resynthesis of an NF-κB inhibitor.

Although much is known about the regulatory events in the cytoplasm that control the activation of NF-κB, much less is known about what happens in the nucleus. Recent studies led by Dr. Lin-Feng Chen in the Greene laboratory have shed new light on these key events. They discovered that NF-κB is acetylated at three different sites and that these modifications control different biological functions of NF-κB. Of particular note, the acetylation of the RelA subunit of NF-κB blocked binding to newly synthesized IκBa proteins, which readily shuttle into and out of the nucleus. However, deacetylation of NF-κB triggered the binding of NF-κB to IκBa, leading to rapid export of the complex out of the nucleus and into the cytoplasm. Thus, deacetylation of NF-κB functions as an “intranuclear molecular switch” that limits both the magnitude and duration of the NF-κB transcriptional response. Nuclear export of these NF-κB/IκBa complexes also helps replenish the supply of latent NF-κB complexes in the cytoplasm, thereby readying the cell for the next NF-κB-inducing stimulus.

NF-κB and the Brain

Exciting recent studies have focused on NF-κB’s actions in the brain. Dr. Alison O’Mahony and Mauricio Montano in the Greene laboratory, together with scientists in the Gladstone Institute of Neurological Disease, showed that genetic inhibition of NF-κB in brain neurons in mice resulted in a loss of fear and significantly improved learning and recall of spatial information. These studies suggest a key role for NF-κB factors in higher cognitive functions, such as learning and memory. These findings promise to open an entirely new chapter in NF-κB biology.

NF-κB and Disease Sometimes, the normally beneficial actions of NF-κB can go awry with devastating pathological consequences. For example, under certain circumstances, our immune cells mistakenly ravage the body’s own tissues, leading to a variety of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis. Alternatively, inflammatory responses may become uncontrolled and chronic as in inflammatory bowel disease. Since NF-κB is a powerful inhibitor of programmed cell death, loss of regulatory control can give rise to uncontrolled cell growth, promoting the development of various forms of cancer, including breast cancer, multiple myeloma, leukemia, lymphoma, and prostate cancer. One form of cancer under study at the Gladstone Institute of Virology and Immunology involves HTLV-I, the first pathogenic human retrovirus ever discovered. Infection with this virus can give rise to		NF-κB Inducers Cytokines Chemokines Viruses Bacteria Ultraviolet light DNA damage Chemical toxins Environmental stresses (heavy metals) Tissue ischemia/reperfusion Liver regeneration Hemorrhagic shock Free radicals Gamma irradiation Oxidized low density lipoproteins Electrical signaling in neurons Amyloid deposits Chemotherapy drugs
an untreatable and rapidly fatal expansion of activated CD4 T cells termed adult T-cell leukemia. Gladstone scientists were among the first to show that HTLV-I encodes an oncogenic protein that induces and sustains the nuclear expression

	NF-κB Target Genes Immunity Cytokines, growth factors, and their receptors Antioxidant regulators Transcription factors Antibodies Complement factors Inflammation Cytokines Chemokines Cell adhesion proteins Anti-clotting factors Other Viruses (HIV) Cell structural proteins Brain signaling receptors High density lipoproteins Programmed cell death genes Mammary gland genes Cell cycle regulators Genes mediating tissue invasion and metastasis		of NF-κB. Because of NF-κB’s central role in the uncontrolled growth of many cancer cells, great interest is focusing on the development of NF-κB inhibitors for testing as a potentially exciting new class of cancer chemotherapeutics. Any cell in which the DNA is damaged either genetically or by chemical insult undergoes cell suicide by a process termed programmed cell death or apoptosis. Normally, NF-κB protects against such cell death and allows the cell to be repaired. However, in some settings like chronic inflammation where NF-κB is over-active, programmed cell death may occur more quickly, leading to unwanted loss of normal cells, tissue degeneration, and organ failure. NF-κB is also a major contributor to the development of atherosclerosis, a focus of research in the Gladstone Institute of Cardiovascular Disease, and Alzheimer’s disease (AD), which is investigated in Gladstone Institute of Neurological Disease. These diseases involve inflammatory responses centrally controlled by NF-κB. Thus, Gladstone scientists are well positioned to apply insights gleaned from the study of NF-κB to modify the course of these diseases. Summary NF-κB is a master regulator of key biological processes. Despite the hugely promising advances made to date, our understanding of the regulatory pathways that control its action remains incomplete. Only by clearly elucidating
the subtleties of NF-κB’s activation and action can we hope to fulfill the promise that its therapeutic manipulation holds. Gladstone will continue to be in the forefront of these efforts.

When Good NF-κB Goes Bad Cancer Inflammatory bowel disease Rheumatoid arthritis Asthma

Autoimmune diseases Atherosclerosis Alzheimer’s disease Neurodegeneration