In many human cancers enhanced NF-κB activity provides proliferative and survival signals. Using a mouse model of prostate cancer, Michael Karin showed that knocking out IKKα in prostate epithelial cells reduces metastases formation without affecting primary prostatic tumor development. This pro-metastatic activity is attributable to a nuclear function of IKKα, which represses the expression of metastasis inhibitor maspin. Karin also described a role for both IKKα and IKKβ in the switch from androgen-dependence to androgen-independence in prostate cancer. IKKα acts in prostate cancer cells in an NF-κB-independent pathway, whereas IKKβ acts in the hematopoietic compartment in an NF-κB-dependent manner to produce cytokines that cause IKKα activation.
Manolis Pasparakis showed that liver-specific deletion of NEMO results in extensive spontaneous hepatocyte apoptosis, followed by hepatocyte proliferation and carcinogenesis. Pasparakis reported that liver-specific expression of a constitutively active IKKβ mutant or administration of the anti-oxidant BHA to mice can block cancer in liver-specific NEMO-deficient mice, suggesting that defective NF-κB signaling is responsible for the development of hepatocellular carcinoma in these NEMO-deficient mice. Using other mouse knockouts, Pasparakis reported that reduced NF-κB signaling in the heart endothelium is protective against atherosclerosis – an effect due, in part, to the downregulation of adhesion molecules such as VCAM1.
Guido Franzoso discussed the basis for NF-κB-JNK crosstalk (controlling cell fate) in the liver. He showed that the NF-κB target gadd45β (a direct inhibitor of the JNK kinase, MKK7), is induced by TNF-R1 during liver regeneration after partial hepatectomy, and that this upregulation of gadd45β is required for hepatocyte survival and proliferation during liver regeneration. He also showed that this hepatic function of Gadd45β is mediated through a suppression of sustained TNF-R1-induced MKK7/JNK signaling.
Macrophages can play a role in promoting inflammation-associated carcinogenesis. Toby Lawrence reported that mice harboring IKKβ-deficient macrophages show an enhanced ability to clear infection, indicating that IKKβ inhibits the development of M1-polarized macrophages during microbial infection. Lawrence also presented evidence that IKKβ is involved in the maintenance of tumor-associated macrophages, and that inhibition of IKKβ in these cells enhances their cytotoxic activity against tumor cells, suggesting that macrophage-specific inactivation of IKKβ has a potential application in anti-cancer therapy.
Antonio Leonardi reported that NGAL, a secreted acute-phase protein that binds to iron, is the product of an NF-κB target gene and a mediator of the pro-tumorigenic activity of NF-κB in thyroid cancer. NGAL is required for malignant transformation and survival of thyroid cancer cells in vitro, and it promotes the growth of thyroid tumor xenografts in mice.
Crosstalk between the Wnt and NF-κB signaling pathways in colon cancer was discussed by Yinon Ben-Neriah. Using mice with gut-specific deletion of CKIα (causing constitutive activation of Wnt/β -catenin signaling), Ben-Neriah showed a causative link between Wnt activation, cellular senescence, induction of NF-κB target genes and activation of the p53 tumor suppressor. Furthermore, he reported that gut-specific, p53 and CKIα double knockout mice show increased epithelial cell proliferation and carcinogenesis. He proposed that gut homeostasis and senescence after CKIα ablation involves both a cell-autonomous and a non-cell-autonomous pathway, dependent on Wnt signaling and NF-κB/TNFα-elicited inflammation, respectively.
CYLD is a tumor suppressor protein with deubiquitinating activity that can block activation of NF-κB in response to various stimuli. Jessica Hutti presented evidence that IKKε can phosphorylate CYLD at Ser418, and that CYLD phosphorylation is required for IKKε-induced transformation of cells in culture.
Tom Gilmore discussed the ability of an overexpressed REL mutant to convert the gene expression profile of the human BJAB B-lymphoma cell line from that of a relatively ‘benign’ lymphoma to one of a more aggressive subtype of B-cell lymphoma. He also described a splice variant of REL with enhanced DNA-binding and transactivating properties that is overexpressed in some B-cell lymphomas.
HTLV-1 can cause adult T-cell leukemia in humans, and HTLV-1’s primary transforming protein is Tax, which promotes NF-κB signaling. Françoise Bex described how Tax assembles into nuclear dense bodies, which contain p50, RelA, and other transcription and splicing factors. Bex reported that Tax is SUMOylated and ubiquitinated at K280/284. She reported that ubiqutinated Tax is found in the cytoplasm, whereas SUMOylation promotes the formation of Tax nuclear bodies. Both of these modifications require Tax phosphorylation at Ser 300/301 and are important for Tax’s ability to induce NF-κB.
Evidence was also presented for new links between the IKK/NF-κB pathway and growth inhibitory pathways in certain cancers. Véronique Baud presented data showing that knockdown of RelB in mouse embryo fibroblasts leads to increased cell proliferation, and that RelB inhibition enhances xenograft tumor growth in vivo. RelB-mediated inhibition of cell proliferation is apparently caused by upregulation of p53. Neil Perkins also linked the alternative NF-κB pathway to p53 function, reporting that NF-κB/p52 and p53 co-operatively regulate autophagy in response to the chemotherapeutic drug cisplatin. Elad Horwitz (Ben-Neriah lab) presented data showing that inhibition of NF-κB in the early stages of a chemically induced liver cancer can enhance tumor growth. Similarly, Antonio Costanzo showed that IKKα nuclear localization inhibits squamous cell carcinoma (SCC) progression in vitro and in vivo, and this IKKα-mediated negative regulation of SCC growth involves crosstalk with the TGFβ pathway.
Mutations in NEMO cause an array of human disorders primarily affecting the skin and the immune system, including incontinentia pigmenti and ectodermal dysplasia with immunodeficiency (EDA-ID). Matilde Valeria Ursini’s lab reported that 60–90% of the patients affected by these disorders have mutations deleting exons 4–10 of the NEMO locus, which severely disable NEMO protein activity; many other single amino acid substitutions or small gene deletions can result in hypomorphic NEMO proteins. Fabrice Agou and Alain Israël showed that most disease-associated point mutants of NEMO interfere with either NEMO dimerization or poly-Ub binding. However, Ashish Jain described two patients with EDA-ID who presented with an 80% reduction in NEMO protein levels due to a chromosomal rearrangement affecting an intronic region of NEMO that contains a transcriptional enhancer. Cells from these patients exhibit impaired transcription of the IL-12-p35 gene, which is associated with an inability of both RelA/c-Rel and IKKα to co-localize to the IL-12-p35 promoter after LPS stimulation.
Anne Puel described the range of gene mutations that occur in a variety of human immunodeficiencies. Namely, some patients have mutations that convert the IκBα protein into a constitutive NF-κB inhibitor, whereas others harbor partially inactivating mutations in NEMO, or completely inactivating mutations in the TLR adapter Myd88 and IRAK4. In most cases, cells from these patients display defects in NF-κB (and JNK/p38) activation in response to IL-1β and LPS.