Activation of the NF-kB transcription factors

NF-kappa B is a highly pleiotropic group of transcriptional factors that regulate a wide range of genes, mainly participating in immune defense and development. All members of the TNF receptor family activate these transcriptional factors, each with different functional consequences. Some promote adaptive immunity, and others, innate immunity; some control embryonic development through NF-kappa B activation, and some employ this transcriptional factor to restrict their own cytotoxic activity. Receptor-associated adapter proteins of the TRAF family serve to initiate this activation, and a kinase complex composed of two protein kinases, IKK1 and IKK2, as well as a non-enzymatic component, NEMO (IKK-gamma), acts as the effector element in it.

Attempting to elucidate the molecular interactions that impose specificity of action on this common set of signaling molecules, we have discovered a novel protein kinase, NIK that, through interaction with receptor-associated adapter proteins of the TRAF family triggers expression of NF-kappa B target genes specifically involved in adaptive immunity. NIK participates in a unique set of proximal signaling events, initiated by specific members of the TNF/NGF family that regulate adaptive immune responses. Its activation by these specific receptors leads to upregulation of several different NF-kappa B proteins.

We were able to delineate a number of sequence motifs in NIK that confer its association with other signaling proteins and are in the process of structure-function analysis of these motifs, both in culture cells and in vivo, taking advantage of cutting edge developments in the CRISPR/Cas9 technology.
To discover new interactions of NIK, we employ proteomic approaches to explore the core protein complex in charge of activation of NIK-dependent NF-kappa B pathway.

We have also discovered the protein CYLD, a protein that possesses de-ubiquitinating activity that is directed towards K63-linked poly-ubiquitin chains, and found that this protein binds specifically to NEMO. CYLD negatively modulates NF kappa B activation by members of the TNF/NGF family by arresting signaling events that depend on K63-linked polyubiquitination of NEMO and of members of the TRAF adapter protein family. CYLD dysfunction leads to excessive activation of NF-kappa B and can trigger cell transformation, apparently through increased resistance to apoptosis or perturbation of the cell cycle. We are currently exploring the involvement of other NF-kappa B and cell death regulating proteins in human cancer.

Another project aims at purification and characterization of novel chromatin-associated protein complexes responsible for distinct ligand-specific profiles of gene induction in response to cytokines of the TNF superfamily.