Our goal is to understand fundamental signaling processes that lead to immune-mediated disease. Our approach is to focus on the molecular mechanisms involved in the activation and regulation of the NF-kB family transcription factors. To this end, we have established a genetics research program to evaluate individuals with known or currently undiagnosed rare genetic syndromes characterized by phenotypes of autoimmunity or inflammatory disease in the setting of immune deficiency.
Molecular Characterization of Signaling Defects in NEMO Syndrome
NF-kB plays a crucial role in gene expression both during normal development and within the context of the immune response. Hypomorphic mutation in NEMO, a key regulator of the NF-kB pathway, results in a primary immunodeficiency, which in some cases, is accompanied by inflammatory disease. At the NIH Clinical Research Center, we study individuals with mutation in NEMO. Our earlier work indicates that genotype/phenotype correlations exist in NEMO Syndrome, and that inflammatory disease phenotypes occur due to mutation in one of two “hot-spots” of the gene. One of these hot-spots codes for a domain in the C-terminus that recognizes polyubiquitin chains. Our most recent work indicates that this domain regulates canonical IKK kinase activity by recruiting a negative regulator upon receptor activation (Figure 1). We found that the second hot-spot appears to be critical in regulating the production of proinflammatory cytokines and type I interferon in response to viral infection (Figure 2).
Ongoing work suggests that processing of the p65 subunit of NF-kB by the kinase TBK1 is dependent on this second domain. The molecular mechanisms elucidated by the study of NEMO mutations found in our patients’ mutations apply to inflammatory diseases as disparate as multiple sclerosis, rheumatoid arthritis, lupus and Crohn’s disease.
Finding Novel Genetic Causes of Inflammatory Disease
In addition to studying individuals with known NEMO mutation, we also evaluate individuals with NEMO-like Syndrome whose clinical phenotypes suggest mutation in a gene that is functionally related to NF-kB activation. In collaboration with investigators at NIAID, we are evaluating two boys with NEMO-like Syndrome, which has led us to the discovery of IL-21R deficiency as a cause of primary immunodeficiency.
We have generated induced pluripotent (IPS) cell lines from our patients bearing NEMO and IL-21R mutation. Current work involves developing methods to differentiate IPS cells to monocyte-like and T cell-like cells in a “xeno-free” system. Our goal is to eventually use these cells therapeutically in humans. Another current major effort is the use of powerful new gene-editing approaches to correct disease-causing mutations in IPS cells derived from patients. Using genomic techniques, we plan to use differentiated patient-derived IPS cells to determine the cell-specific differential roles of NEMO in NF-kB activation. In addition, we are currently generating NEMO knock-in mice to further understand how altered signaling events lead to disease, and how IPS cells and their derivatives may eventually be used therapeutically.
Kotlarz D, Ziętara N, Uzel G, Weidemann T, Braun CJ, Diestelhorst J, Krawitz PM, Robinson PN, Hecht J, Puchałka J, Gertz EM, Schäffer AA, Lawrence MG, Kardava L, Pfeifer D, Baumann U, Pfister ED, Hanson EP, Schambach A, Jacobs R, Kreipe H, Moir S, Milner JD, Schwille P, Mundlos S, Klein C. Loss-of-function mutations in the IL-21 receptor gene cause a primary immunodeficiency syndrome. J Exp Med. 2013 Mar 11;210(3):433-43. doi: 10.1084/jem.20111229. Epub 2013 Feb 25.
Keller MD, Petersen M, Ong P, Church J, Risma K, Burham J, Jain A, Stiehm ER, Hanson EP, Uzel G, Deardorff MA, Orange JS. Hypohidrotic ectodermal dysplasia and immunodeficiency with coincident NEMO and EDA mutations. Front Immunol. 2011 Nov 8;2:61. doi: 10.3389/fimmu.2011.00061
Karamchandani-Patel G1, Hanson EP, Saltzman R, Kimball CE, Sorensen RU, Orange JS. Congenital alterations of NEMO glutamic acid 223 result in hypohidrotic ectodermal dysplasia and immunodeficiency with normal serum IgG levels. Ann Allergy Asthma Immunol. 2011 Jul;107(1):50-6. doi: 10.1016/j.anai.2011.03.009