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Joseph A. DiDonato, Ph.D.
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Area of general research interest:
Proinflammatory cytokine signal transduction, chronic inflammatory diseases Current program:
Investigators:
Collaborators:
Brief Description: The transcription factor NF-kB is the master regulator of many cell-types’ proinflammatory gene program. NF-kB is activated by a wide variety of extracellular stimuli and is a classic stress response factor. It is released from its inhibitor molecules, the IkBs in the cytoplasm and then translocates to the nucleus to bind its target genes and activate their transcription. The key regulatory steps leading to NF-kB activation occurs mainly at two points. The first critical regulatory point is the phosphorylation of the IkBs by their kinase the I Kappa B kinase (IKK) (1,2). This phosphorylation leads to their polyubiquitination and degradation by the 26S proteasome (3). The second critical regulatory point is the posttranslational modifications that occur to NF-kB DNA bound dimers that make them excellent transcriptional activators. Typically, the most potent inducers of IKK activity and hence NF-kB activity are the proinflammatory cytokines TNF and IL-1. We have also demonstrated that pathogenic bacteria, both Gram-negative and Gram-positive, can also potently activate IKK and NF-kB in a kinetically similar fashion (4). In my laboratory, we are interested in identifying the operative mechanisms and purifying and molecularly cloning key signaling proteins that lead to IKK activation in response to cytokines (TNF, IL-1, IL-18) or pathogenic stimuli (bacterial or viral). We are also interested in defining the structural basis for IKK activity on its substrates. We are using traditional standard biochemical fractionation procedures, two-dimensional phosphopeptide mapping, immunoaffinity chromatography, nuclear magnetic resonance (NMR), X-ray crystallography and also new cutting edge technologies such as phage display and ribosome display as tools to study these topics. These studies have direct implications in unraveling the dysregulation in proinflammatory cytokine signaling that is observed in a number of chronic inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease (IBD), asthma and many neurodegenerative diseases. We also have an ongoing project that is investigating the contribution that intestinal epithelial cells make to the induction of IBD-like disease and intestinal inflammation in genetically susceptible mice. Key References: DiDonato, J.A., Hayakawa, M. Rothwarf, D.M; Zandi, E., and Karin M. (1997) A cytokine-responsive I kappaB kinase that activates the transcription factor NF-kappa B. Nature, 388:548-554. DiDonato, J.A., Mercurio, F., Rosette, C., Wu-Li, J., Suyang, H., Ghosh, S., and Karin, M. Mapping of the Inducible IkB Phosphorylation Sites that Signal its Ubiquitination and Degradation. Mol. Cell. Biol. 16:1295-1304. 1996. DiDonato, J.A., Mercurio, F., and Karin, M. Phosphorylation of IkB alpha precedes but is not sufficient for its dissociation from NF-kB. Mol. Cell. Biol. 15:1302-1311, 1995. Elewaut, D., DiDonato, J.A., Kim, J-M., Truong, F., Eckmann, L., and Kagnoff, M.F. (1999) Nuclear Factor-kB is a central regulator of the intestinal epithelial cell innate immune response induced by infection with enteroinvasive bacteria. J. Immunology 163:1457-1466. Chu, Z.L., Shin, Y.A., Yang, J.M., DiDonato, J.A. and Ballard, D.W. (1999) IKKgamma mediates the interaction of cellular IkappaB kinases with the tax transforming protein of human T cell leukemia virus type 1. J. Biol. Chem. 274:15297-15300. Chu, Z-L., DiDonato, J.A., Hawiger, J., and Ballard, D.W. (1998) The Tax oncoprotein of human T-cell leukemia virus Type 1 associates with and peristently activates Ikappa B kinases containing IKK alpha and IKKbeta. J. Biol. Chem. 273:15891-15894. Auphan, N., DiDonato, J.A., Helmberg, A., Rosette, C., and Karin, M. Molecular Basis for Immunosuppression by Glucocorticoids: Inhibition of NF-kB Activity through Induction of IkB Synthesis. Science 270:286-290, 1995. | ||