Regulation of SIGNALLING PATHWAYS INVOLVING NUCLEAR FACTOR KAPPA B

National Institute Of Allergy And Infectious Diseases

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Abstract

Regulation of many immune response genes depend on a 10 bp DNA sequence termed kappaB. This sequence is bound by a family of protein factors related to the Rel oncogene. The prototype transcription complex binding to the sequence, termed NF-kappaB, has been conventionally defined as a heterodimer between a P50 DNA binding protein and a P65 (RelA) activation protein that is typically sequestered in the cytoplasm by a protein called I-kappaB. Following certain types of stimulation to the cell, a specific protein kinase complex called I-kappaB kinase causes the phosphorylation of I-kappaB followed by its ubiquitination and degradation. Among the stimuli that can release NF-kappaB is the triggering of the T cell receptor (TCR) or B cell receptor (BCR) by antigen during an immune response. While studying a rare clinical condition of immunodeficiency, we discovered that NF-kappaB has a more complex subunit composition than previously suspected. Specifically, we found that genes such as IL-2 and I-kB harbor kappaB sites of a particular sequence that bind a trimeric complex containing p50, p65, and ribosomal protein small subunit 3 (RPS3). RPS3 is a K-homology domain-containing protein that binds single-stranded nucleic acids and dramatically enhances the affinity of the p50 and p65 Rel-homology proteins to these select kappaB sites. A subset of all NF-kappaB genes are dependent on RPS3 including crucial physiological functions such as expression of the immunoglobulin kappa light chain gene in B cells and the interleukin-2 gene in T cells. This establishes a new paradigm for NF-kappaB gene regulation that potentially explains the selective activation of genes by distinct inducers of NF-kappaB. Given the pivotal role of NF-kappaB and Indians cell gene regulation, we are looking for other subunits that may also participate in the binding complex. We are also attempting to identify inhibitors of this component, since inhibition of NF-kappaB is a prime therapeutic target for number of inflammatory and degenerative conditions. Inhibition of NF-kappaB may also be useful for various infectious diseases involving pathogens, such as HIV, that utilize this factor for their life cycle or pathogenic effects.[unreadable] We have also been studying the activation circuitry that induces NF-kappaB after triggering the antigen receptor on B cells or T cells. We have found a new kinase that plays a direct role in physically linking the membrane-associated protein complex containing the Carma 1, MALT 1, and the Bcl-10 (CBM) proteins to the I-kappaB kinase complex. We have demonstrated a vital role for the cellular kinase in the induction pathway. This novel kinase has both a positive and negative regulatory role is transducing the signals from antigen receptors at the surface of lymphocytes to the gene induction apparatus. This kinase has been shown to beinvolved in developmental and circadian rhythm pathways and now appears to play a key role in immune function. We will be studying the biochemical features of its regulation to understand how it might be modulated in various diseases of the immune system. Mass spectrometry analysis has also revealed other proteins in the signal transduction pathway involving the CBM complex and experimentation will be directed to elucidating the functional role of these proteins.