The nuclear factor (NF)-?B transcription factors play an evolutionarily conserved and critical role in various biological processes such as immune response, proliferation, and apoptosis. A number of diseases are caused by constitutive and dysregulation of NF-?B function including cancers, a wide variety of autoimmune diseases such as rheumatoid arthritis (RA), insulin-dependent diabetes mellitus, and multiple sclerosis, inflammatory diseases such as Crohns disease, ulcerative colitis, and arotic aneurysms. Inhibition of NF-?B function as a treatment option is not viable because of the essentiality of its transcriptional activity for normal immune response and antiapoptotic function. Thus knowledge of physiological pathways that tame or limit signal responsive NF-?B activation are of pressing clinical relevance. While plethora of different stress stimuli activates NF-?B, a detailed knowledge of the activation pathway is available only for limited number of stimuli including signaling pathways initiated by cytokines such as TNF and IL-1. Usually receptor mediated signaling is turned off by ligand-bound receptor internalization and endocytosis. We hypothesized that proteins that are localized to intracellular compartments such as endocytic vesicles play essential role, under physiological conditions, in keeping the NF-?B transcription activation to optimal healthy levels. Because of the obvious importance of knowledge of such pathways for treating many diseases we focused to investigate the role of proteins that regulate intracellular TNF signaling at membrane bound organelles. Our investigations have identified four proteins as novel regulators of TNF induced NF-?B activation. Our laboratory is focused to understand role of two phospholipids domain containing proteins, CARPs, in (i) endocytosis of TNF receptosomes, (ii) TNF mediated events other than IKK activation, such as JNK activation and caspase activation and (iii) other signaling pathways induced by IL-1, LPS and T cell receptor stimulation. Thus far we have identified that CARP-2, a RING domain-containing ubiquitin protein ligase (E3), is a negative regulator of TNF-induced NF-?B activation. By virtue of its phospholipid-binding FYVE domain, CARP-2 localized to endocytic vesicles where it interacted with RIP in TNF-stimulated cells, resulting in RIP ubiquitination and degradation. Knockdown of CARP-2 stabilized TNFR1-associated polyubiquitinated RIP levels after TNF simulation and enhanced activation of NF-?B. Therefore, CARP-2 acts at the level of endocytic vesicles to limit the intensity of TNF-induced NF-?B activation by the regulated elimination of a necessary signaling component within the receptor complex. Another significant finding is the identification of TRIM32 as an activator of NF-?B in myocytes. We focus our research on the biochemical characterization of TRIM32 with a clear intent to know the role of TRIM32 in cachexia or muscle wasting. We have also identified a novel seven-membrane protein PP1201 as CARP-interacting protein. Interestingly PP1201 deficient mice developed cystic medial degeneration (CMD) a pathological finding aortic aneurysms. These studies with PP1201 have led us to work to develop a new hypothesis that dysregulation of TNF signaling is responsible for cystic medial degeneration (CMD) a pathological finding aortic aneurysms.
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