KSHV interactions with host inflammasome components

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DESCRIPTION: KSHV is etiologically associated with chronic inflammation associated Kaposi's sarcoma (KS) and primary effusion B-cell lymphoma (PEL) in oral and other body sites that occur in HIV-1 infected patients. The inflammatory response is one of the key elements of KSHV pathogenesis. KS lesions are characterized by inflammatory cells and cytokines. The KS lesion endothelial cells and B-cell lines from PEL carry multiple copies of the KSHV genome in a latent state. Our long term goals are to elucidate KSHV's interactions with the host innate response during primary infection and latency, the pathways of cytokine induction and to define their role in KSHV pathogenesis. Our rationale is that such detailed knowledge is crucial for designing therapeutic strategies to control KSHV infection, inflammation and the associated malignancies. KSHV infected cells secrete multi-functional IL-1? and IL-18 cytokines into the supernatants. IL-1? and IL-18 are synthesized as inactive proIL-1? and proIL-18 and then undergo processing by activated caspase-1. However, caspase-1 itself is synthesized as a procaspase-1 and undergoes activation leading into an auto- proteolytic cleavage. Procaspase-1 activation is mediated by a molecular platform called an "inflammasome" that is formed by homotypic interactions of a sensor protein recognizing the danger trigger, an adaptor ASC molecule, and procaspase-1. Our studies have demonstrated that the pathogen sensing functions of the inflammasome also extends into the nucleus. During de novo KSHV infection of human microvascular dermal endothelial (HMVEC-d) cells, gamma-interferon-inducible protein (IFI16) is colocalized with the KSHV genome in the infected endothelial cell nucleus, and interacted with ASC and procaspase-1 to form an inflammasome complex. IFI16 also colocalized with the KSHV genome in the nuclei of latently infected endothelial and PEL cells, and only the IFI16 dependent inflammasome is constitutively activated in KSHV latently infected cells. Human KS and PEL lesions showed evidence of IFI16-ASC inflammasome activation. Constitutive induction of the IFI16-inflammasome was also observed in ?1-EBV latency I, II and III cells. Together with the ability of KSHV and EBV latency in the presence of the IFI16-inflammasome and association of IFI16 with KSHV and EBV genome in the latently infected cells, we hypothesize that "IFI16 is involved in the innate sensing of foreign episomal DNA in the nucleus and KSHV utilizes IFI16 for its latency". This hypothesis will be tested by three innovative and interlinked specific aims. These studies are significant since such elucidation wil lead into designing therapeutic strategies to control KSHV induced inflammation and the associated malignancies. These will also profoundly enhance the current concepts of innate sensing in the nucleus and will lead into new technologies and treatments that will benefit not only the KSHV area of research but also other fields.