The innate immune response is an important line of defense against pathogenic agents and is also an integral component of the wound repair process. In vivo, the cytokines, tumor necrosis factor alpha (TNFalpha) and interleukin (IL 1) activate the innate immune response by increasing NF-kappaB dependent expression of genes. For example, interleukin-8 recruits circulating phagocytic cells and E-selectin facilitates adherence of recruited phagocytes. Together changes in IL-8 and E-selectin gene expression are key events that occur during the innate immune response. A high degree of sequence similarity is shared between the mammalian NF- kappaB/c-rel family and its cytoplasmic inhibitor IkappaBalpha, and the Drosophila Dorsal protein and its regulator Cactus. Genetic analyses of Dorsal have defined components of a signaling pathway for Dorsal activation, including a serine/threonine protein kinases, Pelle, upstream of Dorsal and Cactus. We demonstrated that this pathway is conserved in mammals through the isolation of a cDNA that encodes a novel mouse protein highly related to Pelle, mPLK (mouse Pelle-like protein kinase). Over- expression of the mPLK cDNA in fibroblasts leads to transactivation of the NF-kappaB dependent IL-8 and E-selectin gene promoters. Catalytically inactive mPLK functions as a dominant-negative and blocks TNFalpha mediated transactivation of the IL-8 gene promoter. Moreover in unstimulated cells, mPLK is complexed with the type I tumor necrosis factor receptor (TNFRI) which is required for TNFalpha induced NF kappaB activity. Current TNFRI signaling models predict that TNFRI mediated induction of NF-kappaB activity is mediated by the TNF receptor associated death domain protein (TRADD), which associates with TNFRI after TNFalpha stimulation. However our recent data, demonstrate that mPLK is also a mediator through which TNFRI can induce NF-kappaB activity. The studies in this proposal are aimed at testing the hypothesis that mPLK is a TRADD- independent pathway through which TNFRI can induce NF-kappaB activity. This will be accomplished by: (1) Identifying TNFRI-mPLK complex components; (2) Determining if mPLK signaling activity is TRADD dependent; (3) Identifying mPLK-NIK (NF-kappaB inducing kinase) complex components; (4) Determining if TNFRI and mPLK activities are interdependent; and (5) Identifying additional mPLK regulators.
