Project SummaryToxoplasma gondii is arguably one of the most successful parasitic protozoans on the planet. Itis estimated that T. gondii infects approximately a third of humanity (~2 billion people) andnearly half of all warm-blooded animals. Once established, infection is lifelong andcharacterized by the presence of semi-dormant tissue cysts typically in muscle and neuraltissues. As host conditions change, T. gondii has the capacity to reactivate and induce multiplerounds of recurrent parasitemia, a fact which becomes an issue of serious concern in an agingpopulation or in individuals with compromised immune systems. Currently, there are no drugsavailable that can effectively treat the chronic stage of infection and therapies currently in useagainst acute infection are often accompanied by serious side effects. It is therefore important,especially as population's age, to generate new methods and compounds to treat this disease.Upon invasion of its host cell, Toxoplasma induces a massive reorganization of the host celltranscriptional program and as a result, major pathways related to metabolism, immunity andthe cell cycle become activated. T. gondii has been show to initiate modification of its host cellenvironment through the regulated secretion of its various secretory organelles (micronemes,rhoptries, dense granules). The dense granules, originally characterized as serving only tocondition the parasite vacuole to be a feeding organelle, are now considered a reservoir ofvarious host nuclear targeted parasite effectors with diverse targets and functions. Theseproposed studies aim to characterize a newly identified parasite effector of the dense granuleswe have termed ICC1 for inducer of cell cycle gene 1. We have demonstrated that ICC1 trafficsto the host cell nucleus soon after infection and induces the expression of a multitude of genesinvolved in progression of the host cell cycle into S-phase. Additionally we have found that T.gondii also has 2nd redundant effector to alter the host cell cycle via that is released from itsrhoptry organelle and which we have identified as the host nuclear targeted phosphatase PP2C-hn. To advance our knowledge of ICC1 and PP2C-hn's function, we propose to perform a seriesof immunoprecipitation and mass spectrometry experiments in order to identify the principal hosttargets and determine the functional significance of this interaction as it relates to cell cycleprogression. The results of this proposal will provide the first mechanistic basis for themodulation of the host cell cycle by a protozoan parasite and may give additional insight into thebasic function of our own cells.