The obligate intracellular parasite Toxoplasma gondii is a major opportunistic infection of AIDS patients. Toxoplasma also causes devastating disease to fetuses and other immunocompromised patients. While much work has focused on identifying and characterizing Toxoplasma proteins and pathways important for growth and virulence of this intracellular pathogen, less is known about which host cell pathways are rate- limiting for parasite growth. Identification of these host cell processes is important because if we can inhibit them or the parasite processes dependent on them from functioning then we can block parasite growth and disease. Modulation of host cell transcription is a common mechanism to make the host cell?s environment permissive for pathogen growth. Hypoxia Inducible Factor 1 (HIF-1) is one example of a host cell transcription that is activated by Toxoplasma infection and is required for parasite growth. In the previous funding period, we found that HIF-1 is activated by Toxoplasma triggering the nuclear export and subsequent lysosomal degradation of the PHD2 protein, which is the key negative regulator of HIF-1. Decreases in PHD2 protein is achieved by the parasite activating a host cell receptor named Activin Like Kinase 4 (ALK4). Finally, we discovered that HIF-1 promotes Toxoplasma growth by upregulating the host glycolytic hexokinase 2. In this proposal we will establish how Toxoplasma stimulates PHD2 nuclear export and lysosomal degradation, what ligand binds to ALK4, and how hexokinase 2 acts to promote parasite growth. These studies are likely to provide important information regarding the interaction between Toxoplasma and its host cell.