Trypanosoma cruzi, the causative agent of Chagas heart disease, infects heart and other cells leading to cardiac arrest frequently followed by death (1). The disease affects millions of individuals in the Americas and is posing health problems because of blood transmission in the US due to large Latin American immigration (2-3). Since the current drugs present serious side effects and do not cure the chronic infection (4), it is critically important to understand the early process of cellular infection at the molecular and structural levels to design novel inhibitors to block T. cruzi infection. In this review, the authors critically analyze the molecular and cellular basis of early T. cruzi infection and discuss the future directions in this area. The candidate T. cruzi invasive genes and host genes involved in the process of early infection are just beginning to be understood. The trypanosome invasive proteins are excellent targets for intervention. The progress made in the cell biology of T. cruzi infection will also facilitate the development of novel cell-based therapies to ameliorate the disease.

Naegleria fowleri is the protozoan pathogen that causes primary amoebic meningoencephalitis (PAM), with the death rate exceeding 97%. The amoeba makes sterols and can be targeted by sterol biosynthesis inhibitors. Here, we characterized N. fowleri sterol 14-demethylase, including catalytic properties and inhibition by clinical antifungal drugs and experimental substituted azoles with favorable pharmacokinetics and low toxicity. None of them inhibited the enzyme stoichiometrically. The highest potencies were displayed by posaconazole (IC50 = 0.69 μM) and two of our compounds (IC50 = 1.3 and 0.35 μM). Because both these compounds penetrate the brain with concentrations reaching minimal inhibitory concentration (MIC) values in an N. fowleri cellular assay, we report them as potential drug candidates for PAM. The 2.1 Å crystal structure, in complex with the strongest inhibitor, provides an explanation connecting the enzyme weaker substrate specificity with lower sensitivity to inhibition. It also provides insight into the enzyme/ligand molecular recognition process and suggests directions for the design of more potent inhibitors.

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The cleavage and polyadenylation specificity factor 6 (CPSF6) is a cellular protein involved in RNA cleavage and polyadenylation. Emerging evidence also suggest that CPSF6 plays a key role during HIV‐1 infection by guiding integration of the viral DNA into gene‐dense regions of the host genome. Since viral DNA integration is a critical step of HIV‐1 infection, the role of CPSF6 in the virus lifecycle is being intensely investigated. Surprisingly, the cellular mechanisms that regulate CPSF6 expression are largely unknown. In this study, we report a post‐transcriptional mechanism of regulation of CPSF6. Our initial bioinformatics analysis revealed that the 3′ untranslated region (3′UTR) of Cpsf6 contains a binding site for the cellular miRNA miR‐125b that is strikingly conserved across different mammalian species. Since miRNAs negatively regulate protein expression, we carried out knock‐down and over‐expression studies of miR‐125b. Results from these experiments revealed that miR‐125b expression is negatively associated with CPSF6 protein levels. Interestingly, HIV‐1 infection resulted in the down‐regulation of miR‐125b concurrent with induction of CPSF6. To probe that CPSF6 expression is post‐transcriptionally regulated by miR‐125b, we cloned the 3′UTR regions of Cpsf6 mRNA into a luciferase reporter. Results from luciferase assay provide evidence that miR‐125b expression negatively regulates Cpsf6 3′UTR activity. Accordingly, mutations in the miR‐125b seed sequences abrogated the regulatory effect of the miRNA on Cpsf6 3′UTR. Pull‐down studies demonstrated that miR‐125b physically interacts with the Cpsf6 mRNA. Continuing studies probe the necessity of productive HIV‐1 infection for negatively regulating miR‐125b expression as well as to elucidate the pathway through which HIV‐1 infection can knockdown miR‐125b expression. Collectively, these findings establish a post‐transcriptional mechanism of CPSF6 expression and describe a novel function of miR‐125b in virus‐host interaction. Support or Funding Information This work is partly supported by grants DA024558, DA30896, DA033892 and DA021471 from NIDA/NIH to CD. We also acknowledge the RCMI Grant G12MD007586, the Vanderbilt CTSA grant UL1RR024975, the Meharry Translational Research Center (MeTRC) CTSA grant (U54 RR026140 from NCRR/NIH, the U54 grant MD007593 from NIMHD/NIH, and Tennessee CFAR grant (P30 AI110527).

The protozoan parasite, Trypanosoma cruzi, causes severe morbidity and mortality in afflicted individuals. Approximately 30% of T. cruzi infected individuals present with cardiac pathology. The invasive forms of the parasite are carried in the vascular system to infect other cells of the body. During transportation, the molecular mechanisms by which the parasite signals and interact with host endothelial cells (EC) especially heart endothelium is currently unknown. The parasite increases host thrombospondin-1 (TSP1) expression and activates the Wnt/β-catenin and hippo signaling pathways during the early phase of infection. The links between TSP1 and activation of the signaling pathways and their impact on parasite infectivity during the early phase of infection remain unknown. To elucidate the significance of TSP1 function in YAP/β-catenin colocalization and how they impact parasite infectivity during the early phase of infection, we challenged mouse heart endothelial cells (MHEC) from wild type (WT) and TSP1 knockout mice with T. cruzi and evaluated Wnt signaling, YAP/β-catenin crosstalk, and how they affect parasite infection. We found that in the absence of TSP1, the parasite induced the expression of Wnt-5a to a maximum at 2 h (1.73±0.13), P< 0.001 and enhanced the level of phosphorylated glycogen synthase kinase 3β at the same time point (2.99±0.24), P<0.001. In WT MHEC, the levels of Wnt-5a were toned down and the level of p-GSK-3β was lowest at 2 h (0.47±0.06), P< 0.01 compared to uninfected control. This was accompanied by a continuous significant increase in the nuclear colocalization of β-catenin/YAP in TSP1 KO MHEC with a maximum Pearson correlation coefficient of (0.67±0.02), P< 0.05 at 6 h. In WT MHEC, the nuclear colocalization of β-catenin/YAP remained steady and showed a reduction at 6 h (0.29±0.007), P< 0.05. These results indicate that TSP1 plays an important role in regulating β-catenin/YAP colocalization during the early phase of T. cruzi infection. Importantly, dysregulation of this crosstalk by pre-incubation of WT MHEC with a β-catenin inhibitor, endo-IWR 1, dramatically reduced the level of infection of WT MHEC. Parasite infectivity of inhibitor treated WT MHEC was similar to the level of infection of TSP1 KO MHEC. These results indicate that the β-catenin pathway induced by the parasite and regulated by TSP1 during the early phase of T. cruzi infection is an important potential therapeutic target, which can be explored for the prophylactic prevention of T. cruzi infection.