Recently, we reported the cloning of the nuclear orphan receptor TAK1. In this study, we characterized the sequence requirements for optimal TAK1 binding and analyzed the repression of the peroxisome proliferatoractivated receptor ␣ (PPAR␣) signaling pathway by TAK1. Site selection analysis showed that TAK1 has the greatest affinity for direct repeat-1 response elements (RE) containing AGGTCAAAGGTCA (TAK1-RE) to which it binds as a homodimer. TAK1 is a very weak inducer of TAK1-RE-dependent transcriptional activation. We observed that TAK1, as PPAR␣, is expressed within rat hepatocytes and is able to bind the peroxisome proliferator response elements (PPREs) present in the promoter of the PPAR␣ target genes rat enoyl-CoA hydratase (HD) and peroxisomal fatty acyl-CoA oxidase (ACOX). TAK1 is unable to induce PPRE-dependent transcriptional activation and represses PPAR␣-mediated transactivation through these elements in a dosedependent manner. Two-hybrid analysis showed that TAK1 does not form heterodimers with either PPAR␣ or retinoid X receptor (RXR␣), indicating that this repression does not involve a mechanism by which TAK1 titrates out PPAR␣ or RXR␣ from PPAR⅐RXR complexes. Further studies demonstrated that the PPAR␣ ligand 8(S)-hydroxyeicosatetraenoic acid strongly promotes the interaction of PPAR␣ with the co-activator RIP-140 but decreases the interaction of PPAR␣ with the corepressor SMRT. In contrast, TAK1 interacts with RIP-140 but not with SMRT and competes with PPAR␣ for RIP-140 binding. These observations indicated that the antagonistic effects of TAK1 on PPAR␣⅐RXR␣ transactivation act at least at two levels in the PPAR␣ signaling pathway: competition of TAK1 with PPAR␣⅐RXR for binding to PPREs as well as to common co-activators, such as RIP-140. Our results suggest an important role for TAK1 in modulating PPAR␣-controlled gene expression in hepatocytes.

Increasing evidence indicates that human cytomegalovirus (HCMV) populations under the influence of host environment, can either be stable or rapidly differentiating, leading to tissue compartment colonization. We isolated previously from a 30-years old pregnant woman, a clinical isolate of HCMV, that we refered to as the HCMV-DB strain (accession number KT959235). The HCMV-DB clinical isolate demonstrated its ability to infect primary macrophages and to upregulate the proto-oncogene Bcl-3. We observed in this study that the genome of HCMV-DB strain is close to the genomes of other primary clinical isolates including the Toledo and the JP strains with the later having been isolated from a glandular tissue, the prostate. Using a phylogenetic analysis to compare the genes involved in virus entry, we observed that the HCMV-DB strain is close to the HCMV strain Merlin, the prototype HCMV strain. HCMV-DB infects human mammary epithelial cells (HMECs) which in turn display a ER−/PR−/HER2− phenotype, commonly refered to as triple negative. The transcriptome of HCMV-DB-infected HMECs presents the characteristics of a pro-oncogenic cellular environment with upregulated expression of numerous oncogenes, enhanced activation of pro-survival genes, and upregulated markers of cell proliferation, stemcellness and epithelial mesenchymal transition (EMT) that was confirmed by enhanced cellular proliferation and tumorsphere formation in vitro. Taken together our data indicate that some clinical isolates could be well adapted to the mammary tissue environment, as it is the case for the HCMV-DB strain. This could influence the viral fitness, ultimately leading to breast cancer development.

Annual influenza outbreaks are associated with significant morbidity and mortality worldwide despite the availability of seasonal vaccines. Influenza pathogenesis depends on the manipulation of host cell signaling to promote virus replication. Ceramide is a sphingosine-derived lipid that regulates diverse cellular processes. Studies highlighted the differential role of ceramide de novo biosynthesis on the propagation of various viruses. Whether ceramide plays, a role in influenza virus replication is not known. In this study, we assessed the potential interplay between the influenza A (IAV) and ceramide biosynthesis pathways. The accumulation of ceramide in human lung epithelial cells infected with influenza A/H1N1 virus strains was evaluated using thin-layer chromatography and/or confocal microscopy. Virus replication was assessed upon the regulation of the de novo ceramide biosynthesis pathway. A significant increase in ceramide accumulation was observed in cells infected with IAV in a dose-and time-dependent manner. Inoculating the cells with UV-inactivated IAV did not result in ceramide accumulation in the cells, suggesting that the induction of ceramide required an active virus replication. Inhibiting de novo ceramide significantly decreased ceramide accumulation and enhanced virus replication. The addition of exogenous C 6 -ceramide prior to infection mediated an increase in cellular ceramide levels and significantly attenuated IAV replication and reduced viral titers (Ϸ1 log10 PFU/ml unit). Therefore, our data demonstrate that ceramide accumulation through de novo biosynthesis pathway plays a protective and antiviral role against IAV infection. These findings propose new avenues for development of antiviral molecules and strategies. IMPORTANCE Understanding the effect of sphingolipid metabolism on viral pathogenesis provide important insights into the development of therapeutic strategies against microbial infections. In this study, we demonstrate a critical role of ceramide during influenza A virus infection. We demonstrate that ceramide produced through de novo biosynthesis possess an antiviral role. These observations unlock new opportunities for the development of novel antiviral therapies against influenza.

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