My laboratory is interested in the molecular mechanisms of viral pathogenesis. We focus on two viruses: HIV-1 and Hepatitis C Virus (HCV).

 1) Role of Tat protein in HIV transcription and pathogenesis.
Tat is a unique viral transactivator because it activates HIV transcription through complex interactions with RNA and host cofactors. Our special interest lies in the molecular characterization of posttranslational modifications of Tat and their role in regulating HIV transcription during infection. We have previously shown that Tat is acetylated by the transcriptional coactivator p300 and deacetylated by the NAD+-dependent deacetylase SIRT1. Our most recent results show that Tat is also subject to lysine methylation. We are currently defining the role of this modification in Tat function and characterize the molecular mechanisms associated with this new modification. We are working towards a combinatorial view of Tat modifications, which will integrate the interactions of Tat with TAR RNA and different cellular cofactors.

We are also interested in the role of Tat in HIV-induced immune hyperactivation. T-cell hyperactivation is a hallmark of HIV-1 infection and a significant factor in continuous viral replication and CD4+ T cell depletion. We find that Tat promotes immune hyperactivation of HIV-infected T cells by manipulating the acetylation status of important transcription factors such as NF- kB. We are currently characterizing this novel function of Tat in T-cell biology and HIV-induced T-cell hyperactivation.

 2) Role of core protein in HCV replication and pathogensis.
We recently expanded our research efforts to include the pathogenesis of hepatitis C virus (HCV) infection, particularly the influence of the HCV core protein on liver cell functions. Using confocal microscopy and cellular fractionation assays, we found that a fraction of core protein localizes to mitochondria, and also to mitochondria-associated membranes, a site of physical contact between the ER and mitochondria. Our current studies focus on the function of HCV core protein at mitochondria and on the characterization of the mode by which the core protein is targeted to the mitochondria. Special focus lies on the interaction of core and mitochondria with lipid droplets and the relevance of this interaction for viral replication and the induction of liver steatosis present in individuals with chronic HCV infection.

Approaches: We use a variety of molecular biology techniques in tumor and primary cell cultures, including lentiviral vector systems, infectious HIV and HCV clones, nuclear and cytoplasmic microinjections, modification-specific antibodies as well as biochemical assays, confocal microscopy and transgenic mouse models.