SFB796 - Sub project C6


Effects of Tax and p8 proteins on cell-to-cell transmission of Human T-cell lymphotropic virus type 1 (HTLV-1)


Project summary

Transmission of Human T-cell lymphotropic virus type 1 (HTLV-1), a delta-retrovirus, requires cell-cell contact while cell-free infection of CD4+ T-cells is very inefficient. Viruses are transmitted via virological synapses, extracellular assemblies, actin-containing cellular conduits, or via productively-infected dendritic cells. Independent of the route, cytoskeletal remodeling is a prerequisite for virus transmission as interference with both actin and tubulin polymerization strongly reduces HTLV-1 transmission. Two viral proteins are known to play a role in virus transmission, the transactivator Tax, which is also important for oncogenic transformation, and the p8 protein, a cleavage product of the accessory protein p12. Tax is required for microtubuli polarization of infected CD4+ T-cells towards uninfected recipient cells, while p8 is responsible for the induction of cellular, actin-containing conduits facilitating virus transmission. Thus far, detailed molecular mechanisms of Tax- and p8-mediated virus transmission are unknown. The aim of this project is to elucidate how Tax and p8 reprogram both the cytoskeleton and cell-cell interactions to enhance virus transmission. Recently, we could identify strong and specific upregulation of the actin-bundling protein Fascin upon expression of Tax in T lymphocytes. Fascin co-localizes with actin in the cytoplasm, but can also be found in cellular protrusions of HTLV-1-transformed cells. Preliminary data indicate that knockdown of Fascin in HTLV-1-transformed lymphocytes reduces the infection of reporter cell lines in co-culture experiments. Therefore, the starting point of our project is to further analyse the impact of the Tax-effector Fascin on infectivity, virus release and transmission rates in T-cells and dendritic cells using chronically-infected, virus-producing cells, proviral clones and reporter viruses. In the second part of our project, we seek to identify cellular targets of Tax that are involved in cell-cell interactions, cytoskeletal remodeling and virus transmission. For this purpose, data-mining of known Tax-interaction partners shall be combined with genome-wide expression studies of Tax-expressing cells to identify cellular Tax-targets and signaling pathways involved in cytoskeletal remodeling and cell-to-cell interaction. Use of shRNA-mediated knockdown and inhibitors targeting these Tax-effectors in combination with transmission assays and reporter viruses should help to identify those targets that are required for Tax-mediated virus transmission. Finally, we plan to identify cellular interaction partners of p8 by combinatorial use of bioinformatics and proteomics. Mutagenesis of p8 and the use of shRNAs targeting p8-interaction partners followed by transmission assays and imaging studies of cellular protrusions are planned to identify proteins of the host that are responsible for cytoskeletal changes enhancing p8-mediated virus transmission. Overall, this project should help to dissect novel interactions of the viral proteins Tax and p8 with the host cell during the formation of cellular structures required for cell-to-cell transmission of HTLV-1.


Project relevant publications

Gross C, Thoma-Kress AK.   (2016).   Molecular Mechanisms of HTLV-1 Cell-to-Cell Transmission.   Viruses 8(3),74. (Review)

Mohr CF, Gross C, Bros M, Reske-Kunz AB, Biesinger B, Thoma-Kress AK.   (2015).   Regulation of the tumor marker Fascin by the viral oncoprotein Tax of human T-cell leukemia virus type 1 (HTLV-1) depends on promoter activation and on a promoter-independent mechanism.   Virology. 485:481-491.

Mohr CF, Kalmer M, Gross C, Mann MC, Sterz KR, Kieser A, Fleckenstein B, Kress AK.   (2014).   The tumor marker Fascin is induced by the EBV-encoded oncoprotein LMP1 via NF-kappaB signals in lymphocytes and contributes to their invasive migration.   Cell Commun Signal. 12(1):46.

Mann MC, Strobel S, Fleckenstein B, Kress AK.   (2014).   The transcription elongation factor ELL2 is specifically upregulated in HTLV-1-infected T-cells and is dependent on the viral oncoprotein Tax.   Virology 464-465:98-110.

Ooms M, Krikoni A, Kress AK, Simon V, Münk C.   (2012).   APOBEC3A, APOBEC3B and APOBEC3H haplotype 2 restrict Human T-lymphotropic virus type I (HTLV-1).   J Virol 86:6097-108.

Kress AK, Grassmann R, Fleckenstein B.   (2011a).   Cell Surface Markers in HTLV-1 Pathogenesis.   Viruses 3: 1439-1459.   [Review]

Kress AK, Kalmer M, Rowan A, Grassmann R, Fleckenstein B.   (2011).   The tumor marker Fascin is strongly induced by the Tax oncoprotein of HTLV-1 through NF-kappaB signals.   Blood 117:3609-3612.

Kress AK, Schneider G, Pichler K, Kalmer M, Fleckenstein B, Grassman.   (2010).   Elevated cyclic AMP (cAMP) levels in T lymphocytes transformed by human T cell lymphotropic virus type 1 (HTLV-1).   J Virol 84:8732-8742.

Pichler K, Kattan T, Gentzsch J, Kress AK, Taylor GP, Bangham CRM, Grassmann R.   (2008).   Strong induction of 4-1BB, a growth and survival promoting costimulatory receptor, in HTLV-1-infected cultured and patients' T cells by the viral Tax oncoprotein.   Blood 111(9):4741-51.