Silencing of proviruses in embryonic cells: Efficiency, stability and chromatin modifications

1] Department of Biochemistry and Molecular Biophysics, Columbia University [2] Department of Microbiology and Immunology, Columbia University.
EMBO Reports (Impact Factor: 9.06). 11/2012; 14(1). DOI: 10.1038/embor.2012.182
Source: PubMed

ABSTRACT Embryonic stem cells repress retroviral infection through transcriptional silencing of proviral DNAs. We characterized two distinct mechanisms of silencing in embryonic mouse cells infected by Moloney murine leukaemia virus (MLV): a highly efficient one targeting the proline transfer RNA primer-binding site (PBSpro), and a less efficient one operating independently of the PBS. Rare virus-expressing populations were isolated, and the timing and efficiency of establishment of silencing were determined. Superinfection of the selected virus-expressing cells with a second virus carrying a distinguishable reporter revealed that the PBSpro-directed silencing was still largely intact, whereas the PBS-independent silencing was partially reduced. The timing and stability of silencing, and the associated chromatin modifications on newly established and endogenous proviruses were determined. The results indicate that epigenetic mechanisms with different specificity and efficiency are used to silence the exogenous retroviral sequences in embryonic cells.

Download full-text


Available from: Stephen P Goff, Oct 05, 2014
13 Reads
  • Source
    • "Several cellular mechanisms, however, govern the HIV DNA expression after the integration, which regulate retroviral replication and thereby control the disease phenotypes or symptoms of an acute, chronic, or latent infection, including the cellular mechanisms that silence the replication of ancient human endogenous retroviruses (HERVs) [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]. Development of highly active antiretroviral therapy (HAART) or combination antiretroviral therapy (cART) has changed the natural course of HIV infection. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Hematopoietic stem cell (HSC) belongs to multipotent adult somatic stem cells. A single HSC can reconstitute the entire blood system via self-renewal, differentiation into all lineages of blood cells, and replenishment of cells lost due to attrition or disease in a person’s lifetime. Although all blood and immune cells derive from HSC, immune cells, specifically immune memory cells, have the properties of HSC on self-renewal and differentiation into lineage effector cells responding to the invading pathogens. Moreover, the interplay between immune memory cell and viral pathogen determines the course of a viral infection. Here, we state our point of view on the role of blood stem and progenitor cell in chronic HIV infection, with a focus on memory CD4 T-cell in the context of HIV/AIDS eradication and cure.
    Stem cell International 08/2015; 2015(4):1-7. DOI:10.1155/2015/148064 · 2.81 Impact Factor
  • Source
    • "Retroviral vectors utilizing alternative PBS sequences that are not recognized by this silencing machinery escape the rapid silencing but are still subject to some transcriptional repression [16,17]. The machinery mediating this silencing is also used to repress or regulate expression of many of the endogenous proviruses resident in the mouse genome, most strikingly the so-called IAP elements [18], through the DNA binding factor YY1 [19]. We note, however, that not all endogenous proviruses are equally or even similarly regulated in this pattern, and that some retroelements show the inverse behavior, expressing well in ES cells and not in differentiated cells; these include the HERV-H proviruses in human cells [20] and the virus-related L1td1/Ecat11 gene in mouse [21]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Retroviral DNAs are profoundly silenced at the transcriptional level in embryonic cell types. The transcriptional profile of pluripotent stem cells has been demonstrated to be extremely heterogeneous from cell to cell, and how the silencing of retroviral DNAs is achieved is not yet well characterized. In the current study, we investigated the transcriptional silencing dynamics in stem cells by independently monitoring the expression of two Moloney murine leukemia virus (MMLV) retroviral vectors newly introduced into embryonic carcinoma (EC) cells. Although MMLV is efficiently silenced by epigenetic mechanisms in most such cells, a small number of the doubly-transduced EC cells transiently show double-positive proviral expression. These cells were sorted and their expression patterns were studied over time as silencing is established. Our data suggest that retroviral silencing occurs stochastically, in an individual locus-specific fashion, and often without synchronous silencing of both viruses in the same cells. Surprisingly, the chromatin modifications that mark the silenced proviruses are unchanged even in cells that temporarily escape silencing. This local silencing effect is a feature of stem cell epigenomic regulation that has not previously been revealed.
    Retrovirology 04/2014; 11(1):31. DOI:10.1186/1742-4690-11-31 · 4.19 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Embryonic cells transcriptionally repress the expression of endogenous and exogenous retroelements. Trim28, a key player in this silencing, is known to act in a large DNA-bound complex, but the other components of the complex are not fully characterized. Here, we show that the zinc finger protein Yin Yang 1 (YY1) is one such component. YY1 binds to the long terminal repeat (LTR) region of both exogenous and endogenous retroviruses (ERVs). Deletion of the YY1-binding site from the retroviral genome leads to a major loss of silencing in embryonic cells and a coordinated loss of repressive histone marks from the proviral chromatin. Depletion of YY1 protein results in marked upregulation of expression of exogenous viruses and of selected ERVs. Finally, we report an embryonic cell-specific interaction between YY1 and Trim28. Our results suggest a major role for YY1 in the silencing of both exogenous retroviruses and ERVs in embryonic cells.
    Cell Reports 06/2013; 4(1). DOI:10.1016/j.celrep.2013.06.003 · 8.36 Impact Factor
Show more