KSHV RTA abolishes NFκB responsive gene expression during lytic reactivation by targeting vFLIP for degradation via the proteasome

PLoS One. 2014 Mar 10;9(3):e91359. doi: 10.1371/journal.pone.0091359. eCollection 2014.


Kaposi's sarcoma herpesvirus (KSHV) is a gamma-2 herpesvirus present in all cases of Kaposi's sarcoma, primary effusion lymphoma (PEL), and some cases of multicentric Castleman's disease. Viral FLICE inhibitory protein (vFLIP) is a latently expressed gene that has been shown to be essential for survival of latently infected PEL cells by activating the NFκB pathway. Inhibitors of either vFLIP expression or the NFĸB pathway result in enhanced lytic reactivation and apoptosis. We have observed a decrease in vFLIP protein levels and of NFκB activation in the presence of the KSHV lytic switch protein RTA. Whereas vFLIP alone induced expression of the NFĸB responsive genes ICAM1 and TNFα, inclusion of RTA decreased vFLIP induced ICAM1 and TNFα expression in both co-transfected 293T cells and in doxycycline induced TREx BCBL1 cells. RTA expression resulted in proteasome dependent destabilization of vFLIP. Neither RTA ubiquitin E3 ligase domain mutants nor a dominant-negative RAUL mutant abrogated this effect, while RTA truncation mutants did, suggesting that RTA recruits a novel cellular ubiquitin E3 ligase to target vFLIP for proteasomal degradation, allowing for inhibition of NFĸB responsive gene expression early during lytic reactivation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • CASP8 and FADD-Like Apoptosis Regulating Protein / metabolism*
  • Chlorocebus aethiops
  • Gene Expression Regulation*
  • HEK293 Cells
  • Herpesvirus 8, Human / metabolism*
  • Humans
  • Intercellular Adhesion Molecule-1 / genetics
  • Intercellular Adhesion Molecule-1 / metabolism
  • NF-kappa B / metabolism*
  • Proteasome Endopeptidase Complex / metabolism*
  • Proteolysis
  • Trans-Activators / metabolism*
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / metabolism
  • Ubiquitin-Protein Ligases / metabolism
  • Up-Regulation
  • Vero Cells
  • Virus Activation / genetics*


  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • NF-kappa B
  • ORF 50 transactivator
  • Trans-Activators
  • Tumor Necrosis Factor-alpha
  • Intercellular Adhesion Molecule-1
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex