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

[primary effusion lymphoma]

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 ICAM 1 and TNF α , inclusion of RTA decreased vFLIP induced ICAM 1 and TNF α expression in both co -transfected 293 T cells and in doxycycline induced TREx BCBL 1 cells . RTA expression resulted in proteasome dependent destabilization of vFLIP . Neither RTA ubiquitin E 3 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 E 3 ligase to target vFLIP for proteasomal degradation , allowing for inhibition of NFĸB responsive gene expression early during lytic reactivation .