FIG 7.

KRAB-ZFPs regulate persistence of KSHV, the other oncogenic human herpesvirus. (A) Levels of SZF1, ZNF557, and STAT3 mRNAs in KSHV⁺ primary effusion lymphoma (BCBL-1) cells transfected with scrambled siRNA (open bars) or siSTAT3 (black bars) were quantitated by qRT-PCR. BCBL-1 cells were transfected with scrambled siRNA or siSTAT3 and harvested for immunoblotting with indicated antibodies. (B and C) BCBL-1 cells were transfected with empty vector and scrambled siRNA, SZF1 (B) or ZNF557 (C) plasmid and scrambled siRNA, or SZF1 (B) or ZNF557 (C) plasmid and siTRIM28, exposed to VPA, and harvested for determination of the relative amounts of transcripts from the KSHV latency-to-lytic-cycle switch gene ORF50 and the early lytic gene ORF59 by qRT-PCR. All data represent the averages of results from three independent experiments; error bars indicate standard errors of the means (*, p ≤ 0.05). (D and E) BCBL-1 cells were transfected with combinations of empty vector, HA-tagged KRAB-ZFP plasmids, scrambled siRNA, and siTRIM28, treated with VPA, and harvested for immunoblotting with indicated antibodies. Data are representative of results from two independent experiments. (F) Model of oncogenic human herpesvirus persistence depicting that STAT3 transcriptionally activates the KRAB-ZFPs SZF1 and ZNF557, which localize to EBV and KSHV genomes. Bound SZF1 functions directly through TRIM28 to repress lytic genes despite the presence of lytic triggers, while bound ZNF557 functions in a TRIM28-independent manner (?), thereby maintaining latency and promoting virus persistence.