Kaposi sarcoma-associated herpesvirus (KSHV) ORF57 protein antagonizes the activity of cellular splicing factor SRSF3 to promote viral RNA splicing

Friday, November 08, 2013 — Poster Session IV
2:00 p.m. – 4:00 p.m.	FAES Academic Center (Upper-Level Terrace)	NCI	VIROL-5

Authors

V Majerciak
M Lu
X Li
ZM Zheng

Abstract

KSHV ORF57 is a multifunctional factor essential for proper biogenesis of viral transcripts during KSHV infection and its function depends on interaction with cellular co-factors. We previously showed that members of SPEN protein family, RBM15 and OTT3, cooperate with ORF57 to enhance the expression of intronless KSHV ORF59 RNA. Surprisingly, we found that the increased intracellular level of RBM15 or OTT3 compromised ORF57 role as a viral splicing factor to facilitate splicing of KSHV K8 beta RNA. Pull-down experiments revealed that RBM15 disrupts ORF57 interaction with cellular splicing factor SRSF3 (formally SRp20). Consequently, we found that SRSF3 acts as a negative regulator of splicing of K8beta RNA. Knock-down of SRSF3 promotes the K8beta splicing both in the absence or presence of ORF57. In contrary, the ectopic expression of SFSR3 inhibits ORF57 function to promote splicing of K8beta RNA. These data indicate that ORF57 directly targets SRSF3 and releases its negative effect on viral RNA splicing. Accordingly, we confirmed ORF57 interaction with SRSF3 and this interaction also promote splicing of other RNA transcripts negatively regulated by SRSF3. Our study disclosed for the first time how ORF57 mechanistically regulates RNA splicing by identification of SRSF3 as an interaction partners during KSHV infection.