Kaposi’s sarcoma-associated herpesvirus (KSHV) is one of the few oncogenic human viruses known to date. Its large genome encodes more than 85 proteins and includes both unique viral proteins as well as proteins conserved amongst herpesviruses. KSHV ORF20 is a member of the herpesviral core UL24 family, but the function of ORF20 and its role in the viral life cycle is not well understood. ORF20 encodes three largely uncharacterized isoforms, which we found were localized predominantly in the nuclei and nucleoli. Quantitative affinity purification coupled to mass spectrometry (q-AP-MS) identified numerous specific interacting partners of ORF20, including ribosomal proteins and the interferon-stimulated gene product (ISG) oligoadenylate synthetase-like protein (OASL). Both endogenous and transiently transfected OASL co-immunoprecipitated with ORF20, and this interaction was conserved among all ORF20 isoforms and multiple ORF20 homologs of the UL24 family in other herpesviruses. Characterization of OASL interacting partners by q-AP-MS identified a very similar interactome to that of ORF20. Both ORF20 and OASL copurified with 40S and 60S ribosomal subunits, and when they were co-expressed, they associated with polysomes. Although ORF20 did not have a global effect on translation, ORF20 enhanced RIG-I induced expression of endogenous OASL in an IRF3-dependent but IFNAR-independent manner. OASL has been characterized as an ISG with antiviral activity against some viruses, but its role for gammaherpesviruses was unknown. We show that OASL and ORF20 mRNA expression were induced early after reactivation of latently infected HuARLT-rKSHV.219 cells. Intriguingly, we found that OASL enhanced infection of KSHV. During infection with a KSHV ORF20stop mutant, however, OASL-dependent enhancement of infectivity was lost. Our data have characterized the interaction of ORF20 with OASL and suggest ORF20 usurps the function of OASL to benefit KSHV infection.

Natural killer (NK)1 cells are large granular lymphocytes that provide a first innate immune defense. They are able to kill virus-infected and transformed cells and furthermore release cytokines and chemokines to activate adaptive immune cells (1, 2).The balance of signals from activating and inhibitory NK cell surface receptors tightly regulates NK cell activity. Activated NK cells release lytic granules through a process called degranulation. Therefore, NK cell cytotoxicity requires the formation of the F-actin-rich NK immune synapse (NKIS) and the transport of Perforin-containing lytic granules to the NKIS. Furthermore, this process requires granule-associated MYH9 protein (non-muscle Myosin IIa) mediating the interaction of granules with F-actin at the NKIS (3-5), leading to lytic granule exocytosis. Whereas related phenotypes and functional properties are well characterized, the underlying regulatory protein network mediating differentiation, cytokine release, and cytotoxicity, is still incomplete.NK cells are defined by the expression of the surface molecule CD56 (NCAM1) and the absence of the T cell receptor (TCR) associated protein CD3 and can be further subdivided into subsets (6, 7). CD56 expressing cells originate from CD34 ϩ HSCs. Notably, the commitment to the NK lineage includes discrete steps from HSC to cells, expressing high CD56 levels (CD56 bright ) (8, 9), which act immune regulatory by the release of various cytokines. NK cells with low CD56-expression (CD56 dim ) predominantly constitute cytotoxic responses (10, 11). Contact of CD56 (NCAM1) with fibroblasts (12) and neutrophils (13) supports the differentiation process from CD56 bright to CD56 dim NK cells. The progression of early differentiation steps is proven by telomere length investigation (14 ) and early presence in blood after HSC transplantation (HSCT) (14, 15). Indeed, CD56 dim NK cells are able to change their phenotypic properties, which can be correlated with continued differentiation throughout their whole lifespan (15-18). CD57 was determined to be a senescence marker in T cells (19 1 The abbreviations used are: NK, natural killer; CD56, NK cell marker; NCAM1, neural cell adhesion molecule; CD57, senescence marker in T and NK cells (HNK-1 or Leu-7); CMV, cytomegalovirus; CPDA-1, anticoagulant , containing citric acid, sodium citrate, monobasic sodium phosphate and dextrose; CTLs, cytotoxic T lymphocytes; FDR, false discovery rate; HLA, self-human leukocyte antigen; HSC, hematopoietic stem cell; iTRAQ, isobaric tags for relative and absolute quantification in mass spectrometry; KIR, killer immunoglobulin-related receptors in NK cells; LC-MS/MS, liquid-chromatography coupled with peptide sequencing (mass spectrometry); MAD, median absolute deviation from the median; NKIS, NK cell immune synapse; RF, regulation factor. Research