Comparative analysis of the regulation of the interferoninducible protein kinase PKR by Epstein - Barr virus RNAs EBER-1 and EBER-2 and adenovirus VA, RNA

Abstract

The interferon-inducible protein kinase PKR interacts with a number of small viral RNA species, including adenovirus VAI RNA and the Epstein-Barr virus-encoded RNA EBER-1. These RNAs bind to PKR and protect protein synthesis from inhibition by double-stranded RNA in the reticulocyte lysate system. Using a peptide phosphorylation assay we show here that EBER-1, like VAI, directly inhibits the activation of purified PKR. A second Epstein-Barr virus RNA, EBER-2, also regulates PKR. EBER-1, EBER-2 and VAI RNA exhibit mutually competitive binding to the native or recombinant enzyme, as assessed by U.V. crosslinking experiments and filter binding assays. The affinities of all three RNAs for PKR in vitro are similar (Kd = ca. 0.3 nM). Since this protein kinase has been proposed to exert a tumour suppressor function in vivo, the ability of EBER-1 to inhibit its activation suggests a role for this small RNA in cell transformation by Epstein-Barr virus.

The γ 1 34.5 protein of herpes simplex virus 1 complexes with protein phosphatase 1α to dephosphorylate the α subunit of the eukaryotic translation initiation factor 2 and preclude the shutoff of protein synthesis by double-stranded RNA-activated protein kinase

“…Lastly, most viruses studied to date block phosphorylation of eIF-2␣ by encoding proteins which bind double stranded RNA [e.g., E2L of vaccinia (22)(23)(24), 3 protein of Reo and rotaviruses (25)(26)(27)(28), and NS1 protein of influenza (29)], or proteins or RNA that inactivate PKR by binding to it [e.g., vaccinia K3L, Epstein-Barr virus EBERS 1 and 2 (30), adenovirus VA1 RNA (30,31), influenza virus-induced cellular p58 protein (32)], or degrade PKR [poliovirus (33)]. HIV-1 TAR sequence appears to bind to a cellular TAR binding protein and PKR (34)(35)(36).…”

Epstein–Barr virus-encoded small RNA induces insulin-like growth factor 1 and supports growth of nasopharyngeal carcinoma-derived cell lines

“…EBER is a small RNA, is not transcribed into protein, and is known to bind some cellular proteins such as La, EAP/L22 and PKR . Among them, the association of EBER with PKR has been most intensively studied (Sharp et al, 1993;Yamamoto et al, 2000;Nanbo et al, 2002). We previously demonstrated that EBER binds PKR, inhibits its phosphorylation, and confers resistance to interferon-induced apoptosis (Nanbo et al, 2002).…”

Eukaryotic regulatory RNAs: an answer to the ‘genome complexity’ conundrum

“…As a countermeasure against the action of PKR, some viruses such as Epstein-Barr virus (EBV) constitutively express two ncRNAs, EBER1 and EBER2, which are 167 nt and 172 nt long, respectively. EBER1 has been previously demonstrated to bind to PKR and has been suggested to confer resistance to Fas-mediated apoptosis in tissue culture cells by blocking PKR activity (Clarke et al 1991;Sharp et al 1993;Nanbo et al 2005). EBER1 and EBER2 are the most abundant viral transcripts expressed during viral latency (∼5 × 10 6 per cell) and are predominantly localized in the nucleus (Lerner et al 1981;Howe and Steitz 1986;Fok et al 2006).…”