- Volume 92, Issue 2, 2011

Cells of primary effusion lymphoma (PEL), a B-cell non-Hodgkin's lymphoma, are latently infected by Kaposi's sarcoma-associated herpesvirus (KSHV), with about 80 % of PEL also co-infected with Epstein–Barr virus (EBV). Both viruses can be reactivated into their lytic replication cycle in PEL by chemical inducers. However, simultaneous activation of both lytic cascades leads to mutual lytic cycle co-repression. The plasma cell-differentiation factor X-box binding protein 1 (XBP-1) transactivates the KSHV immediate–early promoter leading to the production of the replication and transcription activator protein (RTA), and reactivation of KSHV from latency. XBP-1 has been reported to act similarly on the EBV immediate–early promoter Zp, leading to the production of the lytic-cycle transactivator protein BZLF1. Here we show that activated B-cell terminal-differentiation transcription factor X-box binding protein 1 (XBP-1s) does not induce EBV BZLF1 and BRLF1 expression in PEL and BL cell lines, despite inducing lytic reactivation of KSHV in PEL. We show that XBP-1s transactivates the KSHV RTA promoter but does not transactivate the EBV BZLF1 promoter in non-B-cells by using a luciferase assay. Co-expression of activated protein kinase D, which can phosphorylate and inactivate class II histone deacetylases (HDACs), does not rescue XBP-1 activity on Zp nor does it induce BZLF1 and BRLF1 expression in PEL. Finally, chemical inducers of KSHV and EBV lytic replication in PEL, including HDAC inhibitors, do not lead to XBP-1 activation. We conclude that XBP-1 specifically reactivates the KSHV lytic cycle in dually infected PELs.

Sobemoviruses possess a viral genome-linked protein (VPg) attached to the 5′ end of viral RNA. VPg is processed from the viral polyprotein. In the current study, Cocksfoot mottle virus (CfMV) and Rice yellow mottle virus (RYMV) VPgs were purified from virions and analysed by mass spectrometry. The cleavage sites in the polyprotein and thereof the termini of VPg were experimentally proven. The lengths of the mature VPgs were determined to be 78 and 79 aa residues, respectively. The amino acid residues covalently linked to RNA in the two VPgs were, surprisingly, not conserved; it is a tyrosine at position 5 of CfMV VPg and serine at position 1 of RYMV VPg. Phosphorylations were identified in CfMV and RYMV VPgs with two positionally similar locations T20/S14 and S71/S72, respectively. RYMV VPg contains an additional phosphorylation site at S41.

The pathogenesis of bovine spongiform encephalopathy (BSE) infections in cattle has been studied in recent years by using highly sensitive transgenic-mouse bioassays. It has been shown that in this species, the BSE agent amplifies almost exclusively in the central and peripheral nervous system. Even in animals that were killed in the clinical end stage of the disease, the lymphoreticular system was shown to be free of the infectious agent. No other animal species investigated to date exhibits such a restricted BSE-infectivity distribution pattern. However, there is growing evidence for a radial spread of infection from the central nervous system (CNS) into the periphery during the late stages of the disease. In this study, we challenged transgenic mice overexpressing the bovine prion protein with homogenates prepared from a wide variety of tissue samples collected from BSE-infected cattle. As prion infections involve the conversion of the cellular prion protein into its abnormally folded isoform (PrPSc), we applied various detection methods, such as the purification of scrapie-associated fibrils, immunohistochemistry, and the protein misfolding cyclic amplification technique. Despite negative results using these highly sensitive biochemical methods, we were, for the first time, able to detect BSE infectivity in the tongue and in the nasal mucosa of terminally diseased BSE field cases as well as experimentally challenged cattle by transgenic-mouse bioassay. This shows that BSE infectivity can be present in the peripheral tissues of terminally diseased cattle, including tissues used for human consumption.