The polymorphic HCMV glycoprotein UL20 is targeted for lysosomal degradation by multiple cytoplasmic dileucine motifs.

Human cytomegalovirus (HCMV) is a widespread and persistent beta-herpesvirus. The large DNA genome of HCMV encodes many proteins that are non-essential for viral replication including numerous proteins subverting host immunosurveillance. One of them is the barely characterized UL20, which is encoded adjacent to the well-defined immunoevasins UL16 and UL18. UL20 is a type I transmembrane glycoprotein with an immunoglobulin-like ectodomain that is highly polymorphic among HCMV strains. Here, we show that the homodimeric UL20, by virtue of its cytoplasmic domain, does not reach the cell surface but is targeted to endosomes and lysosomes. Accordingly, UL20 exhibits a short half-life because of rapid lysosomal degradation. Trafficking of UL20 to lysosomes is determined by several, independently functioning dileucine-based sorting motifs in the cytoplasmic domain of UL20 and involves the adaptor protein (AP) complex AP-1. Combined substitution of three dileucine motifs allowed strong cell surface expression of UL20 comparable to UL20 mutants lacking the cytoplasmic tail. Finally, we show that the intracellularly located UL20 also is subject to lysosomal degradation in the context of viral infection. Altogether, from these data, we hypothesize that UL20 is destined to efficiently sequester yet-to-be defined cellular proteins for degradation in lysosomes.

The Viscum album extract Iscador P does not cause an autocrine interleukin-6 loop in B-Non-Hodgkin's Lymphoma cell lines.

BACKGROUND: Single cases of clinical observations suggest the efficacy of the Viscum album (VA) extract Iscador P in the treatment of follicular B-Non-Hodgkin's Lymphoma (B-NHL). A previously published study aroused a controversial dispute as it indicated that IL-6 serum levels are elevated following i.v. VA treatment. Increased IL-6 levels have been shown to promote the progression of B-cell neoplasia such as B-NHL. Objective of this study was to investigate whether the VA extract influences the expression of IL-6 and its receptor components in follicular B-NHL cell lines. METHODS: Follicular B-NHL cell lines (WSU-NHL, DoHH-2) were incubated with clinically relevant doses of VA extract for up to 3 days. At specified time points (6, 24, 48, 72 h) samples were taken and the expression of IL-6 and its receptor components were analysed by real-time-RT-PCR, flow cytometry and ELISA. RESULTS: Treatment of follicular B-NHL cell lines with VA extract did not alter the expression level of IL-6 and its' receptor components at any time and with any of the applied VA extract concentrations. CONCLUSIONS: Clinically relevant doses of the VA extract do not trigger an autocrine or paracrine IL-6 loop nor do they initiate IL-6 trans-signalling in follicular B-NHL cell lines.