Over the past decade, a variety of advanced silver-based dressings have been developed. There are considerable variations in the structure, composition, and silver content of these new preparations. In the present study, we examined five commercially available silver-based dressings (Acticoat, Aquacel Ag, Contreet Foam, PolyMem Silver, Urgotul SSD). We assessed their cytotoxicity in a monolayer cell culture, a tissue explant culture model, and a mouse excisional wound model. The results showed that Acticoat, Aquacel Ag, and Contreet Foam, when pretreated with specific solutes, were likely to produce the most significant cytotoxic effects on both cultured keratinocytes and fibroblasts, while PolyMem Silver and Urgotul SSD demonstrated the least cytotoxicity. The cytotoxicity correlated with the silver released from the dressings as measured by silver concentration in the culture medium. In the tissue explant culture model, in which the epidermal cell proliferation was evaluated, all silver dressings resulted in a significant delay of reepithelialization. In the mouse excisional wound model, Acticoat and Contreet Foam indicated a strong inhibition of wound reepithelialization on the postwounding-day 7. These findings may, in part, explain the clinical observations of delayed wound healing or inhibition of wound epithelialization after the use of certain topical silver dressings. Caution should be exercised in using silver-based dressings in clean superficial wounds such as donor sites and superficial burns and also when cultured cells are being applied to wounds.

EBV-encoded nuclear antigen-1 (EBNA-1) binding to a cis-acting viral DNA element, oriP, enables plasmids to persist in dividing human cells as multicopy episomes that attach to chromosomes during mitosis. In investigating the significance of EBNA-1 binding to mitotic chromosomes, we identified the basic domains of EBNA-1 within amino acids 1-89 and 323-386 as critical for chromosome binding. In contrast, the EBNA-1 C terminus (amino acids 379-641), which includes the nuclear localization signal and DNAbinding domain, does not associate with mitotic chromosomes or retain oriP plasmid DNA in dividing cell nuclei, but does enable the accumulation of replicated oriP-containing plasmid DNA in transient replication assays. The importance of chromosome association in episome maintenance was evaluated by replacing EBNA-1 amino acids 1-378 with cell proteins that have similar chromosome binding characteristics. High-mobility group-I amino acids 1-90 or histone H1-2 could substitute for EBNA-1 amino acids 1-378 in mediating more efficient accumulation of replicated oriP plasmid, association with mitotic chromosomes, nuclear retention, and long-term episome persistence. These data strongly support the hypothesis that mitotic chromosome association is a critical factor for episome maintenance. The replacement of 60% of EBNA-1 with cell protein is a significant step toward eliminating the need for noncellular protein sequences in the maintenance of episomal DNA in human cells. Materials and Methods Cell Lines, Transfection, and Immunoblot Analysis. BJAB, an EBVnegative Burkitt lymphoma cell line, was cultured, transfected, used to derive cell lines stably expressing FLAG-tagged proteins, and analyzed by immunoblot for protein expression as described (23). Plasmids. Plasmids carrying the expression cassettes for enhanced green fluorescent protein (EGFP) fused EBNA-1 derivatives described in Fig. 1 were derived from pEGFPc1 (CLONTECH) and the BamHI-K fragment of EBV strain B95-8 DNA. The GE expression plasmid was constructed by inserting the 2.6-kb TfiI-HindIII fragment of BamHI-K between the BspEI and Abbreviations: EBV, Epstein-Barr virus; EBNA-1, EBV-encoded nuclear antigen-1; HMG-I, high-mobility group-I; NLS, nuclear localization signal; EGFP, enhanced green fluorescent protein; FISH, fluorescent in situ hybridization; FE, FLAG-tagged EBNA-1; FC, FLAG-tagged EBNA-1 C terminus; FHMC, FLAG-tagged HMG-I 1-90 fused to the EBNA-1 C terminus; FH1C, FLAG-tagged histone H1 fused to the EBNA-1 C terminus.

The Epstein-Barr virus oncoprotein latent infection membrane protein 1 (LMP1) is a constitutively aggregated pseudo-tumor necrosis factor receptor (TNFR) that activates transcription factor NF-B through two sites in its C-terminal cytoplasmic domain. One site is similar to activated TNFRII in associating with TNFR-associated factors TRAF1 and TRAF2, and the second site is similar to TNFRI in associating with the TNFRI death domain interacting protein TRADD. TNFRI has been recently shown to activate NF-B through association with TRADD, RIP, and TRAF2; activation of the NF-B-inducing kinase (NIK); activation of the IB␣ kinases (IKK␣ and IKK␤); and phosphorylation of IB␣. IB␣ phosphorylation on Ser-32 and Ser-36 is followed by its degradation and NF-B activation. In this report, we show that NF-B activation by LMP1 or by each of its effector sites is mediated by a pathway that includes NIK, IKK␣, and IKK␤. Dominant negative mutants of NIK, IKK␣, or IKK␤ substantially inhibited NF-B activation by LMP1 or by each of its effector sites.