By interacting with components of the human host, including extracellular matrix (ECM) proteins, Streptococcus pneumoniae has evolved various strategies for colonization. Here, we characterized the interaction of pneumococci with the adhesive glycoprotein vitronectin and the contribution of this protein to pneumococcal uptake by host cells in an integrin-dependent manner. Specific interaction of S. pneumoniae with the heparin-binding sites of purified multimeric vitronectin was demonstrated by flow cytometry analysis. Host-cell-bound vitronectin promoted pneumococcal adherence to and invasion into human epithelial and endothelial cells. Pneumococci were trapped by microspike-like structures, which were induced upon contact of pneumococci with host-cell-bound vitronectin. αvβ3 integrin was identified as the major cellular receptor for vitronectin-mediated adherence and uptake of pneumococci. Ingestion of pneumococci by host cells via vitronectin required a dynamic actin cytoskeleton and was dependent on integrin-linked kinase (ILK), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt), as demonstrated by gene silencing or in inhibition experiments. In conclusion, pneumococci exploit the vitronectin–αvβ3-integrin complex as a cellular receptor for invasion and this integrin-mediated internalization requires the cooperation between the host signalling molecules ILK, PI3K and Akt.

Summary. White spot syndrome virus (WSSV) is type species of the genusWhispovirus of the new family Nimaviridae. Despite the elucidation of its genomic sequence, very little is known about the virus as only 6% of its ORFs show homology to known genes. One of the structural virion proteins, VP15, is part of the nucleocapsid of the virus and shows homology to some putative baculovirus DNA binding proteins. These DNA-binding or histone-like proteins are thought to be involved in the condensation and packaging of the genome in the nucleocapsid. Using bacterially expressed VP15 fusion proteins in ELISA and Far-Western experiments showed that VP15 interacts with itself, forming homomultimers, but not with the other major structural proteins of the WSSV virion. Antibodies against phosphorylated proteins revealed that VP15 originating from different sources was not phosphorylated. WSSV VP15 binds non-specifically to double-stranded DNA, but has a clear preference to supercoiled DNA suggesting that VP15 is involved in the packaging of the WSSV genome in the nucleocapsid. This research shed further light on the composition of WSSV virions and the function of one of its nucleocapsid proteins.

Epstein-Barr virus (EBV) replicates in superficial differentiated cells of oral hairy leukoplakia (OHL). Differentiation of squamous epithelial cells depends on B-lymphocyte-induced maturation protein 1 (Blimp1).Here we show that expression of the EBV immediate-early protein BZLF1 is restricted to Blimp1-positive epithelial cells in OHL. Luciferase assays revealed Blimp1-dependent induction of the BZLF1 promoter Zp in epithelial cell lines. Expression of ZEB1, a negative regulator of Zp, and of Xbp-1, which mediates the Blimp1 effect on Zp in B-cells, was not affected by enforced Blimp1 expression. Moreover, Xbp-1 protein expression was not detected in differentiated epithelial cells of OHL. Thus, Blimp1 induces BZLF1 expression in epithelial cells independently of ZEB1 and Xbp-1. In contrast to epithelial cells of OHL, BZLF1 expression was also observed in Blimp1-negative lymphoid cells in infectious mononucleosis tonsils, suggesting that EBV replication in B-cells may be induced independently of terminal differentiation.Epstein-Barr virus (EBV) is a B-lymphotropic human herpesvirus infecting .90 % of the adult population worldwide. Primary infection in childhood is usually asymptomatic but may cause a clinical syndrome, infectious mononucleosis (IM), when delayed into adolescence or early adulthood. Following primary infection, a lifelong persistent latent infection of memory B-cells is established. Infectious virus particles are released into the saliva, but their cellular source has been controversial (Niedobitek & Young, 1994). It is now clear that EBV may replicate in B-cells as well as in oral squamous epithelial cells. In both cellular compartments, the switch from latent to lytic infection is triggered by expression of the immediate-early gene BZLF1, which is necessary and sufficient to activate the EBV lytic cascade (Rooney et al., 1989;Miller, 1990). Various lines of evidence have indicated that EBV replication depends on cellular differentiation. Immunohistochemical analysis of B-cells in IM tonsils suggested a restriction of virus replication to cells with plasma-cell morphology (Crawford & Ando, 1986;Niedobitek et al., 1997). Furthermore, terminal differentiation of B-cells towards plasma cells initiates the lytic cycle in vivo (Laichalk & Thorley-Lawson, 2005). Similarly, it has been suggested that, in epithelial cells of oral hairy leukoplakia (OHL), an AIDS-associated lesion of the tongue mucosa, EBV replicates in a differentiation-dependent manner (Young et al., 1991).Plasma-cell differentiation is regulated by B-lymphocyteinduced maturation protein (Blimp)1 (Shapiro-Shelef et al., 2003). By repressing Pax5, Blimp1 indirectly activates the Xbox-binding protein Xbp-1 (Lin et al., 2002). Induction of BZLF1 expression by binding of Xbp-1 to the BZLF1 promoter Zp has been demonstrated in B-cells, but not in epithelial cells (Sun & Thorley-Lawson, 2007). In contrast, Bhende et al. (2007) showed that Xbp-1 transactivates BZLF1 only in combination with activated protein kinase D in B-lymphocytes and e...

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