Influenza virosomes as vaccine adjuvant and carrier system.

The basic concept of virosomes is the controlled in vitro assembly of virus-like particles from purified components. The first generation of influenza virosomes developed two decades ago is successfully applied in licensed vaccines, providing a solid clinical safety and efficacy track record for the technology. In the meantime, a second generation of influenza virosomes has evolved as a carrier and adjuvant system, which is currently applied in preclinical and clinical stage vaccine candidates targeting various prophylactic and therapeutic indications. The inclusion of additional components to optimize particle assembly, to stabilize the formulations, or to enhance the immunostimulatory properties have further improved and broadened the applicability of the platform.

Recent advances in mucosal immunization using virus-like particles.

Mucosal immunization offers the promises of eliciting a systemic and mucosal immune response, as well as enhanced patient compliance. Mucosal vaccination using defined antigens such as proteins and peptides requires delivery systems that combine good safety profiles with strong immunogenicity, which may be provided by virus-like particles (VLP). VLP are assembled from viral structural proteins and thus are devoid of any genetic material. They excel by mimicking natural pathogens, therefore providing antigen-protecting particulate nature, inherent immune-cell stimulatory mechanisms, and tissue-specific targeting depending on their parental virus. Nevertheless, despite of promising preclinical results, VLP remain rarely investigated in clinical studies. This review is intended to give an overview of obstacles and promises of VLP-based mucosal immunization as well as to identify strategies to further improve VLP while maintaining a good safety and tolerability profile.

A peptide derived from the highly conserved protein GAPDH is involved in tissue protection by different antifungal strategies and epithelial immunomodulation.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has an important role not only in glycolysis but also in nonmetabolic processes, including transcription activation and apoptosis. We report the isolation of a human GAPDH (hGAPDH) (2-32) fragment peptide from human placental tissue exhibiting antimicrobial activity. The peptide was internalized by cells of the pathogenic yeast Candida albicans and initiated a rapid apoptotic mechanism, leading to killing of the fungus. Killing was dose-dependent, with 10 µg ml (3.1 µM) and 100 µg ml hGAPDH (2-32) depolarizing 45% and 90% of the fungal cells in a population, respectively. Experimental C. albicans infection induced epithelial hGAPDH (2-32) expression. Addition of the peptide significantly reduced the tissue damage as compared with untreated experimental infection. Secreted aspartic proteinase (Sap) activity of C. albicans was inhibited by the fragment at higher concentrations, with a median effective dose of 160 mg l(-1) (50 µM) for Sap1p and 200 mg l(-1) (63 µM) for Sap2p, whereas Sap3 was not inhibited at all. Interestingly, hGAPDH (2-32) induced significant epithelial IL-8 and GM-CSF secretion and stimulated Toll-like receptor 4 expression at low concentrations independently of the presence of C. albicans, without any toxic mucosal effects. In the future, the combination of different antifungal strategies, e.g., a conventional fungicidal with immunomodulatory effects and the inhibition of fungal virulence factors, might be a promising treatment option.

BRD7, a novel PBAF-specific SWI/SNF subunit, is required for target gene activation and repression in embryonic stem cells.

The composition of chromatin-remodeling complexes dictates how these enzymes control transcriptional programs and cellular identity. In the present study we investigated the composition of SWI/SNF complexes in embryonic stem cells (ESCs). In contrast to differentiated cells, ESCs have a biased incorporation of certain paralogous SWI/SNF subunits with low levels of BRM, BAF170, and ARID1B. Upon differentiation, the expression of these subunits increases, resulting in a higher diversity of compositionally distinct SWI/SNF enzymes. We also identified BRD7 as a novel component of the Polybromo-associated BRG1-associated factor (PBAF) complex in both ESCs and differentiated cells. Using short hairpin RNA-mediated depletion of BRG1, we showed that SWI/SNF can function as both a repressor and an activator in pluripotent cells, regulating expression of developmental modifiers and signaling components such as Nodal, ADAMTS1, BMI-1, CRABP1, and thyroid releasing hormone. Knockdown studies of PBAF-specific BRD7 and of a signature subunit within the BAF complex, ARID1A, showed that these two subcomplexes affect SWI/SNF target genes differentially, in some cases even antagonistically. This may be due to their different biochemical properties. Finally we examined the role of SWI/SNF in regulating its target genes during differentiation. We found that SWI/SNF affects recruitment of components of the preinitiation complex in a promoter-specific manner to modulate transcription positively or negatively. Taken together, our results provide insight into the function of compositionally diverse SWI/SNF enzymes that underlie their inherent gene-specific mode of action.

Remodeling plans for cellular specialization: unique styles for every room.

Chromatin-remodeling complexes are biochemically diverse, functionally selective machines that regulate crucial aspects of DNA metabolism, including transcription and chromatin assembly. These complexes modulate histone-DNA interactions to affect nucleosome repositioning and disassembly, and histone variant exchange, thereby generating compositionally specialized chromatin. Recent studies have revealed precise mechanisms by which specific remodelers control the transition from proliferating progenitors to committed cells through a highly synchronized switch in transcriptional programs. This involves temporal and, often, signal-dependent gene-targeted interactions between individual remodelers and tissue-specific master proteins that regulate myogenesis, neurogenesis and lymphogenesis. Distinct remodelers have also been shown to direct self-renewal of different types of stem cells in response to particular microenvironments.

Promoter-specific p53-dependent histone acetylation following DNA damage.

We have used chromatin immunoprecipitation (ChIP) to measure p53-dependent histone acetylation at the p21, MDM2, and PUMA promoters. The pattern of histone acetylation was different at each promoter. H3 and H4 acetylation increased at both the p21 and PUMA promoters in response to p53 activation, whereas there was only a minimal increase in H4 acetylation and no increase in H3 acetylation at the MDM2 promoter. The high p53 occupancy of the p21, MDM2 and PUMA promoters has been attributed to the presence of two p53 binding sites in these promoters, but mutation of the p53 binding sites in integrated p21 promoter constructs showed that the two sites in the p21 promoter do not cooperate to stabilize p53 binding. Despite 10-fold higher p53 binding to the proximal than the distal site in the p21 promoter, both sites showed similar patterns of H3 and H4 acetylation. Mutation of the binding sites showed that acetylation of the proximal, low-affinity site requires p53 binding to that site but not to the distal, high-affinity site. Since low-affinity p53 binding sites can confer strong acetylation, the DNA binding affinity in vitro is an unreliable guide to the likely importance of p53 in regulating candidate target genes in vivo.

Regulation of p53 stability and function in HCT116 colon cancer cells.

We have used a lentiviral vector to stably express p53 at a physiological level in p53 knockout HCT116 cells. Cells transduced with wild type p53 responded to genotoxic stress by stabilizing p53 and expressing p53 target genes. The reconstituted cells underwent G(1) arrest or apoptosis appropriately depending on the type of stress, albeit less efficiently than parental wild type cells. Compared with cells expressing exogenous wild type p53, the apoptotic response to 5-fluorouracil (5FU) was >50% reduced in cells expressing S15A or S20A mutant p53, and even more reduced by combined mutation of serines 6, 9, 15, 20, 33, and 37 (N6A). Among a panel of p53 target genes tested by quantitative PCR, the gene showing the largest defect in induction by 5FU was BBC3 (PUMA), which was induced 4-fold by wild type p53 and 2-fold by the N6A mutant. Mutation of N-terminal phosphorylation sites did not prevent p53 stabilization by doxorubicin or 5FU. MDM2 silencing by RNA interference activated p53 target gene expression in normal fibroblasts but not in HCT116 cells, and exogenous p53 could be stabilized in HCT116 knockout cells despite combined mutation of p53 phosphorylation sites and silencing of MDM2 expression. The MDM2 feedback loop is thus defective, and other mechanisms must exist to regulate p53 stability and function in this widely used tumor cell line.

Cell type- and promoter-specific roles of Ser18 phosphorylation in regulating p53 responses.

Phosphorylation of mouse p53 at Ser18 occurs after DNA damage. To determine the physiological roles of this phosphorylation event in p53-dependent DNA damage responses, a Ser18 to Ala missense mutation was introduced into the germline of mice. Thymocytes and fibroblasts from the knock-in mice show reduced transactivation of many p53 target genes following DNA damage. p53 protein stabilization and DNA binding are similar in knock-in and wild type mice, but C-terminal acetylation was defective, consistent with a role for Ser18 in the recruitment of transcriptional co-activators. The apoptotic response of knock-in thymocytes to ionizing radiation is intermediate between that of wild type and p53 null thymocytes. Despite impaired transcriptional and apoptotic responses, the knock-in mice are not prone to spontaneous tumorigenesis. This indicates that neither phosphorylation of p53 on Ser18 by ATM nor a full transcriptional response is essential to prevent spontaneous tumor formation in mice.