Echinocandins are a new generation of novel antifungal agent that inhibit cell wall β(1,3)-glucan synthesis and are normally cidal for the human pathogen Candida albicans. Treatment of C. albicans with low levels of echinocandins stimulated chitin synthase (CHS) gene expression, increased Chs activity, elevated chitin content and reduced efficacy of these drugs. Elevation of chitin synthesis was mediated via the PKC, HOG, and Ca2+-calcineurin signalling pathways. Stimulation of Chs2p and Chs8p by activators of these pathways enabled cells to survive otherwise lethal concentrations of echinocandins, even in the absence of Chs3p and the normally essential Chs1p, which synthesize the chitinous septal ring and primary septum of the fungus. Under such conditions, a novel proximally offset septum was synthesized that restored the capacity for cell division, sustained the viability of the cell, and abrogated morphological and growth defects associated with echinocandin treatment and the chs mutations. These findings anticipate potential resistance mechanisms to echinocandins. However, echinocandins and chitin synthase inhibitors synergized strongly, highlighting the potential for combination therapies with greatly enhanced cidal activity.

The outer layer of the Candida albicans cell wall is enriched in highly glycosylated proteins. The major class, the GlycosylPhosphatidylInositol (GPI)-anchored proteins are tethered to the wall by GPI-anchor remnants and include adhesins, glycosyltransferases, yapsins and superoxide dismutases. In silico analysis suggested that C. albicans possesses 115 putative GPI anchored proteins (GpiPs), almost twice the number reported for Saccharomyces cerevisiae. A global approach to characterise in silico predicted GpiPs has been initiated by generating a library of 45 mutants. This library was subjected to a screen for cell wall modifications by testing the cell wall integrity (SDS and Calcofluor White sensitivity) and response to caspofungin. We showed that, when caspofungin sensitivity was modified, in more than half of the cases the susceptibility can be correlated to the level of chitin and cell wall thickness: sensitive strains have low level of chitin and a thin cell wall. We also identified, for the first time, genes that when deleted lead to decreased caspofungin sensitivity: DFG5, PHR1, PGA4 and PGA62. The role of two unknown GpiPs, Pga31 and Pga62 in the cell wall structure and composition was clearly demonstrated during this study.

Nitrogen-containing bisphosphonate drugs inhibit bone resorption by inhibiting FPP synthase and thereby preventing the synthesis of isoprenoid lipids required for protein prenylation in bone-resorbing osteoclasts. NE10790 is a phosphonocarboxylate analogue of the potent bisphosphonate risedronate and is a weak antiresorptive agent. Although NE10790 was a poor inhibitor of FPP synthase, it did inhibit prenylation in J774 macrophages and osteoclasts, but only of proteins of molecular mass ϳ22-26 kDa, the prenylation of which was not affected by peptidomimetic inhibitors of either farnesyl transferase (FTI-277) or geranylgeranyl transferase I (GGTI-298). These 22-26-kDa proteins were shown to be geranylgeranylated by labelling J774 cells with [ 3 H]geranylgeraniol. Furthermore, NE10790 inhibited incorporation of [ 14 C]mevalonic acid into Rab6, but not into H-Ras or Rap1, proteins that are modified by FTase and GGTase I, respectively. These data demonstrate that NE10790 selectively prevents Rab prenylation in intact cells. In accord, NE10790 inhibited the activity of recombinant Rab GGTase in vitro, but did not affect the activity of recombinant FTase or GGTase I. NE10790 therefore appears to be the first specific inhibitor of Rab GGTase to be identified. In contrast to risedronate, NE10790 inhibited bone resorption in vitro without markedly affecting osteoclast number or the F-actin "ring" structure in polarized osteoclasts. However, NE10790 did alter osteoclast morphology, causing the formation of large intracellular vacuoles and protrusion of the basolateral membrane into large, "domed" structures that lacked microvilli. The anti-resorptive activity of NE10790 is thus likely due to disruption of Rabdependent intracellular membrane trafficking in osteoclasts.

The pro-apoptotic protein Bax plays a key role in the mitochondrial signalling pathway. Upon induction of apoptosis, Bax undergoes a conformational change and translocates to mitochondrial membranes, where it inserts and mediates the release of cytochrome c from the intermembrane space into the cytosol. However, the domains of Bax that are essential for the induction of cytochrome c release are still elusive. Therefore various Bax deletion mutants were generated and expressed in Escherichia coli. The proteins were then purified in order to delineate the function of the transmembrane domain, the BH3 (Bcl-2 homology 3) domain and the putative pore-forming alpha-helices-5 and -6. These proteins were used to analyse the mechanism of Bax-induced cytochrome c release from mitochondria. None of the Bax proteins caused cytochrome c release merely through physical perturbation of the mitochondrial outer membrane. The alpha-helices-5 and -6 of Bax were shown to mediate the insertion of the protein into mitochondrial membranes and to be essential for the cytochrome c -releasing activity of Bax. In contrast, neither the transmembrane domain nor a functional BH3 domain is required for the Bax-mediated release of cytochrome c from mitochondria.

Experimental autoimmune uveoretinitis (EAU)'2 is an established model for human endogenous posterior uveitides, the study of which has led to a greater understanding of the underlying immunopathogenesis ofthis group of conditions.5 EAU is a CD4+ T-lymphocyte mediated disease which can be induced by at least two soluble retinal antigens (S-Ag) and interphotoreceptor retinol binding protein (IRBP), both of which have several uveitogenic epitopes.6-8 The S-Ag induced EAU model is of particular interest as patients demonstrate abnormal in vitro T-cell proliferative responses to S-Ag and its peptide fragments,9 although humoral antibody titres to S-Ag occur in both patients and normal subjects.'0 EAU has proved to be an extremely valuable model for preclinical trials of immunosuppressive therapy as has been shown with cyclosporin A" and with several antigen-specific and immunospecific targeted therapies such as anti-S Ag antibody therapy,'2-'4 anti-Ia antibodies,'5 and antigen coupled splenocyte transfer. 16 Recently, tolerance (immune unresponsiveness) to S-Ag induced EAU has been achieved in susceptible animals by oral administration of milligram quantities of S-Ag.'7 Oral feeding of specific immunopathogenic antigens suppresses successfully the inflammatory response in many other models of autoimmune diseases'8 and the mechanism of 'oral tolerance' is mediated by CD8+ T-lymphocytes. ' ANTIGENSSoluble bovine retinal extract (RE) was prepared by hypotonic lysis of the retina in the dark into 0-02% TRIS-HCI pH 8-0, followed by ultracentrifugation at 25 000 rpm for 15 hours at 4°C and was dialysed against phosphate buffered saline (PBS) over 24 hours. Bovine S-Ag was prepared by HPLC on a TSK-DEAE column as previously described'4 or by affinity column extraction. The S-Ag by both methods was homogeneous by silver staining on SDS polyacrylamide gel using Pharmacia Phast System, according to the manufacturer's instructions. The protein concentration of RE used in the experiments ranged from 5-7 mg/ml and S-Ag