Growth of Candida species in cultures of mouse epithelial cells

Structural insights into transcriptional regulation of human RNA polymerase III

RNA polymerase III (Pol III) synthesizes structured, essential small RNAs, such as transfer RNA, 5S ribosomal RNA and U6 small nuclear RNA. Pol III, the largest nuclear RNA polymerase, is composed of a conserved core region and eight constitutive regulatory subunits, but how these factors jointly regulate Pol III transcription remains unclear. Here, we present cryo-EM structures of human Pol III in both apo and elongating states, which unveil both an orchestrated movement during the apo-to-elongating transition and an unexpected apo state in which the RPC7 subunit tail occupies the DNA-RNA-binding cleft of Pol III, suggesting that RPC7 plays important roles in both autoinhibition and transcription initiation. The structures also reveal a proofreading mechanism for the TFIIS-like subunit RPC10, which stably retains its catalytic position in the secondary channel, explaining the high fidelity of Pol III transcription. Our work provides an integrated picture of the mechanism of Pol III transcription regulation.

Macrophages in resistance to candidiasis

Candida albicans, an increasingly common opportunistic pathogenic fungus, frequently causes disease in immunodeficient but not immunocompetent hosts. Clarifying the role of the phagocytic cells that participate in resistance to candidiasis not only is basic to understanding how the host copes with this dimorphic pathogen but also will expedite the development of innovative prophylactic and therapeutic approaches for treating the multiple clinical presentations that candidiasis encompasses. In this review, we present evidence that a diverse population of mononuclear phagocytes, in different states of activation and differentiation and from a variety of host species, can phagocytize C. albicans blastoconidia via an array of opsonic and nonopsonic mechanisms and can kill C. albicans blastoconidia and hyphae by means of oxygen-dependent and -independent mechanisms. Reactive nitrogen intermediates should now be added to the well-established candidacidal reactive oxygen intermediates of macrophages. Furthermore, what were thought to be two independent pathways, i.e., nitric oxide and superoxide anion, have now been shown to combine to form a potent macrophage candidacidal molecule, peroxynitrite. In contrast to monocytes and neutrophils, which are important in resistance to early stages of C. albicans infections, more differentiated macrophages activated by cytokines such as gamma interferon participate in the acquired resistance of hosts with C. albicans-specific, cell-mediated immunity. Evidence presented in this review demonstrates that mononuclear phagocytes, in some instances in the absence of other professional phagocytes such as neutrophils, play an import role in resistance to systemic and mucosal candidiasis.

Factors influencing the interaction of Candida albicans with fibroblast cell cultures

The interaction of Candida albicans clinical isolates with primary and established fibroblast cultures was studied. The intent was to determine whether yeast adherence and invasion of nonendothelial cell monolayer cultures could be quantitated reproducibly and whether this system could be used for future studies on yeast pathogenesis. Our results demonstrated that specific interactions between the yeast cells and fibroblasts only occurred at 37 degrees C and correlated with the germination process. Fluorescent-antibody staining indicated that invasion or tight associations between the germinating yeast cells and mammalian cells occurred after less than 3 h of incubation. Yeast adherence was estimated radiometrically and trypsin-resistant interaction with individual mammalian cells (infection) was measured microscopically after inoculated monolayer cells were detached with trypsin. We demonstrated that both types of association were time dependent at 37 degrees C; neither was affected by the concentration of glucose used to grow the yeast cells. Primary and established fibroblast cell lines were equally susceptible to infection, but primary cells appeared to have more yeast-binding sites. Fibroblasts maintained in confluent culture for an extended period of time also appeared to have more binding sites, and while not quantitatively more susceptible to infection, the older cells were more susceptible to infection-related cell death. An established kidney epithelial cell line (MDCK) was not susceptible to either type of yeast interaction, indicating that the yeast-fibroblast associations were specific.

In vitro determination of phagocytic indices of Candida berkhout species by rat peritoneal macrophages

The aims of this investigation were to study and describe the behaviour of 13 different species of Candida, as compared with C. albicans, by means of phagocytosis assays in vitro. Tests were carried out with rat peritoneal macrophages in contact with quantified suspensions of live yeasts. Phagocytic indices, candidacidal activity and filamentation rat were tested microscopically after 3 h incubation at 37 degrees C. The phagocytic indices obtained allowed us to separate the fungi into four groups. Candida albicans and tropicalis belong to Group I; diddensii and shehatae, among others, belong to Group II; sake, krusei, viswanathii, etc., Group III; and C. glaebosa and haploid strains of Pichia ohmeri (C. guilliermondii var. membranaefaciens), Group IV. These data would suggest a possible correlation between pathogenesis and phagocytic indices. There were no evidences of any phagocytes ability to kill yeasts. Candidacidal activity was absent in the species assayed. Yeast lysis may have been observed if our assays would have taken longer than 3 h.

Factors affecting filamentation in Candida albicans: changes in respiratory activity of Candida albicans during filamentation

Glucose metabolism and respiration of Candida albicans were compared under conditions which permitted either maximal filamentous or maximal yeast growth. Changes in metabolism were monitored by comparing the quantities of ethanol produced, CO2 evolved, and oxygen consumed. Filamenting cultures produced more ethanol and less CO2 than yeasts, with oxygen consumption in the former concomitantly slower than that of the latter. Studies involving cofactors and inhibitors associated with electron transport imply that a transfer of electrons away from flavoprotein is required for maintenance of yeast morphology. Conditions consistent with a buildup of reduced flavoprotein, however, favored filament formation. These changes were expressed metabolically as a shift from an aerobic to a fermentative metabolism. The results presented are consistent with hypotheses correlating filament production with changes in carbohydrate metabolism and an interruption of electron transfer within the cell.

Chick embryo inoculation as a pathogenicity test for Candida species

The lesions produced by six Candida species on the chorioallantoic membrane (CAM) of the developing chick are described and compared. It is suggested that CAM inoculation be used as a pathogenicity test for Candida species.