Objective: Interactions between Candida albicans and mammalian phagocytes is a key determinant of disease initiation and progression whose investigation has proven to be a valuable experimental tool to uncover key virulence traits. To gain further insights into the fungal response to phagocytosis, we used RNA-sequencing to characterize the transcriptome of C. albicans after phagocytosis by murine bone marrow-derived macrophages. Methods: These data confirmed earlier observations of a significant reorganization of carbon metabolism, downregulation of translation and cell cycle progression, and induction of responses to oxidative and nitrosative stresses and DNA damage repair. Beyond these changes, though, nearly half of all upregulated transcripts are uncharacterized. Included in this listwe found a surprising number of newly annotated genes that encode proteins of less than 100 amino acids. Such small proteins are often important as secreted mediators of host-pathogen interactions, and therefore we have begun a genetic analysis of these upregulated small ORFs (SMA1 through SMA13). Results: One of these, Sma12, is a 71aa, serine/threonine rich protein that was newly annotated in Assembly 22 based on conservation in other Candida spp. SMA12 has been shown in previously published transcriptional profiling experiments to be upregulated in response to serum and the FungalRV algorithm predicts it to be an adhesin. While Sma12 does not have a signal sequence, it is indeed a functional microadhesin necessary for robust adhesion to polystyrene surfaces and mammalian cells. Heterologous expression of SMA12 in Saccharomyces cerevisiae increases adhesion to polystyrene, suggesting the mechanism by which it promotes adhesion is conserved. Importantly, the sma12 mutant is deficient in survival upon co-incubation with macrophages, indicating that this small protein is critical for interactions with phagocytes. Conclusion: Current studies aim to understand the role of this microadhesin in mammalian infection models and to determine the subcellular localization using immunohistochemistry and an epitope-tagged variant of Sma12. Additionally, initial characterizations of a second small putative adhesin, Sma5, are currently in progress. Two additional small ORFs, SMA6 and SMA13 have antioxidant properties and are also required for survival in macrophages, demonstrating that these newly identified genes are significant mediators of host-pathogen interactions.
Full conference title:
- ISHAM 20th (2018)