Transcriptional Profiling of the Candida albicans Response to the DNA Damage Agent Methyl Methanesulfonate

Antifungal effects of Metformin against Candida albicans by autophagy regulation

Candida albicans (C. albicans) is a common opportunistic fungal pathogen that can cause infections ranging from superficial to severe systemic diseases. This study investigates the antifungal effects of metformin on C. albicans and explores its underlying mechanisms. Growth inhibition was assessed via XTT assays, and hyphal formation and morphological changes were observed by light microscope and scanning electron microscopy (SEM). Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) levels were measured with JC-1 and DCFH-DA probes, respectively. Gene expression related to ROS and autophagy was quantified by RT-qPCR, and autophagosomes were visualized using transmission electron microscopy (TEM). Metformin significantly inhibited C. albicans growth and hyphal formation, altered cell morphology, reduced MMP, and increased ROS levels. It activated autophagy in planktonic C. albicans but suppressed it in biofilm forms. Additionally, metformin exhibited synergistic effects with amphotericin B against planktonic C. albicans and with caspofungin against biofilms. The findings suggest that metformin exerts antifungal activity by modulating MMP, ROS levels, and autophagy-related pathways, and enhances the efficacy of specific antifungal drugs.

DNA damage repair factor Rad18 controls virulence partially via transcriptional suppression of genes HWP1 and ECE1 in Candida albicans

DNA damage repair is a crucial cellular mechanism for rectifying DNA lesions arising during growth and development. Among the various repair pathways, postreplication repair (PRR) plays a pivotal role in resolving single-stranded gaps induced by DNA damage. However, the contribution of PRR to virulence remains elusive in the fungal pathogen Candida albicans (C. albicans). In this study, we investigated the role of Rad18, a critical component of PRR, in DNA damage response and virulence in C. albicans. We observed that deletion of RAD18 in C. albicans resulted in heightened sensitivity to DNA damage stress. Through deletion of specific internal domains coupled with spot assay analysis, we show that the internal RING and SAP domains play essential roles in DNA damage response, whereas the ZNF domain was less important. Surprisingly, the lack of Rad18 in C. albicans resulted in heightened intracellular survival within macrophages and elevated virulence in the Galleria mellonella model. RNAseq analysis revealed that loss of Rad18 upregulated the transcription of genes encoding transporters and oxidoreductases, as well as virulence genes, including HWP1 and ECE1. Suppression of the transcription of these virulence genes in the RAD18 deletion strain by a dCas9-mediated CRISPRi system reversed this increased virulence. Taken together, these data demonstrate that Rad18 plays a significant role in virulence partially through transcriptional suppression of virulence genes HWP1 and ECE1 in C. albicans. Our findings provide valuable insights into the intricate relationship between DNA damage response and virulence in C. albicans.

Loss of Gst1 enhances resistance to MMS by reprogramming the transcription of DNA damage response genes in a Rad53-dependent manner in Candida albicans

The DNA damage response is a highly conserved protective mechanism that enables cells to cope with various lesions in the genome. Extensive studies across different eukaryotic cells have identified the crucial roles played by components required for response to DNA damage. When compared to the essential signal transducers and repair factors in the DNA damage response circuitry, the negative regulators and underlying mechanisms of this circuitry have been relatively under-examined. In this study, we investigated Gst1, a putative glutathione transferase in the fungal pathogen Candida albicans. We found that under stress caused by the DNA damage agent MMS, GST1 expression was significantly upregulated, and this upregulation was further enhanced by the loss of the checkpoint kinases and DNA repair factors. Somewhat counterintuitively, deletion of GST1 conferred increased resistance to MMS, potentially via enhancing the phosphorylation of Rad53. Furthermore, overexpression of RAD53 or deletion of GST1 resulted in upregulated transcription of DNA damage repair genes, including CAS1, RAD7, and RAD30, while repression of RAD7 transcription in the GST1 deletion reversed the strain's heightened resistance to MMS. Finally, Gst1 physically interacted with Rad53, and their interaction weakened in response to MMS-induced stress. Overall, our findings suggest a negative regulatory role for GST1 in DNA damage response in C. albicans, and position Gst1 within the Rad53-mediated signaling pathway. These findings hold significant implications for understanding the mechanisms underlying the DNA damage response in this fungal pathogen and supply new potential targets for therapeutic intervention.

Analysis of transcriptional response in haploid and diploid Schizosaccharomyces pombe under genotoxic stress

Whole genome duplications are implicated in genome instability and tumorigenesis. Human and yeast polyploids exhibit increased replication stress and chromosomal instability, both hallmarks of cancer. In this study, we investigate the transcriptional response of Schizosaccharomyces pombe to increased ploidy generally, and in response to treatment with the genotoxin methyl methanesulfonate (MMS). We find that treatment of MMS induces upregulation of genes involved in general response to genotoxins, in addition to cell cycle regulatory genes. Downregulated genes are enriched in transport and sexual reproductive pathways. We find that the diploid response to MMS is muted compared to the haploid response, although the enriched pathways remain largely the same. Overall, our data suggests that the global S. pombe transcriptome doubles in response to increased ploidy but undergoes modest transcriptional changes in both unperturbed and genotoxic stress conditions.

DNA Damage Checkpoints Govern Global Gene Transcription and Exhibit Species-Specific Regulation on HOF1 in Candida albicans

DNA damage checkpoints are essential for coordinating cell cycle arrest and gene transcription during DNA damage response. Exploring the targets of checkpoint kinases in Saccharomyces cerevisiae and other fungi has expanded our comprehension of the downstream pathways involved in DNA damage response. While the function of checkpoint kinases, specifically Rad53, is well documented in the fungal pathogen Candida albicans, their targets remain poorly understood. In this study, we explored the impact of deleting RAD53 on the global transcription profiles and observed alterations in genes associated with ribosome biogenesis, DNA replication, and cell cycle. However, the deletion of RAD53 only affected a limited number of known DNA damage-responsive genes, including MRV6 and HMX1. Unlike S. cerevisiae, the downregulation of HOF1 transcription in C. albicans under the influence of Methyl Methanesulfonate (MMS) did not depend on Dun1 but still relied on Rad53 and Rad9. In addition, the transcription factor Mcm1 was identified as a regulator of HOF1 transcription, with evidence of dynamic binding to its promoter region; however, this dynamic binding was interrupted following the deletion of RAD53. Furthermore, Rad53 was observed to directly interact with the promoter region of HOF1, thus suggesting a potential role in governing its transcription. Overall, checkpoints regulate global gene transcription in C. albicans and show species-specific regulation on HOF1; these discoveries improve our understanding of the signaling pathway related to checkpoints in this pathogen.

Discovery of New Antimicrobial Metabolites in the Coculture of Medicinal Mushrooms

Bioactivity screening revealed that the antifungal activities of EtOAc extracts from coculture broths of Trametes versicolor SY630 with either Vanderbylia robiniophila SY341 or Ganoderma gibbosum SY1001 were significantly improved compared to that of monocultures. Activity-guided isolation led to the discovery of five aromatic compounds (1-5) from the coculture broth of T. versicolor SY630 and V. robiniophila SY341 and two sphingolipids (6 and 7) from the coculture broth of T. versicolor SY630 and G. gibbosum SY1001. Tramevandins A-C (1-3) and 17-ene-1-deoxyPS (6) are new compounds, while 1-deoxyPS (7) is a new natural product. Notably, compound 2 represents a novel scaffold, wherein the highly modified p-terphenyl bears a benzyl substituent. The absolute configurations of those new compounds were elucidated by X-ray diffraction, ECD calculations, and analysis of physicochemical constants. Compounds 1, 2, and 5-7 exhibited different degrees of antimicrobial activity, and the antifungal activities of compounds 6 and 7 against Candida albicans and Cryptococcus neoformans are comparable to those of fluconazole, nystatin, and sphingosine, respectively. Transcriptome analysis, propidium iodide staining, ergosterol quantification, and feeding assays showed that the isolated sphingolipids can extensively downregulate the late biosynthetic pathway of ergosterol in C. albicans, representing a promising mechanism to combat antibiotic-resistant fungi.

Investigating the role of Candida albicans as a universal substrate for oral bacteria using a transcriptomic approach: implications for interkingdom biofilm control?

Candida albicans is frequently identified as a colonizer of the oral cavity in health and has recently been termed a "keystone" commensal due to its role on the bacterial communities. However, the role that C. albicans plays in such interactions is not fully understood. Therefore, this study aimed to identify the relationship between C. albicans and bacteria associated with oral symbiosis and dysbiosis. To do this, we evaluated the ability of C. albicans to support the growth of the aerobic commensal Streptococcus gordonii and the anaerobic pathogens Fusobacterium nucleatum and Porphyromonas gingivalis in the biofilm environment. RNA-Sequencing with the Illumina platform was then utilized to identify C. albicans gene expression and functional pathways involved during such interactions in dual-species and a 4-species biofilm model. Results indicated that C. albicans was capable of supporting growth of all three bacteria, with a significant increase in colony counts of each bacteria in the dual-species biofilm (p < 0.05). We identified specific functional enrichment of pathways in our 4-species community as well as transcriptional profiles unique to the F. nucleatum and S. gordonii dual-species biofilms, indicating a species-specific effect on C. albicans. Candida-related hemin acquisition and heat shock protein mediated processes were unique to the organism following co-culture with anaerobic and aerobic bacteria, respectively, suggestive that such pathways may be feasible options for therapeutic targeting to interfere with these fungal-bacterial interactions. Targeted antifungal therapy may be considered as an option for biofilm destabilization and treatment of complex communities. Moving forward, we propose that further studies must continue to investigate the role of this fungal organism in the context of the interkingdom nature of oral diseases.