Role of homologous recombination genesRAD51,RAD52, andRAD59in the repair of lesions caused by γ-radiation to cycling and G2/M-arrested cells ofCandida albicans

Transcriptome analysis reveals diverse Curvularia tsudae strategies in response to cadmium stress

Cadmium (Cd) is a highly toxic heavy metal that poses significant threats to living organisms. Curvularia tsudae has demonstrated remarkable survival capabilities in the presence of high Cd concentrations, exhibiting its exceptional Cd tolerance. Although some physiological studies have been conducted, the molecular mechanisms underlying Cd tolerance in C. tsudae is largely unknown. In this study, a comparative transcriptome analysis was performed to explore the molecular mechanisms of C. tsudae under Cd stress. Among the 10,498 identified unigenes, 2526 differentially expressed genes (DEGs) were identified between the Cd-free and Cd-treated samples. Functional annotation and enrichment analysis of these DEGs identified several key biological processes involved in coping with Cd stress. Genes related to cell wall modification and organic acid metabolism contributes to Cd binding or chelation. Fourier transform infrared spectroscopy (FTIR) analysis further highlighted the modifications in functional groups with the cell wall under Cd stress. Furthermore, the transporters tended to be modulated in response to Cd stress, and up-regulated genes involved in antioxidants likely contributes to high Cd tolerance. The processes from DNA to protein metabolism appeared to responsive to the presence of Cd stress as well. These results contribute to the advance of the current knowledge about the response of C. tsudae to Cd stress and lay the foundation for further advancements in using fungi for the remediation of Cd-polluted environments.

Heterologous Single-Strand DNA-Annealing and Binding Protein Enhance CRISPR-Based Genome Editing Efficiency in Komagataella phaffii

The industrial yeast Komagataella phaffii is a highly effective platform for heterologous protein production, owing to its high protein expression and secretion capacity. Heterologous genes and proteins are involved in multiple processes, including transcription, translation, protein folding, modification, transportation, and degradation; however, engineering these proteins and genes is challenging due to inefficient genome editing techniques. We employed Pseudomonas aeruginosa phage single-stranded DNA-annealing protein (SSAP) PapRecT and P. aeruginosa single-stranded DNA-binding protein (SSB) PaSSB to introduce SSAP-SSB-based homology recombination, which facilitated K. phaffii CRISPR-based genome engineering. Specifically, a host-independent method was developed by expressing sgRNA with PapRecT-PaSSB in a single plasmid, with which only a 50 bp short homologous arm (HA) reached a 100% positive rate for CRISPR-based gene insertion, reaching 18 colony-forming units (CFU) per μg of donor DNA. Single deletion using 1000 bp HA attained 100%, reaching 68 CFUs per μg of donor DNA. Using this efficient CRISPR-based genome editing tool, we integrated three genes (INO4, GAL4-like, and PAB1) at three different loci for overexpression to realize the collaborative regulation of human-lactalbumin (α-LA) production. Specifically, we strengthened phospholipid biosynthesis to facilitate endoplasmic reticulum membrane formation and enhanced recombinant protein transcription and translation by overexpressing transcription and translation factors. The final production of α-LA in the 3 L fermentation reached 113.4 mg L-1, two times higher than that of the strain without multiple site gene editing, which is the highest reported titer in K. phaffii. The CRISPR-based genome editing method developed in this study is suitable for the synergistic multiple-site engineering of protein and biochemical biosynthesis pathways to improve the biomanufacturing efficiency.

RAD51-WSS1-dependent genetic pathways are essential for DNA-Protein crosslink repair and pathogenesis in Candida albicans

Genetic analyses in Saccharomyces cerevisiae suggest that nucleotide excision repair (NER), homologous recombination (HR), and proteases-dependent repair (PDR) pathways coordinately function to remove DNA-protein crosslinks (DPCs) from the genome. DPCs are genomic cytotoxic lesions generated due to the covalent linkage of proteins with DNA. Although NER and HR processes have been studied in pathogenic Candida albicans, their roles in DPCs repair (DPCR) are yet to be explored. Proteases like Wss1 and Tdp1 are known to be involved in DPCR, however, Tdp1 that selectively removes topoisomerase-DNA complexes is intrinsically absent in C. albicans. Therefore, the mechanism of DPCR might have evolved differently in C. albicans. Herein, we investigated the interplay of three genetic pathways and found that RAD51-WSS1 dependent HR and PDR pathways are essential for DPCs removal, and their absence caused an increased rate of loss of heterozygosity in C. albicans. RAD1 but not RAD2 of NER is critical for DPCR. Additionally, we observed truncation of chromosome#6 in the cells defective in both RAD51 and WSS1 genes. While the protease and DNA binding activities are essential, a direct interaction of Wss1 with the eukaryotic DNA clamp PCNA is not a requisite for Wss1's function. DPCR-defective C. albicans cells exhibited filamentous morphology, reduced immune cell evasion, and attenuation in virulence. Thus, we concluded that RAD51-WSS1-dependent DPCR pathways are essential for genome stability and candidiasis development. Since no vaccine against candidiasis is available for human use yet, we propose to explore DPCR defective attenuated strains (rad51ΔΔwss1ΔΔ and rad2ΔΔrad51ΔΔwss1ΔΔ) for whole-cell vaccine development.

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

The infection of a mammalian host by the pathogenic fungus Candida albicans involves fungal resistance to reactive oxygen species (ROS)—induced DNA damage stress generated by the defending macrophages or neutrophils. Thus, the DNA damage response in C. albicans may contribute to its pathogenicity. Uncovering the transcriptional changes triggered by the DNA damage—inducing agent MMS in many model organisms has enhanced the understanding of their DNA damage response processes. However, the transcriptional regulation triggered by MMS remains unclear in C. albicans. Here, we explored the global transcription profile in response to MMS in C. albicans and identified 306 defined genes whose transcription was significantly affected by MMS. Only a few MMS-responsive genes, such as MGT1, DDR48, MAG1, and RAD7, showed potential roles in DNA repair. GO term analysis revealed that a large number of induced genes were involved in antioxidation responses, and some downregulated genes were involved in nucleosome packing and IMP biosynthesis. Nevertheless, phenotypic assays revealed that MMS-induced antioxidation gene CAP1 and glutathione metabolism genes GST2 and GST3 showed no direct roles in MMS resistance. Furthermore, the altered transcription of several MMS—responsive genes exhibited RAD53—related regulation. Intriguingly, the transcription profile in response to MMS in C. albicans shared a limited similarity with the pattern in S. cerevisiae, including COX17, PRI2, and MGT1. Overall, C. albicans cells exhibit global transcriptional changes to the DNA damage agent MMS; these findings improve our understanding of this pathogen’s DNA damage response pathways.

A trifunctional Pt(II) complex alleviates the NHEJ/HR-related DSBs repairs to evade cisplatin-resistance in NSCLC

Cisplatin, a representative of platinum-based drug, is clinically and widely used in the treatment of various types of malignant cancer. However, its non-selectivity to almost all the cell lines and resistance in long-term use severely limit its scope of use. As biotin-specific uptake systems are overexpressed in many types of tumors but rarely occur in normal tissues, making biotin a promising target for cancer treatment. In the study, we synthesized the Pt(II) complex C2 and determined its biological activities. The existence of biotin enhanced the ability of the complex to target tumors, while the introduction of a naphthalimide compound makes it possible to diagnose tumors and monitor their progress. We have also introduced a known Pt(II) complex DN604, which not only retains the excellent cytotoxicity of platinum drugs, but also inhibits the expression of DNA double-strand breaks (DSBs) repair-related NHEJ protein Ku70 and HR protein Rad51. In summary, we report a novel trifunctional Pt(II) complex that could target tumor cells, monitor tumor progression, and reverse DSBs repair-induced cisplatin-resistance.