To fight infections, macrophages undergo a metabolic shift whereby increased glycolysis fuels antimicrobial inflammation and killing of pathogens. Here we demonstrate that the pathogen Candida albicans turns this metabolic reprogramming into an Achilles' heel for macrophages. During Candida-macrophage interactions intertwined metabolic shifts occur, with concomitant upregulation of glycolysis in both host and pathogen setting up glucose competition. Candida thrives on multiple carbon sources, but infected macrophages are metabolically trapped in glycolysis and depend on glucose for viability: Candida exploits this limitation by depleting glucose, triggering rapid macrophage death. Using pharmacological or genetic means to modulate glucose metabolism of host and/or pathogen, we show that Candida infection perturbs host glucose homeostasis in the murine candidemia model and demonstrate that glucose supplementation improves host outcomes. Our results support the importance of maintaining glucose homeostasis for immune cell survival during Candida challenge and for host survival in systemic infection.

Organisms respond to environmental stress by adopting changes in gene expression at the transcriptional level. Rpb4, a nonessential subunit of the core RNA polymerase II has been proposed to play a role in nonstress-specific transcription and in the regulation of stress response in yeast. We find that in addition to the temperature sensitivity of the null mutant of Rpb4, diploid null mutants are also compromised in sporulation and show morphological changes associated with nitrogen starvation. Using whole genome expression analysis, we report here the effects of Rpb4 on expression of genes during normal growth and following heat shock and nutritional starvation. Our analysis shows that Rpb4 affects expression of a small yet significant fraction of the genome in both stress and normal conditions. We found that genes involved in galactose metabolism were dependent on the presence of Rpb4 irrespective of the environmental condition. Rpb4 was also found to affect the expression of several other genes specifically in conditions of nutritional starvation. The general defect in the absence of Rpb4 is in the expression of metabolic genes, especially those involved in carbon metabolism and energy generation. We report that various stresses are affected by RPB4 and that on overexpression the stress-specific activators can partially rescue the corresponding defects.

Wolbachia is currently being developed as a novel tool to block the transmission of dengue viruses (DENV) by Aedes aegypti. A number of mechanisms have been proposed to explain the DENV-blocking phenotype in mosquitoes, including competition for fatty acids like cholesterol, manipulation of host miRNAs and upregulation of innate immune pathways in the mosquito. We examined the various stages in the DENV infection process to better understand the mechanism of Wolbachia-mediated virus blocking (WMVB). Our results suggest that infection with Wolbachia does not inhibit DENV binding or cell entry, but reduces virus replication. In contrast to a previous report, we also observed a similar reduction in replication of West Nile virus (WNV). This reduced replication is associated with rapid viral RNA degradation in the cytoplasm. We didn’t find a role for host miRNAs in WMVB. Further analysis showed that the 3’ end of the virus subgenomic RNA was protected and accumulated over time suggesting that the degradation is XRN1-mediated. We also found that sub genomic flavivirus RNA accumulation inactivated XRN1 in mosquito cells in the absence of Wolbachia and led to enhancement of RNA degradation in its presence. Depletion of XRN1 decreased WMVB which was associated with a significant increase in DENV RNA. We also observed that WMVB is influenced by virus MOI and rate of virus replication. A comparatively elevated blocking was observed for slowly replicating DENV, compared to WNV. Similar results were obtained while analysing different DENV serotypes.

The NLRP3 inflammasome has emerged as a central immune regulator that senses virulence factors expressed by microbial pathogens for triggering inflammation. Inflammation can be harmful and therefore this response must be tightly controlled. The mechanisms by which immune cells, such as macrophages, discriminate benign from pathogenic microbes to control the NLRP3 inflammasome remain poorly defined. Here we used live cell imaging coupled with a compendium of diverse clinical isolates to define how macrophages respond and activate NLRP3 when faced with the human yeast commensal and pathogen Candida albicans. We show that metabolic competition by C. albicans, rather than virulence traits such as hyphal formation, activates NLRP3 in macrophages. Inflammasome activation is triggered by glucose starvation in macrophages, which occurs when fungal load increases sufficiently to outcompete macrophages for glucose. Consistently, reducing Candida's ability to compete for glucose and increasing glucose availability for macrophages tames inflammatory responses. We define the mechanistic requirements for glucose starvationdependent inflammasome activation by Candida and show that it leads to inflammatory cytokine production, but it does not trigger pyroptotic macrophage death. Pyroptosis occurs only with some Candida isolates and only under specific experimental conditions, whereas inflammasome activation by glucose starvation is broadly relevant. In conclusion, macrophages use their metabolic status, specifically glucose metabolism, to sense fungal metabolic activity and activate NLRP3 when microbial load increases. Therefore, a major consequence of Candida-induced glucose starvation in macrophages is activation of inflammatory responses, with implications for understanding how metabolism modulates inflammation in fungal infections.

Highlights d Metabolism and stress responses control histone crotonylation in Candida albicans d The YEATS crotonylation readers Taf14 and Yaf9 are important for Candida virulence d Taf14 participates in stress responses, cell wall, and filamentation pathways d The SCFA crotonate affects transcription and stress susceptibility in Candida

The holoenzyme of prokaryotic RNA polymerase consists of the core enzyme, made of two alpha, beta, beta' and omega subunits, which lacks promoter selectivity and a sigma (sigma) subunit which enables the core enzyme to initiate transcription in a promoter dependent fashion. A stress sigma factor sigma(s), in prokaryotes seems to regulate several stress response genes in conjunction with other stress specific regulators. Since the basic principles of transcription are conserved from simple bacteria to multicellular complex organisms, an obvious question is: what is the identity of a counterpart of sigma(s), that is closest to the core polymerase and that dictates transcription of stress regulated genes in general? In this review, we discuss the logic behind the suggestion that like in prokaryotes,eukaryotes also have a common functional unit in the transcription machinery through which the stress specific transcription factors regulate rapid and highly controlled induction of gene expression associated with generalized stress response and point to some candidates that would fit the bill of the eukaryotic sigma(s).

Regulation of gene expression programs is crucial for the survival of microbial pathogens in host environments and for their ability to cause disease. Here we investigated the epigenetic regulator RSC (Remodels the Structure of Chromatin) in the most prevalent human fungal pathogen Candida albicans. Biochemical analysis showed that CaRSC comprises 13 subunits and contains two novel non-essential members, which we named Nri1 and Nri2 (Novel RSC Interactors) that are exclusive to the CTG clade of Saccharomycotina. Genetic analysis showed distinct essentiality of C. albicans RSC subunits compared to model fungal species suggesting functional and structural divergence of RSC functions in this fungal pathogen. Transcriptomic and proteomic profiling of a conditional mutant of the essential catalytic subunit gene STH1 demonstrated global roles of RSC in C. albicans biology, with the majority of growth-related processes affected, as well as mis-regulation of genes involved in morphotype switching, host-pathogen interaction and adaptive fitness. We further assessed the functions of non-essential CaRSC subunits, showing that the novel subunit Nri1 and the bromodomain subunit Rsc4 play roles in filamentation and stress responses; and also interacted at the genetic level to regulate cell viability. Consistent with these roles, Rsc4 is required for full virulence of C. albicans in the murine model of systemic infection. Taken together, our data builds the first comprehensive study of the composition and roles of RSC in C. albicans, showing both conserved and distinct features compared to model fungal systems. The study illuminates how C. albicans uses RSC-dependent transcriptional regulation to respond to environmental signals and drive survival fitness and virulence in mammals.

No abstract