BOB.1 controls memory B-cell fate in the germinal center reaction.

During T cell-dependent (TD) germinal center (GC) responses, naïve B cells are instructed to differentiate towards GC B cells (GCBC), high-affinity long-lived plasma cells (LLPC) or memory B cells (Bmem). Alterations in the B cell-fate choice could contribute to immune dysregulation leading to the loss of self-tolerance and the initiation of autoimmune disease. Here we show that mRNA levels of the transcription regulator BOB.1 are increased in the lymph node compartment of patients with rheumatoid arthritis (RA), a prototypical autoimmune disease caused by the loss of immunological tolerance. Investigating to what extent levels of BOB.1 impact B cells during TD immune responses we found that BOB.1 has a crucial role in determining the B cell-fate decision. High BOB.1 levels promote the generation of cells with phenotypic and functional characteristics of Bmem. Mechanistically, overexpression of BOB.1 drives ABF1 and suppresses BCL6, favouring Bmem over LLPC or recycling GCBC. Low levels of BOB.1 are sufficient for LLPC but not for Bmem differentiation. Our findings demonstrate a novel role for BOB.1 in B cells during TD GC responses and suggest that its dysregulation may contribute to the pathogenesis of RA by disturbing the B cell-fate determination.

Activation-induced colocalisation of SCAMP5 with IFNα in human plasmacytoid dendritic cells.

INTRODUCTION: Plasmacytoid dendritic cells (pDCs) are the main producers of type I interferon (IFN) in SLE. pDCs express high secretory carrier membrane protein 5 (SCAMP5). Recent work in transfected HEK cells connects SCAMP5 to the type I IFN secretory pathway. To further study the role of SCAMP5 in IFNα secretion by pDCs, we focused on the subcellular distribution of SCAMP5 in human pDCs freshly isolated from peripheral blood. METHODS: We measured SCAMP5 expression by flow cytometry in peripheral blood mononuclear cells of healthy subjects (n=8). Next, we assessed the colocalisation of SCAMP5 with IFNα in pDCs of healthy subjects (n=4) by evaluating bright detail similarity (BDS) scores using ImageStream technology. RESULTS: We confirm that SCAMP5 is highly expressed by pDCs derived from peripheral blood. In activated pDCs, we show that SCAMP5 colocalises with IFNα (mean BDS 2.0±0.1; BDS >2.0 in 44% of pDCs). CONCLUSION: SCAMP5 colocalises with IFNα in activated human pDCs, in support of a role of this trafficking protein in the secretion of type I IFN by pDCs.

A yeast FRET biosensor enlightens cAMP signaling.

The cAMP-PKA signaling cascade in budding yeast regulates adaptation to changing environments. We developed yEPAC, a FRET-based biosensor for cAMP measurements in yeast. We used this sensor with flow cytometry for high-throughput single cell-level quantification during dynamic changes in response to sudden nutrient transitions. We found that the characteristic cAMP peak differentiates between different carbon source transitions and is rather homogenous among single cells, especially for transitions to glucose. The peaks are mediated by a combination of extracellular sensing and intracellular metabolism. Moreover, the cAMP peak follows the Weber-Fechner law; its height scales with the relative, and not the absolute, change in glucose. Last, our results suggest that the cAMP peak height conveys information about prospective growth rates. In conclusion, our yEPAC-sensor makes possible new avenues for understanding yeast physiology, signaling, and metabolic adaptation.

Lost in transition: start-up of glycolysis yields subpopulations of nongrowing cells.

Cells need to adapt to dynamic environments. Yeast that fail to cope with dynamic changes in the abundance of glucose can undergo growth arrest. We show that this failure is caused by imbalanced reactions in glycolysis, the essential pathway in energy metabolism in most organisms. The imbalance arises largely from the fundamental design of glycolysis, making this state of glycolysis a generic risk. Cells with unbalanced glycolysis coexisted with vital cells. Spontaneous, nongenetic metabolic variability among individual cells determines which state is reached and, consequently, which cells survive. Transient ATP (adenosine 5'-triphosphate) hydrolysis through futile cycling reduces the probability of reaching the imbalanced state. Our results reveal dynamic behavior of glycolysis and indicate that cell fate can be determined by heterogeneity purely at the metabolic level.

Fatal attraction in glycolysis: how Saccharomyces cerevisiae manages sudden transitions to high glucose.

In the model eukaryote Saccharomyces cerevisiae, it has long been known that a functional trehalose pathway is indispensable for transitions to high glucose conditions. Upon addition of glucose, cells with a defect in trehalose 6-phosphate synthase (Tps1), the first committed step in the trehalose pathway, display what we have termed an imbalanced glycolytic state; in this state the flux through the upper part of glycolysis outpaces that through the lower part of glycolysis. As a consequence, the intermediate fructose 1,6-bisphosphate (FBP) accumulates at low concentrations of ATP and inorganic phosphate (Pi). Despite significant research efforts, a satisfactory understanding of the regulatory role that trehalose metabolism plays during such transitions has remained infamously unresolved. In a recent study, we demonstrate that the startup of glycolysis exhibits two dynamic fates: a proper, functional, steady state or the imbalanced state described above. Both states are stable, attracting states, and the probability distribution of initial states determines the fate of a yeast cell exposed to glucose. Trehalose metabolism steers the dynamics of glycolysis towards the proper functional state through its ATP hydrolysis activity; a mechanism that ensures that the demand and supply of ATP is balanced with Pi availability under dynamic conditions. [van Heerden et al. Science (2014), DOI: 10.1126/science.1245114.].