Thioredoxin-interacting protein is essential for memory T cell formation via the regulation of the redox metabolism.

CD4+ memory T cells are central to long-lasting protective immunity and are involved in shaping the pathophysiology of chronic inflammation. While metabolic reprogramming is critical for the generation of memory T cells, the mechanisms controlling the redox metabolism in memory T cell formation remain unclear. We found that reactive oxygen species (ROS) metabolism changed dramatically in T helper-2 (Th2) cells during the contraction phase in the process of memory T cell formation. Thioredoxin-interacting protein (Txnip), a regulator of oxidoreductase, regulated apoptosis by scavenging ROS via the nuclear factor erythroid 2-related factor 2 (Nrf2)-biliverdin reductase B (Blvrb) pathway. Txnip regulated the pathology of chronic airway inflammation in the lung by controlling the generation of allergen-specific pathogenic memory Th2 cells in vivo. Thus, the Txnip-Nrf2-Blvrb axis directs ROS metabolic reprogramming in Th2 cells and is a potential therapeutic target for intractable chronic inflammatory diseases.

Heme degradation enzyme biliverdin IXß reductase is required for stem cell glutamine metabolism.

Bioenergetic requirements of hematopoietic stem cells and pluripotent stem cells (PSCs) vary with lineage fate, and cellular adaptations rely largely on substrate (glucose/glutamine) availability and mitochondrial function to balance tricarboxylic acid (TCA)-derived anabolic and redox-regulated antioxidant functions. Heme synthesis and degradation converge in a linear pathway that utilizes TCA cycle-derived carbon in cataplerotic reactions of tetrapyrrole biosynthesis, terminated by NAD(P)H-dependent biliverdin reductases (IXα, BLVRA and IXß, BLVRB) that lead to bilirubin generation and cellular antioxidant functions. We now demonstrate that PSCs with targeted deletion of BLVRB display physiologically defective antioxidant activity and cellular viability, associated with a glutamine-restricted defect in TCA entry that was computationally predicted using gene/metabolite topological network analysis and subsequently validated by bioenergetic and isotopomeric studies. Defective BLVRB-regulated glutamine utilization was accompanied by exaggerated glycolytic accumulation of the rate-limiting hexokinase reaction product glucose-6-phosphate. BLVRB-deficient embryoid body formation (a critical size parameter of early lineage fate potential) demonstrated enhanced sensitivity to the pentose phosphate pathway (PPP) inhibitor 6-aminonicotinamide with no differences in the glycolytic pathway inhibitor 2-deoxyglucose. These collective data place heme catabolism in a crucial pathway of glutamine-regulated bioenergetic metabolism and suggest that early stages of lineage fate potential require glutamine anaplerotic functions and an intact PPP, which are, in part, regulated by BLVRB activity. In principle, BLVRB inhibition represents an alternative strategy for modulating cellular glutamine utilization with consequences for cancer and hematopoietic metabolism.

MicroRNA-127-5p targets the biliverdin reductase B/nuclear factor-κB pathway to suppress cell growth in hepatocellular carcinoma cells.

Nuclear factor-κB (NF-κB) activation is one of the major mediators of inflammation-induced cancer cell growth and progression. In previous studies, we screened a series of microRNAs (miRNAs) that targeted the NF-κB signaling pathway. In this study, we showed that miR-127-5p suppressed NF-κB activity through inhibition of p65 nuclear translocation. In addition, miR-127-5p also inhibited the transcription of downstream targets of the NF-κB signaling pathway. While exploring the mechanism of the inhibition of NF-κB activity by miR-127-5p, we found that miR-127-5p decreased the phosphorylation of p65. MicroRNA-127-5p inhibited the growth and colony formation of hepatocellular carcinoma (HCC) cells and decreased biliverdin reductase B (BLVRB) expression by directly binding to its 3'-UTR. RNA interference of BLVRB suppressed HCC cell growth, whereas the overexpression of BLVRB promoted HCC cell growth. Furthermore, BLVRB blockade inhibited the phosphorylation of p65 protein and the expression of downstream targets of the NF-κB signaling pathway, mimicking the function of miR-127-5p. The restoration of BLVRB in HCC cells overexpressing miR-127-5p impaired the suppression of HCC growth by miR-127-5p. Moreover, miR-127-5p was downregulated in 58% of HCC samples. In summary, we found that miR-127-5p suppressed NF-κB activity by directly targeting BLVRB in HCC cells, and this finding improves our understanding of the molecular mechanism of inflammation-induced HCC growth and proliferation and the successful inhibition of NF-κB activity by cancer treatment.

Identifying structural and dynamic changes during the Biliverdin Reductase B catalytic cycle.

Biliverdin Reductase B (BLVRB) is an NADPH-dependent reductase that catalyzes the reduction of multiple substrates and is therefore considered a critical cellular redox regulator. In this study, we sought to address whether both structural and dynamics changes occur between different intermediates of the catalytic cycle and whether these were relegated to just the active site or the entirety of the enzyme. Through X-ray crystallography, we determined the apo BLVRB structure for the first time, revealing subtle global changes compared to the holo structure and identifying the loss of a critical hydrogen bond that "clamps" the R78-loop over the coenzyme. Amide and Cα chemical shift perturbations were used to identify environmental and secondary structural changes between intermediates, with more distant global changes observed upon coenzyme binding compared to substrate interactions. NMR relaxation rate measurements provided insights into the dynamic behavior of BLVRB during the catalytic cycle. Specifically, the inherently dynamic R78-loop that becomes ordered upon coenzyme binding persists through the catalytic cycle while similar regions experience dynamic exchange. However, the dynamic exchange processes were found to differ through the catalytic cycle with several groups of residues exhibiting similar dynamic responses. Finally, both local and distal structural and dynamic changes occur within BLVRB that are dependent solely on the oxidative state of the coenzyme. Thus, through a comprehensive analysis here, this study revealed structural and dynamic alterations in BLVRB through its catalytic cycle that are not simply relegated to the active site, but instead, are allosterically coupled throughout the enzyme.

Biliverdin reductase B impairs cholangiocarcinoma cell motility by inhibiting the Notch/Snail signaling pathway.

Cholangiocarcinoma (CCA) is one of the most lethal types of solid tumors worldwide. Lymph node metastasis is common in the early stage, which is associated with recurrence and reduced survival time after CCA resection. The molecular pathogenesis of CCA is complex and requires extensive investigation. It involves multiple genomic alterations and the dysregulation of signaling pathways. Biliverdin reductase B (BLVRB) is a non-redundant NAD(P)H-dependent biliverdin reductase that regulates cellular redox status by reducing biliverdin to bilirubin. This study aimed at describing the biological functions and molecular mechanisms of BLVRB in human CCA. Prognostic clinical data showed that low expression BLVRB was associated with poor prognosis and lymph node metastasis. BLVRB depletion accelerated epithelial-mesenchymal transition (EMT), cell migration and invasion. In contrast, BLVRB overexpression was associated with reduced EMT and cell migration and invasion in CCA. BLVRB suppression activated Notch signaling, and activated c-Notch enhanced EMT by upregulating Snail expression levels, thereby increasing cell migration and invasion in CCA. Our results identified an unexpected function of BLVRB in CCA migration and invasion through the regulation of Notch/Snail signaling.