Skp2 E3 ligase is overexpressed in numerous human cancers and plays a critical role in cell cycle progression, senescence, metabolism, cancer progression and metastasis. In the present study, we identified a specific Skp2 inhibitor using high-throughput in silico screening of large and diverse chemical libraries. This Skp2 inhibitor selectively suppresses Skp2 E3 ligase activity, but not activity of other SCF complexes. It also phenocopies the effects observed upon genetic Skp2 deficiency, such as suppressing survival, Akt-mediated glycolysis as well as triggering p53-independent cellular senescence. Strikingly, we discovered a critical function of Skp2 in positively regulating cancer stem cell populations and self-renewal ability through genetic and pharmacological approaches. Notably, Skp2 inhibitor exhibits potent anti-tumor activities in multiple animal models and cooperates with chemotherapeutic agents to reduce cancer cell survival. Our study thus provides pharmacological evidence that Skp2 is a promising target for restricting cancer stem cell and cancer progression.

RLR-mediated type I IFN production plays a pivotal role in elevating host immunity for viral clearance and cancer immune surveillance. Here, we report that glycolysis, which is inactivated during RLR activation, serves as a barrier to impede type I IFN production upon RLR activation. RLR-triggered MAVS-RIG-I recognition hijacks hexokinase binding to MAVS, leading to the impairment of hexokinase mitochondria localization and activation. Lactate serves as a key metabolite responsible for glycolysis-mediated RLR signaling inhibition by directly binding to MAVS transmembrane (TM) domain and preventing MAVS aggregation. Notably, lactate restoration reverses increased IFN production caused by lactate deficiency. Using pharmacological and genetic approaches, we show that lactate reduction by lactate dehydrogenase A (LDHA) inactivation heightens type I IFN production to protect mice from viral infection. Our study establishes a critical role of glycolysis-derived lactate in limiting RLR signaling and identifies MAVS as a direct sensor of lactate, which functions to connect energy metabolism and innate immunity.

IntroductionLymphocyte apoptosis and monocyte dysfunction play a pivotal role in sepsis-induced immunosuppression. Programmed death-1 (PD1) and its ligand programmed death ligand-1 (PD-L1) exert inhibitory function by regulating the balance among T cell activation, tolerance, and immunopathology. PD-1 deficiency or blockade has been shown to improve survival in murine sepsis. However, PD-L1 and PD-1 differ in their expression patterns and the role of PD-L1 in sepsis-induced immunosuppression is still unknown.MethodsSepsis was induced in adult C57BL/6 male mice via cecal ligation and puncture (CLP). The expression of PD-1 and PD-L1 expression on peripheral T cells, B cells and monocytes were measured 24 hours after CLP or sham surgery. Additionally, the effects of anti-PD-L1 antibody on lymphocyte number, apoptosis of spleen and thymus, activities of caspase-8 and caspase-9, cytokine production, bacterial clearance, and survival were determined.ResultsExpression of PD-1 on T cells, B cells and monocytes and PD-L1 on B cells and monocytes were up-regulated in septic animals compared to sham-operated controls. PD-L1 blockade significantly improved survival of CLP mice. Anti-PD-L1 antibody administration prevented sepsis-induced depletion of lymphocytes, increased tumor necrosis factor (TNF)-α and interleukin (IL)-6 production, decreased IL-10 production, and enhanced bacterial clearance.ConclusionsPD-L1 blockade exerts a protective effect on sepsis at least partly by inhibiting lymphocyte apoptosis and reversing monocyte dysfunction. Anti-PD-L1 antibody administration may be a promising therapeutic strategy for sepsis-induced immunosuppression.

Macrophages are critical mediators of tissue homeostasis, with the function of tissue development and repair, but also in defense against pathogens. Tumor-associated macrophages (TAMs) are considered as the main component in the tumor microenvironment and play an important role in tumor initiation, growth, invasion, and metastasis. Recently, metabolic studies have revealeded specific metabolic pathways in macrophages are tightly associated with their phenotype and function. Generally, pro-inflammatory macrophages (M1) rely mainly on glycolysis and exhibit impairment of the tricarboxylic acid (TCA) cycle and mitochondrial oxidative phosphorylation (OXPHOS), whereas anti-inflammatory macrophages (M2) are more dependent on mitochondrial OXPHOS. However, accumulating evidence suggests that macrophage metabolism is not as simple as previously thought. This review discusses recent advances in immunometabolism and describes how metabolism determines macrophage phenotype and function. In addition, we describe the metabolic characteristics of TAMs as well as their therapeutic implications. Finally, we discuss recent obstacles facing this area as well as promising directions for future study.