Dimethylarginine dimethylaminohydrolase-1 (DDAH1) is frequently upregulated in prostate cancer, and its overexpression conveys tumor growth and angiogenesis by metabolizing asymmetric dimethylarginine (ADMA)

Sepsis-related myocardial injury is associated with Mst1 upregulation, mitochondrial dysfunction and the Drp1/F-actin signaling pathway

LPS-induced septic cardiomyopathy has been found to be connected with mitochondrial stress through unknown mechanisms. Mitochondrial fission is an early event in mitochondrial dysfunction. The aim of our study was to determine the role and regulatory mechanism of mitochondrial fission in the progression of LPS-induced septic cardiomyopathy, with a particular focus on Mst1 and F-actin. Our data demonstrated that Mst1 expression was rapidly upregulated in LPS-treated hearts and that increased Mst1 promoted cardiomyocyte death by inducing mitochondrial stress. Mechanistically, elevated expression of Mst1 upregulated Drp1, and the latter initiated mitochondrial fission. Excessive mitochondrial fission caused mitochondrial oxidative injury, mitochondrial membrane potential reduction, mitochondrial proapoptotic element translocation into the cytoplasm/nucleus, mitochondrial energy dysfunction and mitochondrial apoptosis activation. Inhibition of mitochondrial fission sustained mitochondrial function and favored cardiomyocyte survival. Furthermore, we identified F-actin degradation as an apparent downstream event of mitochondrial fission activation in the context of LPS-induced septic cardiomyopathy. Stabilization of F-actin attenuated fission-mediated cardiomyocyte death. Altogether, our results define the Mst1/Drp1/mitochondrial fission/F-actin axis as a new signaling pathway that mediates LPS-related septic cardiomyopathy by inducing mitochondrial stress and cardiomyocyte death. Therefore, Mst1 expression, mitochondrial fission modification and F-actin stabilization may serve as potential therapeutic targets for sepsis-related myocardial injury.

Mst1 facilitates hyperglycemia-induced retinal pigmented epithelial cell apoptosis by evoking mitochondrial stress and activating the Smad2 signaling pathway

Hyperglycemia induces retinal pigmented epithelial cell apoptosis and mitochondrial stress via poorly understood mechanisms. The goal of our current study is to explore whether mammalian sterile 20-like kinase 1 (Mst1) is involved in the pathogenesis of hyperglycemia-mediated retinal pigmented epithelial cell apoptosis by triggering mitochondrial abnormalities and activating the Smad2 signaling pathway. Retinal pigmented epithelial ARPE-19 cells were presented with a high-glucose challenge in vitro. Cell viability and apoptosis were measured via western blotting, ELISAs, and immunofluorescence assays. Mitochondrial function was detected via JC-1 staining, mitochondrial ROS flow cytometry, western blotting, and ELISAs. Loss- and gain-of-function assays were performed via cell transfection and transduction with Mst1 siRNA and Smad2 adenovirus, respectively. The results indicated that hyperglycemia treatment upregulated the levels of Mst1, an effect that was accompanied by an increase in ARPE-19 cell apoptosis. Loss of Mst1 attenuated hyperglycemia-induced cell apoptosis, and this effect seemed to be associated with mitochondrial protection. In response to hyperglycemia stimulus, mitochondrial stress was noted in ARPE-19 cells, including mitochondrial ROS overproduction, mitochondrial respiratory metabolism dysfunction, mitochondrial fission/fusion imbalance, and mitochondrial apoptosis activation. Further, we provided evidence to support the crucial role played by Smad2 in promoting Mst1-mediated cell apoptosis and mitochondrial stress. Overexpression of Smad2 abrogated the beneficial effects of Mst1 deletion on ARPE-19 cell viability and mitochondrial protection. Altogether, our results identified Mst1 as a novel mediator controlling the fate of retinal pigmented epithelial cells and mitochondrial homeostasis via the Smad2 signaling pathway. Based on this finding, strategies to repress Mst1 upregulation and block Smad2 activation are vital to alleviate hyperglycemia-mediated retinal pigmented epithelial cell damage.

LATS2 promotes apoptosis in non-small cell lung cancer A549 cells via triggering Mff-dependent mitochondrial fission and activating the JNK signaling pathway

LATS2 is a classical tumor suppressor that affects non-small cell lung cancer proliferation and mobilization. However, its role in lung cancer cell apoptosis is unknown. The aim of our study is to explore whether LATS2 activates mitochondria-related apoptosis in lung cancer cells. In the present study, A549 non-small cell lung cancer cells were transfected with a LATS2 adenovirus to induce LATS2 overexpression. Cell apoptosis was evaluated via the MTT assay, TUNEL staining, western blotting, trypan blue staining and ELISA. Mitochondrial function was measured using an immunofluorescence assay, western blotting and ELISA. The results demonstrated that LATS2 was downregulated in A549 lung cancer cells. Overexpression of LATS2 induced A549 cell apoptosis via activating mitochondrial fission. Subsequently, we confirmed that LATS2 modulated mitochondrial fission via the JNK-Mff signaling pathway. Inhibition of the JNK pathway and/or knockdown of Mff abolished the pro-apoptotic effect of LATS2 on A549 cells. Taken together, our results identified LATS2 as a classical tumor suppressor of lung cancer via triggering mitochondrial fission and activating the JNK-Mff signaling pathway. Our results lay the foundation for detailed study of the molecular mechanisms of LATS2 overexpression and regulation of mitochondrial fission for lung cancer treatment.

Arginine and the metabolic regulation of nitric oxide synthesis in cancer

Nitric oxide (NO) is a signaling molecule that plays important roles in diverse biological processes and thus its dysregulation is involved in the pathogenesis of various disorders. In cancer, NO has broad and sometimes dichotomous roles; it is involved in cancer initiation and progression, but also restricts cancer proliferation and invasion, and contributes to the anti-tumor immune response. The importance of NO in a range of cellular processes is exemplified by its tight spatial and dosage control at multiple levels, including via its transcriptional, post-translational and metabolic regulation. In this Review, we focus on the regulation of NO via the synthesis and availability of its precursor, arginine, and discuss the implications of this metabolic regulation for cancer biology and therapy. Despite the established contribution of NO to cancer pathogenesis, the implementation of NO-related cancer therapeutics remains limited, likely due to the challenge of targeting and inducing its protective functions in a cell- and dosage-specific manner. A better understanding of how arginine regulates the production of NO in cancer might thus support the development of anti-cancer drugs that target this key metabolic pathway, and other metabolic pathways involved in NO production.

Dissection, Optimization, and Structural Analysis of a Covalent Irreversible DDAH1 Inhibitor

Inhibitors of the human enzyme dimethylarginine dimethylaminohydrolase-1 (DDAH1) can control endogenous nitric oxide production. A time-dependent covalent inactivator of DDAH1, N⁵-(1-imino-2-chloroethyl)-l-ornithine ( K_I = 1.3 μM, k_inact = 0.34 min^-1), was conceptually dissected into two fragments and each characterized separately: l-norvaline ( K_i = 470 μM) and 2-chloroacetamidine ( K_I = 310 μM, k_inact = 4.0 min^-1). This analysis suggested that the two fragments were not linked in a manner that allows either to reach full affinity or reactivity, prompting the synthesis and characterization of three analogues: two that mimic the dimethylation status of the substrate, N⁵-(1-imino-2-chloroisopropyl)-l-ornithine ( k_inact /K_I = 208 M^-1 s^-1) and N⁵-(1-imino-2-chlorisopropyl)-l-lysine ( k_inact /K_I = 440 M^-1 s^-1), and one that lengthens the linker beyond that found in the substrate, N⁵-(1-imino-2-chloroethyl)-l-lysine (Cl-NIL, K_I = 0.19 μM, k_inact = 0.22 min^-1). Cl-NIL is one of the most potent inhibitors reported for DDAH1, inactivates with a second order rate constant (1.9 × 10⁴ M^-1 s^-1) larger than the catalytic efficiency of DDAH1 for its endogenous substrate (1.6 × 10² M^-1 s^-1), and has a partition ratio of 1 with a >100 000-fold selectivity for DDAH1 over arginase. An activity-based protein-profiling probe is used to show inhibition of DDAH1 within cultured HEK293T cells (IC₅₀ = 10 μM) with cytotoxicity appearing only at higher concentrations (ED₅₀ = 118 μM). A 1.91 Å resolution X-ray crystal structure reveals specific interactions made with DDAH1 upon covalent inactivation by Cl-NIL. Dissecting a covalent inactivator and analysis of its constituent fragments proved useful for the design and optimization of this potent and effective DDAH1 inhibitor.