AMPK inhibitor Compound C stimulates ceramide production and promotes Bax redistribution and apoptosis in MCF7 breast carcinoma cells

Dorsomorphin attenuates ABCG2-mediated multidrug resistance in colorectal cancer

Colorectal cancer is a common malignant tumor with high mortality, for which chemotherapy resistance is one of the main reasons. The high expression of ABCG2 in the cancer cells and expulsion of anticancer drugs directly cause multidrug resistance (MDR). Therefore, the development of new ABCG2 inhibitors that block the active causes of MDR may provide a strategy for the treatment of colorectal cancer. In this study, we find that dorsomorphin (also known as compound C or BML-275) potently inhibits the transporter activity of ABCG2, thereby preserving the chemotherapeutic agents mitoxantrone and doxorubicin to antagonize MDR in ABCG2-overexpressing colorectal cancer cells. Additionally, dorsomorphin does not alter ABCG2 protein expression. The results of molecular docking studies show that dorsomorphin is bound stably to the ABCG2-binding pocket, suggesting that dorsomorphin is a potent ABCG2 inhibitor that attenuates ABCG2-mediated MDR in colorectal cancer.

Orientin Promotes Antioxidant Capacity, Mitochondrial Biogenesis, and Fiber Transformation in Skeletal Muscles through the AMPK Pathway

The sleep-breathing condition obstructive sleep apnea (OSA) is characterized by repetitive upper airway collapse, which can exacerbate oxidative stress and free radical generation, thereby detrimentally impacting both motor and sensory nerve function and inducing muscular damage. OSA development is promoted by increasing proportions of fast-twitch muscle fibers in the genioglossus. Orientin, a water-soluble dietary C-glycosyl flavonoid with antioxidant properties, increased the expression of slow myosin heavy chain (MyHC) and signaling factors associated with AMP-activated protein kinase (AMPK) activation both in vivo and in vitro. Inhibiting AMPK signaling diminished the effects of orientin on slow MyHC, fast MyHC, and Sirt1 expression. Overall, orientin enhanced type I muscle fibers in the genioglossus, enhanced antioxidant capacity, increased mitochondrial biogenesis through AMPK signaling, and ultimately improved fatigue resistance in C2C12 myotubes and mouse genioglossus. These findings suggest that orientin may contribute to upper airway stability in patients with OSA, potentially preventing airway collapse.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

Metabolomics Analysis of Sodium Salicylate Improving the Preservation Quality of Ram Sperm

The aim of this study was to investigate the effects of sodium salicylate (SS) on the preservation and metabolic regulation of sheep sperm. Under 4 °C low-temperature conditions, SS (at 10 µM, 20 µM, 30 µM, and 50 µM) was added to the semen diluent to detect sperm motility, plasma membrane, and acrosome integrity. Based on the selected optimal concentration of SS (20 µM), the effects of 20 µM of SS on sperms' antioxidant capacity and mitochondrial membrane potential (MMP) were evaluated, and metabolomics analysis was conducted. The results showed that on the 20th day of low-temperature storage, the sperm motility of the 20 µM SS group was 62.80%, and the activities of catalase (CAT) and superoxide dismutase (SOD) were significantly higher than those of the control group (p < 0.01). The content of Ca2+, reactive oxygen species (ROS), and malondialdehyde (MDA) were significantly lower than those of the control group (p < 0.01), and the total antioxidant capacity (T-AOC) was significantly higher than that of the control group (p < 0.05); mitochondrial activity and the total cholesterol (TC) content were significantly higher than those in the control group (p < 0.01). An ultrastructural examination showed that in the SS group, the sperm plasma membrane and acrosome were intact, the fibrous sheath and axoneme morphology of the outer dense fibers were normal, and the mitochondria were arranged neatly. In the control group, there was significant swelling of the sperm plasma membrane, rupture of the acrosome, and vacuolization of mitochondria. Using metabolomics analysis, 20 of the most significant differential metabolic markers were screened, mainly involving 6 metabolic pathways, with the amino acid biosynthesis pathway being the most abundant. In summary, 20 µM of SS significantly improved the preservation quality of sheep sperm under low-temperature conditions of 4 °C.

The ceramide synthase (CERS/LASS) family: Functions involved in cancer progression

INTRODUCTION

Ceramide synthases (CERSes) are also known longevity assurance (LASS) genes. CERSes play important roles in the regulation of cancer progression. The CERS family is expressed in a variety of human tumours and is involved in tumorigenesis. They are closely associated with the progression of liver, breast, cervical, ovarian, colorectal, head and neck squamous cell, gastric, lung, prostate, oesophageal, pancreatic and blood cancers. CERSes play diverse and important roles in the regulation of cell survival, proliferation, apoptosis, migration, invasion, and drug resistance. The differential expression of CERSes in tumour and nontumour cells and survival analysis of cancer patients suggest that some CERSes could be used as potential prognostic markers. They are also important potential targets for cancer therapy.

METHODS

In this review, we summarize the available evidence on the inhibitory or promotive roles of CERSes in the progression of many cancers. Furthermore, we summarize the identified upstream and downstream molecular mechanisms that may regulate the function of CERSes in cancer settings.

Effects of protocatechuic acid on antioxidant capacity, mitochondrial biogenesis and skeletal muscle fiber transformation

In skeletal muscle, the increased proportion of type I muscle fibers has the potential to improve muscle atrophy and prevent human metabolic diseases. Protocatechuic acid (PCA), as a kind of anthocyanin metabolite, has antioxidant and anti-inflammatory physiological activities. The purpose of this experiment was to use mice and C2C12 myotubes to examine if PCA can induce the transformation of muscle fiber and the mechanisms involved. We found that PCA significantly increased the expression of slow myosin heavy chain (MyHC), and markedly decreased the expression of fast MyHC in gastrocnemius muscle of mice and C2C12 myotubes. In addition, PCA also enhanced the antioxidant capacity and promoted mitochondrial biogenesis in mice. Importantly, the AMP-activated protein kinase (AMPK) signaling pathway was activated and AMPK inhibitor compound C attenuated the positive effect of PCA on myofiber conversion. To sum up, we revealed that PCA was able to promote the conversion of skeletal muscle fiber from type II to type I through the AMPK signaling pathway.

AMPK inhibition induces MCL1 mRNA destabilization via the p38 MAPK/miR-22/HuR axis in chronic myeloid leukemia cells

The oncogenic and tumor-suppressive roles of AMPK in chronic myeloid leukemia (CML) are controvertible. This study aimed to investigate the cytotoxic effects of the AMPK inhibitor Compound C in the CML cell lines K562, KU812, and MEG-01. Compared to K562 cells, KU812 and MEG-01 cells were more sensitive to Compound C-mediated cytotoxicity. Moreover, Compound C induced SIRT3 upregulation in K562 cells but not in KU812 or MEG-01 cells. SIRT3 silencing increased the sensitivity of K562 cells to Compound C. Additionally; Compound C-induced autophagy attenuated its induced apoptosis in KU812 and MEG-01 cells. Compound C-induced ROS-mediated AMPKα inactivation resulted in the downregulation of apoptotic regulator MCL1 in KU812 and MEG-01 cells. Mechanistically, AMPK inhibition activated p38 MAPK-mediated miR-22 expression, which in turn inhibited HuR expression, thereby reducing MCL1 mRNA stability. Overexpression of constitutively active AMPKα1 and abolishment of the activation of p38 MAPK inhibited Compound C-induced cell death and MCL1 downregulation. Furthermore, Compound C synergistically enhanced the cytotoxicity of BCR-ABL inhibitors and the BCL2 inhibitor ABT-199. Collectively, this study indicates that Compound C induces MCL1 downregulation through the AMPK/p38 MAPK/miR-22/HuR pathway, thereby inducing apoptosis of KU812 and MEG-01 cells. Furthermore, our findings suggest that AMPK inhibition is a promising strategy for improving CML therapy.

Targeting apoptosis in MCF-7 and Ehrlich ascites carcinoma cells by saponifiable fractions from green and black Vitis vinifera seed oil

Grape seed (GS) oil is one of the potential functional foods. For the first time, we evaluated the therapeutic effects of GS oil saponifiable (Sap)-fraction from black (BSap) and green (GSap) grapes on MCF-7 cells and Ehrlich ascites carcinoma (EAC) in mice. The fatty acid composition of BSap and GSap was determined using gas chromatography-mass spectrometry analysis. Approximately twelve distinct fatty acids were detected in BSap and eleven in GSap. BSap showed a greater cytotoxic effect on MCF-7 cells than GSap did by inducing apoptosis and reducing inflammation, while both grape fractions had superior potency to 5-FU. Furthermore, BSap massively boosted apoptosis and lowered redox potential (E_h) and CD44⁺ cells in EAC cells of EAC-bearing mice more than GSap, and both fractions were more efficient than 5-FU. Blood tests and liver histopathology revealed significant improvement in EAC-induced pathological alterations with these fractions. The in silico analysis implied the competitive inhibitory impacts of the most abundant fatty acid composites in BSap and GSap on cancer-metastasis-associated proteases (cathepsin B and MMP9). Also, this analysis predicted that the apoptotic action of these Sap fractions is independent of the 5'AMP-activated protein kinase. Therefore, grape Sap-fraction, especially BSap, may be a useful agent for cancer prevention.

Inhibitory targeting cGAS-STING-TBK1 axis: Emerging strategies for autoimmune diseases therapy

The cGAS-STING signaling plays an integral role in the host immune response, and the abnormal activation of cGAS-STING is highly related to various autoimmune diseases. Therefore, targeting the cGAS-STING-TBK1 axis has become a promising strategy in therapy of autoimmune diseases. Herein, we summarized the key pathways mediated by the cGAS-STING-TBK1 axis and various cGAS-STING-TBK1 related autoimmune diseases, as well as the recent development of cGAS, STING, or TBK1 selective inhibitors and their potential application in therapy of cGAS-STING-TBK1 related autoimmune diseases. Overall, the review highlights that inhibiting cGAS-STING-TBK1 signaling is an attractive strategy for autoimmune disease therapy.

Dephosphorylation of AMP-activated kinase exacerbates ischemia/reperfusion-induced acute kidney injury via mitochondrial dysfunction

Kidney tubular epithelial cells are high energy-consuming epithelial cells that depend mainly on fatty acid oxidation for an energy supply. AMP-activated protein kinase (AMPK) is a key regulator of energy production in most cells, but the function of AMPK in tubular epithelial cells in acute kidney disease is unclear. Here, we found a rapid decrease in Thr172-AMPKα phosphorylation after ischemia/reperfusion in both in vivo and in vitro models. Mice with kidney tubular epithelial cell-specific AMPKα deletion exhibited exacerbated kidney impairment and apoptosis of tubular epithelial cells after ischemia/reperfusion. AMPKα deficiency was accompanied by the accumulation of lipid droplets in the kidney tubules and the elevation of ceramides and free fatty acid levels following ischemia/reperfusion injury. Mechanistically, ischemia/reperfusion triggered ceramide production and activated protein phosphatase PP2A, which dephosphorylated Thr172-AMPKα. Decreased AMPK activity repressed serine/threonine kinase ULK1-mediated autophagy and impeded clearance of the dysfunctional mitochondria. Targeting the PP2A-AMPK axis by the allosteric AMPK activator C24 restored fatty acid oxidation and reduced tubular cell apoptosis during ischemia/reperfusion-induced injury, by antagonizing PP2A dephosphorylation and promoting the mitophagy process. Thus, our study reveals that AMPKα plays an important role in protecting against tubular epithelial cell injury in ischemia/reperfusion-induced acute kidney injury. Hence, activation of AMPK could be a potential therapeutic strategy for acute kidney injury treatment.

Novel Strategies for Disrupting Cancer-Cell Functions with Mitochondria-Targeted Antitumor Drug-Loaded Nanoformulations

Any variation in normal cellular function results in mitochondrial dysregulation that occurs in several diseases, including cancer. Such processes as oxidative stress, metabolism, signaling, and biogenesis play significant roles in cancer initiation and progression. Due to their central role in cellular metabolism, mitochondria are favorable therapeutic targets for the prevention and treatment of conditions like neurodegenerative diseases, diabetes, and cancer. Subcellular mitochondria-specific theranostic nanoformulations for simultaneous targeting, drug delivery, and imaging of these organelles are of immense interest in cancer therapy. It is a challenging task to cross multiple barriers to target mitochondria in diseased cells. To overcome these multiple barriers, several mitochondriotropic nanoformulations have been engineered for the transportation of mitochondria-specific drugs. These nanoformulations include liposomes, dendrimers, carbon nanotubes, polymeric nanoparticles (NPs), and inorganic NPs. These nanoformulations are made mitochondriotropic by conjugating them with moieties like dequalinium, Mito-Porter, triphenylphosphonium, and Mitochondria-penetrating peptides. Most of these nanoformulations are meticulously tailored to control their size, charge, shape, mitochondriotropic drug loading, and specific cell-membrane interactions. Recently, some novel mitochondria-selective antitumor compounds known as mitocans have shown high toxicity against cancer cells. These selective compounds form vicious oxidative stress and reactive oxygen species cycles within cancer cells and ultimately push them to cell death. Nanoformulations approved by the FDA and EMA for clinical applications in cancer patients include Doxil, NK105, and Abraxane. The novel use of these NPs still faces tremendous challenges and an immense amount of research is needed to understand the proper mechanisms of cancer progression and control by these NPs. Here in this review, we summarize current advancements and novel strategies of delivering different anticancer therapeutic agents to mitochondria with the help of various nanoformulations.

The fatty acid elongase ELOVL6 regulates bortezomib resistance in multiple myeloma

Resistance to the proteasome inhibitor bortezomib (BTZ) represents a major obstacle in the treatment of multiple myeloma (MM). The contribution of lipid metabolism in the resistance of MM cells to BTZ is mostly unknown. Here we report that levels of fatty acid elongase 6 (ELOVL6) were lower in MM cells from BTZ-nonresponsive vs BTZ-responsive patients and in cultured MM cells selected for BTZ resistance compared with parental counterparts. Accordingly, depletion of ELOVL6 in parental MM cells suppressed BTZ-induced endoplasmic reticulum (ER) stress and cytotoxicity, whereas restoration of ELOVL6 levels in BTZ-resistant MM cells sensitized them to BTZ in tissue culture settings and, as xenografts, in a plasmacytoma mouse model. Furthermore, for the first time, we identified changes in the BTZ-induced lipidome between parental and BTZ-resistant MM cell lines underlying a functional difference in their response to BTZ. We demonstrated that restoration of ELOVL6 levels in BTZ-resistant MM cells resensitized them to BTZ largely via upregulation of ELOVL6-dependent ceramide species, which was a prerequisite for BTZ-induced ER stress and cell death in these cells. Our data characterize ELOVL6 as a major clinically relevant regulator of MM cell resistance to BTZ, which can emerge from the impaired ability of these cells to alter ceramide composition in response to BTZ.

Design and synthesis of new indole containing biaryl derivatives as potent antiproliferative agents

A new series of indole containing biaryl derivatives were designed and synthesized, and further biological evaluations of their antiproliferative activity against cancer cell lines (MGC-803 and TE-1 cells) were also conducted. Of these synthesized biaryls, compound 4-methyl-2-((5-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)methyl)quinazoline (23) performed as the most potent antiproliferative agent that inhibited cell viability of MGC-803 cells with an IC₅₀ value of 8.28 µM. In addition, investigation of mechanism exhibited that the compound 4-methyl-2-((5-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)methyl)quinazoline (23) could inhibit the expression of c-Myc and glycolysis related proteins, decrease the ATP and lactate production, and further induce apoptosis by activating the AMP-activated protein kinase (AMPK) and p53 signaling pathways.

Acetate stimulates lipogenesis via AMPKα signaling in rabbit adipose-derived stem cells

Acetate plays an important role in host lipid metabolism. However, the regulatory network underlying acetate-regulated lipometabolism remains unclear. The aim of this study was to determine whether any cross talk occurs among adenosine 5'-monophosphate-activated protein kinase (AMPK), mitogen-activated protein kinases (MAPKs) and acetate in regulating lipid metabolism. The compound C (an AMPK inhibitor), and SB203580 (a p38 MAPK inhibitor) were used to treat rabbit adipose-derived stem cells (ADSCs) with or without acetate, respectively. It indicated that acetate (6 mM) for 6 h increased the lipid deposition in rabbit ADSCs. Besides, acetate treatment (6 mM) increased significantly phosphorylated protein level of AMPKα and p38 MAPK, but not altered significantly the phosphorylated protein level of extracellular signaling-regulated kinase (ERK) and c-Jun aminoterminal kinase (JNK). The blocking of AMPKα signaling attenuated acetate-induced lipid accumulation, but not that of p38 MAPK signaling. In conclusion, our findings suggest that AMPKα signaling pathway is associated with acetate-induced lipogenesis.

EGR-1 plays a protective role in AMPK inhibitor compound C-induced apoptosis through ROS-induced ERK activation in skin cancer cells

Skin cancer is caused by abnormal proliferation, gene regulation and mutation of epidermis cells. Compound C is commonly used as an inhibitor of AMP-activated protein kinase (AMPK), which serves as an energy sensor in cells. Recently, compound C has been reported to induce apoptotic and autophagic death in various skin cancer cell lines via an AMPK-independent pathway. However, the signaling pathways activated in compound C-treated cancer cells remain unclear. The present oligodeoxynucleotide-based microarray screening assay showed that the mRNA expression of the zinc-finger transcription factor early growth response-1 (EGR-1), which helps regulate cell cycle progression and cell survival, was significantly upregulated in compound C-treated skin cancer cells. Compound C was demonstrated to induce EGR-1 mRNA and protein expression in a time and dose-dependent manner. Confocal imaging showed that compound C-induced EGR-1 protein expression was localized in the nucleus. Compound C was demonstrated to activate extracellular signal-regulated kinase (ERK) phosphorylation. Inhibition of this compound C-induced ERK phosphorylation downregulated the mRNA and protein expression of EGR-1. In addition, removal of compound C-induced reactive oxygen species (ROS) not only decreased ERK phosphorylation, but also inhibited compound C-induced EGR-1 expression. A functional assay showed that knock down of EGR-1 expression in cancer cells decreased the survival rate while also increasing caspase-3 activity and apoptotic marker expression after compound C treatment. However, no difference in autophagy marker light chain 3-II protein expression was observed between compound C-treated control cells and EGR-1-knockdown cells. Thus, it was concluded that that EGR-1 may antagonize compound C-induced apoptosis but not compound C-induced autophagy through the ROS-mediated ERK activation pathway.

Ceramide synthases: Reflections on the impact of Dr. Lina M. Obeid

Sphingolipids are a family of lipids that are critical to cell function and survival. Much of the recent work done on sphingolipids has been performed by a closely-knit family of sphingolipid researchers, which including our colleague, Dr. Lina Obeid, who recently passed away. We now briefly review where the sphingolipid field stands today, focusing in particular on areas of sphingolipid research to which Dr. Obeid made valued contributions. These include the 'many-worlds' view of ceramides and the role of a key enzyme in the sphingolipid biosynthetic pathway, namely the ceramide synthases (CerS). The CerS contain a number of functional domains and also interact with a number of other proteins in lipid metabolic pathways, fulfilling Dr. Obeid's prophecy that ceramides, and the enzymes that generate ceramides, form the critical hub of the sphingolipid metabolic pathway.

Compound C Protects Against Cisplatin-Induced Nephrotoxicity Through Pleiotropic Effects

AICAR (Acadesine/AICA riboside) as an activator of AMPK, can protect renal tubular cells from cisplatin induced apoptosis. But in our experiment, the dorsomorphin (compound C, an inhibitor of AMPK) also significantly reduced cisplatin induced renal tubular cells apoptosis. Accordingly, we tested whether compound C can protect cisplatin-induced nephrotoxicity and the specific mechanism. Here, we treated Boston University mouse proximal tubular cells (BUMPT-306) with cisplatin and/or different dosages of AICAR (Acadesine/AICA riboside) or compound C to confirm the effect of AICAR and compound C in vitro. The AMPK-siRNA treated cells to evaluate whether the protective effect of compound C was through inhibiting AMPK. Male C57BL/6 mice were used to verify the effect of compound C in vivo. Both compound C and AICAR can reduce renal tubular cells apoptosis in dose-dependent manners, and compound C decreased serum creatinine and renal tubular injury induced by cisplatin. Mechanistically, compound C inhibited P53, CHOP and p-IREα during cisplatin treatment. Our results demonstrated that compound C inhibited AMPK, but the renal protective effects of compound C were not through AMPK. Instead, compound C protected cisplatin nephrotoxicity by inhibiting P53 and endoplasmic reticulum (ER) stress. Therefore, compound C may protect against cisplatin-induced nephrotoxicity through pleiotropic effects.

Compound C Reducing Interferon Expression by Inhibiting cGAMP Accumulation

Cyclic GMP-AMP (cGAMP) synthase (cGAS) is a major DNA sensor responsible for cytosolic DNA-mediated innate immune response. Inhibition of cGAS may be an effective strategy for treating autoimmune diseases such as Aicardi-Goutieres syndrome and systemic lupus erythematosus. Compound C (also known as Dorsomorphin) has been annotated as a potent and reversible inhibitor for AMPKs as well as ALK protein kinases. Here, we report a new function of Compound C which can suppress dsDNA-dependent type I interferon induction. These effects were not dependent on the activities of AMPK proteins. In vitro assays and liquid chromatograph-mass spectrometry data show that Compound C has the capability of reducing cGAMP accumulation, suggesting that Compound C may function as a modulator involved in the cGAS-STING-mediated DNA sensing pathway. Furthermore, Compound C is able to rescue the autoimmune phenotypes in a mouse model carrying the Trex1 gene deficiency. These data demonstrate a new and inverse correlation between Compound C and type I interferon production in response to dsDNA signaling.

Cell death induced by dorsomorphin in adult T-cell leukemia/lymphoma is AMPK-independent

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T-cell neoplasm with poor prognosis that develops after chronic infection with human T-cell leukemia virus type 1 (HTLV-1). Although AMP-activated protein kinase (AMPK) is a critical cellular energy sensor, it has recently become clear that AMPK can act as a tumor regulator. Here, we assessed the expression of AMPK in primary ATL cells and the effects of dorsomorphin, an AMPK inhibitor, on primary ATL cells and HTLV-1-infected T-cell lines. AMPK expression in acute and chronic ATL patients was significantly higher than in asymptomatic HTLV-1 carriers and healthy donors. Dorsomorphin induced apoptosis in peripheral blood mononuclear cells from ATL patients. Dorsomorphin also induced dose- and time-dependent apoptosis in HTLV-1-infected T-cell lines. Dorsomorphin increased the production of intracellular reactive oxygen species (ROS) and induced ataxia telangiectasia-mutated Ser1981 phosphorylation and p53 accumulation. These results indicated that dorsomorphin induces apoptosis via ROS-mediated DNA damage in HTLV-1-infected T-cell lines. Furthermore, dorsomorphin suppressed the growth of human ATL tumor xenografts in NOD/SCID mice. Together, these data suggest that AMPK could be a candidate therapeutic target for ATL and that dorsomorphin could be a therapeutic agent for ATL.

Compound C induces autophagy and apoptosis in parental and hydroquinone-selected malignant leukemia cells through the ROS/p38 MAPK/AMPK/TET2/FOXP3 axis

Hydroquinone (HQ), a major metabolic product of benzene, causes acute myeloid leukemia (AML) elicited by benzene exposure. Past studies found that continuous exposure of human AML U937 cells to HQ selectively produces malignant U937/HQ cells in which FOXP3 upregulation modulates malignant progression. Other studies revealed that AMPK promotes TET2 activity on DNA demethylation and that TET2 activity is crucial for upregulating FOXP3 expression. This study was conducted to elucidate whether compound C, an AMPK inhibitor, blocked the AMPK-TET2-FOXP3 axis in AML and in HQ-selected malignant cells. We found higher levels of AMPKα, TET2, and FOXP3 expression in U937/HQ cells compared to U937 cells. Treatment of parental Original Article and HQ-selected malignant U937 cells with compound C induced ROS-mediated p38 MAPK activation, leading to a suppression of AMPKα, TET2, and FOXP3 expression. Moreover, compound C induced apoptosis and mTOR-independent autophagy. The suppression of the autophagic flux inhibited the apoptosis of compound C-treated U937 and U937/HQ cells, whereas co-treatment with rapamycin, a mTOR inhibitor, sensitized the two cell lines to compound C cytotoxicity. Overexpression of AMPKα1 or pretreatment with autophagic inhibitors abrogated compound C-induced autophagy and suppression of TET2 and FOXP3 expression. Restoration of AMPKα1 or FOXP3 expression increased cell survival after treatment with compound C. In conclusion, our results show that compound C suppresses AMPK/TET2 axis-mediated FOXP3 expression and induces autophagy-dependent apoptosis in parental and HQ-selected malignant U937 cells, suggesting that the AMPK/TET2/FOXP3 axis is a promising target for improving AML therapy and attenuating benzene exposure-induced AML progression.

Dorsomorphin induces cancer cell apoptosis and sensitizes cancer cells to HSP90 and proteasome inhibitors by reducing nuclear heat shock factor 1 levels

Objective

Heat shock factor 1 (HSF1), a transcriptional regulator of heat shock proteins (HSPs), is an attractive therapeutic target for cancer. However, only a few HSF1 inhibitors have been identified so far.

Methods

The mRNA and protein levels of HSF1, HSPs, cleaved PARP, and phosphorylated HSF1 were examined by real-time PCR and Western blot. Forced expression, RNA interference, and immunofluorescence assay were used for mechanistic studies. Cell viability and apoptosis were measured by WST-8 assay and flow cytometry, respectively. Xenograft studies were performed in nude mice to evaluate the effect of dorsomorphin and an HSP90 inhibitor on tumor growth.

Results

Dorsomorphin suppressed multiple stimuli-induced and constitutive HSPs expression in cancer cells. Mechanistic studies revealed that dorsomorphin reduced heat-induced HSP expression independent of adenosine monophosphate activated protein kinase. Dorsomorphin reduced heat-stimulated HSF1 Ser320 phosphorylation and nuclear translocation, as well as resting nuclear HSF1 levels in cancer cells. Dorsomorphin induced cancer cell apoptosis by inhibiting HSF1 expression. A structure-activity study revealed that the 4-pyridyl at the 3-site of the pyrazolo [1, 5-a]pyrimidine ring is critical for the anti-HSF1 activities of dorsomorphin. Dorsomorphin sensitized cancer cells to HSP90 and proteasome inhibitors and inhibited HSP70 expression induced by these inhibitors in vitro. In tumor-bearing nude mice, dorsomorphin enhanced HSP90 inhibitor-induced cancer cell apoptosis, tumor growth inhibition, and HSP70 expression.

Conclusions

Dorsomorphin is an HSF1 inhibitor. It induces cancer cell apoptosis, sensitizes cancer cells to both HSP90 and proteasome inhibitors, and suppresses HSP upregulation by these drugs, which may prevent the development of drug resistance. Hence, dorsomorphin and its derivates may serve as potential precursors for developing drugs against cancer.

Alternating magnetic field enhances cytotoxicity of Compound C

We previously reported the efficacy of anti-cancer therapy with hyperthermia using an alternating magnetic field (AMF) and a magnetic compound. In the course of the study, unexpectedly, we found that an AMF enhances the cytotoxicity of Compound C, an activated protein kinase (AMPK) inhibitor, although this compound is not magnetic. Therefore, we examined the cellular mechanism of AMF-induced cytotoxicity of Compound C in cultured human glioblastoma (GB) cells. An AMF (280 kHz, 250 Arms) for 30 minutes significantly enhanced the cytotoxicity of Compound C and promoted apoptosis towards several human GB cell lines in vitro. The AMF also increased Compound C-induced cell-cycle arrest of GB cells at the G2 phase and, thus, inhibited cell proliferation. The AMF increased Compound C-induced reactive oxygen species production. Furthermore, the AMF decreased ERK phosphorylation in the presence of Compound C and suppressed the protective autophagy induced by this compound. The application of an AMF in cancer chemotherapy may be a simple and promising method, which might reduce the doses of drugs used in future cancer treatment and, therefore, the associated side effects.

Compound C inhibits nonsense-mediated RNA decay independently of AMPK

The nonsense mediated RNA decay (NMD) pathway safeguards the integrity of the transcriptome by targeting mRNAs with premature translation termination codons (PTCs) for degradation. It also regulates gene expression by degrading a large number of non-mutant RNAs (including mRNAs and noncoding RNAs) that bear NMD-inducing features. Consequently, NMD has been shown to influence development, cellular response to stress, and clinical outcome of many genetic diseases. Small molecules that can modulate NMD activity provide critical tools for understanding the mechanism and physiological functions of NMD, and they also offer potential means for treating certain genetic diseases and cancer. Therefore, there is an intense interest in identifying small-molecule NMD inhibitors or enhancers. It was previously reported that both inhibition of NMD and treatment with the AMPK-selective inhibitor Compound C (CC) induce autophagy in human cells, raising the possibility that CC may be capable of inhibiting NMD. Here we show that CC indeed has a NMD-inhibitory activity. Inhibition of NMD by CC is, however, independent of AMPK activity. As a competitive ATP analog, CC does not affect the kinase activity of SMG1, an essential NMD factor and the only known kinase in the NMD pathway. However, CC treatment down-regulates the protein levels of several NMD factors. The induction of autophagy by CC treatment is independent of ATF4, a NMD target that has been shown to promote autophagy in response to NMD inhibition. Our results reveal a new activity of CC as a NMD inhibitor, which has implications for its use in basic research and drug development.

Exosomal neutral sphingomyelinase 1 suppresses hepatocellular carcinoma via decreasing the ratio of sphingomyelin/ceramide

Neutral sphingomyelinase 1 (NSMase1) mediates caspase-3 activation and apoptosis. However, the role of NSMase1, especially exosome-borne NSMase1 in hepatocellular carcinoma (HCC), remains unclear. We report that NSMase1, which converts sphingomyelin (SM) to ceramide, was significantly downregulated in HCC tissues. Low NSMase1 expression predicted poor long-term survival of HCC patients. NSMase1 downregulation in HCC resulted in increased SM and reduced ceramide (Cer) that led to an increased SM/Cer ratio. Interestingly, NSMase1 and NSMase activity were also decreased in exosomes isolated from HCC tissues and cell lines. Furthermore, NSMase activity increased in exosomes isolated from the culture medium of L02 cells transfected with pEGFP-C3-NSMase1 (NSMase1-Exo). NSMase1-Exo suppressed HCC cell growth and induced apoptosis via reduction of the SM/Cer ratio. Thus, NSMase1 in exosomes inhibits HCC growth by decreasing the SM/Cer ratio.

AMPK contributes to autophagosome maturation and lysosomal fusion

AMP-activated protein kinase (AMPK) regulates autophagy initiation when intracellular ATP level decreases. However, the role of AMPK during autophagosome maturation is not fully understood. Here, we report that AMPK contributes to efficient autophagosome maturation and lysosomal fusion. Using CRISPR-Cas9 gene editing, we generated AMPK α1 knockout HEK293T cell lines, in which starvation-induced autophagy is impaired. Compound C, an AMPK-independent autophagy inducer, and trehalose, an mTOR-independent autophagy inducer were used to examine the role of AMPK in autophagosome maturation and lysosomal fusion. While the treatment of control cells with either compound C or trehalose induces activation of autophagosomes as well as autolysosomes, the treatment of AMPK α1 knockout cells with compound C or trehalose induces mainly activation of autophagosomes, but not autolysosomes. We demonstrate that this effect is due to interference with the fusion of autophagosomes with lysosomes in AMPK α1 knockout cells. The transient expression of AMPK α1 can rescue autophagosome maturation. These results indicate that AMPK α1 is required for efficient autophagosome maturation and lysosomal fusion.

Probing de novo sphingolipid metabolism in mammalian cells utilizing mass spectrometry

Sphingolipids constitute a dynamic metabolic network that interconnects several bioactive molecules, including ceramide (Cer), sphingosine (Sph), Sph 1-phosphate, and Cer 1-phosphate. The interconversion of these metabolites is controlled by a cohort of at least 40 enzymes, many of which respond to endogenous or exogenous stimuli. Typical probing of the sphingolipid pathway relies on sphingolipid mass levels or determination of the activity of individual enzymes. Either approach is unable to provide a complete analysis of flux through sphingolipid metabolism, which, given the interconnectivity of the sphingolipid pathway, is critical information to identify nodes of regulation. Here, we present a one-step in situ assay that comprehensively probes the flux through de novo sphingolipid synthesis, post serine palmitoyltransferase, by monitoring the incorporation and metabolism of the 17 carbon dihydrosphingosine precursor with LC/MS. Pulse labeling and analysis of precursor metabolism identified sequential well-defined phases of sphingolipid synthesis, corresponding to the activity of different enzymes in the pathway, further confirmed by the use of specific inhibitors and modulators of sphingolipid metabolism. This work establishes precursor pulse labeling as a practical tool for comprehensively studying metabolic flux through de novo sphingolipid synthesis and complex sphingolipid generation.

Dihydroceramide-desaturase-1-mediated caspase 9 activation through ceramide plays a pivotal role in palmitic acid-induced HepG2 cell apoptosis

In this study, results showed that the inhibition of PA-induced HepG2 cell growth takes place in a time- and concentration-dependent manner, that activation of caspase 9 is necessary for PA-induced HepG2 cell apoptosis, that dihydroceramide desaturase 1 (DES1) plays a key role in PA-mediated caspase 9 and caspase 3 activation, and that palmitoleic acid (POA), an omega-7 monounsaturated fatty acid, reverses PA-induced apoptosis through DES1 → Ceramide → Caspase 9 → Caspase 3 signaling.

Potential roles of AMP-activated protein kinase in liver regeneration in mice with acute liver injury

Liver regeneration post severe liver injury is crucial for the recovery of hepatic structure and function. The energy sensor AMP‑activated protein kinase (AMPK) has a crucial role in the regulation of nutrition metabolism in addition to other energy‑intensive physiological and pathophysiological processes. Cellular proliferation requires intensive energy and nutrition support, therefore the present study investigated whether AMPK is involved in liver regeneration post carbon tetrachloride (CCl4)‑induced acute hepatic injury. The experimental data indicated that phosphorylation level of AMPK increased 48 h post‑CCl4 exposure, which was accompanied with upregulation of proliferating cell nuclear antigen (PCNA) and recovery of alanine aminotransferase (ALT) level. Pretreatment with the AMPK inhibitor compound C had no obvious effects on ALT elevation in plasma and histological abnormalities in liver 24 h post CCl4 exposure. However, treatment with compound C 24 h post CCl4 exposure significantly suppressed CCl4‑induced AMPK phosphorylation, PCNA expression and ALT recovery. These data suggest that endogenous AMPK was primarily activated at the regeneration stage in mice with CCl4‑induced acute liver injury and may function as a positive regulator in liver regeneration.

AMP-activated protein kinase is involved in the activation of the Fanconi anemia/BRCA pathway in response to DNA interstrand crosslinks

Fanconi anemia complementation group (FANC) proteins constitute the Fanconi Anemia (FA)/BRCA pathway that is activated in response to DNA interstrand crosslinks (ICLs). We previously performed yeast two-hybrid screening to identify novel FANC-interacting proteins and discovered that the alpha subunit of AMP-activated protein kinase (AMPKα1) was a candidate binding partner of the FANCG protein, which is a component of the FA nuclear core complex. We confirmed the interaction between AMPKα and both FANCG using co-immunoprecipitation experiments. Additionally, we showed that AMPKα interacted with FANCA, another component of the FA nuclear core complex. AMPKα knockdown in U2OS cells decreased FANCD2 monoubiquitination and nuclear foci formation upon mitomycin C-induced ICLs. Furthermore, AMPKα knockdown enhanced cellular sensitivity to MMC. MMC treatment resulted in an increase in AMPKα phosphorylation/activation, indicating AMPK is involved in the cellular response to ICLs. FANCA was phosphorylated by AMPK at S347 and phosphorylation increased with MMC treatment. MMC-induced FANCD2 monoubiquitination and nuclear foci formation were compromised in a U2OS cell line that stably overexpressed the S347A mutant form of FANCA compared to wild-type FANCA-overexpressing cells, indicating a requirement for FANCA phosphorylation at S347 for proper activation of the FA/BRCA pathway. Our data suggest AMPK is involved in the activation of the FA/BRCA pathway.

Compound C/Dorsomorphin: Its Use and Misuse as an AMPK Inhibitor

The evolutionary conserved energy sensor AMPK plays crucial roles in many biological processes-both during normal development and pathology. Loss-of-function genetic studies in mice as well as in lower organisms underscore its importance in embryonic development, stress physiology in the adult, and in key metabolic disorders including cardiovascular disease, diabetes, cancer, and metabolic syndrome. In contrast to several other kinases important in human health and medicine where specific/selective inhibitors are available, no AMPK-specific inhibitors are available. The only reagent called dorsomorphin or compound C that is occasionally used as an AMPK inhibitor unfortunately inhibits several other kinases much more potently than AMPK and is therefore highly non-specific. In this chapter, we discuss the pros and cons of using this reagent to study AMPK functions.

AMPK-dependent and independent effects of AICAR and compound C on T-cell responses

As a master metabolic sensor, AMP-activated protein kinase (AMPK) is involved in different fundamental cellular processes. Regulation of AMPK activity either by agonists (e.g., AICAR) or by antagonists (e.g., Compound C) has been widely employed to study the physiological functions of AMPK. However, mounting evidence indicates AMPK-independent effects for these chemicals and how they regulate immune cell functions remains largely unknown. Herein, using T cells from AMPK conditional knockout mice and their wild type littermates, we demonstrate that AICAR and Compound C can, indeed, activate or inhibit AMPK activity in T cells, respectively. Specifically, AICAR inhibits, but Compound C promotes, Ca²⁺-induced T cell death in an AMPK-dependent manner. In contrast, our data also demonstrate that AICAR and Compound C inhibit T cell activation and cytokine production in an AMPK-independent manner. Moreover, we find that the AMPK-independent activity of AICAR and Compound Cis mediated via the mTOR signaling pathway in activated T cells. Our results not only reveal the critical role of AMPK in regulating T cell survival and function, but also demonstrate AMPK-dependent and independent rolesof AICAR/Compound C in regulating T cell responses, thus suggesting a context-dependent effect of these “AMPK regulators”.

Activation of AMPK by OSU53 protects spinal cord neurons from oxidative stress

The present study tested the potential effect of OSU53, a novel AMPK activator, against hydrogen peroxide (H2O2)-induced spinal cord neuron damages. Treatment with OSU53 attenuated H2O2-induced death and apoptosis of primary murine spinal cord neurons. OSU53 activated AMPK signaling, which is required for its actions in spinal cord neurons. The AMPK inhibitor Compound C or AMPKα1 siRNA almost abolished OSU53-mediated neuroprotection against H2O2. On the other hand, sustained-activation of AMPK by introducing the constitutive-active AMPKα1 mimicked OSU53's actions, and protected spinal cord neurons from oxidative stress. OSU53 significantly attenuated H2O2-induced reactive oxygen species production, lipid peroxidation and DNA damages in spinal cord neurons. Additionally, OSU53 increased NADPH content and heme oxygenase-1 mRNA expression in H2O2-treated spinal cord neurons. Together, we indicate that targeted-activation of AMPK by OSU53 protects spinal cord neurons from oxidative stress.

Activation of AMP-activated protein kinase by metformin ablates angiotensin II-induced endoplasmic reticulum stress and hypertension in mice in vivo

BACKGROUND AND PURPOSE

Metformin, one of the most frequently prescribed medications for type 2 diabetes, reportedly exerts BP-lowering effects in patients with diabetes. However, the effects and underlying mechanisms of metformin on BP in non-diabetic conditions remain to be determined. The aim of the present study was to determine the effects of metformin on angiotensin II (Ang II) infusion-induced hypertension in vivo.

EXPERIMENTAL APPROACH

The effects of metformin on BP were investigated in wild-type (WT) C57BL/6J mice and in mice lacking AMP-activated protein kinase α2 (AMPKα2) mice with or without Ang II infusion. Also, the effect of metformin on Ang II-induced endoplasmic reticulum (ER) stress was explored in cultured human vascular smooth muscle cells (hVSMCs).

KEY RESULTS

Metformin markedly reduced BP in Ang II-infused WT mice but not in AMPKα2-deficient mice. In cultured hVSMCs, Ang II treatment resulted in inactivation of AMPK, as well as the subsequent induction of spliced X-box binding protein-1, phosphorylation of eukaryotic translation initiation factor 2α and expression of glucose-regulated protein 78 kDa, representing three well-characterized ER stress biomarkers. Moreover, AMPK activation by metformin ablated Ang II-induced ER stress in hVSMCs. Mechanistically, metformin-activated AMPKα2 suppressed ER stress by increasing phospholamban phosphorylation.

CONCLUSION AND IMPLICATIONS

Metformin alleviates Ang II-triggered hypertension in mice by activating AMPKα2, which mediates phospholamban phosphorylation and inhibits Ang II-induced ER stress in vascular smooth muscle cells.

Ginsenoside Rb3 strengthens the hypoglycemic effect through AMPK for inhibition of hepatic gluconeogenesis

Ginsenoside Rb3 is one of the major active components in protopanaxdiol type ginsenosides, and has demonstrated anti-diabetic activity. However, the mechanism of this action has yet to be elucidated. The present study investigated the effects of ginsenoside Rb3 on the AMP-activated protein kinase (AMPK) gluconeogenesis pathway. The present study involved the use of HepG2 cells and western blot analysis to systematically evaluate the effect of ginsenoside Rb3 on AMPK signaling proteins and key factors of gluconeogenesis [phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase, forkhead transcription factor 1 (FOXO1) and hepatic nuclear receptor 4α (HNF4α)]. The results indicated that 25 µM ginsenoside Rb3 significantly activated AMPK activity, increased the ratio of p-AMPK/total-AMPK, and had synergistic effects with the activator of AICAR on the activation of AMPK. Further analysis indicated that the expression of the transcription factor FOXO1 and HNF4α protein, two important factors in the pathway of HepG2 cell gluconeogenesis, was significantly suppressed by ginsenoside Rb3. PEPCK and G6Pase were subsequently inhibited, which led to the suppression of gluconeogenesis. These effects were partially blocked by the AMPK inhibitor, Compound C, which indicated that the inhibition effects of ginsenoside Rb3 on hepatic gluconeogenesis were predominantly due to the activation of the AMPK signaling pathway. These data suggested that ginsenoside Rb3 can suppress hepatic gluconeogenesis, at least partially through stimulation of AMPK activity.

Compound C Increases Sestrin2 Expression via Mitochondria-Dependent ROS Production

Compound C is a widely used chemical inhibitor that down-regulates AMP-activated protein kinase (AMPK) activity. However, it has been suggested that compound C exerts AMPK-independent effects in various cells. Here, we investigated whether compound C induces Sestrin2 (SESN2), an antioxidant enzyme induced by diverse stress. In addition, the mechanism responsible for SESN2 induction by compound C was determined. Our results showed that compound C increased SESN2 protein expression in HepG2 cells in a concentration- and time-dependent manner. The induction of SESN2 mRNA was also observed in cells treated with compound C. Increase of SESN2 luciferase activity confirmed transcriptional regulation by compound C and this substance also increased nuclear factor erythroid 2 (NF-E2)-related factor-2 (Nrf2) phosphorylation, which implies that Nrf2 was involved in SESN2 induction. Next, we sought to demonstrate whether production of reactive oxygen species (ROS) accompanied SESN2 expression. Compound C increased ROS production, but this effect was prevented by pretreatment with antioxidants or the mitochondrial complex I inhibitor. Moreover, cyclosporin A, an inhibitor of pore formation in the mitochondrial membrane, attenuated compound C-induced SESN2 induction. However, overexpression of a constitutively active form of AMPK was not able to abolish SESN2 induction by compound C, which implies that its action is independent of AMPK inhibition. In conclusion, this is the first study demonstrating that compound C alters mitochondrial function and induces ROS production, which ultimately leads to phosphorylation of Nrf2 and induction of SESN2.

Pharmacologic regulation of AMPK in breast cancer affects cytoskeletal properties involved with microtentacle formation and re-attachment

The presence of tumor cells in the circulation is associated with a higher risk of metastasis in patients with breast cancer. Circulating breast tumor cells use tubulin-based structures known as microtentacles (McTNs) to re-attach to endothelial cells and arrest in distant organs. McTN formation is dependent on the opposing cytoskeletal forces of stable microtubules and the actin network. AMP-activated protein kinase (AMPK) is a cellular metabolic regulator that can alter actin and microtubule organization in epithelial cells. We report that AMPK can regulate the cytoskeleton of breast cancer cells in both attached and suspended conditions. We tested the effects of AMPK on microtubule stability and the actin-severing protein, cofilin. AMPK inhibition with compound c increased both microtubule stability and cofilin activation, which also resulted in higher McTN formation and re-attachment. Conversely, AMPK activation with A-769662 decreased microtubule stability and cofilin activation with concurrent decreases in McTN formation and cell re-attachment. This data shows for the first time that AMPK shifts the balance of cytoskeletal forces in suspended breast cancer cells, which affect their ability to form McTNs and re-attach. These results support a model where AMPK activators may be used therapeutically to reduce the metastatic efficiency of breast tumor cells.

Adiponectin enhances bone marrow mesenchymal stem cell resistance to flow shear stress through AMP-activated protein kinase signaling

Adiponectin has been demonstrated to protect the cardiovascular system and bone marrow mesenchymal stem cells (BMSCs). However, it is unclear whether adiponectin can protect BMSCs against flow shear stress (FSS). In this study, our aim was to explore the effects of adiponectin on BMSCs and to explore the role of AMP-activated protein kinase (AMPK) signaling in this process. Shear stress significantly inhibits the survival and increases the apoptosis of BMSCs in an intensity-dependent manner. The expression levels of TGF-β, bFGF, VEGF, PDGF, and Bcl2 are simultaneously reduced, and the phosphorylation levels of AMPK and ACC, as well as the expression level of Bax, are increased. Supplementation with adiponectin promotes the survival of BMSCs; reverses the changes in the expression levels of TGF-β, bFGF, VEGF, PDGF, Bcl2, and Bax; and further amplifies the phosphorylation of AMPK and ACC. Furthermore, the protective effects of adiponectin can be partially neutralized by AMPK siRNA. In summary, we have demonstrated for the first time that adiponectin can effectively protect BMSCs from FSS and that this effect depends, at least in part, on the activation of AMPK signaling.

The enigma of ceramide synthase regulation in mammalian cells

Ceramide synthases (CerS) are key enzymes in the lipid metabolism of eukaryotic cells. Their products, ceramides (Cer), are components of cellular membranes but also mediate signaling functions in physiological processes such as proliferation, skin barrier function and cerebellar development. In pathophysiological processes such as multiple sclerosis and tumor progression, ceramide levels are altered, which can be ascribed, partly, to dysregulation of CerS gene transcription. Most publications deal with the effects of altered ceramide levels on physiological and pathophysiological processes, but the regulation of the appropriate CerS is frequently not investigated. This is insufficient for the clarification of the role of ceramides, because most ceramide species are generated by at least two CerS. The mechanisms of CerS regulation are manifold and it seems that each CerS isoform is regulated individually. For this reason, we discuss the different CerS separately in this review. From transcriptional regulation to alteration of protein activity, the possibilities to influence CerS are diverse. Furthermore, CerS are influenced by a variety of molecules including hormones and lipids. Without claiming completeness, we provide a résumé of the regulatory mechanisms for each CerS in mammalian cells and how dysregulation of these mechanisms during physiological processes may lead to pathophysiological processes.

Aldo-keto Reductase Family 1 Member B 10 Mediates Liver Cancer Cell Proliferation through Sphingosine-1-Phosphate

AKR1B10 is involved in hepatocarcinogenesis via modulation of fatty acid and lipid synthesis. AKR1B10 inhibition results in apoptosis of tumor cells whose lipids, especially phospholipids, were decreased by over 50%, suggesting involvement of phospholipids like sphingosine-1-phosphate (S1P) in AKR1B10's oncogenic function. Using a co-culture system, we found that co-culture of QSG-7701 (human hepatocyte) with HepG2 (hepatoma cell line) increases QSG-7701's proliferation, in which AKR1B10-S1P signaling plays a pivotal role. Consistent with previous findings, AKR1B10 mRNA and protein levels were higher in primary hepatocellular carcinoma (PHC) tissues than in peri-tumor tissues. Interestingly, the level of S1P was also higher in PHC tissues than in peri-tumor tissues. After analyzing the correlation between AKR1B10 mRNA expression in PHC tissues and the clinical data, we found that AKR1B10 mRNA expression was associated with serum alpha-fetoprotein (AFP), tumor-node-metastasis (TNM) stage, and lymph node metastasis, but not with other clinicopathologic variables. A higher AKR1B10 mRNA expression level is related to a shorter DFS (disease free survival) and OS (overall survival), serving as an independent predictor of DFS and OS in PHC patients with surgical resection.

Tumor suppressive functions of ceramide: evidence and mechanisms

Studies over the past two decades have identified ceramide as a multifunctional central molecule in the sphingolipid biosynthetic pathway. Given its diverse tumor suppressive activities, molecular understanding of ceramide action will produce fundamental insights into processes that limit tumorigenesis and may identify key molecular targets for therapeutic intervention. Ceramide can be activated by a diverse array of stresses such as heat shock, genotoxic damage, oxidative stress and anticancer drugs. Ceramide triggers a variety of tumor suppressive and anti-proliferative cellular programs such as apoptosis, autophagy, senescence, and necroptosis by activating or repressing key effector molecules. Defects in ceramide generation and metabolism in cancer contribute to tumor cell survival and resistance to chemotherapy. The potent and versatile anticancer activity profile of ceramide has motivated drug development efforts to (re-)activate ceramide in established tumors. This review focuses on our current understanding of the tumor suppressive functions of ceramide and highlights the potential downstream targets of ceramide which are involved in its tumor suppressive action.

Tumor Necrosis Factor-α (TNFα)-induced Ceramide Generation via Ceramide Synthases Regulates Loss of Focal Adhesion Kinase (FAK) and Programmed Cell Death

Ceramide synthases (CerS1-CerS6), which catalyze the N-acylation of the (dihydro)sphingosine backbone to produce (dihydro)ceramide in both the de novo and the salvage or recycling pathway of ceramide generation, have been implicated in the control of programmed cell death. However, the regulation of the de novo pathway compared with the salvage pathway is not fully understood. In the current study, we have found that late accumulation of multiple ceramide and dihydroceramide species in MCF-7 cells treated with TNFα occurred by up-regulation of both pathways of ceramide synthesis. Nevertheless, fumonisin B1 but not myriocin was able to protect from TNFα-induced cell death, suggesting that ceramide synthase activity is crucial for the progression of cell death and that the pool of ceramide involved derives from the salvage pathway rather than de novo biosynthesis. Furthermore, compared with control cells, TNFα-treated cells exhibited reduced focal adhesion kinase and subsequent plasma membrane permeabilization, which was blocked exclusively by fumonisin B1. In addition, exogenously added C6-ceramide mimicked the effects of TNFα that lead to cell death, which were inhibited by fumonisin B1. Knockdown of individual ceramide synthases identified CerS6 and its product C16-ceramide as the ceramide synthase isoform essential for the regulation of cell death. In summary, our data suggest a novel role for CerS6/C16-ceramide as an upstream effector of the loss of focal adhesion protein and plasma membrane permeabilization, via the activation of caspase-7, and identify the salvage pathway as the critical mechanism of ceramide generation that controls cell death.

Glucose regulates amyloid β production via AMPK

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Accumulation of Aβ peptides in the brain has been suggested as the cause of AD (amyloid cascade hypothesis); however, the mechanism for the abnormal accumulation of Aβ in the brains of AD patients remains unclear. A plethora of evidence has emerged to support a link between metabolic disorders and AD. This study was designed to examine the relationship between energy status and Aβ production. Neuro 2a neuroblastoma cells overexpressing human amyloid precursor protein 695 (APP cells) were cultured in media containing different concentrations of glucose and agonist or antagonist of AMP-activated-protein-kinase (AMPK), a metabolic master sensor. The results showed that concentrations of glucose in the culture media were negatively associated with the activation statuses of AMPK in APP cells, but positively correlated with the levels of secreted Aβ. Modulating AMPK activities affected the production of Aβ. If APP cells were cultured in high glucose medium (i.e., AMPK was inactive), stimulation of AMPK activity decreased the production levels of Aβ. On the contrary, if APP cells were incubated in medium containing no glucose (i.e., AMPK was activated), inhibition of AMPK activity largely increased Aβ production. As AMPK activation is a common defect in metabolic abnormalities, our study supports the premise that metabolic disorders may aggravate AD pathogenesis.