Liposomal C6 Ceramide Activates Protein Phosphatase 1 to Inhibit Melanoma Cells

PP1γ regulates neuronal insulin signaling and aggravates insulin resistance leading to AD-like phenotypes

BACKGROUND

PP1γ is one of the isoforms of catalytic subunit of a Ser/Thr phosphatase PP1. The role of PP1γ in cellular regulation is largely unknown. The present study investigated the role of PP1γ in regulating neuronal insulin signaling and insulin resistance in neuronal cells. PP1 was inhibited in mouse neuroblastoma cells (N2a) and human neuroblastoma cells (SH-SY5Y). The expression of PP1α and PP1γ was determined in insulin resistant N2a, SH-SY5Y cells and in high-fat-diet-fed-diabetic mice whole-brain-lysates. PP1α and PP1γ were silenced by siRNA in N2a and SH-SY5Y cells and effect was tested on AKT isoforms, AS160 and GSK3 isoforms using western immunoblot, GLUT4 translocation by confocal microscopy and glucose uptake by fluorescence-based assay.

RESULTS

Results showed that, in one hand PP1γ, and not PP1α, regulates neuronal insulin signaling and insulin resistance by regulating phosphorylation of AKT2 via AKT2-AS160-GLUT4 axis. On the other hand, PP1γ regulates phosphorylation of GSK3β via AKT2 while phosphorylation of GSK3α via MLK3. Imbalance in this regulation results into AD-like phenotype.

CONCLUSION

PP1γ acts as a linker, regulating two pathophysiological conditions, neuronal insulin resistance and AD. Video Abstract.

Ethanol-induced ceramide production causes neuronal apoptosis by increasing MCL-1S-mediated ER-mitochondria contacts

Heavy alcohol consumption causes neuronal cell death and cognitive impairment. Neuronal cell death induced by ethanol may result from increased production of the sphingolipid metabolite ceramide. However, the molecular mechanisms of neuronal cell death caused by ethanol-induced ceramide production have not been elucidated. Therefore, we investigated the mechanism through which ethanol-induced ceramide production causes neuronal cell apoptosis using human induced-pluripotent stem cell-derived neurons and SH-SY5Y cells and identified the effects of ceramide on memory deficits in C57BL/6 mice. First, we found that ethanol-induced ceramide production was decreased by inhibition of the de novo synthesis pathway, mediated by serine palmitoyltransferase (SPT). The associated alterations of the molecules related to the ceramide pathway suggest that the elevated level of ceramide activated protein phosphatase 1 (PP1), which inhibited the nuclear translocation of serine/arginine-rich splicing factor 1 (SRSF1). This led to aberrant splicing of myeloid cell leukemia 1 (MCL-1) pre-mRNA, which upregulated MCL-1S expression. Our results demonstrated that the interaction of MCL-1S with the inositol 1, 4, 5-trisphosphate receptor (IP3R) increases calcium release from the endoplasmic reticulum (ER) and then activated ER-bound inverted formin 2 (INF2). In addition, we discovered that F-actin polymerization through INF2 activation promoted ER-mitochondria contacts, which induced mitochondrial calcium influx and mitochondrial reactive oxygen species (mtROS) production. Markedly, MCL-1S silencing decreased mitochondria-associated ER membrane (MAM) formation and prevented mitochondrial calcium influx and mtROS accumulation, by inhibiting INF2-dependent actin polymerization interacting with mitochondria. Furthermore, the inhibition of ceramide production in ethanol-fed mice reduced MCL-1S expression, neuronal cell death, and cognitive impairment. In conclusion, we suggest that ethanol-induced ceramide production may lead to mitochondrial calcium overload through MCL-1S-mediated INF2 activation-dependent MAM formation, which promotes neuronal apoptosis.

Targeting Sphingolipids for Cancer Therapy

Sphingolipids are an extensive class of lipids with different functions in the cell, ranging from proliferation to cell death. Sphingolipids are modified in multiple cancers and are responsible for tumor proliferation, progression, and metastasis. Several inhibitors or activators of sphingolipid signaling, such as fenretinide, safingol, ABC294640, ceramide nanoliposomes (CNLs), SKI-II, α-galactosylceramide, fingolimod, and sonepcizumab, have been described. The objective of this review was to analyze the results from preclinical and clinical trials of these drugs for the treatment of cancer. Sphingolipid-targeting drugs have been tested alone or in combination with chemotherapy, exhibiting antitumor activity alone and in synergism with chemotherapy in vitro and in vivo. As a consequence of treatments, the most frequent mechanism of cell death is apoptosis, followed by autophagy. Aslthough all these drugs have produced good results in preclinical studies of multiple cancers, the outcomes of clinical trials have not been similar. The most effective drugs are fenretinide and α-galactosylceramide (α-GalCer). In contrast, minor adverse effects restricted to a few subjects and hepatic toxicity have been observed in clinical trials of ABC294640 and safingol, respectively. In the case of CNLs, SKI-II, fingolimod and sonepcizumab there are some limitations and absence of enough clinical studies to demonstrate a benefit. The effectiveness or lack of a major therapeutic effect of sphingolipid modulation by some drugs as a cancer therapy and other aspects related to their mechanism of action are discussed in this review.

Modulation of serine/threonine-protein phosphatase 1 (PP1) complexes: A promising approach in cancer treatment

Cancer is the second leading cause of death worldwide. Despite the availability of numerous therapeutic options, tumor heterogeneity and chemoresistance have limited the success of these treatments, and the development of effective anticancer therapies remains a major focus in oncology research. The serine/threonine-protein phosphatase 1 (PP1) and its complexes have been recognized as potential drug targets. Research on the modulation of PP1 complexes is currently at an early stage, but has immense potential. Chemically diverse compounds have been developed to disrupt or stabilize different PP1 complexes in various cancer types, with the objective of inhibiting disease progression. Beneficial results obtained in vitro now require further pre-clinical and clinical validation. In conclusion, the modulation of PP1 complexes seems to be a promising, albeit challenging, therapeutic strategy for cancer.

Targeted Metabolomics Identifies Plasma Biomarkers in Mice with Metabolically Heterogeneous Melanoma Xenografts

Melanomas are genetically and metabolically heterogeneous, which influences therapeutic efficacy and contributes to the development of treatment resistance in patients with metastatic disease. Metabolite phenotyping helps to better understand complex metabolic diseases, such as melanoma, and facilitates the development of novel therapies. Our aim was to characterize the tumor and plasma metabolomes of mice bearing genetically different melanoma xenografts. We engrafted the human melanoma cell lines A375 (BRAF mutant), WM47 (BRAF mutant), WM3000 (NRAS mutant), and WM3311 (BRAF, NRAS, NF1 triple-wildtype) and performed a broad-spectrum targeted metabolomics analysis of tumor and plasma samples obtained from melanoma-bearing mice as well as plasma samples from healthy control mice. Differences in ceramide and phosphatidylcholine species were observed between melanoma subtypes irrespective of the genetic driver mutation. Furthermore, beta-alanine metabolism differed between melanoma subtypes and was significantly enriched in plasma from melanoma-bearing mice compared to healthy mice. Moreover, we identified beta-alanine, p-cresol sulfate, sarcosine, tiglylcarnitine, two dihexosylceramides, and one phosphatidylcholine as potential melanoma biomarkers in plasma. The present data reflect the metabolic heterogeneity of melanomas but also suggest a diagnostic biomarker signature for melanoma screening.

Protein phosphatase 1 in tumorigenesis: is it worth a closer look?

Cancer cells take advantage of signaling cascades to meet their requirements for sustained growth and survival. Cell signaling is tightly controlled by reversible protein phosphorylation mechanisms, which require the counterbalanced action of protein kinases and protein phosphatases. Imbalances on this system are associated with cancer development and progression. Protein phosphatase 1 (PP1) is one of the most relevant protein phosphatases in eukaryotic cells. Despite the widely recognized involvement of PP1 in key biological processes, both in health and disease, its relevance in cancer has been largely neglected. Here, we provide compelling evidence that support major roles for PP1 in tumorigenesis.

C16:0 ceramide effect on melanoma malignant behavior and glycolysis depends on its intracellular or exogenous location

To investigate the role of C16:0 ceramide in melanoma metastatic behavior and glycolysis, five common long-chain ceramides (C16:0, C18:0, C20:0, C22:0, C24:0) were tested in melanocyte and melanoma cell lines by LC-MS. We then treated non-metastatic and metastatic melanoma cells with PDMP and exogenous C16:0 to explore their effects on proliferation, migration, and glycolysis. The long-chain ceramide was also analyzed by LC-MS after treatment. C16:0 ceramide showed the highest levels in melanocyte and melanoma cells, with all melanomas higher than melanocytes. PDMP inhibited malignant behavior and glycolysis in melanoma, and caused the accumulation of intracellular C16:0. Exogenous C16:0 promoted melanoma glycolysis, but not malignant behavior, and decreased intracellular C16:0. Finally, pyruvate kinase (PK), hexokinase (HK), and lactic acid dehydrogenase (LDH) activity, key enzymes in glycolysis, were altered after treatment with PDMP and exogenous C16:0.

Optimization of the Lipase-Catalyzed Selective Amidation of Phenylglycinol

Ceramides and their analogs have a regulatory effect on inflammatory cytokines expression. It was found that a kind of ceramides analog synthesized from phenylglycinol could inhibit the production of cytokine TNF-α. However, two active hydrogen groups are present in the phenylglycinol molecule. It is difficult to control the process without hydroxyl group protection to dominantly produce amide in the traditional chemical synthesis. A selective catalytic the amidation route of phenylglycinol by lipases was investigated in this research. The results indicated that the commercial immobilized lipase Novozym 435 has the best regio-selectivity on the amide group. Based on the experimental results and in silico simulation, it was found that the mechanism of specific N-acyl selectivity of lipase was not only from intramolecular migration and proton shuttle mechanism, but also from the special structure of active site of enzyme. The optimal reaction yield of aromatic amide compound in a solvent-free system with lipase loading of 15 wt% (to the weight of total substrate) reached 89.41 ± 2.8% with very few of byproducts detected (0.21 ± 0.1% ester and 0.64 ± 0.2% diacetylated compound). Compare to other reported works, this work have the advantages such as low enzyme loading, solvent free, and high N-acylation selectivity. Meanwhile, this Novozym 435 lipase based synthesis method has an excellent regio-selectivity on most kinds of amino alcohol compounds. Compared to the chemical method, the enzymatic synthesis exhibited high regio-selectivity, and conversion rates. The method could be a promising alternative strategy for the synthesis of aromatic alkanolamides.

Emergent Nanotechnological Strategies for Systemic Chemotherapy against Melanoma

Melanoma is an aggressive form of skin cancer, being one of the deadliest cancers in the world. The current treatment options involve surgery, radiotherapy, targeted therapy, immunotherapy and the use of chemotherapeutic agents. Although the last approach is the most used, the high toxicity and the lack of efficacy in advanced stages of the disease have demanded the search for novel bioactive molecules and/or efficient drug delivery systems. The current review aims to discuss the most recent advances on the elucidation of potential targets for melanoma treatment, such as aquaporin-3 and tyrosinase. In addition, the role of nanotechnology as a valuable strategy to effectively deliver selective drugs is emphasized, either incorporating/encapsulating synthetic molecules or natural-derived compounds in lipid-based nanosystems such as liposomes. Nanoformulated compounds have been explored for their improved anticancer activity against melanoma and promising results have been obtained. Indeed, they displayed improved physicochemical properties and higher accumulation in tumoral tissues, which potentiated the efficacy of the compounds in pre-clinical experiments. Overall, these experiments opened new doors for the discovery and development of more effective drug formulations for melanoma treatment.

Metabolic and lipidomic investigation of the antiproliferative effects of coronatine against human melanoma cells

Melanoma is the most aggressive form of skin cancer, with metastatic melanoma being refractory to currently available conventional therapies. In this study, we evaluated the inhibitory effect of coronatine (COR) on the proliferation of metastatic melanoma cells. COR inhibited the proliferation of melanoma cells but negligibly affected the proliferation of normal melanocytes. Comparative metabolic and lipidomic profiling using gas chromatography-mass spectrometry and direct infusion-mass spectrometry was performed to investigate COR-induced metabolic changes. These analyses identified 33 metabolites and 82 lipids. Of these, the levels of lactic acid and glutamic acid, which are involved in energy metabolism, significantly decreased in COR-treated melanoma cells. Lipidomic profiling indicated that ceramide levels increased in COR-treated melanoma cells, suggesting that ceramides could function as a suppressor of cancer cell proliferation. In contrast, the levels of phosphatidylinositol (PI) species, including PI 16:0/18:0, 16:0/18:1, 18:0/18:0, and 18:0/18:1, which were found to be potential biomarkers of melanoma metastasis in our previous study, were lower in the COR-treated cells than in control cells. The findings of metabolomic and lipidomic profiling performed in the present study provide new insights on the anticancer mechanisms of COR and can be used to apply COR in cancer treatment.

Ceramide-Graphene Oxide Nanoparticles Enhance Cytotoxicity and Decrease HCC Xenograft Development: A Novel Approach for Targeted Cancer Therapy

Despite substantial efforts to develop novel therapeutic strategies for treating hepatocellular carcinoma (HCC), the effectiveness and specificity of available drugs still require further improvement. Previous work has shown that exogenous ceramide can play a key role in inducing the apoptotic death of cancer cells, however, the poor water-solubility of this compound has hampered its use for cancer treatment. In the present study, we used polyethylene glycol (PEG) and polyethylenimine (PEI) co-conjugated ultra-small nano-GO (NGO-PEG-PEI) loaded with C6-ceramide (NGO-PEG-PEI/Cer) as a strategy for HCC treatment. We assessed the biological role of NGO-PEG-PEI/Cer, and we assessed its antitumor efficacy against HCC both in vitro and in vivo in combination with the chemotherapeutic drug sorafenib. We found that NGO-PEG-PEI significantly enhanced the cellular uptake of C6-ceramide. By investigating the mechanism of cellular delivery, we determined that the internalization of NGO-PEG-PEI/Cer progressed primarily via a clathrin-mediated mechanism. The combination of NGO-PEG-PEI/Cer and sorafenib exhibited synergy between these two drugs. Further work revealed that NGO-PEG-PEI/Cer may play a role in subverting multidrug resistance (MDR) in HCC cells by inactivating MDR and Akt signaling. NGO-PEG-PEI/Cer also significantly inhibited tumor growth and improved survival times in vivo, and the synergetic effect of NGO-PEG-PEI/Cer combined with sorafenib was also observed in drug-resistant HCC xenografts. In conclusion, our NGO-PEG-PEI nanocomposite is an effective nano-platform for loading C6-ceramide for therapeutic use in treating HCC, exhibiting high cancer cell killing potency in this tumor model. The NGO-PEG-PEI/Cer/sorafenib combination additionally represents a promising potential therapeutic strategy for the treatment of drug-resistant HCC.

C6 ceramide motivates the anticancer sensibility induced by PKC412 in preclinical head and neck squamous cell carcinoma models

The purpose of this study was to evaluate the anti-head and neck squamous cell carcinoma (anti-HNSCC) cell activity by C6 ceramide and multikinase inhibitor PKC412. Experiments were performed on HNSCC cell lines (SQ20B and SCC-9) and primary human oral carcinoma cells. Results showed that PKC412 inhibited HNSCC cell proliferation without provoking apoptosis activation. Cotreatment of C6 ceramide significantly augmented PKC412-induced lethality in HNSCC cells. PKC412 decreased Akt-mammalian target of rapamycin (mTOR) activation in HNSCC cells, facilitated with cotreatment of C6 ceramide. In contrast, exogenous expression of a constitutively active Akt restored Akt-mTOR activation and attenuated lethality by the cotreatment. We propose that Mcl-1 is a primary resistance factor of PKC412. The cytotoxicity of PKC412 in HNSCC cells was potentiated with Mcl-1 short hairpin RNA knockdown, but was attenuated with Mcl-1 overexpression. Intriguingly, C6 ceramide downregulated Mcl-1 in HNSCC cells. In vivo, PKC412 oral administration inhibited SQ20B xenograft tumor growth in severe combined immunodeficient mice. The antitumor activity of PKC412 was further sensitized with coadministration of liposomal C6 ceramide. Together, we suggest that PKC412 could be further studied as a promising anti-HNSCC strategy, alone or in combination with C6 ceramide.

The ceramide pathway is involved in the survival, apoptosis and exosome functions of human multiple myeloma cells in vitro

Multiple myeloma (MM) is characterized by the clonal proliferation of malignant plasma cells and refractoriness to traditional therapies. It has been shown that exosomes are involved in modulating the progression and the metastasis of cancers through microRNAs (miRs). Ceramide is a type of sphingolipid; the ceramide pathway of exosomal secretion has been shown to affect the apoptosis of cancer cells. But the role of this pathway in MM cell function, exosome function and miR regulation remains unknown. In this study, we showed that C6 ceramide (an exogenous ceramide supplement, 1.25-40 μmol/L) dose-dependently inhibited the proliferation and promoted the apoptosis in human MM OPM2 cell line, which were associated with elevated caspase 3/9 and PARP cleavage. We also found that C6 ceramide (5-20 μmol/L) dose-dependently stimulated exosome secretion and increased exosomal levels of tumor-suppressive miRs (miR 202, miR 16, miR 29b and miR 15a). Of note, exosomes from C6 ceramide-treated OPM2 cells could influence the proliferation and apoptosis of the recipient OPM2 cells, which correlated with increased tumor-suppressive exosomal miRs. In contrast, GW4869 (a ceramide inhibitor, 5-20 μmol/L) exerted the opposite effects on the regulation of MM function, exosome secretion and miR levels in MM exosomes. However, exosomes from GW4869-treated OPM2 cells had no effect on these miRs and the survival of targeted OPM2 cells. Taken together, our findings reveal that the ceramide pathway modulates MM survival, probably directly via the caspase pathway and indirectly via exosomal miR mechanisms.

The Many Facets of Sphingolipids in the Specific Phases of Acute Inflammatory Response

This review provides an overview on components of the sphingolipid superfamily, on their localization and metabolism. Information about the sphingolipid biological activity in cell physiopathology is given. Recent studies highlight the role of sphingolipids in inflammatory process. We summarize the emerging data that support the different roles of the sphingolipid members in specific phases of inflammation: (1) migration of immune cells, (2) recognition of exogenous agents, and (3) activation/differentiation of immune cells.

Ginseng Rh2 protects endometrial cells from oxygen glucose deprivation/re-oxygenation

In this study, oxygen glucose deprivation/re-oxygenation (OGDR) was applied to cultured endometrial cells to mimic ischemic-reperfusion injuries. We also tested the potential effect of Ginseng Rh2 (GRh2) against the process. In established T-HESC human endometrial cells and primary murine endometrial cells, GRh2 largely inhibited OGDR-induced viability reduction and cell death. Remarkably, OGDR induced programmed necrosis in the endometrial cells, evidenced by cyclophilin D-p53-adenine nucleotide translocator 1 (ANT-1) mitochondrial association, mitochondrial depolarization, reactive oxygen species production, and lactate dehydrogenase release. Notably, such effects by OGDR were largely attenuated with co-treatment of GRh2. Further, cyclophilin D inhibition or knockdown also protected endometrial cells from OGDR. On the other hand, forced over-expression of cyclophilin D facilitated OGDR-induced T-HESC cell necrosis, which was dramatically inhibited by GRh2. Together, GRh2 protects endometrial cells from OGDR possibly via inhibiting CypD-dependent programmed necrosis pathway.

Activation of Akt by SC79 protects myocardiocytes from oxygen and glucose deprivation (OGD)/re-oxygenation

SC79 is a novel Akt activator. The current study tested its potential effect against oxygen and glucose deprivation (OGD)/re-oxygenation-induced myocardial cell death. We showed that SC79 activated Akt and protected H9c2 myocardial cells and primary murine myocardiocytes from OGD/re-oxygenation. Reversely, Akt inhibitor MK-2206 or Akt1 shRNA knockdown almost completely abolished SC79-mediated myocardial cytoprotection. SC79 treatment in H9c2 cells inhibited OGD/re-oxygenation-induced programmed necrosis pathway, evidenced by mitochondrial depolarization and cyclophilin D-p53-ANT-1 (adenine nucleotide translocator 1) association. Further, SC79 activated Akt downstream NF-E2-related factor 2 (NRF2) signaling to suppress OGD/re-oxygenation-induced reactive oxygen species (ROS) production. Reversely, NRF2 shRNA knockdown in H9c2 cells largely attenuated SC79-induced ROS scavenging ability and cytoprotection against OGD/re-oxygenation. Together, we conclude that activation of Akt by SC79 protects myocardial cells from OGD/re-oxygenation.

Sphingosine metabolism as a therapeutic target in cutaneous melanoma

Melanoma is by far the most aggressive type of skin cancer with a poor prognosis in its advanced stages. Understanding the mechanisms involved in melanoma pathogenesis, response, and resistance to treatment has gained a lot of attention worldwide. Recently, the role of sphingolipid metabolism has been studied in cutaneous melanoma. Sphingolipids are bioactive lipid effector molecules involved in the regulation of various cellular signaling pathways such as inflammation, cancer cell proliferation, death, senescence, and metastasis. Recent studies suggest that sphingolipid metabolism impacts melanoma pathogenesis and is a potential therapeutic target. This review focuses on defining the role of sphingolipid metabolism in melanoma carcinogenesis, discussing sphingolipid-based therapeutic approaches, and highlighting the areas that require more extensive research.