Ceramide limits phosphatidylinositol-3-kinase C2β-controlled cell motility in ovarian cancer: potential of ceramide as a metastasis-suppressor lipid

Exploring the causal associations of the gut microbiota and plasma metabolites with ovarian cancer: an approach of mendelian randomization analysis combined with network pharmacology and molecular docking

BACKGROUND

While increasing evidence suggests that alterations in the gut microbiota and metabolites are associated with ovarian cancer (OC) risk, whether these associations imply causation remains to be identified.

METHODS

We conducted a two-sample Mendelian randomization (MR) study utilizing a large-scale genome-wide association study (GWAS) to explore the causal effects of the gut microbiota of 196/220 individuals and 1,400 plasma metabolites on OC and epithelial ovarian cancer (EOC) subtypes. Data on the gut microbiota were obtained from the MiBioGen consortium of 18,340 subjects and the Dutch Microbiome Project of 7,738 volunteers. Data on plasma metabolites were derived from a GWAS of plasma metabolites in 8,299 participants. Ovarian cancer (n = 25,509) and EOC subtypes were obtained from the Ovarian Cancer Association Consortium (OCAC). Metabolites and associated targets were analyzed via network pharmacology and molecular docking.

RESULTS

At the genus and species levels, we identified seven risk factors for the gut microbiota: the genus Dialister (P = 0.024), genus Ruminiclostridium5 (P = 0.0004), genus Phascolarctobacterium (P = 0.0217), species Bacteroides massiliensis (P = 0.011), species Phascolarctobacterium succinatutens (P = 0.0212), species Paraprevotella clara (P = 0.0247) and species Bacteroides dorei (P = 0.0054). In addition, five gut microbes at the genus and species levels were found to be protective: genus Family XIII AD3011 group (P = 0.006), genus Butyrivibrio (P = 0.0095), genus Oscillibacter (P = 0.0206), species Roseburia hominis (P = 0.0241), and species Bifidobacterium bifidum (P = 0.0224). For plasma metabolites, we revealed five positive and four negative correlations with OC. Among these, caffeic acid and caffeine metabolites and sphingomyelin and ceramide metabolites were identified as risk factors, whereas phenylalanine metabolites, butyric acid metabolites, and some lipid metabolites were recognized as protective factors. A series of sensitivity analyses revealed no abnormalities, including pleiotropy and heterogeneity analyses.

CONCLUSION

Our MR analysis demonstrated that the gut microbiota and metabolites are causally associated with OC, which has significant potential for the early detection and diagnosis of OC and EOC subtypes, providing valuable insights into this area of research.

Phosphoinositide 3-kinase (PI3K) classes: From cell signaling to endocytic recycling and autophagy

Lipid signaling is defined as any biological signaling action in which a lipid messenger binds to a protein target, converting its effects to specific cellular responses. In this complex biological pathway, the family of phosphoinositide 3-kinase (PI3K) represents a pivotal role and affects many aspects of cellular biology from cell survival, proliferation, and migration to endocytosis, intracellular trafficking, metabolism, and autophagy. While yeasts have a single isoform of phosphoinositide 3-kinase (PI3K), mammals possess eight PI3K types divided into three classes. The class I PI3Ks have set the stage to widen research interest in the field of cancer biology. The aberrant activation of class I PI3Ks has been identified in 30-50% of human tumors, and activating mutations in PIK3CA is one of the most frequent oncogenes in human cancer. In addition to indirect participation in cell signaling, class II and III PI3Ks primarily regulate vesicle trafficking. Class III PI3Ks are also responsible for autophagosome formation and autophagy flux. The current review aims to discuss the original data obtained from international research laboratories on the latest discoveries regarding PI3Ks-mediated cell biological processes. Also, we unravel the mechanisms by which pools of the same phosphoinositides (PIs) derived from different PI3K types act differently.

Ceramide Nanoliposomes as Potential Therapeutic Reagents for Asthma

Ceramides are an emerging class of anti-inflammatory lipids, and nanoscale ceramide-delivery systems are potential therapeutic strategies for inflammatory diseases. This study investigated the therapeutic effects of ceramide nanoliposomes (CNL) on type 2 inflammation-based asthma, induced by repeated ovalbumin (OVA) challenges. Asthmatic mice intratracheally treated with ceramide-free liposomes (Ghost) displayed typical airway remodeling including mucosal accumulation and subepithelial fibrosis, whereas, in CNL-treated mice, the degree of airway remodeling was significantly decreased. Compared to the Ghost group, CNL treatment unexpectedly failed to significantly influence formation of type 2 cytokines, including IL-5 and IL-13, known to facilitate pathogenic production of airway mucus predominantly comprising MUC5AC mucin. Interestingly, CNL treatment suppressed OVA-evoked hyperplasia of MUC5AC-generating goblet cells in the airways. This suggests that CNL suppressed goblet cell hyperplasia and airway mucosal accumulation independently of type 2 cytokine formation. Mechanistically, CNL treatment suppressed cell growth and EGF-induced activation of Akt, but not ERK1/2, in a human lung epithelial cell culture system recapitulating airway goblet cell hyperplasia. Taken together, CNL is suggested to have therapeutic effects on airway remodeling in allergic asthma by targeting goblet cell hyperplasia. These findings raise the potential of ceramide-based therapies for airway diseases, such as asthma.

Inhibition of sphingolipid metabolism in osteosarcoma protects against CD151-mediated tumorigenicity

Osteosarcoma is the most common primary bone tumor, with a poor prognosis owing to the lack of efficient molecular-based targeted therapies. Previous studies have suggested an association between CD151 and distinct consequences in osteosarcoma tumorigenicity. However, the potential of CD151 as a therapeutic target has not yet been sufficiently explored. Here, we performed integrated transcriptomic and metabolomic analyses of osteosarcoma and identified sphingolipid metabolism as the top CD151-regulated pathway. CD151 regulates sphingolipid metabolism primarily through SPTCL1, the first rate-limiting enzyme in sphingolipid biosynthesis. Mechanistically, depletion of CD151 enhanced c-myc polyubiquitination and subsequent degradation. c-myc is vital for the transcriptional activation of SPTLC1. Functionally, sphingolipid synthesis and the SPTLC1 inhibitor, myriocin, significantly suppressed the clonogenic growth of CD151-overexpression cells. Importantly, myriocin selectively restrained CD151-high expression tumor growth in preclinical patient-derived xenograft models. Collectively, these data establish that CD151 is a key mediator of sphingolipid metabolism and provide a new approach to developing novel CD151-based targeted therapies for osteosarcoma.

Widely Targeted Lipidomics and Transcriptomics Analysis Revealed Changes of Lipid Metabolism in Spleen Dendritic Cells in Shrimp Allergy

Shrimp allergy (SA) is pathological type 2 inflammatory immune responses against harmless shrimp protein allergen, which is caused by complex interactions between dendritic cells (DCs) and other immune cells. Lipid metabolism in different DCs states are significantly changed. However, the lipid metabolism of spleen DCs in SA remain ambiguous. In this study, we established a BALB/c mouse shrimp protein extract-induced allergy model to determine the lipid profile of spleen DCs in SA, and the molecular mechanism between lipid metabolism and immune inflammation was preliminarily studied. Spleen DCs were sorted by fluorescence-activated cell sorting, and then widely targeted lipidomics and transcriptomics analysis were performed. Principal component analysis presented the lipidome alterations in SA. The transcriptomic data showed that Prkcg was involved in lipid metabolism, immune system, and inflammatory signaling pathway. In the correlation analysis, the results suggested that Prkcg was positively correlated with triacylglycerol (Pearson correlation coefficient = 0.917, p = 0.01). The lipidomics and transcriptomics integrated pathway analysis indicated the activated metabolic conversion from triacylglycerol to 1,2-diacyl-sn-glycerol and the transmission of lipid metabolism to immune inflammation (from triacylglycerol and ceramide to Prkcg) in SA spleen DCs, and cellular experiments in vitro showed that glyceryl trioleate and C16 ceramide treatment induced immune function alteration in DCs.

Targeted liposomal doxorubicin/ceramides combinations: the importance to assess the nature of drug interaction beyond bulk tumor cells

One of the major assets of anticancer nanomedicine is the ability to co-deliver drug combinations, as it enables targeting of different cellular populations and/or signaling pathways implicated in tumorigenesis and thus tackling tumor heterogeneity. Moreover, drug resistance can be circumvented, for example, upon co-encapsulation and delivery of doxorubicin and sphingolipids, as ceramides. Herein, the impact of short (C6) and long (C18) alkyl chain length ceramides on the nature of drug interaction, within the scope of combination with doxorubicin, was performed in bulk triple-negative breast cancer (TNBC) cells, as well as on the density of putative cancer stem cells and phenotype, including live single-cell tracking. C6- or C18-ceramide enabled a synergistic drug interaction in all conditions and (bulk) cell lines tested. However, differentiation among these two ceramides was reflected on the migratory potential of cancer cells, particularly significant against the highly motile MDA-MB-231 cells. This effect was supported by the downregulation of the PI3K/Akt pathway enabled by C6-ceramide and in contrast with C18-ceramide. The decrease of the migratory potential enabled by the targeted liposomal combinations is of high relevance in the context of TNBC, due to the underlying metastatic potential. Surprisingly, the nature of the drug interaction assessed at the level of bulk cancer cells revealed to be insufficient to predict whether a drug combination enables a decrease in the percentage of the master regulators of tumor relapse as ALDH^+/high putative TNBC cancer stem cells, suggesting, for the first time, that it should be extended further down to this level.

The Enhanced Efficacy of Intracellular Delivery of Doxorubicin/C6-Ceramide Combination Mediated by the F3 Peptide/Nucleolin System Is Supported by the Downregulation of the PI3K/Akt Pathway

Simple Summary

Targeted nanomedicine-based approaches that aim at the simultaneous delivery of synergistic drug combinations to multiple cellular populations are of high relevance for tackling heterogeneity on solid tumors. Considering that cancer stem cells (CSC) may originate from non-stem cancer cells, single-drug regimens targeting only one of these cell populations could enable tumors to evade treatments. As such, the identification of a common marker, such as nucleolin, might result in a therapeutic advantage. The results herein generated suggested a transversal role of nucleolin in the internalization of F3 peptide-targeted pegylated pH-sensitive liposomes into bulk ovarian cancer cells, including putative CSC-enriched ovarian cells. The intracellular delivery of a drug combination such as the one tested herein was relevant in the context of cell lines with higher intrinsic resistances to doxorubicin. The enhanced efficacy of the F3 peptide-targeted liposomal combination of doxorubicin/C6-ceramide was supported by the downregulation of the Akt pathway, within a specific range of basal level of expression.

Abstract

Targeting multiple cellular populations is of high therapeutic relevance for the tackling of solid tumors heterogeneity. Herein, the ability of pegylated and pH-sensitive liposomes, functionalized with the nucleolin-binding F3 peptide and containing doxorubicin (DXR)/C6-ceramide synergistic combination, to target, in vitro, ovarian cancer, including ovarian cancer stem cells (CSC), was assessed. The underlying molecular mechanism of action of the nucleolin-mediated intracellular delivery of C6-ceramide to cancer cells was also explored. The assessment of overexpression of surface nucleolin expression by flow cytometry was critical to dissipate differences identified by Western blot in membrane/cytoplasm of SKOV-3, OVCAR-3 and TOV-112D ovarian cancer cell lines. The former was in line with the significant extent of uptake into (bulk) ovarian cancer cells, relative to non-targeted and non-specific counterparts. This pattern of uptake was recapitulated with putative CSC-enriched ovarian SKOV-3 and OVCAR-3 sub-population (EpCAM^high/CD44^high). Co-encapsulation of DXR:C6-ceramide into F3 peptide-targeted liposomes improved cytotoxic activity relative to liposomes containing DXR alone, in an extent that depended on the intrinsic resistance to DXR and on the incubation time. The enhanced cytotoxicity of the targeted combination was mechanistically supported by the downregulation of PI3K/Akt pathway by C6-ceramide, only among the nucleolin-overexpressing cancer cells presenting a basal p-Akt/total Akt ratio lower than 1.

MicroRNA Let-7c Contributes to Paclitaxel Resistance via Aurora-B in Endometrial Serous Carcinoma

The incidence of endometrial cancer has rapidly risen over recent years. Paclitaxel, a key drug for endometrial cancer treatment, inhibits microtubule depolymerization and induces apoptosis in cancer cells. Endometrial serous carcinoma (ESC) accounts for < 10% of all endometrial carcinomas, but its aggressive nature makes it responsible for close to 40% of cancer deaths. Thus, novel therapeutic targets are required for ESC. To identify microRNAs that promote paclitaxel resistance, we established two paclitaxel-resistant cell lines from USPC1 human ESC cells by exposing paclitaxel to parental cells for 12 weeks. Paclitaxel concentrations were increased every 2 weeks, and after 12 weeks of paclitaxel exposure, two replicate paclitaxel-resistant cell lines were established (USPC1-PTSR1 and USPC1-PTXR2). The microarray analysis was performed using USPC1 cells and USPC1-PTXR1 cells, and eight candidate microRNAs were thus selected as potential mediators of paclitaxel sensitivity. Among these candidate microRNAs, let-7c precursor treatment of paclitaxel-resistant USPC1-PTXR1 cells caused the greatest increase in paclitaxel-mediated cytotoxicity. Let-7c inhibition conversely decreased paclitaxel-induced apoptosis. It is known that let-7a microRNA, a member of the let-7 family, inhibits growth of endometrial carcinoma cells targeting Aurora-B that controls progression through each phase of mitosis. We thus studied whether let-7c mediates Aurora-B expression in ESC cells. The expression levels of Aurora-B mRNA and protein were higher in USPC-PTXR1 cells compared with USPC1 cells. Let-7c inhibition increased Aurora-B expression in USPC1 cells but decreased Aurora-B expression in USPC1-PTXR1 cells. These results indicate that let-7c mediates paclitaxel resistance via inhibition of Aurora-B expression in ESC cells.

Sphingolipids as multifaceted mediators in ovarian cancer

Ovarian cancer is the most lethal gynaecological malignancy. It is commonly diagnosed at advanced stage when it has metastasised to the abdominal cavity and treatment becomes very challenging. While current standard therapy involving debulking surgery and platinum + taxane-based chemotherapy is associated with high response rates initially, the large majority of patients relapse and ultimately succumb to chemotherapy-resistant disease. In order to improve survival novel strategies for early detection and therapeutics against treatment-refractory disease are urgently needed. A promising new target against ovarian cancer is the sphingolipid pathway which is commonly hijacked in cancer to support cell proliferation and survival and has been shown to promote chemoresistance and metastasis in a wide range of malignant neoplasms. In particular, the sphingosine kinase 1-sphingosine 1-phosphate receptor 1 axis has been shown to be altered in ovarian cancer in multiple ways and therefore represents an attractive therapeutic target. Here we review the roles of sphingolipids in ovarian cancer progression, metastasis and chemoresistance, highlighting novel strategies to target this pathway that represent potential avenues to improve patient survival.

Ceramide synthase 2-C24:1 -ceramide axis limits the metastatic potential of ovarian cancer cells

Regulation of sphingolipid metabolism plays a role in cellular homeostasis, and dysregulation of these pathways is involved in cancer progression. Previously, our reports identified ceramide as an anti-metastatic lipid. In the present study, we investigated the biochemical alterations in ceramide-centered metabolism of sphingolipids that were associated with metastatic potential. We established metastasis-prone sublines of SKOV3 ovarian cancer cells using an in vivo selection method. These cells showed decreases in ceramide levels and ceramide synthase (CerS) 2 expression. Moreover, CerS2 downregulation in ovarian cancer cells promoted metastasis in vivo and potentiated cell motility and invasiveness. Moreover, CerS2 knock-in suppressed the formation of lamellipodia required for cell motility in this cell line. In order to define specific roles of ceramide species in cell motility controlled by CerS2, the effect of exogenous long- and very long-chain ceramide species on the formation of lamellipodia was evaluated. Treatment with distinct ceramides increased cellular ceramides and had inhibitory effects on the formation of lamellipodia. Interestingly, blocking the recycling pathway of ceramides by a CerS inhibitor was ineffective in the suppression of exogenous C24:1 -ceramide for the formation of lamellipodia. These results suggested that C24:1 -ceramide, a CerS2 metabolite, predominantly suppresses the formation of lamellipodia without the requirement for deacylation/reacylation. Moreover, knockdown of neutral ceramidase suppressed the formation of lamellipodia concomitant with upregulation of C24:1 -ceramide. Collectively, the CerS2-C24:1 -ceramide axis, which may be countered by neutral ceramidase, is suggested to limit cell motility and metastatic potential. These findings may provide insights that lead to further development of ceramide-based therapy and biomarkers for metastatic ovarian cancer.

Sesquiterpene Alcohol Cedrol Chemosensitizes Human Cancer Cells and Suppresses Cell Proliferation by Destabilizing Plasma Membrane Lipid Rafts

Chemosensitization of cancer cells with small molecules may improve the therapeutic index of antitumoral agents by making tumor cells sensitive to the drug regimen and thus overcome the treatment resistance and side effects of single therapy. Cell membrane lipid rafts are known to transduce various signaling events in cell proliferation. Sensitizing cancer cells may cause modulation of membrane lipid rafts which may potentially be used in improving anticancer drug response. Cedrol, a natural sesquiterpene alcohol, was used to treat human leukemia K562 and colon cancer HT-29 cell lines, and effects were observed. Cedrol decreased the cell viability by inducing apoptosis in both cell lines by activation of pro-apoptosis protein BID and inhibition of anti-apoptosis proteins Bcl-X_L, Bcl-2, and XIAP. Cedrol activated the caspase-9-dependent mitochondrial intrinsic pathway of apoptosis. Furthermore, cedrol inhibited the levels of pAKT, pERK, and pmTOR proteins as well as nuclear and cytoplasmic levels of the p65 subunit of NF-κB. Cedrol caused redistribution of cholesterol and sphingomyelin contents from membrane lipid raft, which was confirmed by a combined additive effect with methyl-β-cyclodextrin (lipid raft-disrupting agent). Lipid raft destabilization by cedrol led to the increased production of ceramides and inhibition of membrane-bound NADPH oxidase 2 enzyme activity. Cholesterol/sphingomyelin-redistributing abilities of cedrol appear as a novel mechanism of growth inhibition of cancer cells. Cedrol can be classified as a natural lipid raft-disrupting agent with possibilities to be used in general studies involving membrane lipid raft modifications.

Circulating Lysophosphatidylcholines, Phosphatidylcholines, Ceramides, and Sphingomyelins and Ovarian Cancer Risk: A 23-Year Prospective Study

BACKGROUND

Experimental evidence supports a role of lipid dysregulation in ovarian cancer progression. We estimated associations with ovarian cancer risk for circulating levels of four lipid groups, previously hypothesized to be associated with ovarian cancer, measured 3-23 years before diagnosis.

METHODS

Analyses were conducted among cases (N = 252) and matched controls (N = 252) from the Nurses' Health Studies. We used logistic regression adjusting for risk factors to investigate associations of lysophosphatidylcholines (LPCs), phosphatidylcholines (PCs), ceramides (CERs), and sphingomyelins (SMs) with ovarian cancer risk overall and by histotype. A modified Bonferroni approach (0.05/4 = 0.0125, four lipid groups) and the permutation-based Westfall and Young approach were used to account for testing multiple correlated hypotheses. Odds ratios (ORs; 10th-90th percentile), and 95% confidence intervals of ovarian cancer risk were estimated. All statistical tests were two-sided.

RESULTS

SM sum was statistically significantly associated with ovarian cancer risk (OR = 1.97, 95% CI = 1.16 to 3.32; P = .01/permutation-adjusted P = .20). C16:0 SM, C18:0 SM, and C16:0 CERs were suggestively associated with risk (OR = 1.95-2.10; P = .004-.01; permutation-adjusted P = .08-.21). SM sum, C16:0 SM, and C16:0 CER had stronger odds ratios among postmenopausal women (OR = 2.16-3.22). Odds ratios were similar for serous/poorly differentiated and endometrioid/clear cell tumors, although C18:1 LPC and LPC to PC ratio were suggestively inversely associated, whereas C18:0 SM was suggestively positively associated with risk of endometrioid/clear cell tumors. No individual metabolites were associated with risk when using the permutation-based approach.

CONCLUSIONS

Elevated levels of circulating SMs 3-23 years before diagnosis were associated with increased risk of ovarian cancer, regardless of histotype, with stronger associations among postmenopausal women. Further studies are required to validate and understand the role of lipid dysregulation in ovarian carcinogenesis.

The molecular mechanisms mediating class II PI 3-kinase function in cell physiology

The phosphoinositide 3-kinase (PI3K) family of lipid-modifying enzymes plays vital roles in cell signaling and membrane trafficking through the production of 3-phosphorylated phosphoinositides. Numerous studies have analyzed the structure and function of class I and class III PI3Ks. In contrast, we know comparably little about the structure and physiological functions of the class II enzymes. Only recent studies have begun to unravel their roles in development, endocytic and endolysosomal membrane dynamics, signal transduction, and cell migration, while the mechanisms that control their localization and enzymatic activity remain largely unknown. Here, we summarize our current knowledge of the class II PI3Ks and outline open questions related to their structure, enzymatic activity, and their physiological and pathophysiological functions.

C6-ceramide Inhibits the Motility of Anaplastic Thyroid Carcinoma Cells

Background

Anaplastic thyroid carcinoma (ATC) is an aggressive type of thyroid cancer, and its metastasis requires cell motility. Ceramide is involved in a variety of biological processes, including inflammation, cell signaling, cell motility, and induction of apoptosis, however has not previously been reported to inhibit the motility of ATC cells. We evaluated the effect of short chain C₆-ceramide on motility of ATC cells.

Methods

Cell motility of 8305C thyroid carcinoma cell line treated with C₆-ceramide was assessed using a transwell migration assay and a pseudopodia formation assay.

Results

Treatment with 10 µM C₆-ceramide resulted in significantly fewer migratory cells than control treatment in a transwell migration assay (P < 0.002). In condition medium, 82.6% of C₆-ceramide-treated cells formed lamellipodia. Importantly, treatment with 10 µM C₆-ceramide drastically decreased the number of cells forming lamellipodia by 17.6% (P < 0.01).

Conclusion

Our results suggest that treatment with a low concentration of ceramide may prevent metastasis and recurrence of ATC by inhibiting cell motility. Further studies are necessary to investigate the mechanism of inhibition of cell motility by ceramide. Ceramide shows promise as a therapeutic treatment for ATC.

Metabolic Reprogramming and Epithelial-Mesenchymal Plasticity: Opportunities and Challenges for Cancer Therapy

Metabolic reprogramming and epithelial-mesenchymal plasticity are both hallmarks of the adaptation of cancer cells for tumor growth and progression. For metabolic changes, cancer cells alter metabolism by utilizing glucose, lipids, and amino acids to meet the requirement of rapid proliferation and to endure stressful environments. Dynamic changes between the epithelial and mesenchymal phenotypes through epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are critical steps for cancer invasion and metastatic colonization. Compared to the extensively studied metabolic reprogramming in tumorigenesis, the metabolic changes in metastasis are relatively unclear. Here, we review metabolic reprogramming, epithelial-mesenchymal plasticity, and their mutual influences on tumor cells. We also review the developing treatments for targeting cancer metabolism and the impact of metabolic targeting on EMT. In summary, understanding the metabolic adaption and phenotypic plasticity will be mandatory for developing new strategies to target metastatic and refractory cancers that are intractable to current treatments.

Class II phosphatidylinositol 3-kinase α and β isoforms are required for vascular smooth muscle Rho activation, contraction and blood pressure regulation in mice

Class II phosphatidylinositol 3-kinases (PI3K), PI3K-C2α and PI3K-C2β, are involved in cellular processes including endocytosis, cilia formation and autophagy. However, the role of PI3K-C2α and PI3K-C2β at the organismal level is not well understood. We found that double knockout (KO) mice with both smooth muscle-specific KO of PI3K-C2α and global PI3K-C2β KO, but not single KO mice of either PI3K-C2α or PI3K-C2β, exhibited reductions in arterial blood pressure and substantial attenuation of contractile responses of isolated aortic rings. In wild-type vascular smooth muscle cells, double knockdown of PI3K-C2α and PI3K-C2β but not single knockdown of either PI3K markedly inhibited contraction with reduced phosphorylation of 20-kDa myosin light chain and MYPT1 and Rho activation, but without inhibition of the intracellular Ca2+ mobilization. These data indicate that PI3K-C2α and PI3K-C2β play the redundant but essential role for vascular smooth muscle contraction and blood pressure regulation mainly through their involvement in Rho activation.

Regulation of Necroptosis by Phospholipids and Sphingolipids

Several non-apoptotic regulated cell death pathways have been recently reported. Necroptosis, a form of necrotic-regulated cell death, is characterized by the involvement of receptor-interacting protein kinases and/or the pore-forming mixed lineage kinase domain-like protein. Recent evidence suggests a key role for lipidic molecules in the regulation of necroptosis. The purpose of this mini-review is to outline the regulation of necroptosis by sphingolipids and phospholipids.

WDR74 modulates melanoma tumorigenesis and metastasis through the RPL5-MDM2-p53 pathway

The key molecules and underlying mechanisms of melanoma metastasis remain poorly understood. Using isobaric tag for relative and absolute quantitation (iTRAQ) proteomic screening, probing of patients' samples, functional verification, and mechanistic validation, we identified the important role of the WD repeat-containing protein 74 (WDR74) in melanoma progression and metastasis. Through gain- and loss-of-function approaches, WDR74 was found to promote cell proliferation, apoptosis resistance, and aggressive behavior in vitro. Moreover, WDR74 contributed to melanoma growth and metastasis in vivo. Mechanistically, WDR74 modulates RPL5 protein levels and consequently regulates MDM2 and insulates the ubiquitination degradation of p53 by MDM2. Our study is the first to reveal the oncogenic role of WDR74 in melanoma progression and the regulatory effect of WDR74 on the RPL5-MDM2-p53 pathway. Collectively, WDR74 can serve as a candidate target for the prevention and treatment of melanoma in the clinic.

The metabolic footprint during adipocyte commitment highlights ceramide modulation as an adequate approach for obesity treatment

BACKGROUND

Metabolic modulation is capable of maintaining cell potency, regulating niche homeostasis, or determining cell fate. However, little is known regarding the metabolic landscape during early adipogenesis or whether metabolic modulation could be a potential approach for obesity treatment.

METHODS

The metabolic footprint during adipocyte commitment was evaluated by metabolomics analysis in mouse embryonic fibroblasts (MEFs). The role of apoptosis induced by ceramide and how ceramide is regulated were evaluated by omics analysis in vitro, human database and the adipocyte-specific Sirt1 knockout mouse.

FINDINGS

The metabolic footprint showed that a complicated diversity of metabolism was enriched as early as 3 h and tended to fluctuate throughout differentiation. Subsequently, the scale of these perturbed metabolic patterns was reduced to reach a balanced state. Of high relevance is the presence of apoptosis induced by ceramide accumulation, which is associated with metabolic dynamics. Interestingly, apoptotic cells were not merely a byproduct of adipogenesis but rather promoted the release of lipid components to facilitate adipogenesis. Mechanistically, ceramide accumulation stemming from hydrolysis and the de novo pathway during early adipogenesis is regulated by Sirt1 upon epigenetic alterations of constitutive Histone H3K4 methylation and H3K9 acetylation.

INTERPRETATION

The metabolic footprint during adipocyte commitment highlights that apoptosis induced by ceramide is essential for adipogenesis, which is reversed by suppression of Sirt1. Therefore, Sirt1 may constitute a target to treat obesity or other ceramide-associated metabolic syndromes.

FUNDING

This project was supported by grants from the University of Macau (SRG2015-00008-FHS, MYRG2016-00054-FHS and MYRG2017-00096-FHS to RHW; CPG2019-00019-FHS to CXD) and from the National Natural Science Foundation of China (81672603 and 81401978) to QC.

Downregulation of class II phosphoinositide 3-kinase PI3K-C2β delays cell division and potentiates the effect of docetaxel on cancer cell growth

Background

Alteration of signalling pathways regulating cell cycle progression is a common feature of cancer cells. Several drugs targeting distinct phases of the cell cycle have been developed but the inability of many of them to discriminate between normal and cancer cells has strongly limited their clinical potential because of their reduced efficacy at the concentrations used to limit adverse side effects. Mechanisms of resistance have also been described, further affecting their efficacy. Identification of novel targets that can potentiate the effect of these drugs or overcome drug resistance can provide a useful strategy to exploit the anti-cancer properties of these agents to their fullest.

Methods

The class II PI3K isoform PI3K-C2β was downregulated in prostate cancer PC3 cells and cervical cancer HeLa cells using selective siRNAs and the effect on cell growth was determined in the absence or presence of the microtubule-stabilizing agent/anti-cancer drug docetaxel. Mitosis progression was monitored by time-lapse microscopy. Clonogenic assays were performed to determine the ability of PC3 and HeLa cells to form colonies upon PI3K-C2β downregulation in the absence or presence of docetaxel. Cell multi-nucleation was assessed by immunofluorescence. Tumour growth in vivo was assessed using a xenograft model of PC3 cells upon PI3K-C2β downregulation and in combination with docetaxel.

Results

Downregulation of PI3K-C2β delays mitosis progression in PC3 and HeLa cells, resulting in reduced ability to form colonies in clonogenic assays in vitro. Compared to control cells, PC3 cells lacking PI3K-C2β form smaller and more compact colonies in vitro and they form tumours more slowly in vivo in the first weeks after cells implant. Stable and transient PI3K-C2β downregulation potentiates the effect of low concentrations of docetaxel on cancer cell growth. Combination of PI3K-C2β downregulation and docetaxel almost completely prevents colonies formation in clonogenic assays in vitro and strongly inhibits tumour growth in vivo.

Conclusions

These data reveal a novel role for the class II PI3K PI3K-C2β during mitosis progression. Furthermore, data indicate that blockade of PI3K-C2β might represent a novel strategy to potentiate the effect of docetaxel on cancer cell growth.

Mechanisms of Ceramide-Dependent Cancer Cell Death

Mechanistic details for the roles of sphingolipids and their downstream targets in the regulation of tumor growth, response to chemo/radiotherapy, and metastasis have been investigated in recent studies using innovative molecular, genetic and pharmacologic tools in various cancer models. Induction of ceramide generation in response to cellular stress by chemotherapy, radiation, or exogenous ceramide analog drugs mediates cell death via apoptosis, necroptosis, or mitophagy. In this chapter, distinct functions and mechanisms of action of endogenous ceramides with different fatty acyl chain lengths in the regulation of cancer cell death versus survival will be discussed. In addition, importance of ceramide subcellular localization, trafficking, and lipid-protein binding between ceramide and various target proteins in cancer cells will be reviewed. Moreover, clinical trials from structure-function-based studies to restore antiproliferative ceramide signaling by activating ceramide synthesis will also be analyzed. Future studies are important to understand the mechanistic involvement of ceramide-mediated cell death in anticancer therapy, including immunotherapy.

Class II PI3Ks at the Intersection between Signal Transduction and Membrane Trafficking

Phosphorylation of inositol phospholipids by the family of phosphoinositide 3-kinases (PI3Ks) is crucial in controlling membrane lipid composition and regulating a wide range of intracellular processes, which include signal transduction and vesicular trafficking. In spite of the extensive knowledge on class I PI3Ks, recent advances in the study of the three class II PI3Ks (PIK3C2A, PIK3C2B and PIK3C2G) reveal their distinct and non-overlapping cellular roles and localizations. By finely tuning membrane lipid composition in time and space among different cellular compartments, this class of enzymes controls many cellular processes, such as proliferation, survival and migration. This review focuses on the recent developments regarding the coordination of membrane trafficking and intracellular signaling of class II PI3Ks through the confined phosphorylation of inositol phospholipids.

The class II phosphoinositide 3-kinases PI3K-C2α and PI3K-C2β differentially regulate clathrin-dependent pinocytosis in human vascular endothelial cells

Pinocytosis is an important fundamental cellular process that is used by the cell to transport fluid and solutes. Phosphoinositide 3-kinases (PI3Ks) regulate a diverse array of dynamic membrane events. However, it is not well-understood which PI3K isoforms are involved in specific mechanisms of pinocytosis. We performed knockdown studies of endogenous PI3K isoforms and clathrin heavy chain (CHC) mediated by small interfering RNA (siRNA). The results demonstrated that the class II PI3K PI3K-C2α and PI3K-C2β, but not the class I or III PI3K, were required for pinocytosis, based on an evaluation of fluorescein-5-isothiocyanate (FITC)-dextran uptake in endothelial cells. Pinocytosis was partially dependent on both clathrin and dynamin, and both PI3K-C2α and PI3K-C2β were required for clathrin-mediated-but not clathrin-non-mediated-FITC-dextran uptake at the step leading up to its delivery to early endosomes. Both PI3K-C2α and PI3K-C2β were co-localized with clathrin-coated pits and vesicles. However, PI3K-C2β, but not PI3K-C2α, was highly co-localized with actin filament-associated clathrin-coated structures and required for actin filament formation at the clathrin-coated structures. These results indicate that PI3K-C2α and PI3K-C2β play differential, indispensable roles in clathrin-mediated pinocytosis.

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.

La-Related Protein 4 as a Suppressor for Motility of Ovarian Cancer Cells

The La-related proteins (LARPs) are a family of RNA binding proteins that control the degradation and stabilization of RNAs. As emerging research reveals the biology of each LARP, it is evident that LARPs are dysregulated in some types of cancer. Upregulation of cell motility potentiates the metastatic potential of ovarian cancer cells; however, the roles of LARPs in cell motility remain unknown. In the present study, we investigated the roles of LARPs in the progression of ovarian cancer using SKOV3 human ovarian cancer cells and a public database that integrates microarray-based gene expression data and clinical data. To explore the involvement of LARPs in the cell motility, we performed RNA interference screening for LARP mRNAs in SKOV3 cells. The screening identified LARP4 as a potential suppressor of the formation of lamellipodia. Conversely, enforced expression of LARP4 suppressed the formation of lamellipodia. Moreover, cell migration was significantly increased in LARP4-depleted SKOV3 cells. Mechanistically, LARP4 depletion was associated with the decrease in RhoA protein expression. These results suggest that LARP4 may limit RhoA-dependent cell motility. In a mouse xenograft model with SKOV3 cells, LARP4 depletion potentiated peritoneal metastasis. Upon analysis of a public database of patients with ovarian cancer, the LARP4 mRNA-high expression group (n = 166) showed longer overall survival compared with the LARP4 mRNA-low expression group (n = 489), implying a positive correlation of LARP4 mRNA levels in ovarian cancer tissues with patient prognosis. Taken together, we propose that LARP4 could suppress motility and metastatic potential of ovarian cancer cells.

Visualizing bioactive ceramides

In the last 30 years, ceramides have been found to mediate a myriad of biological processes. Ceramides have been recognized as bioactive molecules and their metabolizing enzymes are attractive targets in cancer therapy and other diseases. The molecular mechanism of action of cellular ceramides are still not fully established, with insights into roles through modification of lipid rafts, creation of ceramide platforms, ceramide channels, or through regulation of direct protein effectors such as protein phosphatases and kinases. Recently, the 'Many Ceramides' hypothesis focuses on distinct pools of subcellular ceramides and ceramide species as potential defined bioactive entities. Traditional methods that measure changes in ceramide levels in the whole cell, such as mass spectrometry, fluorescent ceramide analogues, and ceramide antibodies, fail to differentiate specific bioactive species at the subcellular level. However, a few ceramide binding proteins have been reported, and a smaller subgroup within these, have been shown to translocate to ceramide-enriched membranes, revealing these localized pools of bioactive ceramides. In this review we want to discuss and consolidate these works and explore the possibility of defining these binding proteins as new tools are emerging to visualize bioactive ceramides in cells. Our goal is to encourage the scientific community to explore these ceramide partners, to improve techniques to refine the list of these binding partners, making possible the identification of specific domains that recognize and bind ceramides to be used to visualize the 'Many Ceramides' in the cell.

Sphingolipid metabolism and drug resistance in ovarian cancer

Despite progress in understanding molecular aberrations that contribute to the development and progression of ovarian cancer, virtually all patients succumb to drug resistant disease at relapse. Emerging data implicate bioactive sphingolipids and regulation of sphingolipid metabolism as components of response to chemotherapy or development of resistance. Increases in cytosolic ceramide induce apoptosis in response to therapy with multiple classes of chemotherapeutic agents. Aberrations in sphingolipid metabolism that accelerate the catabolism of ceramide or that prevent the production and accumulation of ceramide contribute to resistance to standard of care platinum- and taxane-based agents. The aim of this review is to highlight current literature and research investigating the influence of the sphingolipids and enzymes that comprise the sphingosine-1-phosphate pathway on the progression of ovarian cancer. The focus of the review is on the utility of sphingolipid-centric therapeutics as a mechanism to circumvent drug resistance in this tumor type.

Tyrosine kinase receptor TIE-1 mediates platinum resistance by promoting nucleotide excision repair in ovarian cancer

Platinum resistance is one of the most challenging problems in ovarian cancer treatment. High-throughput functional siRNA screening identified tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE-1) as a gene that confers cells resistant to cisplatin. Conversely enforced over-expression of TIE-1 was validated to decrease cisplatin sensitivity in multiple ovarian cancer cell lines and up-regulation of TIE-1 was correlated with poor prognosis and cisplatin resistance in patients with ovarian cancer. Mechanistically, TIE-1 up-regulates the nucleotide excision repair (NER) system mediated by xeroderma pigmentosum complementation group C (XPC), thereby leading to decreased susceptibility to cisplatin-induced cell death without affecting cisplatin uptake and excretion. Importantly potentiation of therapeutic efficacy by TIE-1 inhibition was selective to DNA-adduct-type chemotherapeutic platinum reagents. Therefore, TIE-1 is suggested to promote XPC-dependent NER, rendering ovarian cancer cells resistant to platinum. Accompanied with novel findings, TIE-1 could represent as a novel therapeutic target for platinum-resistant ovarian cancer.

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.

Controlled drug delivery vehicles for cancer treatment and their performance

Although conventional chemotherapy has been successful to some extent, the main drawbacks of chemotherapy are its poor bioavailability, high-dose requirements, adverse side effects, low therapeutic indices, development of multiple drug resistance, and non-specific targeting. The main aim in the development of drug delivery vehicles is to successfully address these delivery-related problems and carry drugs to the desired sites of therapeutic action while reducing adverse side effects. In this review, we will discuss the different types of materials used as delivery vehicles for chemotherapeutic agents and their structural characteristics that improve the therapeutic efficacy of their drugs and will describe recent scientific advances in the area of chemotherapy, emphasizing challenges in cancer treatments.

Improving the delivery of cancer therapies to tumor sites is crucial to reduce unwanted side effects and patient mortality rates. Pralay Maiti and colleagues at the Indian Institute of Technology in Varanasi, India, review the latest developments in drug delivery vehicles and treatment approaches designed to enhance the effectiveness of current cancer therapies. New nanoparticle-based carriers, hydrogels and hybrid materials that offer controlled and sustained drug release are showing great promise in animal models. Furthermore, materials that respond to stimuli such as heat, light, magnetic or electric fields are also being tested to aid target-specific drug delivery and, thus, avoid damage to healthy tissues. Although there are some challenges in translating these findings to the clinic, there is no doubt that technological advances are shaping better and safer treatment options.

Ceramide Nanoliposomes as a MLKL-Dependent, Necroptosis-Inducing, Chemotherapeutic Reagent in Ovarian Cancer

Ceramides are bioactive lipids that mediate cell death in cancer cells, and ceramide-based therapy is now being tested in dose-escalating phase I clinical trials as a cancer treatment. Multiple nanoscale delivery systems for ceramide have been proposed to overcome the inherent toxicities, poor pharmacokinetics, and difficult biophysics associated with ceramide. Using the ceramide nanoliposomes (CNL), we now investigate the therapeutic efficacy and signaling mechanisms of this nanoscale delivery platform in refractory ovarian cancer. Treatment of ovarian cancer cells with CNL decreased the number of living cells through necroptosis but not apoptosis. Mechanistically, dying SKOV3 ovarian cancer cells exhibit activation of pseudokinase mixed lineage kinase domain-like (MLKL) as evidenced by oligomerization and relocalization to the blebbing membranes, showing necroptotic characteristics. Knockdown of MLKL, but not its upstream protein kinases such as receptor-interacting protein kinases, with siRNA significantly abolished CNL-induced cell death. Monomeric MLKL protein expression inversely correlated with the IC50 values of CNL in distinct ovarian cancer cell lines, suggesting MLKL as a possible determinant for CNL-induced cell death. Finally, systemic CNL administration suppressed metastatic growth in an ovarian cancer cell xenograft model. Taken together, these results suggest that MLKL is a novel pronecroptotic target for ceramide in ovarian cancer models. Mol Cancer Ther; 17(1); 50-59. ©2017 AACR.

Sphingolipid metabolism in cancer signalling and therapy

Sphingolipids, including the two central bioactive lipids ceramide and sphingosine-1-phosphate (S1P), have opposing roles in regulating cancer cell death and survival, respectively, and there have been exciting developments in understanding how sphingolipid metabolism and signalling regulate these processes in response to anticancer therapy. Recent studies have provided mechanistic details of the roles of sphingolipids and their downstream targets in the regulation of tumour growth and response to chemotherapy, radiotherapy and/or immunotherapy using innovative molecular, genetic and pharmacological tools to target sphingolipid signalling nodes in cancer cells. For example, structure-function-based studies have provided innovative opportunities to develop mechanism-based anticancer therapeutic strategies to restore anti-proliferative ceramide signalling and/or inhibit pro-survival S1P-S1P receptor (S1PR) signalling. This Review summarizes how ceramide-induced cellular stress mediates cancer cell death through various mechanisms involving the induction of apoptosis, necroptosis and/or mitophagy. Moreover, the metabolism of ceramide for S1P biosynthesis, which is mediated by sphingosine kinase 1 and 2, and its role in influencing cancer cell growth, drug resistance and tumour metastasis through S1PR-dependent or receptor-independent signalling are highlighted. Finally, studies targeting enzymes involved in sphingolipid metabolism and/or signalling and their clinical implications for improving cancer therapeutics are also presented.

Therapeutic PEG-ceramide nanomicelles synergize with salinomycin to target both liver cancer cells and cancer stem cells

AIM

Salinomycin (SAL)-loaded PEG-ceramide nanomicelles (SCM) were prepared to target both liver cancer cells and cancer stem cells.

MATERIALS & METHODS

The synergistic ratio of SAL/PEG-ceramide was evaluated to prepare SCM, and the antitumor activity of SCM was examined both in vitro and in vivo.

RESULTS

SAL/PEG-ceramide molar ratio of 1:4 was chosen as the synergistic ratio, and SCM showed superior cytotoxic effect and increased apoptosis-inducing activity in both liver cancer cells and cancer stem cells. In vivo, SCM showed the best tumor inhibitory effect with a safety profile.

CONCLUSION

Thus, PEG-ceramide nanomicelles could serve as an effective and safe therapeutic drug carrier to deliver SAL into liver cancer, opening up the avenue of using PEG-ceramide as therapeutic drug carriers.

C2-ceramide enhances sorafenib-induced caspase-dependent apoptosis via PI3K/AKT/mTOR and Erk signaling pathways in HCC cells

Sorafenib as an effective multikinase inhibitor has been approved for the clinical treatment against advanced hepatocellular carcinoma (HCC). HCC treatment requires usually combined therapy because of its complex pathogenesis. Ceramide has been confirmed to induce remarkable apoptosis in human tumor cells and has attracted increasing attention in investigations on combination therapy. In this paper, the anti-HCC effect of sorafenib combined with C2-ceramide was investigated on cell vitality, apoptosis, and migration, and the underlying mechanism was examined using flow cytometry and western blot. Bel7402 cells coincubated with sorafenib and C2-ceramide exhibited lower cell vitality and more irregular cellular morphology and cell cycle arrest. Sorafenib plus C2-ceramide stimulated significantly the production of reactive oxygen species (ROS) and mitochondrial depolarization, which promoted caspases-dependent cell apoptosis as illustrated by related protein expression including caspase 3, caspase 9, Bax, Bcl-2, and cytochrome c. Combination treatment of sorafenib and C2-ceramide inhibited obviously cell growth and proliferation via PI3K/AKT/mTOR and Erk signaling pathways. Furthermore, the combination treatment was proved to inhibit cell migration and epithelial-mesenchymal transition (EMT). These findings indicated that the combination of C2-ceramide and sorafenib provided synergistic inhibitory effects on HCC cells.

Inactivation of class II PI3K-C2α induces leptin resistance, age-dependent insulin resistance and obesity in male mice

AIMS/HYPOTHESIS

While the class I phosphoinositide 3-kinases (PI3Ks) are well-documented positive regulators of metabolism, the involvement of class II PI3K isoforms (PI3K-C2α, -C2β and -C2γ) in metabolic regulation is just emerging. Organismal inactivation of PI3K-C2β increases insulin signalling and sensitivity, whereas PI3K-C2γ inactivation has a negative metabolic impact. In contrast, the role of PI3K-C2α in organismal metabolism remains unexplored. In this study, we investigated whether kinase inactivation of PI3K-C2α affects glucose metabolism in mice.

METHODS

We have generated and characterised a mouse line with a constitutive inactivating knock-in (KI) mutation in the kinase domain of the gene encoding PI3K-C2α (Pik3c2a).

RESULTS

While homozygosity for kinase-dead PI3K-C2α was embryonic lethal, heterozygous PI3K-C2α KI mice were viable and fertile, with no significant histopathological findings. However, male heterozygous mice showed early onset leptin resistance, with a defect in leptin signalling in the hypothalamus, correlating with a mild, age-dependent obesity, insulin resistance and glucose intolerance. Insulin signalling was unaffected in insulin target tissues of PI3K-C2α KI mice, in contrast to previous reports in which downregulation of PI3K-C2α in cell lines was shown to dampen insulin signalling. Interestingly, no metabolic phenotypes were detected in female PI3K-C2α KI mice at any age.

CONCLUSIONS/INTERPRETATION

Our data uncover a sex-dependent role for PI3K-C2α in the modulation of hypothalamic leptin action and systemic glucose homeostasis.

ACCESS TO RESEARCH MATERIALS

All reagents are available upon request.

Novel roles for class II Phosphoinositide 3-Kinase C2β in signalling pathways involved in prostate cancer cell invasion

Phosphoinositide 3-kinases (PI3Ks) regulate several cellular functions such as proliferation, growth, survival and migration. The eight PI3K isoforms are grouped into three classes and the three enzymes belonging to the class II subfamily (PI3K-C2α, β and γ) are the least investigated amongst all PI3Ks. Interest on these isoforms has been recently fuelled by the identification of specific physiological roles for class II PI3Ks and by accumulating evidence indicating their involvement in human diseases. While it is now established that these isoforms can regulate distinct cellular functions compared to other PI3Ks, there is still a limited understanding of the signalling pathways that can be specifically regulated by class II PI3Ks. Here we show that PI3K-C2β regulates mitogen-activated protein kinase kinase (MEK1/2) and extracellular signal-regulated kinase (ERK1/2) activation in prostate cancer (PCa) cells. We further demonstrate that MEK/ERK and PI3K-C2β are required for PCa cell invasion but not proliferation. In addition we show that PI3K-C2β but not MEK/ERK regulates PCa cell migration as well as expression of the transcription factor Slug. These data identify novel signalling pathways specifically regulated by PI3K-C2β and they further identify this enzyme as a key regulator of PCa cell migration and invasion.

Enhanced Cytotoxicity of Folic Acid-Targeted Liposomes Co-Loaded with C6 Ceramide and Doxorubicin: In Vitro Evaluation on HeLa, A2780-ADR, and H69-AR Cells

Current research in cancer therapy is beginning to shift toward the use of combinational drug treatment regimens. However, the efficient delivery of drug combinations is governed by a number of complex factors in the clinical setting. Therefore, the ability to synchronize the pharmacokinetics of the individual therapeutic agents present in combination not only to allow for simultaneous tumor accumulation but also to allow for a synergistic relationship at the intracellular level could prove to be advantageous. In this work, we report the development of a novel folic acid-targeted liposomal formulation simultaneously co-loaded with C6 ceramide and doxorubicin [FA-(C6+Dox)-LP]. In vitro cytotoxicity assays showed that the FA-(C6+Dox)-LP was able to significantly reduce the IC50 of Dox when compared to that after the treatment with the doxorubicin-loaded liposomes (Dox-LP) as well as the untargeted drug co-loaded (C6+Dox)-LP on HeLa, A2780-ADR, and H69-AR cells. The analysis of the cell cycle distribution showed that while the C6 liposomes (C6-LP) did not cause cell cycle arrest, all the Dox-containing liposomes mediated cell cycle arrest in HeLa cells in the G2 phase at Dox concentrations of 0.3 and 1 μM and in the S phase at the higher concentrations. It was also found that this arrest in the S phase precedes the progression of the cells to apoptosis. The targeted FA-(C6+Dox)-LP were able to significantly enhance the induction of apoptotic events in HeLa cell monolayers as compared to the other treatment groups. Next, using time-lapse phase holographic imaging microscopy, it was found that upon treatment with the FA-(C6+Dox)-LP, the HeLa cells underwent rapid progression to apoptosis after 21 h as evidenced by a drastic drop in the average area of the cells after loss of cell membrane integrity. Finally, upon evaluation in a HeLa spheroid cell model, treatment with the FA-(C6+Dox)-LP showed significantly higher levels of cell death compared to those with C6-LP and Dox-LP. Overall, this study clearly shows that the co-delivery of C6 ceramide and Dox using a liposomal platform significantly correlates with an antiproliferative effect due to cell cycle regulation and subsequent induction of apoptosis and thus warrants its further evaluation in preclinical animal models.