Sphingosine kinase 1/sphingosine-1-phosphate (S1P)/S1P receptor axis is involved in ovarian cancer angiogenesis

SPHK1 enhances olaparib resistance in ovarian cancer through the NFκB/NRF2/ferroptosis pathway

PARPis resistance is a challenge in the treatment of ovarian cancer. To investigate the potential mechanism involved in olaparib resistance of ovarian cancer, high-throughput sequencing was performed on olaparib-resistant SKOV3 cell line named SK/Ola. SPHK1 was upregulated in SK/Ola cells and was related to the PFS and OS in ovarian cancer patients. However, the effect and mechanism of SPHK1 on olaparib sensitivity in ovarian cancer were obscure. In this study, we found that SPHK1 promoted olaparib resistance. While, SPHK1 knockdown and SPHK1 inhibitor (PF-543 hydrochloride, named PF-543 in this article) enhanced the effect of olaparib on ovarian cancer cells. In mechanism, SPHK1 activated the NF-κB pathway through promoting p-IκBα degradation. Moreover, SPHK1 inhibited, but PF-543 activated ferroptosis in OC cells. Further investigation revealed that SPHK1 activated NF-κB p65, which in turn transcriptionally regulated NRF2 to inhibit ferroptosis in OC cells. Functionally, NF-κB p65 attenuated the PF-543-induced ferroptosis, and this effect was rescued by ferroptosis inducer erastin and RSL3. We conclude that SPHK1 inhibition triggers ferroptosis by restricting NF-κB-activated NRF2 transcription, thereby enhancing olaparib sensitivity in ovarian cancer. In vivo experiments also confirmed that the SPHK1 inhibitor increased olaparib sensitivity. A combination of SPHK1 inhibitors and olaparib may provide a therapeutic strategy for ovarian cancer.

SPHK1 Promotes Pancreatic Cancer Lymphangiogenesis Through the Activation of ERK in LECs

Lymphatic metastasis is related to an unsatisfactory prognosis in pancreatic cancer. Sphingosine kinase 1 (SPHK1) is an oncogene in cancer. However, the potential effect of SPHK1 on the lymphangiogenesis of pancreatic cancer is little known. In this study, the expression level and role of SPHK1 in pancreatic cancer were evaluated to explore the underlying mechanism involved. The expression of SPHK1 and the lymphatic vessel density (LVD) in pancreatic cancer patient tissue were investigated by immunohistochemistry. The role of SPHK1 in lymphangiogenesis was verified in vitro. Elevated expression of SPHK1 was strongly related to high LVD in pancreatic cancer patient tissue. Silencing of SPHK1 in pancreatic cancer cells observably inhibited lymphangiogenesis. Furthermore, the downregulation of SPHK1 markedly attenuated the phosphorylation of extracellular signal-regulated kinase in lymphatic endothelial cells. This study revealed that SPHK1 might play a crucial role in pancreatic cancer lymphangiogenesis.

Assessment of the Effects of Sphingosine Kinase 1/Sphingosine-1-Phosphate on Microangiogenesis at Rat Myofascial Trigger Points Using Contrast-Enhanced Ultrasonography

Purpose

Few studies have assessed the effects of sphingosine kinase 1/sphingosine-1-phosphate (SPHK1/S1P) on microangiogenesis at rat myofascial trigger points (MTrPs) using contrast-enhanced ultrasonography (CEUS). This study aimed to address these deficiencies. Here, we investigated the effects of SPHK1/S1P on MTrP microangiogenesis and the value of CEUS in evaluating these effects.

Methods

Forty Sprague‒Dawley rats were subdivided into two groups: control and MTrP groups. MTrPs were established by 8 weeks of the strike procedure combined with eccentric motion and 4 weeks of recovery. All rats were euthanized after having undergone CEUS with an overdose of pentobarbital sodium. MTrP and control tissue samples were removed for haematoxylin and eosin (H&E) staining and transmission electron microscopy (TEM) imaging. The tissue was dehydrated, cleared, and embedded before sectioning. The sections were then incubated overnight at 4°C, and immunohistochemistry was carried out with primary antibodies including rabbit anti-CD31, rabbit anti-SPHK1and rabbit anti-S1PR1.

Results

MTrP rats exhibited spontaneous electrical activity (SEA) and a local twitch response (LTR) during electromyography (EMG) examination. The CEUS time-intensity curves (TICs) showed that the perfusion intensity in the MTrPs and surrounding tissue area was increased, with faster perfusion than in normal sites, while the TICs in the control group slowly increased and then slowly decreased. The correlation coefficient between the microvessel density (MVD) and sphingosine 1-phosphate receptor 1 (S1PR1) was 0.716 (p <0.01). Spearman correlation analysis revealed that Spearman's rho (ρ) values between the MVD and peak intensity (PI), between the MVD and area under the curve (AUC), and between the MVD and SPHK1 were > 0.5 (p <0.05), > 0.7 (p <0.01), and > 0.7 (p <0.01), respectively.

Conclusion

CEUS is valuable for detecting microangiogenesis within MTrPs, and SPHK1/S1P plays an important role in promoting MTrP tissue microangiogenesis.

S1PR1 regulates ovarian cancer cell senescence through the PDK1-LATS1/2-YAP pathway

Cell senescence deters the activation of various oncogenes. Induction of senescence is, therefore, a potentially effective strategy to interfere with vital processes in tumor cells. Sphingosine-1-phosphate receptor 1 (S1PR1) has been implicated in various cancer types, including ovarian cancer. The mechanism by which S1PR1 regulates ovarian cancer cell senescence is currently elusive. In this study, we demonstrate that S1PR1 was highly expressed in human ovarian cancer tissues and cell lines. S1PR1 deletion inhibited the proliferation and migration of ovarian cancer cells. S1PR1 deletion promoted ovarian cancer cell senescence and sensitized ovarian cancer cells to cisplatin chemotherapy. Exposure of ovarian cancer cells to sphingosine-1-phosphate (S1P) increased the expression of 3-phosphatidylinositol-dependent protein kinase 1 (PDK1), decreased the expression of large tumor suppressor 1/2 (LATS1/2), and induced phosphorylation of Yes-associated protein (p-YAP). Opposite results were obtained in S1PR1 knockout cells following pharmacological inhibition. After silencing LATS1/2 in S1PR1-deficient ovarian cancer cells, senescence was suppressed and S1PR1 expression was increased concomitantly with YAP expression. Transcriptional regulation of S1PR1 by YAP was confirmed by chromatin immunoprecipitation. Accordingly, the S1PR1-PDK1-LATS1/2-YAP pathway regulates ovarian cancer cell senescence and does so through a YAP-mediated feedback loop. S1PR1 constitutes a druggable target for the induction of senescence in ovarian cancer cells. Pharmacological intervention in the S1PR1-PDK1-LATS1/2-YAP signaling axis may augment the efficacy of standard chemotherapy.

Decoding systems immunological model of sphingolipids with IL-6/IL-17/IL-23 axes in L. major infection

IL-6, IL-17, IL-23 and IL-1β are the crucial cytokines controlling inflammatory and immune response during L. major infection. During cutaneous leishmaniasis, an important T helper cell type CD4⁺ Th17 subset plays a deterministic role in lesion formation through channelling infected macrophages and production of IL-1β, IL-6, IL-23 and IFN-γ. Ceramide derived sphingosine precursors may assist in pro-inflammatory cytokine response. However, the role of these metabolites in inflammation with pleiotropic pro-inflammatory cytokines in L. major infection is unknown. The present study indicates IL-6/IL-17/IL-23 and SPHK1-S1P-S1PRs signaling axes with the overexpression of SATB1 aiding in disease progression. Targeting SATB1 might modulate the secretion of pro-inflammatory cytokines and abnormal immune functioning, thereby killing the intracellular parasite. Systems immunological methods assisted in a step towards identifying the key to the mystery of crucial components and serving as an approach for therapeutic intervention in L. major infection.

Sphingosine kinase 1 contributes to the metastatic potential of epithelial ovarian cancer to the adipocyte-rich niche

Unlike many solid tumors, epithelial ovarian cancer (EOC) has a clear metastatic predilection to the adipocyte-rich niche, especially the omentum. However, the underlying mechanism driving this process remains incomplete. Here we show that SphK1 is over-expressed in omental metastases compared with ovarian primary tumors in EOC patients. In vitro, inhibition of SphK1 suppressed the metastatic ability of EOC induced by adipocytes. In vivo, blockage of SphK1 could attenuate the omental metastasis of EOC. Importantly, SphK1 modulates adipocyte-induced E/N-cadherin switch through Twist1, a key process in EOC metastasis. Our study reveals a previously unrecognized role of SphK1 in modulating the metastatic tropism of EOC to the adipocyte-rich niche, suggesting a new target for EOC therapy.

Pathogenic Role of the Sphingosine 1-Phosphate (S1P) Pathway in Common Gynecologic Disorders (GDs): A Possible Novel Therapeutic Target

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid, noteworthy for its involvement both in the modulation of various biological processes and in the development of many diseases. S1P signaling can be either pro or anti-inflammatory, and the sphingosine kinase (SphK)–S1P–S1P receptor (S1PR) axis is a factor in accelerating the growth of several cells, including endometriotic cells and fibrosis. Gynecologic disorders, including endometriosis, adenomyosis, and uterine fibroids are characterized by inflammation and fibrosis. S1P signaling and metabolism have been shown to be dysregulated in those disorders and they are likely implicated in their pathogenesis and pathophysiology. Enzymes responsible for inactivating S1P are the most affected by the dysregulation of S1P balanced levels, thus causing accumulation of sphingolipids within these cells and tissues. The present review highlights the past and latest evidence on the role played by the S1P pathways in common gynecologic disorders (GDs). Furthermore, it discusses potential future approaches in the regulation of this signaling pathway that could represent an innovative and promising therapeutical target, also for ovarian cancer treatment.

Anomaly of cornea and ocular adnexa in spinster homolog 2 (Spns2) knockout mice

Spinster 2 (Spns2) is a transporter that pumps sphingosine-1-phosphate (S1P), a bioactive lipid mediator synthesized in the cytoplasm, out of cells into the inter cellular space. S1P is a signal that modulates cellular behavior during embryonic development, inflammation and tissue repair, etc. A Spns2-null (KO) mouse is born with failure of eyelid closure (eyelid-open-at birth; EOB) and develop corneal fibrosis in adulthood. It remains elusive whether corneal lesion is caused by exposure to keratitis (lagophthalmos) of EOB phenotype or the loss of Spns2 directly perturbs the corneal tissue morphogenesis and intra-eyelid structures. Therefore, we investigated differences between the cornea and ocular adnexa morphogenesis in KO and wild-type (WT) embryos and adults as well. The loss of Spns2 perturbs cornea morphogenesis during embryonic development as early as E16.5 besides EOB phenotype. Histology showed that the corneal stroma was thinner with less extracellular matrix accumulation, e.g., collagen and keratocan in the KO mouse. Epithelial stratification, expression of keratin 12 and formation of desmosomes and hemidesmosomes were also perturbed in these KO corneas. Lacking Spns2 impaired morphogenesis of the Meibomian glands and of orbicularis oculi muscles. KO glands were labeled for ELOVL4 and PPARγ and were Oil-Red O-positive, suggesting KO acinar cells possessed functionality as the glands. This is the first report on the roles of Spns2 in corneal and Meibomian gland morphogenesis. Corneal tissue destruction in an adult KO mouse might be due to not only lagophthalmos but also to an impaired morphogenesis of cornea, Meibomian glands, and orbicularis oculi muscle.

Metabolic Reprogramming of Ovarian Cancer Spheroids during Adhesion

Ovarian cancer remains a deadly disease and its recurrence disease is due in part to the presence of disseminating ovarian cancer aggregates not removed by debulking surgery. During dissemination in a dynamic ascitic environment, the spheroid cells' metabolism is characterized by low respiration and fragmented mitochondria, a metabolic phenotype that may not support secondary outgrowth after adhesion. Here, we investigated how adhesion affects cellular respiration and substrate utilization of spheroids mimicking early stages of secondary metastasis. Using different glucose and oxygen levels, we investigated cellular metabolism at early time points of adherence (24 h and less) comparing slow and fast-developing disease models. We found that adhesion over time showed changes in cellular energy metabolism and substrate utilization, with a switch in the utilization of mostly glutamine to glucose but no changes in fatty acid oxidation. Interestingly, low glucose levels had less of an impact on cellular metabolism than hypoxia. A resilience to culture conditions and the capacity to utilize a broader spectrum of substrates more efficiently distinguished the highly aggressive cells from the cells representing slow-developing disease, suggesting a flexible metabolism contributes to the stem-like properties. These results indicate that adhesion to secondary sites initiates a metabolic switch in the oxidation of substrates that could support outgrowth and successful metastasis.

Activation of SphK2 contributes to adipocyte-induced EOC cell proliferation

Epithelial ovarian cancer (EOC) is the leading cause of deaths due to cancer in women. Adipocytes have been suggested to play a key role in the stimulation of EOC growth. However, the mechanisms underlying the adipocyte-induced EOC proliferation remain undefined. Here, we provide the first evidence that adipocytes induce the activation of sphingosine kinase (SphK) 2 in EOC, which represents a novel pathway that mediates the adipocyte-induced EOC growth. SphK2 inhibition in EOC cells led to a remarkable inhibition of the adipocyte-induced cell proliferation. Moreover, the adipocyte-induced SphK2 activation in EOC cells was extracellular signal-regulated protein kinases (ERK) dependent. Furthermore, silencing SphK2 in EOC significantly inhibited the adipocyte-induced expression of phospho-ERK and c-Myc, two crucial players in EOC growth. Collectively, the current study unraveled a previously unrecognized role of SphK2 in the adipocyte-induced growth-promoting action in EOC, suggesting a novel target for EOC treatment.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

The S1PR1 agonist SEW2871 promotes the survival of skin flap

Skin flap transfer is an important method to repair and reconstruct various tissue defects; however, avascular necrosis largely affects the success of flap transfer. The sphingosine 1-phosphate receptor 1 (S1PR1) agonist SEW2871 has been proven to ameliorate ischemic injury; however, its effect on flap survival has not been reported. In this study, an experimental skin flap model was established in rats to investigate the roles of SEW2871. The results indicated that SEW2871 greatly increased the survival of the skin flap, alleviated pathological injury, promoted the angiogenesis, and inhibited cells apoptosis in skin flap tissues. SEW2871 activated S1PR1 downstream signaling pathways, including heat shock protein 27 (HSP27), extracellular regulated protein kinases (ERK), and protein kinase B (Akt). In addition, SEW2871 promoted the expression of S1PR1. These findings may provide novel insights for skin flap transfer.

Angiogenesis as a potential treatment strategy for rheumatoid arthritis

Angiogenesis is an early and key event in the pathogenesis of rheumatoid arthritis (RA) and is crucial for the proliferation of synovial tissue and the formation of pannus. This process is regulated by both angiogenesis-stimulating factors and angiogenesis inhibitors, the basis for the "on-off hypothesis of angiogenesis." In RA, inflammation, immune imbalance, and hypoxia can further turn on the switch for blood vessel formation and induce angiogenesis. The new vasculature can recruit white blood cells, induce immune imbalance, and aggravate inflammation. At the same time, it also can provide oxygen and nutrients for the proliferating synovial tissue, which can accelerate the process of RA. The current therapies for RA mainly target the inflammatory response of autoimmune activation. Although these therapies have been greatly improved, there are still many patients whose RA is difficult to treat or who do not fully respond to treatment. Therefore, new innovative therapies are still urgently needed. This review covers the mechanism of synovial angiogenesis in RA, including the detailed process of angiogenesis and the relationship between inflammation, immune imbalance, hypoxia, and synovial angiogenesis, respectively. At the same time, in the context of the development of angiogenesis inhibition therapy for cancer, we also discuss similar treatment strategies for RA, especially the combination of targeted angiogenesis inhibition therapy and immunotherapy.

Interaction of microRNAs with sphingosine kinases, sphingosine-1 phosphate, and sphingosine-1 phosphate receptors in cancer

Sphingosine-1-phosphate (S1P), a pleiotropic lipid mediator, participates in various cellular processes during tumorigenesis, including cell proliferation, survival, drug resistance, metastasis, and angiogenesis. S1P is formed by two sphingosine kinases (SphKs), SphK1 and SphK2. The intracellularly produced S1P is delivered to the extracellular space by ATP-binding cassette (ABC) transporters and spinster homolog 2 (SPNS2), where it binds to five transmembrane G protein-coupled receptors to mediate its oncogenic functions (S1PR1-S1PR5). MicroRNAs (miRNAs) are small non-coding RNAs, 21-25 nucleotides in length, that play numerous crucial roles in cancer, such as tumor initiation, progression, apoptosis, metastasis, and angiogenesis via binding to the 3'-untranslated region (3'-UTR) of the target mRNA. There is growing evidence that various miRNAs modulate tumorigenesis by regulating the expression of SphKs, and S1P receptors. We have reviewed various roles of miRNAs, SphKs, S1P, and S1P receptors (S1PRs) in malignancies and how notable miRNAs like miR-101, miR-125b, miR-128, and miR-506, miR-1246, miR-21, miR-126, miR499a, miR20a-5p, miR-140-5p, miR-224, miR-137, miR-183-5p, miR-194, miR181b, miR136, and miR-675-3p, modulate S1P signaling. These tumorigenesis modulating miRNAs are involved in different cancers including breast, gastric, hepatocellular carcinoma, prostate, colorectal, cervical, ovarian, and lung cancer via cell proliferation, invasion, angiogenesis, apoptosis, metastasis, immune evasion, chemoresistance, and chemosensitivity. Therefore, understanding the interaction of SphKs, S1P, and S1P receptors with miRNAs in human malignancies will lead to better insights for miRNA-based cancer therapy.

Malignant Ascites in Ovarian Cancer: Cellular, Acellular, and Biophysical Determinants of Molecular Characteristics and Therapy Response

Ascites refers to the abnormal accumulation of fluid in the peritoneum resulting from an underlying pathology, such as metastatic cancer. Among all cancers, advanced-stage epithelial ovarian cancer is most frequently associated with the production of malignant ascites and is the leading cause of death from gynecologic malignancies. Despite decades of evidence showing that the accumulation of peritoneal fluid portends the poorest outcomes for cancer patients, the role of malignant ascites in promoting metastasis and therapy resistance remains poorly understood. This review summarizes the current understanding of malignant ascites, with a focus on ovarian cancer. The first section provides an overview of heterogeneity in ovarian cancer and the pathophysiology of malignant ascites. Next, analytical methods used to characterize the cellular and acellular components of malignant ascites, as well the role of these components in modulating cell biology, are discussed. The review then provides a perspective on the pressures and forces that tumors are subjected to in the presence of malignant ascites and the impact of physical stress on therapy resistance. Treatment options for malignant ascites, including surgical, pharmacological and photochemical interventions are then discussed to highlight challenges and opportunities at the interface of drug discovery, device development and physical sciences in oncology.

Targeting sphingosine kinase-1 with the low MW inhibitor SKI-5C suppresses the development of endometriotic lesions in mice

BACKGROUND AND PURPOSE

Limited evidence suggests that the sphingosine-1-phosphate/sphingosine kinase 1 (S1P/SPHK1) signalling pathway is involved in the pathogenesis of endometriosis. Therefore, we analyzed in this study whether the inhibition of SPHK1 and, consequently, decreased levels of S1P affected the vascularization and growth of endometriotic lesions.

EXPERIMENTAL APPROACH

Endometriotic lesions were surgically induced in the peritoneal cavity and the dorsal skinfold chamber of female BALB/c mice. The animals received a daily dose of the SPHK1 inhibitor SKI-5C or vehicle (control). Analyses involved the determination of lesion growth, cyst formation, microvessel density and cell proliferation within peritoneal endometriotic lesions by means of high-resolution ultrasound imaging, caliper measurement, histology and immunohistochemistry. In the dorsal skinfold chamber model the development of newly formed microvascular networks and their microhemodynamic parameters within endometriotic lesions were investigated by means of intravital fluorescence microscopy.

KEY RESULTS

SKI-5C significantly inhibited the development and vascularization of peritoneal endometriotic lesions, as indicated by a reduced growth and cyst formation, a lower microvessel density and a suppressed cell proliferation, when compared to vehicle-treated controls. Endometriotic lesions in dorsal skinfold chambers of SKI-5C-treated animals exhibited a significantly smaller lesion size, lower functional microvessel density, smaller microvessel diameters and a reduced blood perfusion of the newly developing microvascular networks.

CONCLUSIONS AND IMPLICATIONS

SPHK1/S1P signalling promotes the establishment and progression of endometriotic lesions. The inhibition of this pathway suppresses the development of endometriotic lesions, suggesting SPHK1 as a potential novel target for future endometriosis therapy.

The Role of Ceramide Metabolism and Signaling in the Regulation of Mitophagy and Cancer Therapy

Simple Summary

Sphingolipids are membrane-associated lipids that are involved in signal transduction pathways regulating cell death, growth, and migration. In cancer cells, sphingolipids regulate pathways relevant to cancer therapy, such as invasion, metastasis, apoptosis, and lethal mitophagy. Notable sphingolipids include ceramide, a sphingolipid that induces death and lethal mitophagy, and sphingosine-1 phosphate, a sphingolipid that induces survival and chemotherapeutic resistance. These sphingolipids participate in regulating the process of mitophagy, where cells encapsulate damaged mitochondria in double-membrane vesicles (called autophagosomes) for degradation. Lethal mitophagy is an anti-tumorigenic mechanism mediated by ceramide, where cells degrade many mitochondria until the cancer cell dies in an apoptosis-independent manner.

Abstract

Sphingolipids are bioactive lipids responsible for regulating diverse cellular functions such as proliferation, migration, senescence, and death. These lipids are characterized by a long-chain sphingosine backbone amide-linked to a fatty acyl chain with variable length. The length of the fatty acyl chain is determined by specific ceramide synthases, and this fatty acyl length also determines the sphingolipid’s specialized functions within the cell. One function in particular, the regulation of the selective autophagy of mitochondria, or mitophagy, is closely regulated by ceramide, a key regulatory sphingolipid. Mitophagy alterations have important implications for cancer cell proliferation, response to chemotherapeutics, and mitophagy-mediated cell death. This review will focus on the alterations of ceramide synthases in cancer and sphingolipid regulation of lethal mitophagy, concerning cancer therapy.

Activation of SphK1 by adipocytes mediates epithelial ovarian cancer cell proliferation

Background

Adipocytes, active facilitators of epithelial ovarian cancer (EOC) growth, have been implicated in the link between obesity and EOC. However, the current understanding of the mechanisms underlying adipocyte-induced EOC cell proliferation remains incomplete.

Results

We provide the first evidence showing that sphingosine kinase (SphK) 1 is critical for adipocyte-induced EOC cell proliferation. Adipocytes are capable of activating SphK1, which then leads to extracellular signal-regulated kinase (ERK) phosphorylation. Moreover, adipocyte-induced SphK1 activation is ERK dependent. Furthermore, sphingosine 1-phosphate receptor (S1PR) 1 and S1PR3, key components of the SphK1 signalling pathway, participate in adipocyte-mediated growth-promoting action in EOC cells.

Conclusions

Our study reveals a previously unrecognized role of SphK1 in adipocyte-induced growth-promoting action in EOC, suggesting a new target for EOC therapy.

Targeting the Sphingosine Kinase/Sphingosine-1-Phosphate Signaling Axis in Drug Discovery for Cancer Therapy

Sphingolipid metabolites have emerged as critical players in the regulation of various physiological processes. Ceramide and sphingosine induce cell growth arrest and apoptosis, whereas sphingosine-1-phosphate (S1P) promotes cell proliferation and survival. Here, we present an overview of sphingolipid metabolism and the compartmentalization of various sphingolipid metabolites. In addition, the sphingolipid rheostat, a fine metabolic balance between ceramide and S1P, is discussed. Sphingosine kinase (SphK) catalyzes the synthesis of S1P from sphingosine and modulates several cellular processes and is found to be essentially involved in various pathophysiological conditions. The regulation and biological functions of SphK isoforms are discussed. The functions of S1P, along with its receptors, are further highlighted. The up-regulation of SphK is observed in various cancer types and is also linked to radio- and chemoresistance and poor prognosis in cancer patients. Implications of the SphK/S1P signaling axis in human pathologies and its inhibition are discussed in detail. Overall, this review highlights current findings on the SphK/S1P signaling axis from multiple angles, including their functional role, mechanism of activation, involvement in various human malignancies, and inhibitor molecules that may be used in cancer therapy.

Inhibition of sphingosine kinase 2 down-regulates ERK/c-Myc pathway and reduces cell proliferation in human epithelial ovarian cancer

Background

Epithelial ovarian cancer (EOC) is the leading cause of death from female cancers. In our previous study, sphingosine kinase 2 (SphK2) inhibitor was shown to display anti-EOC activities. The purpose of this study was to evaluate further the expression characteristics and clinical significance of SphK2 in EOC and to explore the roles and underlying mechanisms of SphK2 in EOC cell survival.

Methods

The expression of SphK2 was examined by immunohistochemistry (IHC) and Western blot, and its clinical implications and prognostic significance were analyzed. We performed a cellular proliferation assay, and a mouse xenograft model was established to confirm the roles of SphK2 in vitro and in vivo. Cell cycle analysis, apoptosis assay, and Western blot were performed to examine cell cycle progression and apoptosis rate. Gene set enrichment analysis (GSEA), and Western blot were used to investigate the downstream signaling pathways related to SphK2 function.

Results

The expression level of SphK2 was shown to be associated with stage, histological grade, lymph node metastasis, and ascites status. More importantly, a high SphK2 expression level was a prognostic indicator of overall survival (OS) and relapse-free survival (RFS). Moreover, knockdown of SphK2 arrested cell cycle progression and inhibited EOC cell proliferation both in vitro and in vivo. Furthermore, ERK/c-Myc, the key pathway in EOC progression, was important for SphK2-mediated mitogenic action in EOC cells.

Conclusions

Our findings provided the first evidence that SphK2 played a crucial role in EOC proliferation by regulating the ERK/c-Myc pathway. This indicated that SphK2 might serve as a prognostic marker and potential therapeutic target in EOC.

Sphingosine-kinase-1 expression is associated with improved overall survival in high-grade serous ovarian cancer

Purpose

Sphingosine-kinase-1 (SPHK1) is a key enzyme of sphingolipid metabolism which is involved in ovarian cancer pathogenesis, progression and mechanisms of drug resistance. It is overexpressed in a variety of cancer subtypes. We investigated SPHK1 expression as a prognostic factor in epithelial ovarian cancer patients.

Methods

Expression analysis of SPHK1 was performed on formalin-fixed paraffin-embedded tissue from 1005 ovarian cancer patients with different histological subtypes using immunohistochemistry. Staining intensity of positive tumor cells was assessed semi-quantitatively, and results were correlated with clinicopathological characteristics and survival.

Results

In our ovarian cancer collective, high levels of SPHK1 expression correlated significantly with complete surgical tumor resection (p = 0.002) and lower FIGO stage (p = 0.04). Progression-free and overall survival were further significantly longer in patients with high-grade serous ovarian cancer and overexpression of SPHK1 (p = 0.002 and p = 0.006, respectively).

Conclusion

Our data identify high levels of SPHK1 expression as a potential favorable prognostic marker in ovarian cancer patients.

Supplementary Information

The online version of this article (10.1007/s00432-021-03558-x) contains supplementary material, which is available to authorized users.

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.

Loss of sphingosine 1-phosphate receptor 3 gene function impairs injury-induced stromal angiogenesis in mouse cornea

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid generated through sphingosine kinase1 (SPK1)-mediated phosphorylation of sphingosine. We show here that injury-induced S1P upregulation increases corneal neovascularization through stimulating S1PR3, a cognate receptor. since this response was suppressed in S1PR3-knockout mice. Furthermore, Cayman10444, a selective S1PR3 inhibitor, reduced this response in WT mice. Such reductions in neovascularization were associated with reduced vascular endothelial growth factor A (VEGF-A) mRNA expression levels in WT TKE2 corneal epithelial cells and macrophages treated with CAY10444 as well as macrophages isolated from S1PR3 KO mice. S1P increased tube-like vessel formation in human vascular endothelial cells (HUVEC) and human retinal microvascular endothelial cells (HRMECs) cells expressing S1PR3. In S1PR3 KO mice, TGFβ1-induced increases in αSMA gene expression levels were suppressed relative to those in the WT counterparts. In S1PR3 deficient macrophages, VEGF-A expression levels were lower than in WT macrophages. Transforming growth factor β1(TGFβ1) upregulated SPK1 expression levels in ocular fibroblasts and TKE2 corneal epithelial cells. CAY10444 blocked S1P-induced increases in VEGF-A mRNA expression levels in TKE2 corneal epithelial cells. Endogenous S1P signaling upregulated VEGF-A and VE-cadherin mRNA expression levels in HUVEC. Unlike in TKE2 cells, SIS3 failed to block TGFβ1-induced VEGF-A upregulation in ocular fibroblasts. Taken together, these results indicate that injury-induced TGFβ1 upregulation increases S1P generation through increases in SPK1 activity. The rise in S1P formation stimulates the S1PR3-linked signaling pathway, which in turn increases VEGF-A expression levels and angiogenesis in mouse corneas.

The Tumorigenic Effect of Sphingosine Kinase 1 and Its Potential Therapeutic Target

Sphingosine kinase 1 (SPHK1) regulates cell proliferation and survival by converting sphingosine to the signaling mediator sphingosine 1-phosphate (S1P). SPHK1 is widely overexpressed in most cancers, promoting tumor progression and is associated with clinical prognosis. Numerous studies have explored SPHK1 as a promising target for cancer therapy. However, due to insufficient knowledge of SPHK1 oncogenic mechanisms, its inhibitors’ therapeutic potential in preventing and treating cancer still needs further investigation. In this review, we summarized the metabolic balance regulated by the SPHK1/S1P signaling pathway and highlighted the oncogenic mechanisms of SPHK1 via the upregulation of autophagy, proliferation, and survival, migration, angiogenesis and inflammation, and inhibition of apoptosis. Drug candidates targeting SPHK1 were also discussed at the end. This review provides new insights into the oncogenic effect of SPHK1 and sheds light on the future direction for targeting SPHK1 as cancer therapy.

Effects of Sphingosine-1-Phosphate on Cell Viability, Differentiation, and Gene Expression of Adipocytes

Sphingosine-1-phosphate (S1P) is a highly potent sphingolipid metabolite, which controls numerous physiological and pathological process via its extracellular and intracellular functions. The breast is mainly composed of epithelial cells (mammary gland) and adipocytes (stroma). Adipocytes play an important role in regulating the normal functions of the breast. Compared to the vast amount studies on breast epithelial cells, the functions of S1P in breast adipocytes are much less known. Thus, in the current study, we used human preadipocyte cell lines SGBS and mouse preadipocyte cell line 3T3-L1 as in vitro models to evaluate the effects of S1P on cell viability, differentiation, and gene expression in adipocytes. Our results showed that S1P increased cell viability in SGBS and 3T3-L1 preadipocytes but moderately reduced cell viability in differentiated SGBS and 3T3-L1 adipocytes. S1P was also shown to inhibit adipogenic differentiation of SGBS and 3T3-L1 at concentration higher than 1000 nM. Transcriptome analyses showed that S1P was more influential on gene expression in differentiated adipocytes. Furthermore, our network analysis in mature adipocytes showed that the upregulated DEGs (differentially expressed genes) were related to regulation of lipolysis, PPAR (peroxisome proliferator-activated receptor) signaling, alcoholism, and toll-like receptor signaling, whereas the downregulated DEGs were overrepresented in cytokine-cytokine receptor interaction, focal adhesion, starch and sucrose metabolism, and nuclear receptors pathways. Together previous studies on the functions of S1P in breast epithelial cells, the current study implicated that S1P may play a critical role in modulating the bidirectional regulation of adipocyte-extracellular matrix-epithelial cell axis and maintaining the normal physiological functions of the breast.

Small Molecule Soluble Epoxide Hydrolase Inhibitors in Multitarget and Combination Therapies for Inflammation and Cancer

The enzyme soluble epoxide hydrolase (sEH) plays a central role in metabolism of bioactive lipid signaling molecules. The substrate-specific hydrolase activity of sEH converts epoxyeicosatrienoic acids (EETs) to less bioactive dihydroxyeicosatrienoic acids. EETs exhibit anti-inflammatory, analgesic, antihypertensive, cardio-protective and organ-protective properties. Accordingly, sEH inhibition is a promising therapeutic strategy for addressing a variety of diseases. In this review, we describe small molecule architectures that have been commonly deployed as sEH inhibitors with respect to angiogenesis, inflammation and cancer. We juxtapose commonly used synthetic scaffolds and natural products within the paradigm of a multitarget approach for addressing inflammation and inflammation induced carcinogenesis. Structural insights from the inhibitor complexes and novel strategies for development of sEH-based multitarget inhibitors are also presented. While sEH inhibition is likely to suppress inflammation-induced carcinogenesis, it can also lead to enhanced angiogenesis via increased EET concentrations. In this regard, sEH inhibitors in combination chemotherapy are described. Urea and amide-based architectures feature prominently across multitarget inhibition and combination chemotherapy applications of sEH inhibitors.

Unveiling role of sphingosine-1-phosphate receptor 2 as a brake of epithelial stem cell proliferation and a tumor suppressor in colorectal cancer

Background

Sphingosine-1-phosphate receptor 2 (S1PR2) mediates pleiotropic functions encompassing cell proliferation, survival, and migration, which become collectively de-regulated in cancer. Information on whether S1PR2 participates in colorectal carcinogenesis/cancer is scanty, and we set out to fill the gap.

Methods

We screened expression changes of S1PR2 in human CRC and matched normal mucosa specimens [N = 76]. We compared CRC arising in inflammation-driven and genetically engineered models in wild-type (S1PR2^+/+) and S1PR2 deficient (S1PR2^−/−) mice. We reconstituted S1PR2 expression in RKO cells and assessed their growth in xenografts. Functionally, we mimicked the ablation of S1PR2 in normal mucosa by treating S1PR2^+/+ organoids with JTE013 and characterized intestinal epithelial stem cells isolated from S1PR2^−/−Lgr5-EGFP- mice.

Results

S1PR2 expression was lost in 33% of CRC; in 55%, it was significantly decreased, only 12% retaining expression comparable to normal mucosa. Both colitis-induced and genetic Apc^+/min mouse models of CRC showed a higher incidence in size and number of carcinomas and/or high-grade adenomas, with increased cell proliferation in S1PR2^−/− mice compared to S1PR2^+/+ controls. Loss of S1PR2 impaired mucosal regeneration, ultimately promoting the expansion of intestinal stem cells. Whereas its overexpression attenuated cell cycle progression, it reduced the phosphorylation of AKT and augmented the levels of PTEN.

Conclusions

In normal colonic crypts, S1PR2 gains expression along with intestinal epithelial cells differentiation, but not in intestinal stem cells, and contrasts intestinal tumorigenesis by promoting epithelial differentiation, preventing the expansion of stem cells and braking their malignant transformation. Targeting of S1PR2 may be of therapeutic benefit for CRC expressing high Lgr5.

Graphical Abstract. Schematic drawing of the role of S1PR2 in normal mucosa and colorectal cancer. In the normal mucosa, S1PR2 is highly expressed by differentiated cells at the upper region of both colon and intestinal crypts (S1PR2 ON), but not by the undifferentiated stem cell at the base of the crypts (S1PR2 OFF), in which acts as a negative proliferative regulator promoting epithelial differentiation. Its loss leads to the expansion of stem cells and reduced levels of PTEN and Axin-2, two negative regulators respectively of PI3K/AKT and Wnt signaling that control β-catenin signaling. The translocation of β-catenin into the nucleus promotes the transcription of target genes involved in the proliferation and malignant transformation. Thereby, S1PR2 works in the intestine as a tumor suppressor

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01740-6.

Development of a novel immune-related genes prognostic signature for osteosarcoma

Immune-related genes (IRGs) are responsible for osteosarcoma (OS) initiation and development. We aimed to develop an optimal IRGs-based signature to assess of OS prognosis. Sample gene expression profiles and clinical information were downloaded from the Therapeutically Applicable Research to Generate Effective Treatments (TARGET) and Genotype-Tissue Expression (GTEx) databases. IRGs were obtained from the ImmPort database. R software was used to screen differentially expressed IRGs (DEIRGs) and functional correlation analysis. DEIRGs were analyzed by univariate Cox regression and iterative LASSO Cox regression analysis to develop an optimal prognostic signature, and the signature was further verified by independent cohort (GSE39055) and clinical correlation analysis. The analyses yielded 604 DEIRGs and 10 hub IRGs. A prognostic signature consisting of 13 IRGs was constructed, which strikingly correlated with OS overall survival and distant metastasis (p < 0.05, p < 0.01), and clinical subgroup showed that the signature's prognostic ability was independent of clinicopathological factors. Univariate and multivariate Cox regression analyses also supported its prognostic value. In conclusion, we developed an IRGs signature that is a prognostic indicator in OS patients, and the signature might serve as potential prognostic indicator to identify outcome of OS and facilitate personalized management of the high-risk patients.

Follicle-stimulating hormone promotes the proliferation of epithelial ovarian cancer cells by activating sphingosine kinase

Follicle-stimulating hormone (FSH) is closely related to the pathogenesis and progression of epithelial ovarian cancer (EOC). However, until now, knowledge relating to FSH-driven signalling pathways that lead to the growth of EOC remained incomplete. We sought to explore whether sphingosine kinase (SphK) could mediate FSH-induced ovarian cancer cell proliferation and which pathway might be involved in this process. The expression of phospho-SphK1 and phospho-SphK2 was detected in sections of EOC tissues by Immunohistochemical staining, and clinical significances were analyzed by statistical analysis. EOC cells were treated with FSH or/and SKI-II. CCK8 assays and colony formation assays were used to investigate cell proliferation. Western blot was carried out to detect protein expression in EOC cell line after treated with FSH. Here, for the first time, we provide evidence that high expression levels of phospho-SphK1 and phospho-SphK2 were both prognostic indicators of overall survival (OS) in EOC. Additionally, the expression levels of both phospho-SphK1 and phospho-SphK2 were closely correlated with the expression level of follicle-stimulating hormone receptor (FSHR) in ovarian cancer tissues. FSH stimulated the phosphorylation of both SphK1 and SphK2 and was able to regulate the survival and growth of ovarian cancer cells by activating SphK1 and SphK2 through ERK1/2. Both isoenzymes of SphK were equally responsible for FSH-induced cell proliferation of EOC. Both Erk1/2 and Akt activation play important roles in mediating FSH-induced cell proliferation after phosphorylation of SphK. Moreover, our data demonstrated that S1P receptor 1 (S1PR1) and S1PR3, key components of the SphK signalling system, were involved in FSH-mediated proliferation of EOC. Taken together, the results of the current study revealed that SphK is an essential mediator in FSH-induced proliferation of ovarian cancer cells in EOC, which indicates a new signalling pathway that controls FSH-mediated growth in EOC and suggests a new strategy that pharmaceutically targets both isoenzymes of SphK for the management of ovarian cancer.

S1PR1 as a Novel Promising Therapeutic Target in Cancer Therapy

Sphingosine-1-phosphate (S1P) can regulate several physiological and pathological processes. S1P signaling via its cell surface receptor S1PR1 has been shown to enhance tumorigenesis and stimulate growth, expansion, angiogenesis, metastasis, and survival of cancer cells. S1PR1-mediated tumorigenesis is supported and amplified by activation of downstream effectors including STAT3, interleukin-6, and NF-κB networks. S1PR1 signaling can also trigger various other signaling pathways involved in carcinogenesis including activation of PI3K/AKT, MAPK/ERK1/2, Rac, and PKC/Ca, as well as suppression of cyclic adenosine monophosphate (cAMP). It also induces immunological tolerance in the tumor microenvironment, while the immunosuppressive function of S1PR1 can also lead to the generation of pre-metastatic niches. Some tumor cells upregulate S1PR1 signaling pathways, which leads to drug resistant cancer cells, mainly through activation of STAT3. This signaling pathway is also implicated in some inflammatory conditions leading to the instigation of inflammation-driven cancers. Furthermore, it can also increase survival via induction of anti-apoptotic pathways, for instance, in breast cancer cells. Therefore, S1PR1 and its signaling pathways can be considered as potential anti-tumor therapeutic targets, alone or in combination therapies. Given the oncogenic nature of S1PR1 and its distribution in a variety of cancer cell types along with its targeting advantages over other molecules of this family, S1PR1 should be considered a favorable target in therapeutic approaches to cancer. This review describes the role of S1PR1 in cancer development and progression, specifically addressing breast cancer, glioma, and hematopoietic malignancies. We also discuss the potential use of S1P signaling modulators as therapeutic targets in cancer therapy.

Roles of lncRNAs in cancer: Focusing on angiogenesis

Approximately 98% of the human genome consists of non-coding sequences that are classified into two classes by size: small non-coding RNAs (≤200 nucleotides) and long non-coding RNAs (≥200 nucleotides). Long non-coding RNAs (lncRNAs) are involved in various cellular events and act as guides, signals, decoys, and dynamic scaffolds. Due to their oncogenic and tumor suppressive roles, lncRNAs are important in cancer development and growth. LncRNAs play their roles by modulating cancer hallmarks, including DNA damage, metastasis, immune escape, cell stemness, drug resistance, metabolic reprogramming, and angiogenesis. Angiogenesis is vital for solid tumors which guarantees their growth beyond 2 mm³. Tumor angiogenesis is a complex process and is regulated through interaction between pro-angiogenic and anti-angiogenic factors within the tumor microenvironment. There are accumulating evidence that different lncRNAs regulate tumor angiogenesis. In this paper, we described the functions and mechanisms of lncRNAs in tumor angiogenesis.

Acid Ceramidase: A Novel Therapeutic Target in Cancer

Sphingolipids are important constituents of the eukaryotic cell membrane which govern various signaling pathways related to different aspects of cell survival. Ceramide and Sphingosine are interconvertible sphingolipid metabolites, out of which Ceramide is pro-apoptotic and sphingosine is anti-apoptotic in nature. The conversion of ceramide to sphingosine is mediated by Acid Ceramidase (ASAH1) thus maintaining a rheostat between a tumor suppressor and a tumor promoter. This rheostat is completely altered in many tumors leading to uncontrolled proliferation. This intriguing property of ASAH1 can be used by cancer cells to their advantage, by increasing the expression of the tumor promoter, sphingosine inside cells, thus creating a favorable environment for cancer growth. The different possibilities through which this enzyme serves its role in formation, progression and resistance of different types of cancers will lead to the possibility of making Acid Ceramidase a promising drug target. This review discusses the current understanding of the role of acid ceramidase in cancer progression, metastasis and resistance, strategies to develop novel natural and synthetic inhibitors of ASAH1 and their usefulness in cancer therapy.

Sphingosine kinase 2 inhibitor ABC294640 displays anti-epithelial ovarian cancer activities in vitro and in vivo

Background: ABC294640 is a non-lipid competitive inhibitor of SphK2. It exhibited anti-proliferative activities in many human malignancies, including ovarian cancer. However, its potential mechanism of action remains poorly understood.

Methods: In this paper, epithelial ovarian cancer (EOC) cell lines SKOV3 and HO8910 were treated with ABC294640. In order to explore the effect of ABC294640 on the behavior of ovarian cancer cells in vitro, we used cell counting kit-8 (CCK-8) assays, colony formation assays, flow cytometry, quantitative real-time PCR (qRT-PCR), Western blot analysis and immunohistochemistry to detect the effect of ABC294640 on cell proliferation, cell cycle distribution, cell apoptosis, the expression of related factors at mRNA levels, and the expression of related factors at protein level. An intra-abdominal xenograft tumor model of EOC was set up to assess the tumor growth in nude mice.

Results: The results obtained indicate that EOC cell proliferation was noticeably inhibited in a concentration-dependent manner by ABC294640. ABC294640 caused cell cycle arrest in S phase and increased cell apoptosis rate in EOC cells. Also, the proteins, including phosphorylated retinoblastoma protein (P-Rb), cyclin D1, cyclin B1, and Bcl-2 were significantly inhibited, while cleaved-caspase 3 was activated. ABC294640 inhibited the expression of c-Myc in EOC. The in vivo assay showed an inhibitory effect of ABC294640 on tumor growth.

Conclusions: ABC294640 could downregulate the expression of c-Myc in EOC both in vitro and in vivo. ABC294640 inhibited tumor growth in EOC via cell cycle arrest and inducing cell apoptosis both in vitro and in vivo, partially by decreasing the expression of cell cycle–associated proteins (such as P-Rb, cyclin B1, and cyclin D1) and promoting caspase 3 activation via downregulation expression of c-Myc. It suggested that ABC294640 had the potential to serve as an agent in EOC treatment.

SPHK1 Is a Novel Target of Metformin in Ovarian Cancer

The role of phospholipid signaling in ovarian cancer is poorly understood. Sphingosine-1-phosphate (S1P) is a bioactive metabolite of sphingosine that has been associated with tumor progression through enhanced cell proliferation and motility. Similarly, sphingosine kinases (SPHK), which catalyze the formation of S1P and thus regulate the sphingolipid rheostat, have been reported to promote tumor growth in a variety of cancers. The findings reported here show that exogenous S1P or overexpression of SPHK1 increased proliferation, migration, invasion, and stem-like phenotypes in ovarian cancer cell lines. Likewise, overexpression of SPHK1 markedly enhanced tumor growth in a xenograft model of ovarian cancer, which was associated with elevation of key markers of proliferation and stemness. The diabetes drug, metformin, has been shown to have anticancer effects. Here, we found that ovarian cancer patients taking metformin had significantly reduced serum S1P levels, a finding that was recapitulated when ovarian cancer cells were treated with metformin and analyzed by lipidomics. These findings suggested that in cancer the sphingolipid rheostat may be a novel metabolic target of metformin. In support of this, metformin blocked hypoxia-induced SPHK1, which was associated with inhibited nuclear translocation and transcriptional activity of hypoxia-inducible factors (HIF1α and HIF2α). Further, ovarian cancer cells with high SPHK1 were found to be highly sensitive to the cytotoxic effects of metformin, whereas ovarian cancer cells with low SPHK1 were resistant. Together, the findings reported here show that hypoxia-induced SPHK1 expression and downstream S1P signaling promote ovarian cancer progression and that tumors with high expression of SPHK1 or S1P levels might have increased sensitivity to the cytotoxic effects of metformin. IMPLICATIONS: Metformin targets sphingolipid metabolism through inhibiting SPHK1, thereby impeding ovarian cancer cell migration, proliferation, and self-renewal.

S1P/S1PR3 axis promotes aerobic glycolysis by YAP/c-MYC/PGAM1 axis in osteosarcoma

Background

Osteosarcoma (OS) is a malignant tumor mainly occurring in young people. Due to the limited effective therapeutic strategies, OS patients cannot achieve further survival improvement. G-protein-coupled receptors (GPCRs) constitute the largest family of cell membrane receptors and consequently hold the significant promise for tumor imaging and targeted therapy. We aimed to explore the biological functions of Sphingosine 1-phosphate receptor 3 (S1PR3), one of the members of GPCRs family, in OS and the possibility of S1PR3 as an effective target for the treatment of osteosarcoma.

Methods

The quantitative real time PCR (qRT-PCR) and western blotting were used to analyze the mRNA and protein expressions. Cell counting kit-8 (CCK8), colony formation assay and cell apoptosis assay were performed to test the cellular proliferation in vitro. Subcutaneous xenograft mouse model was generated to evaluate the functions of S1PR3 in vivo. RNA sequencing was used to compare gene expression patterns between S1PR3-knockdown and control MNNG-HOS cells. In addition, metabolic alternations in OS cells were monitored by XF96 metabolic flux analyzer. Co-immunoprecipitation (Co-IP) assay was used to explore the interaction between Yes-associated protein (YAP) and c-MYC. Chromatin immunoprecipitation was used to investigate the binding capability of PGAM1 and YAP or c-MYC. Moreover, the activities of promoter were determined by the luciferase reporter assay.

Findings

S1PR3 and its specific ligand Sphingosine 1-phosphate (S1P) were found elevated in OS, and the higher expression of S1PR3 was correlated with the poor survival rate. Moreover, our study has proved that the S1P/S1PR3 axis play roles in proliferation promotion, apoptosis inhibition, and aerobic glycolysis promotion of osteosarcoma cells. Mechanistically, the S1P/S1PR3 axis inhibited the phosphorylation of YAP and promoted the nuclear translocation of YAP, which contributed to the formation of the YAP–c-MYC complex and enhanced transcription of the important glycolysis enzyme PGAM1. Moreover, the S1PR3 antagonist TY52156 exhibited in vitro and in vivo synergistic inhibitory effects with methotrexate on OS cell growth.

Interpretation

Our study unveiled a role of S1P, a bioactive phospholipid, in glucose metabolism reprogram through interaction with its receptor S1PR3. Targeting S1P/S1PR3 axis might serve as a potential therapeutic target for patients with OS.

Fund

This research was supported by National Natural Science Foundation of China (81472445 and 81672587).

SphK1/S1P mediates TGF-β1-induced proliferation of pulmonary artery smooth muscle cells and its potential mechanisms

The upregulation of Sphingosine kinase 1 (SphK1) expression and accompanied sphingosine-1-phosphate (S1P) production have been reported to contribute to the proliferation of pulmonary artery smooth muscle cells (PASMC) and pulmonary arterial remodeling. However, the molecular mechanisms of SphK1/S1P upregulation in PASMC and the specific mechanisms of how SphK1/S1P pathway promotes PASMC proliferation remain largely unclear. This study aims to address these issues. Here, we demonstrated that TGF-β1 significantly upregulated SphK1 expression and S1P production by promoting the phosphorylation of Smad2/3 in PASMC. Further study indicated that SphK1/S1P pathway mediated TGF-β1-induced Notch3 activation in PASMC. In addition, we showed that TGF-β1 significantly induced proliferation of PASMC, while pre-inhibition of Smad2/3 phosphorylation with SB431542 or silencing SphK1 using small interfering RNA in advance, or pre-blocking Notch3 pathway with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), attenuated TGF-β1-induced PASMC proliferation. Taken together, our study indicates that Smad2/3/SphK1/S1P/Notch3 pathway mediates TGF-β1-induced PASMC proliferation and suggests this pathway as a potential therapeutic target in the prevention and treatment of pulmonary hypertension.

The sphingosine kinase-1/sphingosine-1-phosphate axis in cancer: Potential target for anticancer therapy

Sphingolipid metabolites, such as ceramide, sphingosine and sphingosine-1-phosphate (S1P), play many important roles in cellular activities. Ceramide and sphingosine inhibit cell proliferation and induce cell apoptosis while S1P has the opposite effect. Maintaining a metabolic balance of sphingolipids is essential for growth and development of cells. Sphingosine kinase (SPHK) is an important regulator for keeping this balance. It controls the level of S1P and plays important roles in proliferation, migration, and invasion of cancer cells and tumor angiogenesis. There are two isoenzymes of sphingosine kinase, SPHK1 and SPHK2. SPHK1 is ubiquitously expressed in most cancers where it promotes survival and proliferation, while SPHK2 is restricted to only certain tissues and its functions are not well characterized. SPHK1 is currently considered as a novel target for the treatment of cancers. Targeting SPHK1 would provide new strategies for cancer treatment and improve the prognosis of cancer patients. Here we review and summarize the current research findings on the SPHK1-S1P axis in cancer from many aspects including structure, expression, regulation, mechanism, and potential inhibitors.

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.

Generation of sphingosine-1-phosphate is enhanced in biliary tract cancer patients and is associated with lymphatic metastasis

Lymphatic metastasis is known to contribute to worse prognosis of biliary tract cancer (BTC). Recently, sphingosine-1-phosphate (S1P), a bioactive lipid mediator generated by sphingosine kinase 1 (SPHK1), has been shown to play an important role in lymphangiogenesis and lymph node metastasis in several types of cancer. However, the role of the lipid mediator in BTC has never been examined. Here we found that S1P is elevated in BTC with the activation of ceramide-synthetic pathways, suggesting that BTC utilizes SPHK1 to promote lymphatic metastasis. We found that S1P, sphingosine and ceramide precursors such as monohexosyl-ceramide and sphingomyelin, but not ceramide, were significantly increased in BTC compared to normal biliary tract tissue using LC-ESI-MS/MS. Utilizing The Cancer Genome Atlas cohort, we demonstrated that S1P in BTC is generated via de novo pathway and exported via ABCC1. Further, we found that SPHK1 expression positively correlated with factors related to lymphatic metastasis in BTC. Finally, immunohistochemical examination revealed that gallbladder cancer with lymph node metastasis had significantly higher expression of phospho-SPHK1 than that without. Taken together, our data suggest that S1P generated in BTC contributes to lymphatic metastasis.

Lysophospholipid Signaling in the Epithelial Ovarian Cancer Tumor Microenvironment

As one of the important cancer hallmarks, metabolism reprogramming, including lipid metabolism alterations, occurs in tumor cells and the tumor microenvironment (TME). It plays an important role in tumorigenesis, progression, and metastasis. Lipids, and several lysophospholipids in particular, are elevated in the blood, ascites, and/or epithelial ovarian cancer (EOC) tissues, making them not only useful biomarkers, but also potential therapeutic targets. While the roles and signaling of these lipids in tumor cells are extensively studied, there is a significant gap in our understanding of their regulations and functions in the context of the microenvironment. This review focuses on the recent study development in several oncolipids, including lysophosphatidic acid and sphingosine-1-phosphate, with emphasis on TME in ovarian cancer.