Sphingosine kinase 1 promotes malignant progression in colon cancer and independently predicts survival of patients with colon cancer by competing risk approach in South asian population. Clin Transl Gastroenterol. 2014;5:e51. [PMID: 24572701 PMCID: PMC3940836 DOI: 10.1038/ctg.2013.21]

DHRS2-induced SPHK1 downregulation contributes to the cell growth inhibition by Trichothecin in colorectal carcinoma

BACKGROUND

Deregulation of lipid metabolism is one of the most prominent metabolic features in cancer. The activation of sphingolipid metabolic pathways affects the proliferation, invasion, angiogenesis, chemoresistance, and immune escape of tumors, including colorectal cancer (CRC). Dehydrogenase/reductase member 2 (DHRS2), which belongs to the short-chain dehydrogenase/reductase (SDR) family, has been reported to participate in the regulation of lipid metabolism and impact on cancer progression. Trichothecin (TCN) is a sesquiterpenoid metabolite originating from an endophytic fungus of the herbal plant Maytenus hookeri Loes. Studies have shown that TCN exerts a broad-spectrum antitumor activity.

METHODS

We evaluated the proliferative ability of CRC cells by CCK8 and colony formation assays. A metabolite profiling using liquid chromatography coupled with mass spectrometry (LC/MS) was adopted to identify the proximal metabolite changes linked to DHRS2 overexpression. RNA stability assay and RNA immunoprecipitation (RIP) experiments were applied to determine the post-transcriptional regulation of SPHK1 expression by DHRS2. We used flow cytometry to detect changes in cell cycle and cell apoptosis of CRC cells in the absence or presence of TCN.

RESULTS

We demonstrate that DHRS2 hampers the sphingosine kinases 1 (SPHK1)/sphingosine 1-phosphate (S1P) metabolic pathway to inhibit CRC cell growth. DHRS2 directly binds to SPHK1 mRNA to accelerate its degradation in a post-transcriptionally regulatory manner. Moreover, we illustrate that SPHK1 downregulation induced by DHRS2 contributes to TCN-induced growth inhibition of CRC.

CONCLUSIONS

The present study provides a mechanistic connection among metabolic enzymes, metabolites, and the malignant progression of CRC. Moreover, TCN could be developed as a potential pharmacological tool against CRC by the induction of DHRS2 and targeting SPHK1/S1P metabolic pathway.

The sphingosine kinase 2 inhibitors ABC294640 and K145 elevate (dihydro)sphingosine 1-phosphate levels in various cells

Sphingosine kinases (SphKs), enzymes that produce the bioactive lipids dihydrosphingosine 1-phosphate (dhS1P) and sphingosine 1-phosphate (S1P), are associated with various diseases, including cancer and infections. For this reason, a number of SphK inhibitors have been developed. Although off-target effects have been described for selected agents, SphK inhibitors are mostly used in research without monitoring the effects on the sphingolipidome. We have now investigated the effects of seven commonly used SphK inhibitors (5c, ABC294640 (opaganib), N,N-dimethylsphingosine, K145, PF-543, SLM6031434, and SKI-II) on profiles of selected sphingolipids in Chang, HepG2, and human umbilical vein endothelial cells. While we observed the expected (dh)S1P reduction for N,N-dimethylsphingosine, PF-543, SKI-II, and SLM6031434, 5c showed hardly any effect. Remarkably, for K145 and ABC294640, both reported to be specific for SphK2, we observed dose-dependent strong increases in dhS1P and S1P across cell lines. Compensatory effects of SphK1 could be excluded, as this observation was also made in SphK1-deficient HK-2 cells. Furthermore, we observed effects on dihydroceramide desaturase activity for all inhibitors tested, as has been previously noted for ABC294640 and SKI-II. In additional mechanistic studies, we investigated the massive increase of dhS1P and S1P after short-term cell treatment with ABC294640 and K145 in more detail. We found that both compounds affect sphingolipid de novo synthesis, with 3-ketodihydrosphingosine reductase and dihydroceramide desaturase as their targets. Our study indicates that none of the seven SphK inhibitors tested was free of unexpected on-target and/or off-target effects. Therefore, it is important to monitor cellular sphingolipid profiles when SphK inhibitors are used in mechanistic studies.

The Effect of Silencing the Genes Responsible for the Level of Sphingosine-1-phosphate on the Apoptosis of Colon Cancer Cells

Sphingosine-1-phosphate (S1P) and ceramides (Cer) are engaged in key events of signal transduction, but their involvement in the pathogenesis of colorectal cancer is not conclusive. The aim of our study was to investigate how the modulation of sphingolipid metabolism through the silencing of the genes involved in the formation (SPHK1) and degradation (SGPL1) of sphingosine-1-phosphate would affect the sphingolipid profile and apoptosis of HCT-116 human colorectal cancer cells. Silencing of SPHK1 expression decreased S1P content in HCT-116 cells, which was accompanied by an elevation in sphingosine, C18:0-Cer, and C18:1-Cer, increase in the expression and activation of Caspase-3 and -9, and augmentation of apoptosis. Interestingly, silencing of SGLP1 expression increased cellular content of both the S1P and Cer (C16:0-; C18:0-; C18:1-; C20:0-; and C22:0-Cer), yet inhibited activation of Caspase-3 and upregulated protein expression of Cathepsin-D. The above findings suggest that modulation of the S1P level and S1P/Cer ratio regulates both cellular apoptosis and CRC metastasis through Cathepsin-D modulation. The cellular ratio of S1P/Cer seems to be a crucial component of the above mechanism.

Sphingosine 1-phosphate lyase facilitates cancer progression through converting sphingolipids to glycerophospholipids

BACKGROUND

In addition to potent agonist properties for sphingosine 1-phosphate (S1P) receptors, intracellularly, S1P is an intermediate in metabolic conversion pathway from sphingolipids to glycerolysophospholipids (glyceroLPLs). We hypothesized that this S1P metabolism and its products might possess some novel roles in the pathogenesis of cancer, where S1P lyase (SPL) is a key enzyme.

METHODS

The mRNA levels of sphingolipid-related and other cancer-related factors were measured in human hepatocellular carcinoma (HCC), colorectal cancer, and esophageal cancer patients' tumours and in their adjacent non-tumour tissues. Phospholipids (PL) and glyceroLPLs were measured by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In-vitro experiments were performed in Colon 26 cell line with modulation of the SPL and GPR55 expressions. Xenograft model was used for determination of the cancer progression and for pharmacological influence.

RESULTS

Besides high SPL levels in human HCC and colon cancer, SPL levels were specifically and positively linked with levels of glyceroLPLs, including lysophosphatidylinositol (LPI). Overexpression of SPL in Colon 26 cells resulted in elevated levels of LPI and lysophosphatidylglycerol (LPG), which are agonists of GPR55. SPL overexpression-enhanced cell proliferation was inhibited by GPR55 silencing. Conversely, inhibition of SPL led to the opposite outcome and reversed by adding LPI, LPG, and metabolites generated during S1P degradation, which is regulated by SPL. The xenograft model results suggested the contribution of SPL and glyceroLPLs to tumour progression depending on levels of SPL and GPR55. Moreover, the pharmacological inhibition of SPL prevented the progression of cancer. The underlying mechanisms for the SPL-mediated cancer progression are the activation of p38 and mitochondrial function through the LPI, LPG-GPR55 axis and the suppression of autophagy in a GPR55-independent manner.

CONCLUSION

A new metabolic pathway has been proposed here in HCC and colon cancer, SPL converts S1P to glyceroLPLs, mainly to LPI and LPG, and facilitates cancer development.

Sphingosine Kinase 1 Signaling in Breast Cancer: A Potential Target to Tackle Breast Cancer Stem Cells

Sphingosine kinases (SPHKs) are conserved lipid enzymes that catalyze the formation of sphingosine-1-phosphate (S1P) through ATP-dependent phosphorylation of sphingosine. Two distinct SPHK isoforms, namely SPHK1 and SPHK2, have been identified to date, and the former has been implicated for its oncogenic roles in cancer development and progression. While SPHK1 signaling axis has been extensively studied in non-stem breast cancer cells, recent evidence has emerged to suggest a role of SPHK1 in regulating cancer stem cells (CSCs). With the clinical implications of CSCs in disease relapse and metastasis, it is believed that therapeutic approaches that can eradicate both non-stem cancer cells and CSCs could be a key to cancer cure. In this review, we first explore the oncogenic functions of sphingosine kinase 1 in human cancers and summarize current research findings of SPHK1 signaling with a focus on breast cancer. We also discuss the therapeutic potentials and perspectives of targeting SPHK1 signaling in breast cancer and cancer stem cells. We aim to offer new insights and inspire future studies looking further into the regulatory functions of SPHK1 in CSC-driven tumorigenesis, uncovering novel therapeutic avenues of using SPHK1-targeted therapy in the treatment of CSC-enriched refractory cancers.

Differential Expression of the Sphingolipid Pathway Is Associated with Sensitivity to the PP2A Activator FTY720 in Colorectal Cancer Cell Lines

Protein phosphatase 2A (PP2A) is a ubiquitously expressed intracellular serine/threonine phosphatase. Deregulation of PP2A is a common event associated with adenocarcinomas of the colon and rectum. We have previously shown that breast cancer cell lines are sensitive to the PP2A activator FTY720, and that sensitivity is predicted by high Aurora kinase A (AURKA) mRNA expression. In this study, we hypothesized that high relative AURKA expression could predict sensitivity to FTY720-induced apoptosis in colorectal cancer (CRC). The CRC cell lines NCI H716, COLO320DM, DLD-1, SW480, and HT-29 show a high relative AURKA expression as compared to LS411N, T84, HCT116, SW48, and LOVO. Following viability assays, LS411N, T84, HCT116, and SW480 were shown to be sensitive to FTY720, whereas DLD-1 and HT-29 were non-sensitive. Hence, AURKA mRNA expression does not predict sensitivity to FTY720 in CRC cell lines. Differentially expressed genes (DEGs) were obtained by comparing the sensitive CRC cell lines (LS411N and HCT116) against the non-sensitive (HT-29 and DLD-1). We found that 253 genes were significantly altered in expression, and upregulation of CERS4, PPP2R2C, GNAZ, PRKCG, BCL2, MAPK12, and MAPK11 suggests the involvement of the sphingolipid signaling pathway, known to be activated by phosphorylated-FTY720. In conclusion, although AURKA expression did not predict sensitivity to FTY720, it is evident that specific CRC cell lines are sensitive to 5 µM FTY720, potentially because of the differential expression of genes involved in the sphingolipid pathway.

S1P signaling, its interactions and cross-talks with other partners and therapeutic importance in colorectal cancer

Sphingosine-1-Phosphate (S1P) plays an important role in normal physiology, inflammation, initiation and progression of cancer. Deregulation of S1P signaling causes aberrant proliferation, affects survival, leads to angiogenesis and metastasis. Sphingolipid rheostat is crucial for cellular homeostasis. Discrepancy in sphingolipid metabolism is linked to cancer and drug insensitivity. Owing to these diverse functions and being a potent mediator of tumor growth, S1P signaling might be a suitable candidate for anti-tumor therapy or combination therapy. In this review, with a focus on colorectal cancer we have summarized the interacting partners of S1P signaling pathway, its therapeutic approaches along with the contribution of S1P signaling to various cancer hallmarks.

Study and analysis of antitumor resistance mechanism of PD1/PD-L1 immune checkpoint blocker

Immunocheckpoint proteins of tumor infiltrating lymphocytes play an important role in tumor prognosis in the course of tumor clinicopathology. PD‐1 (Programmed cell death protein 1) is an important immunosuppressive molecule. By binding to PD‐L1 (programmed cell death‐ligand 1), it blocks TCR and its costimulus signal transduction, inhibits the activation and proliferation of T cells, depletes the function of effector T cells, and enables tumor cells to achieve immune escape. In recent years, immunocheckpoint blocking therapy targeting the PD‐1/PD‐L1 axis has achieved good results in a variety of malignant tumors, pushing tumor immunotherapy to a new milestone, such as anti‐PD‐1 monoclonal antibody Nivolumab, Pembrolizumab, and anti‐PD‐L1 monoclonal antibody Atezolizumab, which are considered as potential antitumor drugs. It was found in clinical use that some patients obtained long‐term efficacy, but most of them developed drug resistance recurrence in the later stage. The high incidence of drug resistance (including primary and acquired drug resistance) still cannot be ignored, which limited its clinical application and became a new problem in this field. Due to tumor heterogeneity, current limited research shows that PD‐1 or PD‐L1 monoclonal antibody drug resistance may be related to the following factors: mutation of tumor antigen and antigen presentation process, multiple immune checkpoint interactions, immune microenvironment changes dynamically, activation of oncogenic pathways, gene mutation and epigenetic changes of key proteins in tumors, tumor competitive metabolism, and accumulation of metabolites, etc, mechanisms of resistance are complex. Therefore, it is the most urgent task to further elucidate the mechanism of immune checkpoint inhibitor resistance, discover multitumor universal biomarkers, and develop new target agents to improve the response rate of immunotherapy in patients. In this study, the mechanism of anti‐PD‐1/PD‐L1 drug resistance in tumors, the potential biomarkers for predicting PD‐1 acquired resistance, and the recent development of combination therapy were reviewed one by one. It is believed that, based on the complex mechanism of drug resistance, it is of no clinical significance to simply search for and regulate drug resistance targets, and it may even produce drug resistance again soon. It is speculated that according to the possible tumor characteristics, three types of treatment methods should be combined to change the tumor microenvironment ecology and eliminate various heterogeneous tumor subsets, so as to reduce tumor drug resistance and improve long‐term clinical efficacy.

Sphingosine 1-Phosphate Signaling and Metabolism in Chemoprevention and Chemoresistance in Colon Cancer

Colorectal carcinoma (CRC) is the leading cause of cancer-related deaths worldwide. Despite advances in prevention and treatment modalities for CRC, rapidly developing resistance to chemotherapy limits its effectiveness. For that reason, it is important to better understand the mechanisms that undergird the process of chemoresistance to enable design of novel anticancer agents specifically targeting malignant properties of cancer cells. Over recent decades, bioactive sphingolipid species have come under the spotlight for their recognized role in cancer development and progression, and the evidence has surfaced to support their role as regulators of anti-cancer drug resistance. Colon cancer is characterized by a shift in sphingolipid balance that favors the production and accumulation of oncogenic species such as sphingosine 1-phosphate (S1P). S1P is known to govern the processes that facilitate cancer cell growth and progression including proliferation, survival, migration, invasion and inflammation. In this review paper, we will give a comprehensive overview of current literature findings on the molecular mechanisms by which S1P turnover, transport and signaling via receptor-dependent and independent pathways shape colon cancer cell behavior and influence treatment outcome in colon cancer. Combining available modulators of S1P metabolism and signaling with standard chemotherapy drugs could provide a rational approach to achieve enhanced therapeutic response, diminish chemoresistance development and improve the survival outcome in CRC patients.

Establishment of a Measurement System for Sphingolipids in the Cerebrospinal Fluid Based on Liquid Chromatography-Tandem Mass Spectrometry, and Its Application in the Diagnosis of Carcinomatous Meningitis

Objectives

Sphingolipids have been demonstrated to be involved in many human diseases. However, measurement of sphingolipids, especially of sphingosine 1-phosphate (S1P) and dihydro-sphingosine 1-phosphate (dhS1P), in blood samples requires strict sampling, since blood cells easily secrete these substances during sampling and storage, making it difficult to introduce measurement of sphingolipids in clinical laboratory medicine. On the other hand, cerebrospinal fluid (CSF) contains few blood cells. Therefore, we attempted to establish a system based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the measurement of sphingolipids in the CSF, and applied it for the diagnosis of carcinomatous meningitis.

Methods

We developed and validated a LC-MS/MS-based measurement system for S1P and dhS1P and for ceramides and sphingosines, used this system to measure the levels of these sphingolipids in the CSF collected from the subjects with cancerous meningitis, and compared the levels with those in normal routine CSF samples.

Results

Both the measurement systems for S1P/dhS1P and for ceramides/sphingosines provided precision with the coefficient of variation below 20% for sphingolipids in the CSF samples. We also confirmed that the levels of S1P, as well as ceramides/sphingosines, in the CSF samples did not increase after the sampling. In the CSF samples collected from patients with cancerous meningitis, we observed that the ratio of S1P to ceramides/sphingosine and that of dhS1P to dihydro-sphingosine were higher than those in control samples.

Conclusions

We established and validated a measurement system for sphingolipids in the CSF. The system offers promise for being introduced into clinical laboratory testing.

Resistance of melanoma to immune checkpoint inhibitors is overcome by targeting the sphingosine kinase-1

Immune checkpoint inhibitors (ICIs) have dramatically modified the prognosis of several advanced cancers, however many patients still do not respond to treatment. Optimal results might be obtained by targeting cancer cell metabolism to modulate the immunosuppressive tumor microenvironment. Here, we identify sphingosine kinase-1 (SK1) as a key regulator of anti-tumor immunity. Increased expression of SK1 in tumor cells is significantly associated with shorter survival in metastatic melanoma patients treated with anti-PD-1. Targeting SK1 markedly enhances the responses to ICI in murine models of melanoma, breast and colon cancer. Mechanistically, SK1 silencing decreases the expression of various immunosuppressive factors in the tumor microenvironment to limit regulatory T cell (Treg) infiltration. Accordingly, a SK1-dependent immunosuppressive signature is also observed in human melanoma biopsies. Altogether, this study identifies SK1 as a checkpoint lipid kinase that could be targeted to enhance immunotherapy.

There are many patients who do not respond to immune checkpoint inhibitor (ICI) immunotherapy. Here, the authors show a significant negative correlation between sphingosine kinase-1 (SK1) expression and survival for ICI-treated melanoma patients, and further show that targeting SK1 improves response to ICI in mouse cancer models.

Colon Cancer and Perturbations of the Sphingolipid Metabolism

The development and progression of colorectal cancer (CRC), a major cause of cancer-related death in the western world, is accompanied with alterations of sphingolipid (SL) composition in colon tumors. A number of enzymes involved in the SL metabolism have been found to be deregulated in human colon tumors, in experimental rodent studies, and in human colon cancer cells in vitro. Therefore, the enzymatic pathways that modulate SL levels have received a significant attention, due to their possible contribution to CRC development, or as potential therapeutic targets. Many of these enzymes are associated with an increased sphingosine-1-phosphate/ceramide ratio, which is in turn linked with increased colon cancer cell survival, proliferation and cancer progression. Nevertheless, more attention should also be paid to the more complex SLs, including specific glycosphingolipids, such as lactosylceramides, which can be also deregulated during CRC development. In this review, we focus on the potential roles of individual SLs/SL metabolism enzymes in colon cancer, as well as on the pros and cons of employing the current in vitro models of colon cancer cells for lipidomic studies investigating the SL metabolism in CRC.

Phospho-Sphingosine Kinase 1 Expression in Lymphatic Spread of Esophageal Squamous Cell Carcinoma

BACKGROUND

Lymphatic spread is the main mode of progression of esophageal squamous cell carcinoma (ESCC). Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid mediator, which produced by sphingosine kinase 1 (SphK1) activated by phosphorylation. The SphK1-S1P axis has a crucial role in lymphangiogenesis. However, the significance of phospho-SphK1 (pSphK1) in the progression of ESCC has not been fully investigated.

MATERIALS AND METHODS

We evaluated pSphK1 expression in 92 surgically resected tumor tissues of ESCC by the immunohistochemistry. Fifty-nine (64%) patients with moderate or strong expression and 33 (36%) with negative or weak expression were classified in the pSphK1-high and pSphK1-low groups, respectively.

RESULTS

Higher pathological N category (pN) was more frequently observed in the pSphK1-high group (P < 0.01). The median number of lymph node metastasis (pSphK1-high: 2 versus pSphK1-low: 0; P < 0.01), the proportion of patients with lymphatic invasion (69% versus 18%; P < 0.01) and that with intramural metastasis (27% versus 3%; P < 0.01) were significantly higher in the pSphK1-high group. The presence of lymphatic invasion (odds ratio [OR] 5.63; P < 0.01) and pN1-3 (OR 3.26; P = 0.04) were independently associated with high pSphK1 expression. The 5-y overall survival rate of the pSphK1-high group was significantly lower than that of the pSphK1-low group (50.8% versus 67.3%; P = 0.01). High pSphK1 expression was not identified as a significant independent prognostic factor.

CONCLUSIONS

We provide the first evidence of the association between high expression of pSphK1 and both lymphatic spread and patient outcomes in ESCC.

Pharmacological Inhibition of Serine Palmitoyl Transferase and Sphingosine Kinase-1/-2 Inhibits Merkel Cell Carcinoma Cell Proliferation

The majority of Merkel cell carcinoma, a highly aggressive neuroendocrine cancer of the skin, is associated with Merkel cell polyomavirus infection. Polyomavirus binding, internalization, and infection are mediated by glycosphingolipids. Besides receptor function, bioactive sphingolipids are increasingly recognized as potent regulators of several hallmarks of cancer. Merkel cell polyomavirus⁺ and Merkel cell polyomavirus^- cells express serine palmitoyl transferase subunits and sphingosine kinase (SK) 1/2 mRNA. Induced expression of Merkel cell polyomavirus-large tumor antigen in human lung fibroblasts resulted in upregulation of SPTLC1-3 and SK 1/2 expression. Therefore, we exploited pharmacological inhibition of sphingolipid metabolism as an option to interfere with proliferation of Merkel cell polyomavirus⁺ Merkel cell carcinoma cell lines. We used myriocin (a serine palmitoyl transferase antagonist) and two SK inhibitors (SKI-II and ABC294640). In MKL-1 and WaGa cells myriocin decreased cellular ceramide, sphingomyelin, and sphingosine-1-phosphate content. SKI-II increased ceramide species but decreased sphingomyelin and sphingosine-1-phosphate concentrations. Aberrant sphingolipid homeostasis was associated with reduced cell viability, increased necrosis, procaspase-3 and PARP processing, caspase-3 activity, and decreased AKT^S473 phosphorylation. Myriocin and SKI-II decreased tumor size and Ki-67 staining of xenografted MKL-1 and WaGa tumors on the chorioallantoic membrane. Our data suggest that pharmacological inhibition of sphingolipid synthesis could represent a potential therapeutic approach in Merkel cell carcinoma.

Sphingolipids and their metabolism in physiology and disease

Studies of bioactive lipids in general and sphingolipids in particular have intensified over the past several years, revealing an unprecedented and unanticipated complexity of the lipidome and its many functions, which rivals, if not exceeds, that of the genome or proteome. These results highlight critical roles for bioactive sphingolipids in most, if not all, major cell biological responses, including all major cell signalling pathways, and they link sphingolipid metabolism to key human diseases. Nevertheless, the fairly nascent field of bioactive sphingolipids still faces challenges in its biochemical and molecular underpinnings, including defining the molecular mechanisms of pathway and enzyme regulation, the study of lipid-protein interactions and the development of cellular probes, suitable biomarkers and therapeutic approaches.

Predictive and prognostic value of sphingosine kinase 1 expression in patients with invasive ductal carcinoma of the breast

Sphingosine kinase 1 (SPHK1) has been found to be upregulated in many different types of human malignancy and plays a crucial role in cancer development and progression. However, the potential of SPHK1 to act as a predictive and prognostic biomarker in breast cancer remains to be clarified. In the present study, SPHK1 expression was evaluated in breast cancer cell lines and 224 breast cancer tissue samples using immunohistochemical staining. Compared to the normal mammary epithelial cell line MCF-10A, SPHK1 mRNA and protein expression levels increased in the breast cancer cell lines SK-BR-3, MDA-MB-231, MDA-MB-436, and MCF-7. Immunohistochemical staining revealed SPHK1 expression to be significantly increased in breast cancer tissue compared to normal breast tissue, with 85 (37.9%) of the 224 invasive ductal carcinomas (IDC) exhibiting high SPHK1 expression. High SPHK1 expression in IDC showed a significant association with higher histological grade, distant metastasis, and triple negativity, and was shown to be an independent predictor for distant metastasis development. In addition, patients with high SPHK1 expression had significantly lower progression-free survival and overall survival rates compared to those with low SPHK1 expression. Our data suggest that SPHK1 is involved in the development and progression of breast cancer and can serve as a potential predictive biomarker of distant metastasis and patient outcome.

S1P Lyase Regulation of Thymic Egress and Oncogenic Inflammatory Signaling

Sphingosine-1-phosphate (S1P) is a potent lipid signaling molecule that regulates pleiotropic biological functions including cell migration, survival, angiogenesis, immune cell trafficking, inflammation, and carcinogenesis. It acts as a ligand for a family of cell surface receptors. S1P concentrations are high in blood and lymph but low in tissues, especially the thymus and lymphoid organs. S1P chemotactic gradients are essential for lymphocyte egress and other aspects of physiological cell trafficking. S1P is irreversibly degraded by S1P lyase (SPL). SPL regulates lymphocyte trafficking, inflammation and other physiological and pathological processes. For example, SPL located in thymic dendritic cells acts as a metabolic gatekeeper that controls the normal egress of mature T lymphocytes from the thymus into the circulation, whereas SPL deficiency in gut epithelial cells promotes colitis and colitis-associated carcinogenesis (CAC). Recently, we identified a complex syndrome comprised of nephrosis, adrenal insufficiency, and immunological defects caused by inherited mutations in human SGPL1, the gene encoding SPL. In the present article, we review current evidence supporting the role of SPL in thymic egress, inflammation, and cancer. Lastly, we summarize recent progress in understanding other SPL functions, its role in inherited disease, and SPL targeting for therapeutic purposes.

Evidence Suggests Sphingosine 1-Phosphate Might Be Actively Generated, Degraded, and Transported to Extracellular Spaces With Increased S1P2 and S1P3 Expression in Colon Cancer

BACKGROUND

A pivotal role of sphingosine 1-phosphate (S1P) in cancer has been suggested based on the ceramide-S1P rheostat theory that the intracellular balance between prosurvival S1P and proapoptotic ceramide determines cell fate. Upregulation of S1P-generating sphingosine kinases (SKs) and downregulation of S1P-degrading S1P lyase (SPL) might increase intracellular S1P levels to exert a prosurvival effect in cancer in general, such as colon cancer. However, we recently observed a distinct S1P metabolism in hepatocellular carcinoma tissues that increased SPL mRNA levels with reduced S1P levels. Thus, we investigated S1P metabolism in colon cancer.

PATIENTS AND METHODS

We enrolled 26 consecutive colon cancer patients, who had undergone surgical treatment.

RESULTS

Not only SK, but also SPL, mRNA levels were increased in colon cancer tissues compared with the adjacent nontumorous tissues. Furthermore, the mRNA levels of another S1P degrading enzyme, S1P phosphatase 1, S1P transporters, spinster homolog 2, adenosine triphosphate-binding cassette subfamily C member 1, and S1P receptors, S1P₂ and S1P₃ were also increased, but the S1P levels were not increased in the colon cancer tissues. The reduction of SPL expression by silencing led to reduced proliferation and invasion, and overexpression of SPL caused enhanced proliferation in colon cancer cell lines.

CONCLUSION

In human colon cancer tissues, mRNA levels of S1P-generating and S1P-degrading enzymes, transporters from inside to outside the cells, and S1P receptors, S1P₂ and S1P₃ were elevated, suggesting active S1P metabolism and movement. This altered S1P metabolism might play a role in colon cancer pathophysiology.

Targeting sphingosine kinase 1 induces MCL1-dependent cell death in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive malignancy where despite improvements in conventional chemotherapy and bone marrow transplantation, overall survival remains poor. Sphingosine kinase 1 (SPHK1) generates the bioactive lipid sphingosine 1-phosphate (S1P) and has established roles in tumor initiation, progression, and chemotherapy resistance in a wide range of cancers. The role and targeting of SPHK1 in primary AML, however, has not been previously investigated. Here we show that SPHK1 is overexpressed and constitutively activated in primary AML patient blasts but not in normal mononuclear cells. Subsequent targeting of SPHK1 induced caspase-dependent cell death in AML cell lines, primary AML patient blasts, and isolated AML patient leukemic progenitor/stem cells, with negligible effects on normal bone marrow CD34⁺ progenitors from healthy donors. Furthermore, administration of SPHK1 inhibitors to orthotopic AML patient-derived xenografts reduced tumor burden and prolonged overall survival without affecting murine hematopoiesis. SPHK1 inhibition was associated with reduced survival signaling from S1P receptor 2, resulting in selective downregulation of the prosurvival protein MCL1. Subsequent analysis showed that the combination of BH3 mimetics with either SPHK1 inhibition or S1P receptor 2 antagonism triggered synergistic AML cell death. These results support the notion that SPHK1 is a bona fide therapeutic target for the treatment of AML.

Role of neutral ceramidase in colon cancer

Alterations in sphingolipid metabolism, especially ceramide and sphingosine 1-phosphate, have been linked to colon cancer, suggesting that enzymes of sphingolipid metabolism may emerge as novel regulators and targets in colon cancer. Neutral ceramidase (nCDase), a key enzyme in sphingolipid metabolism that hydrolyzes ceramide into sphingosine, is highly expressed in the intestine; however, its role in colon cancer has not been defined. Here we show that molecular and pharmacological inhibition of nCDase in colon cancer cells increases ceramide, and this is accompanied by decreased cell survival and increased apoptosis and autophagy, with minimal effects on noncancerous cells. Inhibition of nCDase resulted in loss of β-catenin and inhibition of ERK, components of pathways relevant for colon cancer development. Furthermore, inhibition of nCDase in a xenograft model delayed tumor growth and increased ceramide while decreasing proliferation. It is noteworthy that mice lacking nCDase treated with azoxymethane were protected from tumor formation. Taken together, these studies show that nCDase is pivotal for regulating initiation and development of colon cancer, and these data suggest that this enzyme is a suitable and novel target for colon cancer therapy.-García-Barros, M., Coant, N., Kawamori, T., Wada, M., Snider, A. J., Truman, J.-P., Wu, B. X., Furuya, H., Clarke, C. J., Bialkowska, A. B., Ghaleb, A., Yang, V. W., Obeid, L. M., Hannun, Y. A. Role of neutral ceramidase in colon cancer.

Sphingosine kinase 1 is a reliable prognostic factor and a novel therapeutic target for uterine cervical cancer

Sphingosine kinase 1 (SPHK1), an oncogenic kinase, has previously been found to be upregulated in various types of human malignancy and to play a crucial role in tumor development and progression. Although SPHK1 has gained increasing prominence as an important enzyme in cancer biology, its potential as a predictive biomarker and a therapeutic target in cervical cancer remains unknown. SPHK1 expression was examined in 287 formalin-fixed, paraffin-embedded cervical cancer tissues using immunohistochemistry, and its clinical implications and prognostic significance were analyzed. Cervical cancer cell lines including HeLa and SiHa were treated with the SPHK inhibitors SKI-II or FTY720, and effects on cell survival, apoptosis, angiogenesis, and invasion were examined. Moreover, the effects of FTY720 on tumor growth were evaluated using a patient-derived xenograft (PDX) model of cervical cancer. Immunohistochemical analysis revealed that expression of SPHK1 was significantly increased in cervical cancer compared with normal tissues. SPHK1 expression was significantly associated with tumor size, invasion depth, FIGO stage, lymph node metastasis, and lymphovascular invasion. Patients with high SPHK1 expression had lower overall survival and recurrence-free survival rates than those with low expression. Treatment with SPHK inhibitors significantly reduced viability and increased apoptosis in cervical cancer cells. Furthermore, FTY720 significantly decreased in vivo tumor weight in the PDX model of cervical cancer. We provide the first convincing evidence that SPHK1 is involved in tumor development and progression of cervical cancer. Our data suggest that SPHK1 might be a potential prognostic marker and therapeutic target for the treatment of cervical cancer.

Visualizing red blood cell sickling and the effects of inhibition of sphingosine kinase 1 using soft X-ray tomography

Sickle cell disease is a destructive genetic disorder characterized by the formation of fibrils of deoxygenated hemoglobin, leading to the red blood cell (RBC) morphology changes that underlie the clinical manifestations of this disease. Using cryogenic soft X-ray tomography (SXT), we characterized the morphology of sickled RBCs in terms of volume and the number of protrusions per cell. We were able to identify statistically a relationship between the number of protrusions and the volume of the cell, which is known to correlate to the severity of sickling. This structural polymorphism allows for the classification of the stages of the sickling process. Recent studies have shown that elevated sphingosine kinase 1 (Sphk1)-mediated sphingosine 1-phosphate production contributes to sickling. Here, we further demonstrate that compound 5C, an inhibitor of Sphk1, has anti-sickling properties. Additionally, the variation in cellular morphology upon treatment suggests that this drug acts to delay the sickling process. SXT is an effective tool that can be used to identify the morphology of the sickling process and assess the effectiveness of potential therapeutics.

Sphingosine kinase 1 is upregulated with lysophosphatidic acid receptor 2 in human colorectal cancer

AIM: To examine the expression of SphK1, an oncogenic kinase that produces sphingosine 1-phosphate (S1P), and its correlation with the expression of LPAR2, a major lysophosphatidic acid (LPA) receptor overexpressed in various cancers, in human colorectal cancer.

METHODS: Real-time reverse-transcription polymerase chain reaction was used to measure the mRNA expression of SphK1, LPAR2, and the three major S1P receptors in 27 colorectal cancer samples and corresponding normal tissue samples. We also examined the correlation between the expression of SphK1 and LPAR2.

RESULTS: Colorectal cancer tissue in 22 of 27 patients had higher levels of SphK1 mRNA than in normal tissue. In two-thirds of the samples, SphK1 mRNA expression was more than two-fold higher than in normal tissue. Consistent with previous reports, LPAR2 mRNA expression in 20 of 27 colorectal cancer tissue samples was higher compared to normal tissue samples. Expression profiles of all three major S1P receptors, S1PR1, S1PR2, and S1PR3, varied without any trend, with no significant difference in expression between cancer and normal tissues. A highly significant positive correlation was found between SphK1 and LPAR2 expression [Pearson’s correlation coefficient (r) = 0.784 and P < 0.01]. The mRNA levels of SphK1 and LPAR2 did not correlate with TNM stage.

CONCLUSION: Our findings suggest that S1P and LPA may play important roles in the development of colorectal cancer via the upregulation of SphK1 and LPAR2, both of which could serve as new therapeutic targets in the treatment of colorectal cancer.

Overexpression of SphK1 enhances cell proliferation and invasion in triple-negative breast cancer via the PI3K/AKT signaling pathway

Sphingosine kinase 1 (SphK1) expression is elevated in various cancers and is associated with shorter survival times for patients. However, the molecular mechanism of SphK1 up-regulation in triple-negative breast cancer (TNBC) remains unclear. In this study, we assayed the expression level of SphK1 in TNBC tissues by qRT-PCR and immunohistochemistry. The level of S1P was quantified by ELISA in the serum of TNBC patients. Our results found that the levels of SphK1 and S1P were significantly increased in TNBC patients compared with normal control. Furthermore, knockdown of SphK1 with siRNA decreased TNBC cell proliferation and inhibited cell migration/invasion. These data suggest that SphK1 has an important role in TNBC and presents an attractive therapeutic target for the treatment for TNBC.

SPHK1 regulates proliferation and survival responses in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is characterized by unique aggressive behavior and lack of targeted therapies. Among the various molecular subtypes of breast cancer, it was observed that TNBCs express elevated levels of sphingosine kinase 1 (SPHK1) compared to other breast tumor subtypes. High levels of SPHK1 gene expression correlated with poor overall and progression- free survival, as well as poor response to Doxorubicin-based treatment. Inhibition of SPHK1 was found to attenuate ERK1/2 and AKT signaling and reduce growth of TNBC cells in vitro and in a xenograft SCID mouse model. Moreover, SPHK1 inhibition by siRNA knockdown or treatment with SKI-5C sensitizes TNBCs to chemotherapeutic drugs. Our findings suggest that SPHK1 inhibition, which effectively counteracts oncogenic signaling through ERK1/2 and AKT pathways, is a potentially important anti-tumor strategy in TNBC. A combination of SPHK1 inhibitors with chemotherapeutic agents may be effective against this aggressive subtype of breast cancer.

Sphingosine Kinase 2 and Ceramide Transport as Key Targets of the Natural Flavonoid Luteolin to Induce Apoptosis in Colon Cancer Cells

The plant flavonoid luteolin exhibits different biological effects, including anticancer properties. Little is known on the molecular mechanisms underlying its actions in colorectal cancer (CRC). Here we investigated the effects of luteolin on colon cancer cells, focusing on the balance between ceramide and sphingosine-1-phosphate (S1P), two sphingoid mediators with opposite roles on cell fate. Using cultured cells, we found that physiological concentrations of luteolin induce the elevation of ceramide, followed by apoptotic death of colon cancer cells, but not of differentiated enterocytes. Pulse studies revealed that luteolin inhibits ceramide anabolism to complex sphingolipids. Further experiments led us to demonstrate that luteolin induces an alteration of the endoplasmic reticulum (ER)-Golgi flow of ceramide, pivotal to its metabolic processing to complex sphingolipids. We report that luteolin exerts its action by inhibiting both Akt activation, and sphingosine kinase (SphK) 2, with the consequent reduction of S1P, an Akt stimulator. S1P administration protected colon cancer cells from luteolin-induced apoptosis, most likely by an intracellular, receptor-independent mechanism. Overall this study reveals for the first time that the dietary flavonoid luteolin exerts toxic effects on colon cancer cells by inhibiting both S1P biosynthesis and ceramide traffic, suggesting its dietary introduction/supplementation as a potential strategy to improve existing treatments in CRC.

[Role of SPHK1 regulates multi-drug resistance of small cell lung cancer and its clinical significance]

背景与目的

小细胞肺癌约占全部肺癌的15%，化疗是其主要的治疗方法之一，虽然早期对一线化疗方案敏感，但极易出现多药耐药而导致治疗失败。前期基因芯片发现SPHK1与小细胞肺癌的耐药性相关，本研究进一步探讨SPHK1在小细胞肺癌多药耐药中的作用。

方法

首先通过QRT-PCR和Western blot从基因和蛋白水平检测化疗敏感细胞株H69及多药耐药细胞株H69AR中SPHK1的差异表达；转染siRNA下调H69AR细胞中的SPHK1的表达，通过CCK8检测细胞对各种化疗药物（ADM, DDP, VP-16）的敏感性变化，流式细胞仪检测细胞周期及凋亡的变化。同时收集小细胞肺癌化疗前组织和血液标本，将其分为化疗敏感组和耐药组，QRT-PCR检测小细胞肺癌患者血液标本中SPHK1的表达，免疫组化法检测小细胞肺癌患者组织标本中SPHK1的表达，分析SPHK1与小细胞肺癌患者预后相关性。

结果

SPHK1在耐药细胞H69AR中的表达明显高于H69，下调H69AR中SPHK1的表达能够增加细胞对化疗药物的敏感性，促进细胞的凋亡，细胞周期发生G₀/G₁期阻滞，SPHK1在小细胞肺癌耐药患者中的表达较敏感患者明显增加，SPHK1的表达与患者的性别、年龄无关，与疾病的分期、对化疗的敏感性及生存时间密切相关，差异具有统计学意义（P＜0.05）。

结论

SPHK1参与调节小细胞肺癌多药耐药，SPHK1可作为评估小细胞肺癌化疗敏感性及临床预后的潜在靶基因。