C2-ceramide signaling in glioma cells: synergistic enhancement of CD95-mediated, caspase-dependent apoptosis

RIPK1 and RIPK3 are positive prognosticators for cervical cancer patients and C2 ceramide can inhibit tumor cell proliferation in vitro

Introduction

The enzymes Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) und 3 (RIPK3) as well as the protein Mixed lineage kinase domain like pseudokinase (pMLKL) play a role in the signaling cascade of necroptosis. This is a form of programmed cell death which is caspase-independent. High-risk human papilloma virus infection can inhibit necroptosis. Thereby, a persistent infection and consequently the development of cervical cancer can be triggered. Aim of this study was the analysis of the expression of RIPK1, RIPK3 and pMLKL in cervical cancer tissue and the evaluation of its prognostic value on overall survival, progression-free survival and additional clinical parameters.

Methods

The expression of RIPK1, RIPK3, and pMLKL in cervical cancer tissue microarrays of n = 250 patients was analyzed immunohistochemically. Further, the effect of C2 ceramide on several cervical cancer cell lines (CaSki, HeLa, SiHa) was examined. C2 ceramide is a biologically active short-chain ceramide that induces necroptosis in human luteal granulosa cells.

Results

Significantly longer overall survival and progression-free survival rates could be detected in cervical cancer patients expressing nuclear RIPK1 or RIPK3 alone or simultaneously (RIPK1 and RIPK3). Cell viability and proliferation was reduced through C2 ceramide stimulation of cervical cancer cells. Simultaneous stimulation of C2 ceramide and the pan-caspase inhibitor Z-VAD-fmk, or the RIPK1-inhibitor necrostatin-1, partly reversed the negative effect of C2 ceramide on cell viability. This observation could imply that caspase-dependent and -independent forms of cell death, including necroptosis, can occur. AnnexinV-FITC apoptosis staining induced a significant increase in apoptotic cells in CaSki and SiHa cells. The stimulation of CaSki cells with C2 ceramide led to a significant percentual increase in necrotic/intermediate (dying) cells after stimulation with C2 ceramide. In addition, after stimulation with C2 ceramide, CaSki and HeLa cells live cell imaging showed morphological changes which are common for necroptosis.

Discussion

In conclusion, RIPK1 and RIPK3 are independent positive predictors for overall survival and progression-free survival in cervical cancer patients. C2 ceramide can reduce cell viability and proliferation in cervical cancer cells by inducing most likely both apoptosis and necroptosis.

Oxidized graphene nanoparticles as a delivery system for the pro-apoptotic sphingolipid C6 ceramide

Sphingolipids such as ceramide have attracted much attention as possible anticancer agents due to their potent pro-apoptotic effects. However, due to their extreme hydrophobicity, there is currently no clinically approved delivery method for in vivo use as a therapeutic agent. To this end, we have developed a novel method for loading the short-chain C₆ ceramide onto oxidized graphene nanoribbons (O-GNRs) and graphene nanoplatelets (GNPs). Mass spectrometry revealed loading efficiencies of 57% and 51.5% for C₆ ceramide onto O-GNRs and GNPs, respectively. The PrestoBlue viability assay revealed that 100 µg/mL of C₆ ceramide-loaded O-GNRs and C₆ ceramide-loaded GNPs reduced HeLa cell viability by approximately 93% and approximately 76%, respectively, compared to untreated HeLa cells, while equal concentrations of these nanoparticles without C₆ ceramide did not significantly reduce HeLa cell viability. We confirmed that this cytotoxicity was apoptotic in nature via capase-3 activity and Hoechst staining. Using live-cell confocal imaging with the fluorescent NBD-ceramide loaded on O-GNRs, we observed robust uptake into HeLa cells within 30 min while NBD-ceramide on its own was uptaken much more rapidly. Transmission electron microscopy confirmed that C₆ ceramide-loaded O-GNRs were actually entering cells. Taken together, these data show that O-GNRs are a promising delivery agent for ceramide. To our knowledge, this study is the first to use such a loading method. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 25-37, 2019.

Sphingosine 1-phosphate activation of ERM contributes to vascular calcification

Vascular calcification is the deposition of mineral in the artery wall by vascular smooth muscle cells (VSMCs) in response to pathological stimuli. The process is similar to bone formation and is an independent risk factor for cardiovascular disease. Given that ceramide and sphingosine 1-phosphate (S1P) are involved in cardiovascular pathophysiology and biomineralization, their role in VSMC matrix mineralization was investigated. During phosphate-induced VSMC mineralization, endogenous S1P levels increased accompanied by increased sphingosine kinase (SK) activity and increased mRNA expression of SK1 and SK2. Consistent with this, mineralization was increased by exogenous S1P, but decreased by C2-ceramide. Mechanistically, exogenous S1P stimulated ezrin-radixin-moesin (ERM) phosphorylation in VSMCs and ERM phosphorylation was increased concomitantly with endogenous S1P during mineralization. Moreover, inhibition of acid sphingomyelinase and ceramidase with desipramine prevented increased S1P levels, ERM activation, and mineralization. Finally, pharmacological inhibition of ERM phosphorylation with NSC663894 decreased mineralization induced by phosphate and exogenous S1P. Although further studies will be needed to verify these findings in vivo, this study defines a novel role for the SK-S1P-ERM pathways in phosphate-induced VSMC matrix mineralization and shows that blocking these pathways with pharmacological inhibitors reduces mineralization. These results may inform new therapeutic approaches to inhibit or delay vascular calcification.

Estimation of PKCδ autophosphorylation in U87 MG glioma cells: combination of experimental, conceptual and numerical approaches

Golgi apparatus (GA) is a center for lipid metabolism and the final target of ceramide pathway, which may result in apoptosis. In this work localization of highly hydrophobic hypericin is followed by time-resolved imaging of NBDC₆ (fluorescent ceramide) in U87 MG glioma cells. Decrease of NBDC₆ fluorescence lifetimes in cells indicates that hypericin can also follow this pathway. It is known that both, ceramide and hypericin can significantly influence protein kinase C (PKC) activity. Western blotting analysis shows increase of PKCδ autophosphorylation at Ser645 (p(S645)PKCδ) in glioma cells incubated with 500 nM hypericin and confocal-fluorescence microscopy distinguishes p(S645)PKCδ localization between GA related compartments and nucleus. Experimental and numerical methods are combined to study p(S645)PKCδ in U87 MG cell line. Image processing based on conceptual qualitative description is combined with numerical treatment via simple exponential saturation model which describes redistribution of p(S645)PKCδ between nucleus and GA related compartments after hypericin administration. These results suggest, that numerical methods can significantly improve quantification of biomacromolecules (p(S645)PKCδ) directly from the fluorescence images and such obtained outputs are complementary if not equal to typical used methods in biology.

Glioma cell death induced by irradiation or alkylating agent chemotherapy is independent of the intrinsic ceramide pathway

BACKGROUND/AIMS

Resistance to genotoxic therapy is a characteristic feature of glioma cells. Acid sphingomyelinase (ASM) hydrolyzes sphingomyelin to ceramide and glucosylceramide synthase (GCS) catalyzes ceramide metabolism. Increased ceramide levels have been suggested to enhance chemotherapy-induced death of cancer cells.

METHODS

Microarray and clinical data for ASM and GCS in astrocytomas WHO grade II-IV were acquired from the Rembrandt database. Moreover, the glioblastoma database of the Cancer Genome Atlas network (TCGA) was used for survival data of glioblastoma patients. For in vitro studies, increases in ceramide levels were achieved either by ASM overexpression or by the GCS inhibitor DL-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP) in human glioma cell lines. Combinations of alkylating chemotherapy or irradiation and ASM overexpression, PPMP or exogenous ceramide were applied in parental cells. The anti-glioma effects were investigated by assessing proliferation, metabolic activity, viability and clonogenicity. Finally, viability and clonogenicity were assessed in temozolomide (TMZ)-resistant cells upon treatment with PPMP, exogenous ceramide, alkylating chemotherapy, irradiation or their combinations.

RESULTS

Interrogations from the Rembrandt and TCGA database showed a better survival of glioblastoma patients with low expression of ASM or GCS. ASM overexpression or PPMP treatment alone led to ceramide accumulation but did not enhance the anti-glioma activity of alkylating chemotherapy or irradiation. PPMP or exogenous ceramide induced acute cytotoxicity in glioblastoma cells. Combined treatments with chemotherapy or irradiation led to additive, but not synergistic effects. Finally, no synergy was found when TMZ-resistant cells were treated with exogenous ceramide or PPMP alone or in combination with TMZ or irradiation.

CONCLUSION

Modulation of intrinsic glioma cell ceramide levels by ASM overexpression or GCS inhibition does not enhance the anti-glioma activity of alkylating chemotherapy or irradiation.

Ceramide-orchestrated signalling in cancer cells

One crucial barrier to progress in the treatment of cancer has been the inability to control the balance between cell proliferation and apoptosis: enter ceramide. Discoveries over the past 15 years have elevated this sphingolipid to the lofty position of a regulator of cell fate. Ceramide, it turns out, is a powerful tumour suppressor, potentiating signalling events that drive apoptosis, autophagic responses and cell cycle arrest. However, defects in ceramide generation and metabolism in cancer cells contribute to tumour cell survival and resistance to chemotherapy. This Review focuses on ceramide signalling and the targeting of specific metabolic junctures to amplify the tumour suppressive activities of ceramide. The potential of ceramide-based therapeutics in the treatment of cancer is also discussed.

Subcellular compartmentalization of FADD as a new level of regulation in death receptor signaling

Fas-associated protein with death domain (FADD) is an essential adaptor protein in death receptor-mediated signal transduction. During apoptotic signaling, FADD functions in the cytoplasm, where it couples activated receptors with initiator caspase-8. However, in resting cells, FADD is predominantly stored in the nucleus. In this study, we examined the modalities of FADD intracellular trafficking. We demonstrate that, upon CD95 activation, FADD redistributes from the nucleus to the cytoplasm. This inducible nuclear-cytoplasmic translocation of FADD is independent of CD95 internalization, formation of the death-inducing signaling complex, and caspase-8 activation. In contrast to nuclear export of FADD, its subsequent recruitment and accumulation at endosomes containing internalized CD95 requires a caspase-8-dependent feedback loop. These data indicate the existence of differential pathways directing FADD nuclear export and cytoplasmic trafficking, and identify subcellular compartmentalization of FADD as a novel regulatory mechanism in death receptor signaling.

GSK-3beta acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 in ceramide-induced mitochondrial apoptosis

The signaling of glycogen synthase kinase-3beta (GSK-3beta) has been implicated in stress-induced apoptosis. However, the pro-apoptotic role of GSK-3beta is still unclear. Here, we show the involvement of GSK-3beta in ceramide-induced mitochondrial apoptosis. Ceramide induced GSK-3beta activation via protein dephosphorylation at serine 9. We previously reported that ceramide induced caspase-2 and caspase-8 activation, Bid cleavage, mitochondrial damage, and apoptosis. In this study, we found that caspase-2 activation and the subsequent apoptotic events were abolished by the GSK-3beta inhibitors lithium chloride and SB216763, and by GSK-3beta knockdown using short interfering RNA. We also found that ceramide-activated protein phosphatase 2A (PP2A) indirectly caused GSK-3beta activation, and that the PP2A-regulated PI 3-kinase-Akt pathway was involved in GSK-3beta activation. These results indicate a role for GSK-3beta in ceramide-induced apoptosis, in which GSK-3beta acts downstream of PP2A and the PI 3-kinase-Akt pathway, and upstream of caspase-2 and caspase-8.

Cationic long-chain ceramide LCL-30 induces cell death by mitochondrial targeting in SW403 cells

Ceramides are sphingolipid second messengers that are involved in the mediation of cell death. There is accumulating evidence that mitochondria play a central role in ceramide-derived toxicity. We designed a novel cationic long-chain ceramide [omega-pyridinium bromide D-erythro-C16-ceramide (LCL-30)] targeting negatively charged mitochondria. Our results show that LCL-30 is highly cytotoxic to SW403 cells (and other cancer cell lines) and preferentially accumulates in mitochondria, resulting in a decrease of the mitochondrial membrane potential, release of mitochondrial cytochrome c, and activation of caspase-3 and caspase-9. Ultrastructural analyses support the concept of mitochondrial selectivity. Interestingly, levels of endogenous mitochondrial C16-ceramide decreased by more than half, whereas levels of sphingosine-1-phosphate increased dramatically and selectively in mitochondria after administration of LCL-30, suggesting the presence of a mitochondrial sphingosine kinase. Of note, intracellular long-chain ceramide levels and sphingosine-1-phosphate remained unaffected in the cytosolic and extramitochondrial (nuclei/cellular membranes) cellular fractions. Furthermore, a synergistic effect of cotreatment of LCL-30 and doxorubicin was observed, which was not related to alterations in endogenous ceramide levels. Cationic long-chain pyridinium ceramides might be promising new drugs for cancer therapy through their mitochondrial preference.

Ceramide induces non-apoptotic cell death in human glioma cells

Ceramide causes either apoptosis or non-apoptotic cell death depending on model system and experimental conditions. The present study was undertaken to examine the effect of ceramide on cell viability and its molecular events leading to cell death in A172 human glioma cells. Ceramide induced cell death in a dose-dependent manner and the cell death was dependent on generation of reactive oxygen species and lipid peroxidation. TUNEL assay, Hoechst 33258 staining, and flow cytometric analysis did not show typical apoptotic morphological features. Ceramide caused phosphorylation of extracellular signal-regulated kinase (ERK) and p38, but the cell death was not affected by inhibitors of MAPK subfamilies. Ceramide caused ATP depletion without loss of mitochondrial membrane potential. Ceramide did not induce caspase activation and ceramide-induced cell death was also not altered by inhibitors of caspase activation. Transfection of dominant inhibitory mutant of IkappaBalpha (S32A/36A) and pretreatment of pyrrolidinedithiocarbamate, an inhibitor of NF-kappaB, enhanced ceramide-induced cell death. These results indicate that ceramide causes non-apoptotic, caspase-independent cell death by inducing reactive oxygen species generation in A172 human glioma cells. NF-kappaB is involved in the regulation of ceramide-induced cell death in human glioma cells.

Sphingolipid metabolites in neural signalling and function

Sphingolipid metabolites, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P) and complex sphingolipids (gangliosides), are recognized as molecules capable of regulating a variety of cellular processes. The role of sphingolipid metabolites has been studied mainly in non-neuronal tissues. These studies have underscored their importance as signals transducers, involved in control of proliferation, survival, differentiation and apoptosis. In this review, we will focus on studies performed over the last years in the nervous system, discussing the recent developments and the current perspectives in sphingolipid metabolism and functions.

Enhancement of C2-ceramide antitumor activity by small interfering RNA on X chromosome-linked inhibitor of apoptosis protein in resistant human glioma cells

OBJECT

Many human glioma cells are resistant to ceramide. In this study the authors investigated the mechanisms of that resistance and considered ways to overcome it.

METHODS

The authors first administered C2-ceramide (N-acetylsphingosine) to human glioma cells from rare cell lines susceptible to C2-ceramide (SKMG1 and U87MG) and other cell lines resistant to it (U251SP, T98G, SKAO2, and U251MG). Following this, the authors analyzed the statuses of transduction signals such as cell viability, morphological changes, caspases, mitochondrial membrane potential, apoptosis-inducing factor, oligonucleosomal DNA fragmentation, and the inhibitor of apoptosis protein (IAP) family.

CONCLUSIONS

Ceramide resistance was found to arise from the inhibition of caspase-7 induced by IAPs, especially X chromosome-linked IAP (XIAP). Small interfering RNA (siRNA) on XIAP quenched that resistance in ceramide-resistant human glioma cells (U251SP, T98G, SKAO2, U251MG), indicating that a siRNA for XIAP may be a useful tool for overcoming the resistance to ceramide in human glioma cells.

C2-ceramide as a cell death inducer in HC11 mouse mammary epithelial cells

Ceramide is a lipid mediator in cell proliferation, differentiation, and apoptosis in many cell lines. However, the molecular mechanisms for ceramide have not been clarified in HC11 mouse mammary epithelial cells. Under phase contrast microscope, C2-ceramide-treated cells clearly showed morphological changes, which were characteristic features of apoptosis. Treatment with C2-ceramide at 10 microM specifically resulted in the death of 50% of the cells after 48 h as assessed by MTT assay. To further investigate which genes contribute to cell death in C2-ceramide-treated cells, we used the reverse transcription-polymerase chain reaction to assess mRNA levels for five genes in the Bcl-2 family and five genes in the caspases family. The steady-state mRNA levels of Bax, Bad and Bak were not significantly changed for 48 h of C2-ceramide treatment. The increases of mRNA levels of Bcl-2 and Bcl-w were observed for the first 3 h of C2-ceramide treatment and the last 24 h between 24 and 48 h. We also found that in HC11 cells, C2-ceramide increased mRNA levels of the caspases family from 6 to 24 h. These results suggest that in the HC11 cells, C2-ceramide promote cell death by mediating the induction of caspases and that HC11 mouse mammary epithelial cells paradoxically up-regulate the expression of Bcl-2 and Bcl-w to prevent C2-ceramide-mediated cell death.

Brefeldin A induces apoptosis and cell cycle blockade in glioblastoma cell lines

Brefeldin A (BFA), a fungal metabolite known to affect the structure and function of the Golgi apparatus, has recently been shown to induce apoptosis and cell growth inhibition in various human cell lines. Glioblastomas (GB) are cerebral tumors with poor prognosis, which display resistance to current therapies including radio- and chemotherapy. The objective of this study was to investigate BFA effects in three human GB cell lines (SA4, SA146 and U87MG cells). Compared with control cells, about 60% of cell growth inhibition was observed in BFA (100 ng/ml for 24 h)-exposed cells in the three cell lines. Furthermore, in SA4 and SA146 cells, BFA was able to induce a time- and dose-dependent apoptosis detected by DAPI staining, TUNEL assay and flow-cytometric analysis. Since p53 expression was not modified after BFA exposure, BFA-induced apoptosis may follow a p53-independent pathway, as already reported. In the same way, BFA did not alter Bcl-2, Bax and Mcl-1 expression. Cell cycle analysis revealed a cell cycle arrest in early G0/G1 phase with an increase in G0/G1 cell population (70% in control cells vs. 83% in exposed cells) associated with a decrease in the S cell population (14% in control cells vs. 5.5% in exposed cells). The Ki67 labeling index also confirmed the cell cycle blockade. Our results suggest that BFA may be a potent cell cycle modulator and inducer of apoptosis in GB cell lines, and therefore may become a promising candidate for the chemotherapeutic treatment of gliomas.

Role of ceramide in mediating apoptosis of irradiated LNCaP prostate cancer cells

The sphingomyelin metabolites ceramide and sphingosine are mediators of cell death induced by gamma-irradiation. We studied the production of ceramide and the effects of exogenous ceramide on apoptosis in LNCaP prostate cancer cells that are highly resistant to gamma-irradiation-induced cell death. LNCaP cells can be sensitized to gamma-irradiation by tumor necrosis factor alpha (TNF-alpha) and, to a lesser degree, by the agonistic FAS antibody CH-11. TNF-alpha activated intrinsic and extrinsic apoptosis pathways and increased ceramide and sphingosine levels in irradiated LNCaP cells. CH-11 activated only the extrinsic apoptosis pathways and had a negligible effect on ceramide and sphingosine levels in irradiated LNCaP cells. Exogenous ceramide and bacterial sphingomyelinase sensitized LNCaP cells to radiation-induced apoptosis and had a synergistic effect on cell death after irradiation with TNF-alpha, but not with CH-11. Cell death effects after exposure to ceramide and irradiation were blocked by the serine protease inhibitor TLCK (Na-p-tosyl-L-lysine-chloromethylketone), but not by the caspase inhibitor z-VAD (2-val-Ala-Asp(oMe)-CH(2)F). During LNCaP cell apoptosis induced by exogenous ceramide, we observed activation of caspase-9, but not caspases-8, -3, or -7. The effect of ceramide occurred largely via the intrinsic mitochondrial apoptosis pathway and enhanced TNF-alpha, but not CH-11 effects on irradiated cells. The data show that ceramide enhanced activation of the intrinsic apoptotic pathway and enhanced cell death induced by TNF-alpha with or without gamma-irradiation. TNF-alpha and gamma-irradiation elevated levels of endogenous ceramide and activated the intrinsic cell death pathway.

Impact of mitochondrial beta-oxidation in fatty acid-mediated inhibition of glioma cell proliferation

Tetradecylthioacetic acid (TTA), which cannot be beta-oxidized, exerts growth-limiting properties in glioma cells. In order to investigate the importance of modulated lipid metabolism and alterations in mitochondrial properties in this cell death process, we incubated glioma cells both with TTA and the oxidizable fatty acid palmitic acid (PA), in the presence of L-carnitine and the carnitine palmitoyltransferase inhibitors etomoxir and aminocarnitine. L-carnitine partly abolished the PA-mediated growth reduction of glioma cells, whereas etomoxir and aminocarnitine enhanced the antiproliferative effect of PA. The production of acid-soluble products increased and the incorporation of PA into glycerolipids decreased after L-carnitine supplementation. L-carnitine was found to enhance the antiproliferative effect of TTA, but did not affect the incorporation of TTA into glycerolipids, or ceramide. PDMP, sphingosine 1-phosphate, desipramine, fumonisin B(1), and L-cycloserine were able not to rescue the glioma cells from PA and TTA-induced growth inhibition, suggesting that increased ceramide production is not important in the growth reduction. TTA-mediated growth inhibition was accompanied with an increased uptake of PA and increased incorporation of PA into triacylglycerol (TG). Our data suggest that mitochondrial functions are involved in fatty acid-mediated growth inhibition. Whether there is a causal relationship between TG accumulation and the apoptotic process remains to be determined.

Slight impairment of Na+,K+-ATPase synergistically aggravates ceramide- and beta-amyloid-induced apoptosis in cortical neurons

Dysfunction of the Na(+),K(+)-ATPase (Na(+),K(+)-pump), due to reduced energy supply or increased endogenous ouabain-like inhibitors, likely occurs under pathological conditions in the central nervous system. In cultured mouse cortical neurons, we examined the hypothesis that a mild non-toxic inhibition of the Na(+),K(+)-ATPase could synergistically sensitize the vulnerability of neurons to normally non-lethal apoptotic signals. Ouabain at a low concentration of 0.1 microM slightly lessened the Na(+),K(+)-pump activity measured as an ouabain-sensitive current, yet did not affect K(+) homeostasis and viability of cortical neurons. Co-exposure to 0.1 microM ouabain plus non-lethal C(2)-ceramide (5 microM) or beta-amyloid 1-42 (5 microM), however, induced marked intracellular K(+) loss, caspase-3 cleavage, DNA laddering, and synergistically triggered neuronal death. The caspase inhibitor Z-Val-Ala-Asp(OMe)-fluoromethyl ketone (Z-VAD-FMK) predominantly blocked the caspase activation and neuronal death. These results suggest that slight impairment of Na(+),K(+)-pump activity may amplify the disruption of K(+) homeostasis in the presence of a non-lethal apoptotic insult, leading to activation of apoptotic cascade and substantial neuronal injury.

Ceramide increases Fas-mediated apoptosis in glioblastoma cells through FLIP down-regulation

Ceramide is a physiologic regulator of growth and differentiation in mammalian cells. In this study, the relationship between ceramide and FLICE inhibitory protein (FLIP) in the induction of apoptosis in glioblastoma cell lines was investigated. We found that LN215 cells were slightly more sensitive to Fas-mediated apoptosis than LN319 cells, which were more sensitive to ceramide than LN215 cells. FLIP was expressed in LN319 and LN215 cells constitutively, and this expression decreased with treatment of ceramide in LN215 cells, which might cause LN215 cells to be more sensitive to Fas-mediated apoptosis at lower level stimulation. In LN319 cells FLIP levels were not modified by ceramide treatment and the level of cell death induced by anti-Fas antibody was not affected. Our results suggest that FLIP may be down-regulated by low levels of ceramide in LN215 cells, which causes LN215 cells to be more sensitive to Fas-mediated apoptosis, whereas LN319 cells remain resistant.

Modulation of the expression of membrane-bound CD54 (mCD54) and soluble form of CD54 (sCD54) in endothelial cells by glucosyl transferase inhibitor: possible role of ceramide for the shedding of mCD54

1-Phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) is a synthetic inhibitor toward glucosyl transferase. Here, we showed the functional role of sphingolipids on CD54 expression of endothelial cells (ECs) by the use of PDMP. CD54 mRNA expression in human umbilical vein endothelial cells (HUVECs) was not changed by PDMP; however, PDMP treatment significantly enhanced the expression of membrane-bound CD54 (mCD54) on HUVECs. In contrast, the amount of soluble form of CD54 (sCD54) in the culture supernatants of HUVECs was diminished by PDMP. Similar results were obtained when HUVECs were incubated with metalloproteinase inhibitor, KB-R8301, or in the presence of C2-ceramide. The above effect of PDMP, KB-R8301, and C2-ceramide in HUVECs was commonly found in unstimulated, TNF-alpha-stimulated, and IL-1beta-stimulated HUVECs. These data provide the possibility that the shedding of mCD54 into sCD54 by metalloproteinase-like enzyme is inhibited by PDMP, in which PDMP-induced accumulation of ceramide may act as a second messenger.