Disease relevance of SPHK1

• Collectively, our results suggest that SPHK1 may play an important role in breast cancer progression by regulating tumor cell growth and survival [1].
• These data demonstrate the critical role of SPK1 in LPS signaling in macrophages and suggest that SPK1 is a potential therapeutic target to block hyperimmune responses induced by gram-negative bacteria [2].
• Sphingosine kinase mediates activation of extracellular signal-related kinase and Akt by respiratory syncytial virus [3].
• The effect of hypoxia on lipid phosphate receptor and sphingosine kinase expression and mitogen-activated protein kinase signaling in human pulmonary smooth muscle cells [4].
• Enhancement of SPHK1 in vitro by carbon ion irradiation in oral squamous cell carcinoma [5].
• We report that hypoxia increases SK1 mRNA levels, protein expression, and enzyme activity, followed by intracellular S1P production and S1P release [6].
• SPHK1 in astrocytoma cell lines was elevated at both mRNA and protein levels, and the SPHK1 mRNA and protein were significantly up-regulated by up to 6.8- and 40-fold, respectively, in primary astrocytomas compared with those in the adjacent noncancerous brain tissues [7].

High impact information on SPHK1

• Furthermore, inhibition of ceramide-mediated apoptosis by activation of protein kinase C results from stimulation of sphingosine kinase and the concomitant increase in intracellular sphingosine-1-phosphate [8].
• The sphingosine analogue, D-L-threo-dihydrosphingosine (DHS), inhibits the SK enzyme competitively with a dissociation constant, K1, of 5 to 18 microM [9].
• Here we show that antigen clustering of Fc epsilon RI on the rat mast-cell line (RBL-2H3) activates a sphingosine kinase (SK) and produces sphingosine-1-phosphate (S1P), and alternative second messenger for intracellular calcium mobilization [9].
• Here we report that activation of sphingosine kinase and the formation of sphingosine-1-phosphate are important in the signal transduction pathways activated by the potent mitogens platelet-derived growth factor (PDGF) and fetal calf serum (FCS) [10].
• Stimulation of mast cells by allergens induces two mammalian sphingosine kinases (Sphk1 and Sphk2) to produce sphingosine-1-phosphate (S1P) [11].

Chemical compound and disease context of SPHK1

• Sphingosine kinase type 1 promotes estrogen-dependent tumorigenesis of breast cancer MCF-7 cells [1].
• Stimulation of SK activity by killed M.tb, live Staphylococcus aureus, or latex beads was associated with translocation of cytosolic SK1 to the phagosome membrane [12].
• High expression of sphingosine kinase 1 and S1P receptors in chemotherapy-resistant prostate cancer PC3 cells and their camptothecin-induced up-regulation [13].
• We now demonstrate that hyperglycemia induces activation of sphingosine kinase (SphK), which represents a novel signaling pathway that mediates endothelial damage under ambient high glucose conditions [14].
• We took advantage of the known differential effect of camptothecin and docetaxel on human PC-3 and LNCaP prostate cancer cells to determine their effect on sphingosine kinase-1 (SphK1) activity and subsequent ceramide/sphingosine 1-phosphate (S1P) balance in relation with cell survival [15].

Biological context of SPHK1

• While activity of SPHK2 toward sphingosine was generally lower than of SPHK1, FTY720 phosphorylation was higher under conditions favoring SPHK2 [16].
• In addition, SPHK1-enhanced cell proliferation was also abolished by SKIP, with a corresponding decrease in activation of ERK [17].
• Using an antisense oligonucleotide against SPHK1, we show that knockdown of SPHK1 abolishes the C5a-triggered intracellular Ca(2+) signals, degranulation, cytokine generation, and chemotaxis [18].
• Northern blot analysis revealed that SPHK2 mRNA expression had a strikingly different tissue distribution from that of SPHK1 and appeared later in embryonic development [19].
• Using human A549 epithelial lung carcinoma cells as a model system, we observed transient upregulation of sphingosine kinase type 1 (SPHK1) enzyme activity upon stimulation with both TNF-alpha or IL-1beta [20].

Anatomical context of SPHK1

• In human endothelial cells, while activity of SPHK1 toward sphingosine was 2-fold higher than of SPHK2, FTY720 phosphorylation was 7-fold faster under SPHK2 assay conditions [16].
• Furthermore, SKIP overexpression in NIH 3T3 fibroblasts reduced SPHK1 activity and interfered with its biological functions [17].
• Moreover, an antisense oligonucleotide against SPHK1, in neutrophil-differentiated HL-60 cells, had similar inhibitory properties as DMS, suggesting that the SPHK utilized by C5a is SPHK1 [21].
• RPK118 is also shown to co-localize with SPHK1 on early endosomes in COS7 cells expressing both recombinant proteins [22].
• VEGF or phorbol 12-myristate 13-acetate treatment of the T24 bladder tumor cell line resulted in a time- and dose-dependent stimulation of SPK activity [23].

Associations of SPHK1 with chemical compounds

• Thus, only SPHK1 and 2 appear to be capable of phosphorylating FTY720 [16].
• SPHK1 also conferred a growth advantage, as determined by proliferation and growth in soft agar, which was estrogen dependent [1].
• Inhibition of basal SPHK1 activity by N,N-dimethylsphingosine or by downregulation of its expression using siRNA induced spontaneous apoptosis in A549 cells, an effect that can be explained through interference with constitutive NFkappaB activity in this cell type [20].
• Sphingosine-1-phosphate (S1P), the bioactive product of sphingosine kinase (SK) activation, is a survival factor for endothelial cells [24].
• Triton X-100 inhibited SPHK2 and stimulated SPHK1, whereas phosphatidylserine stimulated both type 1 and type 2 SPHK [19].
• The elevated ceramide formation induced by SPHK inhibition and l-OHP was inhibited by fumonisin B1 but not myriocin, suggesting that ceramide formation was through the salvage pathway [25].

Physical interactions of SPHK1

• In the present study, we investigated whether the sphingosine kinase/SPP pathway is involved in cellular signaling of the Gi protein-coupled formyl peptide receptor in myeloid differentiated human leukemia (HL-60) cells [26].

Enzymatic interactions of SPHK1

• These studies demonstrate that SK1 is cleaved by cathepsin B in a sequential manner after basic amino acids, and that the initial cleavages at the two identified sites occur independently of each other [27].
• In vitro phosphatase assays showed that PP2Ac dephosphorylated both recombinant SK1 and a phosphopeptide based on the phospho-Ser(225) region of SK1 [28].

Regulatory relationships of SPHK1

• Interestingly, only depletion of PKC-alpha leads to a complete loss of TPA- and histamine-triggered SK-1 induction and cell migration [29].
• These data show that SPHK1 participates in the dbcAMP-induced differentiation of HL60 cells by activating the MEK/ERK pathway [30].
• In this study, we show that in the human breast cancer cell line MCF7, epidermal growth factor (EGF) stimulates SK-1 activity in a biphasic manner with a first peak after 15 min and a second delayed activation occurring after 1 h up to 18 h and thereafter declining again [31].
• In this study, we show that prolonged treatment of MCF-7 cells with tumor necrosis factor (TNF) induces a dose- and time-dependent decrease in SK1 protein [32].
• In BMM single cultures, the osteoclastogenic factor receptor activator of NF-kappaB ligand (RANKL) upregulated SPHK1 and increased S1P production and secretion [33].

Other interactions of SPHK1

• Unlike the proliferative action of SPHK1, another isozyme, SPHK2, has been shown to possess anti-proliferative or pro-apoptotic action [34].
• Identification and characterization of RPK118, a novel sphingosine kinase-1-binding protein [22].
• The overexpression of wild-type SPHK1, but not dominant negative SPHK1, resulted in high basal levels of ERK1/2 phosphorylation and stimulated granulocytic differentiation in HL60 cells [30].
• Histamine increases sphingosine kinase-1 expression and activity in the human arterial endothelial cell line EA.hy 926 by a PKC-alpha-dependent mechanism [29].
• Further SPHK superfamily members, namely ceramide kinase and a "SPHK-like" protein, failed to phosphorylate sphingosine and FTY720 [16].

Analytical, diagnostic and therapeutic context of SPHK1

• The pseudokinase 2 domain of RPK118 is responsible for SPHK1 binding as judged by yeast two-hybrid screening and immunoprecipitation studies [22].
• Molecular cloning and functional characterization of a novel mammalian sphingosine kinase type 2 isoform [19].
• We evaluated the role of SPHK1 and S1P in osteoclastogenesis using bone marrow-derived macrophage (BMM) single and BMM/osteoblast coculture systems [33].
• By using a combination of limited proteolysis, peptide interaction analysis, and site-directed mutagenesis, we have identified that the CaM-binding site of hSK1 resides in the region spanned by residues 191-206 [35].
• Real-time PCR analysis showed higher SPHK-1 mRNA expression levels in RA patients compared with paired controls [36].

References