Sphingosine Kinase 1 As A Potential Prognostic Factor And Therapeutic Target In Nasopharyngeal Carcinoma

Background and purposeSphingolipid metabolites such as ceramide(Cer),sphingosine(Sph),1 sphingosine phosphate(S1P),etc.,play important roles in the development of tumors,and sphingosine kinase 1(SPHK1)is the key enzyme regulating the balance of sphingolipid.Studies have shown that SPHK1 is over-expressed in varieties of solid tumors,promotes tumor progression via SPHK1/S1 P pathway,and affects tumor prognosis.FTY720(fingolimod),a sphingosine analogues,has a strong immunosuppressive activity.Recent studies found that FTY720 could inhibit proliferation and induce apoptosis in several types of cancers.In this study,we investigated the expression of SPHK1 and the association between SPHK1 expression with clinical stage and prognosis of nasopharyngeal carcinoma,as well as the possibility of SPHK1 as a potential therapeutic target.Materials and methodsProtein and m RNA levels of SPHK1 expression in non-tumorous cancer tissues and NPC tissues were examined by Western blotting and qRT-PCR.Immunohistochemistry was employed to analyze SPHK1 expression in 142 clinicopathologically characterized NPC cases and 10 non-tumoral cancer tissue samples.Statistical analyses were applied to derive prognostic and diagnostic associations.In cell experiments,the expression of SPHK1 was measured in nasopharyngeal carcinoma cell lines CNE1 and CNE2 after si-SPHK1 transfection using q RT-PCR and Western blot;the cell proliferation and viability of NPC cells after si-SPHK1 transfection and FTY720 treatment was determined by CCK-8 Kit;the cell cycle distribution and apoptosis was examined by flow cytometry;the activity of sphingosine kinase was quantified by using a commercial Sphingosine Kinase Activity Assay Kit as the manufacturer instructed.ResultsThe SPHK1 mRNA level in NPC tissues was significantly higher than in the non-tumorous nasopharyngeal epithelial tissues.Positive staining of SPHK1 was observed in almost all among the 142 NPC biopsies,and 93 out of 142(65.5%)biopsies showed high expressions of SPHK1.Statistical analyses revealed that high levels of SPHK1 expression were associated with the clinical stages,locoregional recurrence and distant metastasis of NPC.NPC patients with high levels of SPHK1 expression had shorter survival time,whereas those with lower levels of SPHK1 expression survived longer.Moreover,multivariate analysis suggested that SPHK1 up-regulation was an independent prognostic factor for NPC.The expression of SPHK1 was decreased in NPC cells transfected with siR-SPHK1 using qRT-PCR and Western blotting.Down-regulation of SPHK1 inhibited cell proliferation,induced cell cycle arrest and promoted apoptosis.FTY720 inhibited SPHK1 activity and the proliferation of NPC cells,induced apoptosis,and enhanced radio-sensitivity(all P<0.05).ConclusionOur results suggest that high expression SPHK1 is associated with clinical stage,local recurrence and prognosis in NPC patients.Down-regulation of SPHK1 inhibited cell proliferation,induced cell cycle arrest and promoted apoptosis.FTY720 could inhibit SPHK1 enzyme activity,suppress cell proliferation and induce apoptosis,enhance radio-sensitivity of NPC cells.SPHK1 protein could be a useful marker for the prognosis of NPC and the study on the use of SPHK1 as a potential therapeutic target is also warranted.