Upregulation of phosphorylated sphingosine kinase 1 expression in colitis-associated cancer

Background: Colitis-associated cancer (CAC) is the most serious complication of inflammatory bowel disease. Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator that is generated by sphingosine kinase 1 (SphK1) and is known to play an important role in inflammation and cancer progression. Moreover, SphK1 and S1P act as upstream mediators of proinflammatory cytokine interleukin 6 (IL-6) and signal transducer and activator of transcription-3 (STAT3). We hypothesized that the expression levels of phosphorylated SphK1 (pSphK1), phosphorylated STAT3 (pSTAT3), and IL-6 are universally higher in CAC patients than in sporadic colorectal cancer (CRC) patients because all of these factors are associated with inflammation. In this study, we determined the expression levels of pSphK1 in patients with sporadic CRC and CAC and clarified the importance of S1P in CAC patients. Materials and methods: We randomly selected 10 sporadic CRC patients and 10 CAC patients who underwent curative resection, and we examined their surgical specimens by immunohistochemistry. We determined the expression levels of pSphK1, pSTAT3, and IL-6 in these samples. Results: We found pSphK1 expression to be more prevalent in CAC patients (P = 0.019) and to have a higher immunohistochemistry score (P = 0.005) than in sporadic CRC patients. However, the expression of pSTAT3 and IL-6 did not differ between the patient groups. Conclusions: To our knowledge, this is the first report comparing pSphK1 expression levels in CAC with those in sporadic CRC. The high levels of pSphK1 expression in CAC suggest an important role of S1P in the disease process of CAC.