DOP007. Intestinal epithelial-specific deletion of Sphingosine kinase 1 protects against colitis-associated cancer in mice models
B.J. Lee, M.K. Joo, J.-J. Park, J.S. Kim, Y.-T. Bak, Y.T. Jeen, Korea University Medical center, Gastroenterology, Seoul, South Korea
Sphingosine kinase 1 (Sphk1) is a crucial enzyme in the sphingolipid pathway, responsible for generating sphingosine-1-phosphate. Sphk1 is an oncogene capable of inducing both tumor initiation and progression. The aim of this study is to define the effect of intestinal epithelial deletion of Sphk1 on the colitis associated tumorigenesis using Apcmin/+-dextran sodium sulfate (DSS) and azoxymethane (AOM)/DSS models.
The Sphk1 was conditionally deleted from intestinal epithelial cells in mice, villin-cre Sphk1flox/flox mice. For the experiment of colitis, Sphk1flox/flox and Villin-Cre Sphk1flox/flox mice received 2.5% DSS for 5 days and were enuthanized 12 days after the initiation of DSS. Villin-Cre Sphk1flox/flox and Apcmin/+ mice were crossed to generate villin-Cre Sphk1flox/flox Apcmin/+ mice. Four-weeks old villin-Cre Sphk1flox/flox Apcmin/+ mice and littermates control Sphk1flox/flox Apcmin/+ littermates, were given 2% DSS for 7 days and were sacrificed 6 weeks after the initiation of DSS. Sphk1flox/flox and Villin-Cre Sphk1flox/flox mice were used for the experiment of AOM/DSS-induced colitis-associated cancer (CAC). Macroscopic tumor were measured with caliper and histologic analyses were done. Real-time PCR, immuhistochemistry (IHC) and Western blot for Sphk1/2, β-catenin, cyclin D1 and c-myc were performed.
Villin-Cre Sphk1flox/flox mice had significant higher colitis with longer segment of ulceration compared to Sphk1flox/flox mice (p < 0.05). Mean tumor incidence (7.55±4.51 vs 20.72±11.09, p < 0.05), tumor size (2.87±1.69 vs 3.63±2.01 p < 0.05) and the tumor portion in >3 mm were significantly decreased in villin-Cre Sphk1flox/flox Apcmin/+ mice compared with littermates. Histologic grade was more severe in Sphk1flox/flox Apcmin/+ mice compared with villin-Cre Sphk1flox/flox Apcmin/+ mice (invasive caricinoma, 71% vs 13%, p < 0.05). The expression of Sphk2 and the β-catenin target genes cyclin D1/c-myc were decreased in Sphk1-deficient tumors. The activities of β-catenin (nucleus), cyclin D1 and c-myc and were significantly decreased in villin-Cre Sphk1flox/flox Apcmin/+ mice compared with littermates in both IHC and Western blot analyses. In AOM/DSS CAC model, tumor number and size were not significantly different between Sphk1flox/flox and villin-Cre Sphk1flox/flox mice but there was a change of tumor size distribution between two groups.
Epithelial deletion of Sphk1 inhibits CAC in Apcmin/+-DSS model in mice by the modulation of β-catenin and its target signal pathway.