The Role and Mechanism of S1PR5 in Colon Cancer

PURPOSE: To investigate the role and mechanism of S1PR5 in colon cancer. MATERIALS AND METHODS: Lentiviral infection and drug screening helped to establish colon cancer cell lines with stable overexpression and knockdown of S1PR5. Effects of S1PR5 expression on cell growth, proliferation, migration, and invasion were analyzed using a subcutaneous xenograft model in nude mice. Western blot (WB) was used to detect the effects of S1PR5 expression on p-AKT, STAT3, NF-κB, and p-JNK. The distribution of p65 was evaluated in nuclear and cytoplasmic fractions using WB. CCK-8, Transwell migration, and Transwell invasion assays analyzed cell growth, proliferation, migration, and invasion. qRT-PCR analysis revealed that S1PR5 expression was associated with altered expression levels of NF-κB downstream target genes, such as IL-6, TNF-α, and indoleamine 2, 3-dioxygenase 1 (IDO1). RESULTS: qRT-PCR and WB analysis showed that the S1PR5 level in colon cancer cell lines—SW480, SW620, HCT116, and LoVo—was significantly higher than in NCM460, a healthy colonic epithelial cell line. SW620 and SW480, with high and low expression of S1PR5, respectively, were selected as model cell lines. S1PR5 knockdown in SW620 caused the growth rate, proliferation, migration, invasion, and subcutaneous tumor formation rate to decrease in mice, whereas S1PR5 overexpression in SW480 caused all of these parameters to increase. WB analysis showed an increase in phospho-p65 and its nuclear translocation. S1PR5 knockdown caused a decrease in phospho-p65 levels and its nuclear import, thereby inhibiting its activity. In S1PR5 knockdown and overexpressing cells, p65 was overexpressed and knocked down, respectively. qRT-PCR and WB showed that S1PR5 over-expression up-regulates IDO1, and S1PR5 knockdown inhibits IDO1. CCK-8 and Transwell assays showed that p65 and IDO1 overexpression antagonizes the antitumor effect of S1PR5 knockdown, and that p65 and IDO1 knockdown antagonizes the tumorigenic effect of S1PR5 overexpression. CONCLUSION: S1PR5 overexpression promotes the growth, migration, and invasion of cancer by activating the NF-κB/IDO1 signaling pathway.