SPHK1 and colorectal cancer: SGPL1 mRNA expression was by far the highest among all S1P metabolizing enzymes in two human colorectal cancer cell lines; selective reduction of SGPL1 mRNA expression (SPHK1, SPHK2, SGPP1, and SGPP2 remained unchanged) and complementary reduction of the SGPL1 enzyme level increased intracellular S1P levels but did not affect cell proliferation or metabolic activity of the cells [77].