Abstract
Background: Reduction of the Sphingosine-1-phosphate (S1P) degrading enzyme S1P lyase 1 (SGPL1) initiates colorectal cancer progression with parallel loss of colon function in mice. We aimed to investigate the effect of SGPL1 knockout on the stem cell niche in these mice. Methods: We performed immunohistochemical and multi-fluorescence imaging on tissue sections of wildtype and SGPL1 knockout colons under disease conditions. Furthermore, we generated SGPL1 knockout DLD-1 cells (SGPL1−/−M.Ex1) using CRISPR/Cas9 and characterized cell cycle and AKT signaling pathway via Western blot, immunofluorescence, and FACS analysis. Results: SGPL1 knockout mice were absent of anti-Ki-67 staining in the stem cell niche under disease conditions. This was accompanied by an increase of the negative cell cycle regulator FOXO3 and attenuation of CDK2 activity. SGPL1−/−M.Ex1 cells show a similar FOXO3 increase but no arrest of proliferation, although we found a suppression of the PDK1/AKT signaling pathway, a prolonged G1-phase, and reduced stem cell markers. Conclusions: While already established colon cancer cells find escape mechanisms from cell cycle arrest, in vivo SGPL1 knockout in the colon stem cell niche during progression of colorectal cancer can contribute to cell cycle quiescence. Thus, we propose a new function of the S1P lyase 1 in stemness.
Highlights
Sphingolipids and their bioactive metabolites are involved in structural maintenance of cell membranes and mediate cellular functions such as migration, proliferation, and apoptosis during inflammation and cancer [1,2,3]
An endogenous increase in Sphingosine kinases (SPHK) 1 levels has been demonstrated in human colon adenomas and mouse models of colon cancer [4,5], and a recent publication showed that intestinal epithelial deletion of SPHK1 prevents colitis-associated cancer development in mice [6]
During inflammation induced colorectal cancer progression, Ki-67 abundance increased in SGPL1 knockout colon tumors, indicating an increased proliferation rate of cancerous cells (Figure 1d)
Summary
Sphingolipids and their bioactive metabolites are involved in structural maintenance of cell membranes and mediate cellular functions such as migration, proliferation, and apoptosis during inflammation and cancer [1,2,3]. Sphingolipids and their corresponding enzymes are prone to regulate cell fate. Results: SGPL1 knockout mice were absent of anti-Ki-67 staining in the stem cell niche under disease conditions. This was accompanied by an increase of the negative cell cycle regulator FOXO3 and attenuation of CDK2 activity. We propose a new function of the S1P lyase 1 in stemness
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