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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.
Nucleoredoxin (NXN) is a redox regulator of Disheveled and thereby of WNT signaling. Deficiency in mice leads to cranial dysmorphisms and defects of heart, brain, and bone, suggesting defects of cell fate determination. We used shRNA-mediated knockdown of NXN in SH-SY5Y neuroblastoma cells to study its impact on neuronal cells. We expected that shNXN cells would easily succumb to redox stress, but there were no differences in viability on stimulation with hydrogen peroxide. Instead, the proliferation of naïve shNXN cells was increased with a higher rate of mitotic cells in cell cycle analyses. In addition, basal respiratory rates were higher, whereas the relative change in oxygen consumption upon mitochondrial stressors was similar to control cells. shNXN cells had an increased expression of redox-sensitive heat shock proteins, Hsc70/HSPA8 and HSP90, and autophagy markers suggested an increase in autophagosome formation upon stimulation with bafilomycin and higher flux under low dose rapamycin. A high rate of self-renewal, autophagy, and upregulation of redox-sensitive chaperones appears to be an attractive anti-aging combination if it were to occur in neurons in vivo for which SH-SY5Y cells are a model.