Induction of LGR5 by H2O2 treatment is associated with cell proliferation via the JNK signaling pathway in colon cancer cells

Recently, the leucine-rich repeat G protein-coupled receptor 5 (LGR5/GPR49) was identified as a potential marker of intestinal stem cells in human. The LGR5 is known as a Wnt signaling target gene, and its expression pattern is related with beta-catenin mutation. H2O2 is a member of reactive oxygen species (ROS) and regulates metabolism, aging, apoptosis and the intensity of growth factor signaling. In addition, it acts as a negative or positive regulator of Wnt signaling. However, the effect of H2O2 on Wnt signaling and its target gene LGR5 is not clear. In this study, we investigated the effects of ROS on cancer stem cells, in colorectal cancer cells. Colorectal cancer cells were treated with exogenous H2O2, after which cellular responses and the expression of LGR5 were examined. In SNU-C2A cells, proliferation increased following treatment with 50-300 mu M of H2O2, whereas cell viability significantly decreased after treatment with 600-900 mu M of H2O2. Expression of heme oxygenase (HO)-1 and jun, which aid in the reduction of oxidative stress, were induced in the low dose H2O2-treated SNU-C2A cells. The LGR5 expression level was significantly increased following 50-300 mu M H2O2 treatment; in addition, beta-catenin was increased in H2O2-treated colon cancer cells. However, the increased beta-catenin was detected not in the nucleus but in the cytoplasm, which means that beta-catenin was stabilized in the cytoplasm and not translocated into the nucleus where it could function as a transcription factor for the expression of LGR5. In addition, there was no direct interaction between LGR5 and beta-catenin. In this study, we found that LGR5 expression increased when cancer cells were treated with a low dose of H2O2. Our results indicate that the LGR5 increase resulted via activation of the JNK signaling pathway. The induction of LGR5 expression influenced cell proliferation in colorectal cancer cells.