p21 Regulates Wnt-Notch Balance via DREAM/MMB/Rb-E2F1 and Maintains Intestinal Stem Cell Homeostasis
The crosstalk and balance regulation of Wnt-Notch have been known to be essential for cell fate decision and tissue regeneration, while how the balance is maintained and how the Wnt-Notch pathways are connected with the cell cycle regulation are still not clear. In the mouse model with accelerated aging phenotypes due to the loss of cell cycle inhibitor p21 function in Werner syndrome background, we observed the imbalance of Wnt-Notch signaling, along with the fast turnover of intestinal epithelia, which might cause the abnormal mobilization of stem cells, exhaust the stem cell reservoir, and result in the accelerated aging phenotypes. We revealed that the loss of p21 caused the shift of DREAM/Rb complex to MMB/E2F1 complex and the fast turnover of intestinal epithelia. Importantly, we identified the E2F1 as the transcriptional regulator for Notch1, which connected the p21-DREAM/MMB/Rb-E2F1 pathway with Wnt-Notch pathway. The overexpression of p21 rescued the imbalance of Wnt-Notch pathway. Our data identify p21 as an important factor in maintaining sequential mobilization, proliferation, and homeostasis of intestinal stem cells. Overall design: To understand the molecular pathways altered after p21 deletion, we applied RNA-seq to the liver tissue of 3rd generation of TKO mice (G3 p21TKO, p21-/-mTR-/-Wrn-/-), which already showed progeroid symptoms. The G3 DKO mice (mTR-/-Wrn-/-) were used as control. The RNA-seq data was analyzed by ssGSEA (single sample gene set enrichment analysis) to get the differentially regulated pathways in response to the loss of p21 function.