Hence, it is possible that the pathways of cell signaling in response to DNA-damaging agents differ due to the types of DNA-damaging agents and also the stage of cell differentiation, because in colorectal cancer, it was observed that the extent of Skp2-p21/p27 degradation by β-catenin or ubiquitination depends on the degree of cancer cell differentiation [34]. Here, SKP2 is linked to colorectal cancer.