To determine the effects of these E3 ligases on protein levels of endogenous cyclin D1, we transfected Keap1, DDB2, WSB2, and Rbx1 siRNA into human colon cancer cell line HCT-116 cells and found that knocking down of Keap1, DDB2, WSB2, or Rbx1 significantly enhanced endogenous cyclin D1 protein levels (Figure 2A, D, G, and J). Here, KEAP1 is linked to malignant colon neoplasm.