ABCB1 and malignant colon neoplasm: For instance, PXR has been shown to regulate ABCB1 expression in human colon cancer LS174T cells through direct binding to the direct repeat separated by four base pairs (DR4) motif within the ABCB1 promoter region, and thus PXR ligand rifampin induces ABCB1 expression (Geick et al., 2001).