APC and malignant colon neoplasm: However, FasL promoter constructs containing either one mutant TBE (single mutant TBE1  =  TBE1M/2W or single mutant TBE2  =  TBE1W/2M) failed to affect promoter activities in SW480 cells (Fig. 4D), suggesting that a single TBE (TBE1 or TBE2) may be necessary and sufficient to support FasL promoter function in APC-/- colon cancer cells.