PTGS1 and malignant colon neoplasm: To determine if there was any correlation between the basal expression level of FasL and the EP1 receptor, five different colon cancer cell lines were grown in complete media and the expression of COX-1, COX-2, FasL and EP1 was assessed by Western blotting (Figure 6A), whereas PGE2 secretion was determined by ELISA (Figure 6B).