PTGS2 and breast cancer: To investigate if the amounts of adenovirus-encoded miRNA expressed and processed in the RNAi machinery were sufficient for effective gene silencing, we measured expression levels of validated miR-1 and miR-26b target genes in infected cancer cells.19, 20, 21, 22 MDA-MB-231 breast cancer cells, which express high endogenous levels of miR-1 target genes FOXP1 and MET as well as miR-26b target gene PTGS2, were infected with AdΔ24E3-U6.pri-miR-1 or AdΔ24E3-U6.pri-miR-26b, and FOXP1, MET, and PTGS2 mRNA was quantified by qRT-PCR.