miR-21 binds to SMAD7 3′UTR. (A) The nucleotide sequence complementary to nt 2–5 of miR-21 in the 3′UTR of SMAD7 was mutated to the same sequence as that in miR-21 (from AGCT to TCGA). (B) Luciferase reporters containing wild-type and mutant 3′UTR of the SMAD7 gene were used for transfection with control miRNA or miR-21 precursors into bone marrow stromal HS-5 cells. Dual luciferase activity was measured and shows decreased luciferase activity caused by miR-21 that is abrogated by mutation in its binding site on the UTR (Student’s t-test, P = .001) compared with cells transfected with control mimics.