To construct the luciferase reporter to screen the binding of miRNAs in the XIAP 3′UTR, 6.8 kb in length, we divided the whole XIAP 3′UTR into four fragments UTR1, UTR2, UTR3 and UTR4 (Figure 1). These four fragments, as well as the fragment containing two predicted miR-137 binding sites, and the predicted miR-137 binding site mutated fragments were fused to the Renilla luciferase reporter gene at the 3′UTR in the psiCHECK2 vector (Promega, Madison, WI, USA) with modified cloning sites. These constructs were named UTR1, UTR2, UTR3, UTR4, WT, site 1-MUT, site 2-MUT, and site (1+2) MUT. All of the miRNA expression vectors containing the miRNA precursors used in this study were described previously (Zhou et al, 2013b (link)). To overexpress XIAP, human XIAP cDNA without its native 3′UTR was cloned downstream of the CMV promoter in the lentiviral expression vector pCDH-CMV-MCS-EF1-copGFP (pCDH; System Biosciences, Mountain View, CA, USA), and the construct was named LV-XIAP. All of the primers employed above are listed in Supplementary Table S1. DNA sequencing was performed to confirm all of the constructs.