APT1 and APT2 are regulated by miR-138 and miR-424. Quantitative PCR was used to compare expression of miRNAs potentially regulating APT1 and APT2 in CLL cells (n = 19 [miR-138] or n = 7 [miR-424]) and healthy B cells (n = 9 [miR-138] or n = 5 [miR-424]). miR-138 and miR-424 are significantly downregulated in primary CLL cells (A). Luciferase assays were performed to analyze the binding of both miRNAs to the respective 3′-UTR of APT1 or APT2. It could be shown that both miRNAs are in principle able to regulate APT1 (n = 4) or APT2 expression (n = 3) (B). By western blotting it could be demonstrated that miR-138 regulates APT1 (n = 3) and miR-424 regulates APT2 protein expression (n = 3) (C). MiR-138 and miR-424 regulate APT1- and APT2-mRNA levels by reducing mRNA levels (D). Means are given with their SEM. The statistical significance was determined using the Student t test. *P < .05, **P < .01, or ***P < .001 were considered significant. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; SEM, standard error of the mean.