STAT3 inhibits miR-219 expression and miR-219 inhibits ICOS expression. (A) Schematic representation of the miR-219 binding site in 3′-untranslated region of ICOS mRNA and the sequence complementarity of miR-219 and the ICOS 3′-untranslated region target sequence. (B) Schematic depiction of miR-219 gene and molecular structure. The potential STAT3 binding sites in the miR-219 gene 3′ region, including the promoter, are indicated by arrows. (C) miR-219 expression in the depicted T-cell lymphoma lines and PHA-stimulated PBMCs detected by quantitative RT-PCR. (D) STAT3 siRNA-induced miR-219 expression detected by quantitative RT-PCR. (E) Inhibitory effect of miR-219 mimic on ICOS expression by SUDHL-1 cells detected by quantitative RT-PCR. Cell treatment with miR-48 mimic was used as control. The number in parentheses indicates the percentage of ICOS expression inhibition by miR-219 mimic relative to the miR-48 mimic control.