Feedback regulations of miR-21 and MAPKs via Pdcd4 and Spry1 in arsenite-induced malignant transformation of HELF cells.

<p>In arsenite-transformed HELF cells, miR-21 levels are up-regulated by the activations of ERK/NF-κB and JNK/c-Jun. miR-21 inhibits the target proteins, Pdcd4 and Spry1, which form two feedback regulation loops, miR-21-Spry1-ERK/NF-κB and miR-21-Pdcd4-JNK/c-Jun.