YY1 and acute myeloid leukemia: On the one hand, YY1 is a negative regulator of let-7a, a tumor suppressor miRNA that inhibits the expression of anti-apoptotic protein B-cell lymphoma-extra-large (BCL-xL) in chemoresistance in acute myeloid leukemia 126; YY1 is also a negative regulator of miR-29b, a suppressor of tumor proliferation in rhabdomyosarcoma 125.