Similarly, increased Topo IIβ levels were also reported in an acute promyelocytic leukemia (APL) line that was resistant to treatment with retinoic acid, and these increased levels were attributed to protein kinase C-δ (PKCδ)-mediated phosphorylation of Topo IIβ [39,40]. This evidence concerns the gene PRKCD and acute promyelocytic leukemia.