Figure 6(b) confirms that rottlerin treatment inhibited PKCδ in response to ATRA in NB4 cells. To provide further link between PKCδ and PKR we knockdown PKCδ by a specific siRNA and found that inhibition of PKCδ expression and reduced activity (phosphorylation) of PKR (Thr446) (Figure 7(c) and densitometry, right panel), indicating that PKCδ regulates PKR activity/phosphorylation in APL cells. Here, EIF2AK2 is linked to acute promyelocytic leukemia.