XIAP and B-cell chronic lymphocytic leukemia: Whether in CLL cells, Notch receptors act directly on Mcl-1 protein to stabilize it, as Notch1 does to stabilize XIAP protein [16], or indirectly, by influencing some of the pathways which regulate Mcl-1 proteasome-mediated degradation in these cells, including the Syk/PKCδ [45] and AKT/GSK3 [46] pathways, remains to be defined.