MCL1 and acute lymphoblastic leukemia: Considering that fenretinide promotes MCL-1 degradation in ALL cell lines [18], the possibility arises that the fenretinide-induced apoptosis may involve PKC δ. In the present study, we examined PKC δ expression and cleavage and MCL-1 expression in response to fenretinide in three ALL cell lines (REH, CCRF-CEM, and MOLT4) and in a Mixed Lineage Leukemia (MLL) cell line (RS4;11).