MERTK and leukemia: When the human leukemia monocytic cell line THP-1 was treated with 100 ng/mL of phorbol 12-myristate 13-acetate (PMA) for up to 48 h to activate Protein Kinase C (PKC) and differentiate monocytes into macrophages, Mertk was observed to be robustly up-regulated between 12 and 24 h, reaching a maximum at 24 h, consistent with previous observations that Mertk is up-regulated in differentiated macrophages (Figure 1A, top panel) [11,15].