To investigate whether RBM1-151 was hydrolyzed by each of the five known ceramidases, the probe was tested on lysates from human AC-overexpressing melanoma A375 cells (A375/AC), rhNC, microsomes from HeLa overexpressing tetracycline-induced ACER1 or ACER2 (26), and lysates from ASAH2-null MEFs as a source of ACER3 (35) using the appropriate buffers (supplemental Table S1). Here, ACER3 is linked to melanoma.