Pharicin B stabilizes RAR-α protein in AML cells. (A) Chemical structure of pharicin B. (B) NB4, U937, or THP-1 cells were incubated with 2μM of pharicin B for hours, as indicated. The RAR-α/PML-RAR-α protein was detected by anti–RAR-α antibody with β-actin as the loading control. The number on the bottom indicates signal intensity of RAR-α or PML-RAR-α protein against β-actin. (C) NB4 cells were stably transfected with FLAG-RAR-α or the negative control (NC) vector (top panel). Pulse-chase analysis of catabolism of FLAG-RAR-α in the presence or absence of pharicin B was performed in NB4^FLAG-RARα cells (bottom panel). The number on the bottom indicates the signal intensity of the FLAG-RAR-α relative to untreated cells, which was designated as 1. (D) NB4, U937, or THP-1 cells were incubated with 2μM of pharicin B for the number of hours indicated, and RXR-α protein was detected by anti–RXR-α antibody with β-actin as the loading control. The number on the bottom indicates signal intensity of RXR-α protein against β-actin. The arrow (<) points to an unknown band responsive to anti–RXR-α antibody. All experiments were repeated 3 times.