Objective  To explore the role of receptor-interaction proteins (RIP) in phenethylisothiocyanate (PEITC)-induced apoptosis in human leukemia cells.   Methods  U937 cells were exposed to PEITC at various concentrations of 0

2

4

6 and 8 μmol/L for 3 and 6 h

or at 8 μmol/L for different time intervals of 1

3

6

9

12 and 24 h. Cells were stained with Annexin V/PI

and apoptosis was determined by using flow cytometry. Total protein extracts were prepared and subjected to Western blot assay using antibodies against poly(ADP-ribose)polymerase (PARP)

Caspase-3

Caspase-8

and RIP. β-actin was used to ensure equivalent loading.   Results  After exposure to PEITC at concentrations of 2

4

6 and 8 μmol/L for 3 h

U937 cells showed an increase in cell apoptosis (9%

25%

44% and 56% respectively). While when the time expanded to 6 h

the amount of apoptotic cells was increased to 16%

28%

51% and 82% respectively. A dose-dependent manner was seen when U937 cells were exposure to PEITC at different concentrations. When U937 cells were treated by PEITC at concentration of 8 μmol/L for 1

3

6

9

12

and 24 h

the apoptotic cells covered 12%

57%

79%

86%

90%

and 91% of all cells respectively

indicating a time-dependent manner. Western blot assay showed that PEITC caused the activation/cleavage of Caspase-3 and -8

and improved the PARP cleavage

and also decreased the expression of RIP. PEITC-induced apoptosis was proceeded by degradation of RIP.   Conclusion  Our results indicate that PEITC induces the apoptosis in human leukemia cells through a process that involves death receptor pathway

and RIP may play an important role in the apoptosis.