Objective: To investigate the apoptotic effect of rhein on human proximal tubular epithelial cell line (HK-2) and the underlying mechanisms. Method: HK-2 cells were seeded in 96-well plates at an initial density of 4× 104 cells/mL for 24 h

and then the four different concentration of rhein (0

25

50

100 μmol · L-1) were applied to test cells for 12

24

48 h respectively. MTT assay was used to detect the viability of HK-2 cells. Rhein-induced apoptosis in HK-2 cells was evaluated by Hoechst 33258 staining and Flow cytometry. The expression of proto-oncogene c-jun(c-jun)

activating transcription factor 2(ATF-2) and cysteine proteinases with specificity for aspartic acid residues 3(Caspase-3) mRNA was detected by real-time quantitative polymerase chain reaction (RT-qPCR).The changes of phosphorylated c-jun N-terminal kinase (p-JNK)

c-jun N-terminal kinase(JNK)

phosphorylated p38 mitogen-activated protein kinase(p-p38 MAPK)

p38 mitogen-activated protein kinase (p38 MAPK) and Cleaved Caspase-3 protein were detected by Western blotting. The specific inhibitors of JNK and p38 MAPK were applied for identifying the roles of the corresponding signal pathways in rhein-induced apoptosis of HK-2 cells. Result: Rhein inhibited the viability of HK-2 cells in a dose-and time-dependent manners. The apoptosis rate of HK-2 cells in rhein groups was apparently increased. The RT-qPCR found that the expression of c-jun

ATF-2

Caspase-3 mRNA was significantly increased in rhein-treated groups. The results of Western blotting showed that there was no significant change in p38 and JNK protein

but an increasing trend in p-p38

p-JNK and Cleaved Caspase-3 was observed. After treatment with SP600125 (an inhibitor of JNK) and SB203580 (an inhibitor of p38) respectively

the apoptosis rates of rhein on HK-2 cells were significantly weak. Conclusion: Rhein induces apoptosis involving MAPK signal transduction pathway in HK-2 cells.