Carcinogenesis Advance Access originally published online on June 23, 2009
Carcinogenesis 2009 30(10):1744-1753; doi:10.1093/carcin/bgp157
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Benzyl isothiocyanate-mediated generation of reactive oxygen species causes cell cycle arrest and induces apoptosis via activation of MAPK in human pancreatic cancer cells
Department of Biomedical and Pharmaceutical Sciences and Cancer Biology Center, School of Pharmacy, Texas Tech University Health Sciences Center, Suite 1103, 1406 Coulter Drive, Amarillo, TX 79106, USA
* To whom correspondence should be addressed. Tel: +806 356 4750 ext. 224; Fax: +806 356 4770; Email: sanjay.srivastava{at}ttuhsc.edu
In our previous studies, we have shown that benzyl isothiocyanate (BITC) inhibits the growth of human pancreatic cancer cells by inducing apoptosis. In the present study, we demonstrate the activation of all the three (MAPK) family members [extracellular signal-regulated protein kinase (ERK), c-jun N-terminal kinase (JNK) and P38] in response to BITC treatment. Exposure of Capan-2 cells with varying concentrations of BITC for 24 h resulted in the phosphorylation (activation) of ERK at Thr202/Tyr204, JNK at Thr183/Tyr185 and P38 at Thr180/Tyr182, leading to the induction of apoptosis. Similar MAPK activation was also observed in MiaPaCa-2 cells in response to BITC treatment. However, normal human pancreatic ductal epithelial cells did not show the activation of MAPK's and remained unaffected by BITC treatment. To confirm the role of ERK, JNK and P38 in BITC-induced G2/M arrest and apoptosis, Capan-2 cells were pre-treated with MAPK-specific inhibitors or MAPK8-short hairpin RNA (shRNA) prior to BITC treatment. Significant protection from BITC-induced G2/M arrest was observed in the cells pre-treated with MAPK kinase (MEK-1) but not JNK or P38 inhibitors. On the other hand, BITC-induced apoptosis was almost completely abrogated in the cells pre-treated with MEK-1, JNK or P38 inhibitors. Similarly, MAPK8-shRNA also offered almost complete protection against BITC-induced G2/M arrest and apoptosis. Furthermore, we observed that BITC treatment leads to the generation of reactive oxygen species (ROS) in Capan-2 and MiaPaCa-2 cells, which in part was orchestrated by depletion of reduced glutathione (GSH) level. Blocking ROS generation with N-acetyl-L-cysteine (NAC) significantly prevented GSH depletion and activation of ERK and JNK but not P38. Further, NAC or tiron prevented G2/M arrest by blocking G2/M regulatory proteins and completely protected the cells from BITC-induced apoptosis. Taken together, our results suggest that BITC-mediated G2/M arrest is mediated through ERK activation, whereas apoptosis is via ERK, JNK and P38.
Abbreviations: APF, aminophenyl fluorescein; BITC, benzyl isothiocyanate; Cdc25C, cell division cycle 25C; Cdk1, cyclin-dependent kinase-1; DMSO, dimethyl sulfoxide; ELISA, enzyme-linked immunosorbent assay; ERK, extracellular signal-regulated protein kinase; FBS, fetal bovine serum; GSH, glutathione; GSSG, oxidized GSH; HPDE-6, human pancreatic ductal epithelial cells; hROS, highly reactive oxygen species; JNK, c-jun N-terminal kinase; MAPK, mitogen-activated protein kinase; MEK-1, MAPK kinase; NAC, N-acetyl-L-cysteine; PARP, poly (ADP-ribose) polymerase; PSN, penicillin-streptomycin-neomycin; ROS, reactive oxygen species; shRNA, short hairpin RNA; SOD, superoxide dismutase
Received March 24, 2009; revised June 15, 2009; accepted June 16, 2009.