Abstract
We have shown previously that diallyl trisulfide (DATS), a constituent of processed garlic, inhibits proliferation of PC-3 and DU145 human prostate cancer cells by causing G(2)-M phase cell cycle arrest in association with inhibition of cyclin-dependent kinase 1 activity and hyperphosphorylation of Cdc25C at Ser(216). Here, we report that DATS-treated PC-3 and DU145 cells are also arrested in mitosis as judged by microscopy following staining with anti-alpha-tubulin antibody and 4',6-diamidino-2-phenylindole and flow cytometric analysis of Ser(10) phosphorylation of histone H3. The DATS treatment caused activation of checkpoint kinase 1 and checkpoint kinase 2, which are intermediaries of DNA damage checkpoints and implicated in Ser(216) phosphorylation of Cdc25C. The diallyl trisulfide-induced Ser(216) phosphorylation of Cdc25C as well as mitotic arrest were significantly attenuated by knockdown of check-point kinase 1 protein in both PC-3 and DU145 cells. On the other hand, depletion of checkpoint kinase 2 protein did not have any appreciable effect on G(2) or M phase arrest or Cdc25C phosphorylation caused by diallyl trisulfide. The lack of a role of checkpoint kinase 2 in diallyl trisulfide-induced phosphorylation of Cdc25C or G(2)-M phase cell cycle arrest was confirmed using HCT-15 cells stably transfected with phosphorylation-deficient mutant (T68A mutant) of checkpoint kinase 2. In conclusion, the results of the present study suggest existence of a checkpoint kinase 1-dependent mechanism for diallyl trisulfide-induced mitotic arrest in human prostate cancer cells.
Highlights
Epidemiological studies continue to support the premise that dietary intake of Allium vegetables such as garlic may reduce the risk of different types of malignancies including cancer of the prostate [1,2,3,4,5], which is the second leading cause of cancerrelated deaths among men in the United States [6]
We explored this possibility by immunofluorescence microscopy following staining of control and DATStreated PC-3 cells with anti-␣-tubulin antibody and DAPI
diallyl trisulfide (DATS) Treatment Promoted Phosphorylation of checkpoint kinase 1 (Chk1) at Ser317 and checkpoint kinase 2 (Chk2) at Thr68 in PC-3 Cells—We have shown previously that the DATS-induced G2-M phase cell cycle arrest in PC-3 cells is associated with a marked increase in Ser216 phosphorylation of Cdc25C [31], which together with other Cdc25 family members plays an important role in activation of Cdk1cyclin B1 kinase [47,48,49]
Summary
Epidemiological studies continue to support the premise that dietary intake of Allium vegetables such as garlic may reduce the risk of different types of malignancies including cancer of the prostate [1,2,3,4,5], which is the second leading cause of cancerrelated deaths among men in the United States [6]. DADS inhibited proliferation of HCT-15 human colon cancer cells by causing G2-M phase cell cycle arrest and apoptosis induction (20 –22). We determined the effects of OSC analogues with varying oligosulfide chain length (diallyl sulfide, DADS, and DATS) on proliferation of human prostate cancer cells [29]. We have shown previously that DATS-induced G2-M phase cell cycle arrest in human prostate cancer cells is associated with reactive oxygen species-dependent destruction as well as hyperphosphorylation of Cdc25C at Ser216 [31]. The present study indicates that the DATS-induced mitotic arrest in human prostate cancer cells is regulated by Chk, which is an intermediary of DNA damage checkpoint [32,33,34]
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