Role of Cdc25C phosphatase in benzyl isothiocyanate-mediated G2/M arrest in pancreatic cancer cells.

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Epidemiological studies continue to support the existence of an inverse relationship between dietary intake of cruciferous vegetables and incidence of various types of cancer including pancreatic cancer. Recent studies including those from our laboratory suggested that benzyl isothiocyanate (BITC), a constituent of cruciferous vegetables, could inhibit the growth of cultured cancer cells. However, the exact mechanism by which BITC exerts antiproliferative effects is not clear. We therefore, sought to determine the mechanism of BITC-mediated growth arrest in Capan-2 human pancreatic cancer cells. We found that BITC has an antiproliferative effect on Capan-2 cells with an IC₅₀ of about 5 μM, causes cell cycle arrest in G2/M phase and induces apoptosis in a dose-dependent manner. Our results demonstrate that BITC causes irreversible cell cycle arrest in these cells, which is associated with down regulation of the expression of key G2/M cell cycle regulatory proteins such as cdk1, cyclinB1 and Cdc25C as well as phosphorylation of cdk1 and Cdc25C. The BITC-mediated drastic reduction in the level of Cdc25C was almost completely blocked when Capan-2 cells were pretreated with proteasome inhibitor lactacystin. These results suggest that BITC-mediated down-regulation of Cdc25C may involve the proteasomal degradation pathway. Interestingly, lactacystin pretreatment partially protected Capan-2 cells from BITC-induced apoptosis. Taken together our results suggest that BITC-induced cell growth arrest and apoptosis may in part, mediated by Cdc25C. [Supported in part by RO1 grant CA 106953 (to S.K.S.) awarded by the National Cancer Institute].