Abstract
Purpose: Cyclooxygenase-2 (COX-2) is involved in antiapoptosis signaling, and its induction may require activation of protein kinase C (PKC). Safingol (SAF), a PKC inhibitor, has been shown to enhance apoptosis induced by mitomycin-C (MMC) in human gastric cancer MKN-74 cells. The aim of this study was to identify the role of COX-2 in MMC-induced apoptosis in MKN- 74 cells. Methods: Protein expression of COX-2 and Bcl-2 and activation of PKCα were examined by Western blot analysis. Apoptosis induction was examined by staining with bisbenzimide trihydrochloride (Hoechst-33258) of condensed chromatin, which characterizes the cells undergoing apoptosis. COX- 2 mRNA levels were examined by Northern blot analysis. Results: After exposure for 1-2 h to 1 μg/ml MMC, upregulation of COX-2 and Bcl-2 protein expression was noted. The activation of PKCα occurred within 1 h of MMC exposure, and temporally preceded the induction of COX-2. Similar results were observed in cells exposed to the PKC activator, 3-phorbol 12-myristate 13-acetate. Cotreatment with SAF and MMC abolished the induction of COX-2 by MMC. Furthermore, NS-398, a selective COX-2 inhibitor, significantly enhanced MMC-induced apoptosis by fivefold from 4 ± 2% (MMC alone) to 20 ± 2% (MMC plus NS-398). There was no discernible change in COX-2 mRNA levels after a 2- h exposure to MMC but a twofold increase after a 24-h exposure. Conclusions: MMC upregulates COX-2 expression, which appears to be an antiapoptotic signal downstream of PKC. Selective inhibition of COX-2 can therefore provide a novel way to enhance MMC-induced apoptosis independent of inhibiting PKC.
Original language | English |
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Pages (from-to) | 389-396 |
Number of pages | 8 |
Journal | Cancer Chemotherapy and Pharmacology |
Volume | 45 |
Issue number | 5 |
DOIs | |
State | Published - 2000 |
Externally published | Yes |
Keywords
- Bcl-2
- Gene expression
- Phorbol esters
- Protein kinase C
- Safingol