| Triptolide Inhibits the Proliferation of Immortalized HT22 Hippocampal Cells Via Persistent Activation of Extracellular Signal-Regulated Kinase-1/2 by Down-Regulating Mitogen-Activated Protein Kinase Phosphatase-1 Expression. |
| Hee Sang Koo, Sung Don Kang, Ju Hwan Lee, Nam Ho Kim, Hun Taeg Chung, Hyun Ock Pae |
1Department of Neurosurgery, Wonkwang University School of Medicine, Iksan, Korea.
2Department of Anesthesiology and Pain Medicine, Wonkwang University School of Medicine, Iksan, Korea.
3Department of Cardiovascular Medicine, Wonkwang University Hospital, Iksan, Korea.
4Department of Biological Science, University of Ulsan College of Medicine, Ulsan, Korea.
5Department of Microbiology and Immunology, Wonkwang University School of Medicine, Iksan, Korea. hopae@wku.ac.kr |
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| ABSTRACT |
OBJECTIVE
Triptolide (TP) has been reported to suppress the expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), of which main function is to inactivate the extracellular signal-regulated kinase-1/2 (ERK-1/2), the p38 MAPK and the c-Jun N-terminal kinase-1/2 (JNK-1/2), and to exert antiproliferative and pro-apoptotic activities. However, the mechanisms underlying antiproliferative and pro-apoptotic activities of TP are not fully understood. The purpose of this study was to examine whether the down-regulation of MKP-1 expression by TP would account for antiproliferative activity of TP in immortalized HT22 hippocampal cells. METHODS: MKP-1 expression and MAPK phosphorylation were analyzed by Western blot. Cell proliferation was assessed by 3H-thymidine incorporation.
Small interfering RNA (siRNA) against MKP-1, vanadate (a phosphatase inhibitor), U0126 (a specific inhibitor for ERK-1/2), SB203580 (a specific inhibitor for p38 MAPK), and SP600125 (a specific inhibitor for JNK-1/2) were employed to evaluate a possible mechanism of antiproliferative action of TP. RESULTS: At its non-cytotoxic dose, TP suppressed MKP-1 expression, reduced cell growth, and induced persistent ERK-1/2 activation. Similar growth inhibition and ERK-1/2 activation were observed when MKP-1 expression was blocked by MKP-1 siRNA and its activity was inhibited by vanadate.
The antiproliferative effects of TP, MKP-1 siRNA, and vanadate were significantly abolished by U0126, but not by SB203580 or SP600125. CONCLUSION: Our findings suggest that TP inhibits the growth of immortalized HT22 hippocampal cells via persistent ERK-1/2 activation by suppressing MKP-1 expression. Additionally, this study provides evidence supporting that MKP-1 may play an important role in regulation of neuronal cell growth. |
| Key Words:
Triptolide; HT22 hippocampal cell; Mitogen-activated protein kinase phosphatase-1; Extracellular signal-regulated kinase-1/2; Mitogen-activated protein kinase; Proliferation |
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