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

• Published in: Journal of Korean Neurosurgical Society Vol. 46; no. 4; pp. 389 - 396
• Main Authors: Koo, Hee Sang, Kang, Sung Don, Lee, Ju Hwan, Kim, Nam-Ho, Chung, Hun-Taeg, Pae, Hyun-Ock
• Format: Journal Article
• Language: English
• Published: Korea (South) The Korean Neurosurgical Society 01.10.2009; 대한신경외과학회
• Subjects: Laboratory Investigation; 신경외과학; Extracellular signal-regulated kinase-1/2; Mitogen-activated protein kinase; Mitogen-activated protein kinase phosphatase-1; Proliferation; HT22 hippocampal cell; Triptolide
• ISSN: 2005-3711; 1598-7876; 1598-7876
• DOI: 10.3340/jkns.2009.46.4.389

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. MKP-1 expression and MAPK phosphorylation were analyzed by Western blot. Cell proliferation was assessed by (3)H-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. 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. 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.