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SEK1-dependent JNK1 activation prolongs cell survival during G-Rh2-induced apoptosis
Young-Mi Ham1, Kwang-Hoon Chun, Joon-Seok Choi
1Division of Pharmaceutical Biosciences, College of Pharmacy, Research Institute of Pharmaceutical Sciences, Seoul National University, San 56-1, Shillim-Dong, Kwanak-Gu, 151-742, Seoul, Republic of Korea.
Abstract:
We provide here evidence that c-Jun N-terminal protein kinase 1 (JNK1) activity is differentially up-regulated during apoptosis of SK-HEP-1 cells after treatment with ginsenoside Rh2 (G-Rh2). The G-Rh2-mediated JNK1 activation that occurred for the first 10-30min was associated with SEK1 activity, but thereafter, the sustained activation was associated not with SEK1 activity, but with proteolytic cleavage of JNK1-associated p21(WAF1/CIP1). Supporting this is that the expression of the dominant negative SEK1 mutant effectively blocked the early JNK1 activation phase but did not alter the sustained activation phase or apoptosis. Furthermore, expression of p21D112N, an uncleavable mutant of p21(WAF1/CIP1), suppressed the later JNK1 activation. Moreover, the stable overexpression of ectopic JNK1 suppressed apoptosis while expression of the dominant negative JNK1 mutant promoted it. We propose that the early SEK1-associated JNK1 activation phase acts to prolong cell survival in response to apoptosis-inducing agents, thereby serving as an intervening checkpoint prior to the commitment to apoptosis.
Insights
Ginsenoside Rh2 (G-Rh2) triggers c-Jun N-terminal protein kinase 1 (JNK1) activation in SK-HEP-1 cells. Early JNK1 activation promotes cell survival, while later sustained activation is linked to apoptosis.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Apoptosis is a critical cellular process.
- Ginsenoside Rh2 (G-Rh2) is a compound with potential therapeutic properties.
- The role of c-Jun N-terminal protein kinase 1 (JNK1) in apoptosis is complex and requires further elucidation.
Purpose of the Study:
- To investigate the role of JNK1 activation in G-Rh2-induced apoptosis of SK-HEP-1 cells.
- To differentiate the mechanisms underlying early and sustained JNK1 activation.
- To determine the involvement of SEK1 and p21(WAF1/CIP1) in G-Rh2-mediated JNK1 signaling.
Main Methods:
- Treatment of SK-HEP-1 cells with G-Rh2.
- Analysis of JNK1 activity and its association with SEK1 and p21(WAF1/CIP1).
- Expression of dominant-negative SEK1 and uncleavable p21(WAF1/CIP1) mutants.
- Overexpression of ectopic JNK1 and dominant-negative JNK1 mutants.
Main Results:
- G-Rh2 treatment induced differential JNK1 activation in SK-HEP-1 cells.
- Early JNK1 activation (10-30 min) was SEK1-dependent, while sustained activation involved p21(WAF1/CIP1) cleavage.
- Dominant-negative SEK1 blocked early JNK1 activation but not sustained activation or apoptosis.
- Uncleavable p21(WAF1/CIP1) mutant suppressed later JNK1 activation.
- JNK1 overexpression suppressed apoptosis, while dominant-negative JNK1 promoted it.
Conclusions:
- The early SEK1-associated JNK1 activation phase may prolong cell survival.
- Sustained JNK1 activation, linked to p21(WAF1/CIP1) cleavage, is associated with apoptosis commitment.
- JNK1 acts as a critical checkpoint in the cellular response to apoptosis-inducing agents like G-Rh2.