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Resistance to TNF-alpha cytotoxicity can be achieved through different signaling pathways in rat mesangial cells
Y L Guo1, B Kang, J R Williamson
1Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Abstract:
We reported previously that Ro-318220 blocked expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) induced by tumor necrosis factor-alpha (TNF-alpha) and subsequently caused apopotosis in mesangial cells (Y.-L. Guo, B. Kang, and J. R. Williamson. J. Biol. Chem. 273: 10362-10366, 1998). These data support our hypothesis that a TNF-alpha-inducible phosphatase may be responsible for preventing sustained activation of c-Jun NH2-terminal protein kinase (JNK) and consequent cell death in these cells (Y.-L. Guo, K. Baysal, B. Kang, L.-J. Yang, and J. R. Williamson. J. Biol. Chem. 273: 4027-4034, 1998). In this study, we investigated the involvement of protein kinase C (PKC) in regulation of MKP-1 expression in mesangial cells together with effects on viability. Although originally characterized as a PKC inhibitor, Ro-318220 inhibited TNF-alpha-induced MKP-1 expression through a mechanism other than blocking the PKC pathway. Furthermore, inhibition of the PKC pathway neither significantly affected TNF-alpha-induced MKP-1 expression nor made cells susceptible to toxic effect of TNF-alpha. Thus PKC activation is not essential for cells to achieve the resistance to TNF-alpha cytotoxicity displayed by normal mesangial cells. However, activation of PKC by phorbol 12-myristate 13-acetate (PMA) dramatically increased cellular resistance to the apoptotic effect of TNF-alpha. Coincidentally, PMA stimulated MKP-1 expression and suppressed JNK activation. Therefore, PMA-induced MKP-1 expression may contribute to the protective effect of PMA. These results provide a mechanistic explanation for previous documentation that PKC activation can rescue some cells from apopotosis.
Insights
Protein kinase C (PKC) activation protects mesangial cells from tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis by upregulating mitogen-activated protein kinase phosphatase-1 (MKP-1) and suppressing c-Jun NH2-terminal protein kinase (JNK) activation.
Area of Science:
- Cellular and Molecular Biology
- Immunology
- Biochemistry
Background:
- Previous studies indicated that Ro-318220 blocks tumor necrosis factor-alpha (TNF-alpha)-induced mitogen-activated protein kinase phosphatase-1 (MKP-1) expression, leading to mesangial cell apoptosis.
- A hypothesis suggested that a TNF-alpha-inducible phosphatase prevents sustained c-Jun NH2-terminal protein kinase (JNK) activation and subsequent cell death.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) in regulating MKP-1 expression and mesangial cell viability in response to TNF-alpha.
- To determine if PKC inhibition affects TNF-alpha-induced MKP-1 expression or cell susceptibility to TNF-alpha toxicity.
Main Methods:
- Investigated the involvement of PKC in MKP-1 regulation and mesangial cell viability.
- Utilized TNF-alpha to induce MKP-1 expression and apoptosis.
- Examined the effects of Ro-318220 (a PKC inhibitor) and phorbol 12-myristate 13-acetate (PMA) on MKP-1 expression, JNK activation, and cell survival.
Main Results:
- Ro-318220 inhibited TNF-alpha-induced MKP-1 expression via a non-PKC pathway.
- PKC pathway inhibition did not significantly alter TNF-alpha-induced MKP-1 expression or increase susceptibility to TNF-alpha.
- PMA activation of PKC significantly enhanced cellular resistance to TNF-alpha-induced apoptosis.
- PMA stimulated MKP-1 expression and suppressed JNK activation, suggesting a protective role for PMA-induced MKP-1.
Conclusions:
- PKC activation is not essential for the inherent resistance of mesangial cells to TNF-alpha cytotoxicity.
- PKC activation, via PMA, confers significant resistance to TNF-alpha-induced apoptosis.
- PMA-induced MKP-1 expression likely contributes to the protective effects of PKC activation against TNF-alpha-induced cell death.