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Insulin-like growth factor 1 inhibits apoptosis using the phosphatidylinositol 3'-kinase and mitogen-activated
M Párrizas1, A R Saltiel, D LeRoith
1Diabetes Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Abstract:
The role of insulin-like growth factor 1 (IGF-1) in preventing apoptosis was examined in differentiated PC12 cells. Induction of differentiation was achieved using nerve growth factor, and apoptosis was provoked by serum withdrawal. After 4-6 h of serum deprivation, apoptosis was initiated, concomitant with a 30% decrease in cell number and a 75% decrease in MTT activity. IGF-1 was capable of preventing apoptosis at concentrations as low as 10(-9) M and as early as 4 h. The phosphatidylinositol 3' (PI3')-kinase inhibitors wortmannin (at concentrations of 10(-8) M) and LY294002 (10(-6) M) blocked the effect of IGF-1. The pp70 S6 kinase (pp70S6K) inhibitor rapamycin (10(-8) M) was, however, less effective in blocking IGF-1 action. Moreover, stable transfection of a dominant-negative p85 (subunit of PI3'-kinase) construct in PC12 cells enhanced apoptosis provoked by serum deprivation. Interestingly, in the cells overexpressing the dominant-negative p85 protein, IGF-1 was still capable of inhibiting apoptosis, suggesting the existence of a second pathway involved in the IGF-1 effect. Blocking the mitogen-activated protein kinase pathway with the specific mitogen-activated protein kinase/extracellular-response kinase kinase inhibitor PD098059 (10(-5) M) inhibited the IGF-1 effect. When wortmannin and PD098059 were given together, the effect was synergistic. The results presented here suggest that IGF-1 is capable of preventing apoptosis by activation of multiple signal transduction pathways.
Insights
Insulin-like growth factor 1 (IGF-1) prevents cell death (apoptosis) in nerve cells by activating multiple signaling pathways, including PI3-kinase and MAPK. This protective effect is robust and occurs even when one pathway is blocked.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Apoptosis, or programmed cell death, is a critical process in cellular homeostasis.
- Insulin-like growth factor 1 (IGF-1) is known to play a role in cell survival.
- PC12 cells are a widely used model for studying neuronal differentiation and survival.
Purpose of the Study:
- To investigate the role of IGF-1 in preventing apoptosis in differentiated PC12 cells.
- To elucidate the specific signaling pathways involved in IGF-1-mediated cell survival.
Main Methods:
- PC12 cells were differentiated using nerve growth factor.
- Apoptosis was induced by serum withdrawal.
- The effects of IGF-1 and various pathway inhibitors (wortmannin, LY294002, rapamycin, PD098059) were assessed.
- Stable transfection with a dominant-negative PI3-kinase construct was performed.
Main Results:
- IGF-1 effectively prevented apoptosis in a dose- and time-dependent manner.
- Phosphatidylinositol 3' (PI3')-kinase inhibitors blocked the anti-apoptotic effect of IGF-1.
- Mitogen-activated protein kinase (MAPK) pathway inhibition also reduced IGF-1's protective effect.
- A dominant-negative PI3-kinase construct enhanced apoptosis, but IGF-1 still provided protection, suggesting an alternative pathway.
Conclusions:
- IGF-1 prevents apoptosis in differentiated PC12 cells through the activation of multiple signaling pathways.
- Both the PI3-kinase and MAPK pathways are involved in IGF-1-mediated cell survival.
- The findings highlight the complex signaling network underlying IGF-1's neuroprotective role.