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PTEN/MMAC1 overexpression decreases insulin-like growth factor-I-mediated protection from apoptosis in neuroblastoma
C M van Golen1, T S Schwab, K M Ignatoski
1University of Michigan Department of Neurology, Neuroscience Program, Ann Arbor, Michigan 48109, USA.
Abstract:
Insulin-like growth factor I (IGF-I) protects cells from apoptosis primarily through the action of phosphatidylinositol-3 kinase and the downstream serine/threonine kinase Akt. The PTEN gene product, a protein which dephosphorylates phosphatidylinositol lipids, prevents activation of Akt and regulates several cellular functions, including cell cycle progression, cell migration, and survival from apoptosis. In this study, PTEN overexpression decreases IGF-I-induced Akt activity, enhances serum withdrawal-induced apoptosis, and decreases IGF-I protection and cell growth in SHEP cells. The PTEN lipid phosphatase mutant G129E fails to inhibit IGF-I-stimulated Akt activity and protection from apoptosis. The C124S mutation, which abolishes both lipid and protein phosphatase activity, fails to inhibit Akt activity and IGF-I protection against hyperosmotic-induced apoptosis but still inhibits growth and IGF-I protection against serum withdrawal-induced apoptosis. These data suggest a role for PTEN in modulating the effect of IGF-I on Akt activity, neuroblastoma cell growth, and protection against apoptotic stimuli.
Insights
Insulin-like growth factor I (IGF-I) signaling is modulated by PTEN, which impacts cell survival and growth. PTEN
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Insulin-like growth factor I (IGF-I) promotes cell survival by activating phosphatidylinositol-3 kinase and Akt.
- PTEN negatively regulates the PI3K/Akt pathway, controlling cell cycle, migration, and apoptosis.
- Understanding PTEN's role is crucial for neuroblastoma and cancer research.
Purpose of the Study:
- To investigate the role of PTEN in modulating IGF-I signaling and cellular responses.
- To determine how PTEN mutations affect IGF-I-mediated Akt activation and apoptosis.
- To elucidate PTEN's function in neuroblastoma cell growth and survival.
Main Methods:
- Overexpression of wild-type PTEN and PTEN mutants (G129E, C124S) in SHEP neuroblastoma cells.
- Assessment of Akt activity using biochemical assays.
- Evaluation of apoptosis induction via serum withdrawal and hyperosmotic stress.
- Measurement of cell growth and IGF-I protection.
Main Results:
- PTEN overexpression inhibited IGF-I-induced Akt activity, enhanced apoptosis, and reduced cell growth and IGF-I protection.
- The PTEN lipid phosphatase-dead mutant (G129E) failed to block IGF-I-stimulated Akt activity and apoptosis protection.
- The PTEN C124S mutant (lacking both lipid and protein phosphatase activity) inhibited growth and serum withdrawal-induced apoptosis but not hyperosmotic-induced apoptosis or Akt activity.
Conclusions:
- PTEN plays a significant role in regulating IGF-I's effects on Akt activity, neuroblastoma cell growth, and apoptosis.
- PTEN's lipid phosphatase activity is critical for inhibiting IGF-I-mediated Akt activation and promoting apoptosis.
- Specific PTEN mutations differentially affect cellular responses to IGF-I and apoptotic stimuli.