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Selective involvement of the PI3K/PKB/bad pathway in retinal cell death
Claudia B L Campos1, Pierre-André Bédard, Rafael Linden
1Instituto de Biofísica da UFRJ, CCS, bloco G, Cidade Universitaria, Rio de Janeiro, RJ, Brasil 21949-900.
Abstract:
The phosphoinositide-3-kinase (PI3K)/protein kinase B (PKB)/Bad signal transduction pathway is engaged in the control of apoptosis in many different cell types, particularly through phosphorylation of the Bcl-2 family protein Bad. We examined the involvement of this pathway in the control of programmed cell death in the retina of developing rats. PKB is constitutively phosphorylated in retinal tissue in vitro, whereas Bad was dephosphorylated both in Ser112 and Ser136. Cell death induced by either the PI3K inhibitor LY294002, or the general kinase inhibitor 2-aminopurine, were followed by PKB dephosphorylation, but PKB was not modulated during cell death induced by the protein synthesis inhibitor anisomycin. Treatment of retinal tissue cultures with forskolin, which increases intracellular levels of cAMP, partially blocked apoptosis induced by both anisomycin and 2-aminopurine, but not by LY294002, whereas forskolin invariably induced phosphorylation of Bad on both Ser112 and Ser136. The data suggest that Bad may be engaged in survival pathways in the immature retina, but pathways other than PI3K/PKB/Bad, and phosphorylation sites other than Ser112 and Ser136 in the Bad protein control cell survival in retinal tissue.
Insights
The phosphoinositide-3-kinase (PI3K)/protein kinase B (PKB)/Bad pathway regulates apoptosis. In developing rat retinas, Bad phosphorylation, not PI3K/PKB activity, influences cell survival, suggesting alternative pathways are involved.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- The PI3K/PKB/Bad pathway is crucial for apoptosis regulation in various cell types.
- This pathway often involves the phosphorylation of the Bcl-2 family protein Bad.
Purpose of the Study:
- To investigate the role of the PI3K/PKB/Bad pathway in programmed cell death within developing rat retinas.
- To determine if Bad phosphorylation sites Ser112 and Ser136 are involved in retinal cell survival.
Main Methods:
- Cultured retinal tissue from developing rats.
- Inhibition of PI3K with LY294002 and general kinases with 2-aminopurine.
- Induction of apoptosis using LY294002, 2-aminopurine, and anisomycin.
- Treatment with forskolin to modulate cAMP levels and assess effects on apoptosis and Bad phosphorylation.
Main Results:
- PKB was constitutively phosphorylated, while Bad was dephosphorylated at Ser112 and Ser136 in retinal tissue.
- PI3K inhibition or general kinase inhibition led to PKB dephosphorylation, but anisomycin did not affect PKB levels.
- Forskolin partially inhibited apoptosis induced by anisomycin and 2-aminopurine, but not LY294002, and induced Bad phosphorylation at Ser112 and Ser136.
Conclusions:
- Bad may function in survival pathways in the immature retina.
- Cell survival in retinal tissue appears to be controlled by pathways independent of PI3K/PKB/Bad.
- Phosphorylation sites other than Ser112 and Ser136 on Bad may play a role in regulating cell survival in the retina.