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Published on: December 7, 2021
A stress survival response in retinal cells mediated through inhibition of the serine/threonine phosphatase PP2A
Sorcha Finnegan1, Ashley M Mackey, Thomas G Cotter
1Biochemistry Department, Biosciences Institute, University College Cork, Cork, Ireland.
Abstract:
Cell survival signalling involving the PI3K/Akt survival pathway can be negatively regulated by several phosphatases including PP2A. When retinal-derived 661W cells were subjected to trophic factor deprivation this initiated a survival response through inhibition of the activity of PP2A and subsequent upregulation of the Erk and Akt survival pathways. We show this survival response via inhibition of PP2A activity was due in part to increased reactive oxygen species production when retinal cells were deprived of trophic factors. Inhibition of PP2A activity was mediated by a rapid and transient increase in phosphorylation at Tyr307, accompanied by an increase in demethylation and a decrease in the methylated form. Pre-treatment with N-acetyl-L-cysteine, which is involved in scavenging reactive oxygen species, prevented PP2A inhibition and subsequent upregulation of survival pathways. Pre-treatment with the Src family kinase inhibitor PP2 resulted in approximately 50% reduction in cellular levels of phospho-PP2A in trophic factor-deprived 661W cells, suggesting an Src tyrosine kinase had a role to play in this redox regulation of cell survival. We observed similar events in the rd10 mouse retina where there was an increased survival response prior to retinal cell death mediated through an increase in both phospho-PP2A and phospho-Gsk. Together, these results demonstrate that when retinal cells are stressed there is an initial struggle to survive, mediated through inhibition of PP2A and subsequent upregulation of survival pathways, and that these events occur simultaneously with production of reactive oxygen species, thus suggesting an important cell-signalling role for reactive oxygen species.
Insights
Retinal cells under stress activate survival pathways by inhibiting protein phosphatase 2A (PP2A) via reactive oxygen species (ROS). This initial survival response involves upregulation of Erk and Akt pathways, suggesting a key role for ROS in cell signaling.
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Cell survival is regulated by signaling pathways like PI3K/Akt.
- Protein phosphatase 2A (PP2A) is a key negative regulator of these survival pathways.
- Understanding stress responses in retinal cells is crucial for neuroprotection.
Purpose of the Study:
- To investigate the role of PP2A inhibition in retinal cell survival under stress.
- To elucidate the involvement of reactive oxygen species (ROS) in this survival mechanism.
- To explore the upstream regulators of PP2A inhibition in stressed retinal cells.
Main Methods:
- Utilized 661W retinal cell line and rd10 mouse retina model.
- Induced stress via trophic factor deprivation.
- Assessed PP2A activity, phosphorylation (Tyr307), methylation, and ROS production.
- Employed N-acetyl-L-cysteine (ROS scavenger) and PP2 (Src kinase inhibitor) for pre-treatment.
Main Results:
- Trophic factor deprivation inhibited PP2A activity in 661W cells, upregulating Erk and Akt survival pathways.
- PP2A inhibition was linked to increased ROS production and altered PP2A phosphorylation/methylation.
- N-acetyl-L-cysteine blocked PP2A inhibition and survival pathway activation.
- Src family kinase inhibition reduced phospho-PP2A levels, indicating a role in redox regulation.
- Similar PP2A and Gsk3beta phosphorylation was observed in rd10 mouse retinas prior to cell death.
Conclusions:
- Stressed retinal cells initially attempt to survive by inhibiting PP2A, leading to Erk and Akt pathway activation.
- Reactive oxygen species play a significant role in mediating PP2A inhibition during cellular stress.
- Src family kinases are implicated in the redox regulation of PP2A during retinal cell stress.
- These findings highlight an early survival mechanism in retinal cells involving ROS and PP2A signaling.
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