The effect of cellular oxidative stress on PTEN interactions

Redox sensing is a complex process that is essential for cellular homeostasis and survival. When cells experience oxidative stress, intracellular proteins undergo redox changes that affect signaling patterns, mediating diverse cellular responses. Phosphatase and tensin homolog (PTEN) is a redox-sensitive, dual-specificity protein phosphatase involved in regulating the PI3K/Akt pathway and thus a range of cellular processes including metabolism, apoptosis, cell proliferation and survival. We recently showed that the PTEN interactome was sensitive to redox changes in the protein in vitro, but this effect has not been investigated in vivo.

Aims
HCT116 cells were treated with H2O2 concentrations from 1–10 mM to induce oxidative stress and the effect on cell viability was examined using the XTT assay. Under the conditions tested, even at the highest concentration only a minimal decrease in viability was observed (~10%), so for subsequent experiments cells were treated with 1–5 mM H2O2 for 30 mins. Activation of the Akt signaling pathway (measured by phospho-Akt) and interaction with the key redox proteins thioredoxin (Trx) and peroxyredoxin (Prdx) was studied by (co)-immunoprecipitation and Western blotting to examine the effect of H2O2 treatment on interaction between PTEN and proteins identified in the in vitro screen.

Results
Changes were seen in the levels of Trx and Prdx dimers, which appeared to decrease following oxidative stress. Interestingly, while moderate levels of H2O2 (1 mM) induced activation of the Akt pathway, treatment with higher concentrations caused a decrease in p-Akt levels. This suggests that oxidation of PTEN during moderate oxidative stress inhibits the PI3K/Akt pathway, but under more severe conditions this effect is reversed. Further work is required to identify the mechanisms of this effect.