H<sub>2</sub>O<sub>2</sub> inhibits proteasome activity and proteasome inhibitor lactacystin induces p62 up-regulation.

<p><b>(A)</b> ARPE-19 cells were treated with 200 or 400μM H<sub>2</sub>O<sub>2</sub> and then chymotrypsin-like proteasome activity was measured at 24h post-exposure using a fluorogenic substrate. Control (Ctrl) = No H<sub>2</sub>O<sub>2</sub> <b>(B)</b> Chymotrypsin-like proteasome activity was detected in RPE cells treated with the proteasome specific inhibitor lactacystin (4nM and 25μM, 12h). Ctrl = DMSO control <b>(C)</b> qRT-PCR was used to measure the p62 mRNA level following lactacystin treatment (25μM, 12h). Ctrl = DMSO control <b>(D)</b> p62 protein level was examined by western blot after proteasome specific inhibitor lactacystin (25μM, 12h) exposure. Ctrl = DMSO control. Data represent the mean + S.E.M. for three samples per group. Differences in means were considered statistically significant when p<0.05.</p>