| Oncogene expression in normal cells can cause an irreversible growth arrest called oncogene-induced senescence (OIS), which serves as a barrier to cancer initiation. Elevated reactive oxygen species (ROS) have been detected in most senescent cells and are thought to play a causal role in OIS. ROS are believed to have a second messenger function in transducing signals, however their molecular role in senescence remains elusive. We hypothesize that PTPs, which are prone to redox regulation, act as specific target of ROS and the redox regulation of PTPs mediates the signaling transduction in oncogene-induced senescence.;In our study, we utilized a modified cysteine labeling assay to profile the PTPs undergoing reversible oxidation in senescent cells. We demonstrated that PTP1B underwent redox regulation during oncogenic RAS (H-RASV12)-induced senescence in IMR90 cells. Inhibition of PTP1B function accelerated, and overexpressing PTP1B attenuated, H-RASV12-induced senescence. Furthermore, using the PTP1B substrate trapping mutant strategy, we found that AGO2, an Argonaute protein which is required for RISC complex function in the RNAi pathway, is a substrate of PTP1B in senescent cells. Reversible oxidation of PTP1B during senescence caused hyper-phosphorylation of AGO2 on its Y393 site. Phosphorylation of AGO2 at Tyr 393 inhibited its loading with microRNAs (miRNA) and thus miRNA-mediated gene silencing, which counteracted the function of H-RASV12-induced oncogenic miRNAs. The decrease in loading of miRNA targeted against p21 facilitated the de-repression of p21 translation and hence provoked senescence onset.;In this project, we revealed a novel mechanism that ROS promotes senescence through inactivation of PTP1B thereby enhancing tyrosine phosphorylation of AGO2 and altering translation repression. We demonstrated PTP1B is important in regulating miRNA pathway and OIS. The novel ROS/PTP1B/Ago2 pathway identified in our study might provide a potential mechanism for the development of cancer therapeutics. |
