Oxidative stress in health and disease: role of PKCζ and p66Shc.

Reactive oxygen species (ROS) are short-living and highly reactive molecules formed by incomplete one-electron reduction of oxygen. Mitochondria produce low levels of ROS as an inevitable consequence of oxidative metabolism. Low levels of ROS are normally reduced by nonenzymatic and enzymatic oxidizing agents, such as glutathione, thioredoxin, superoxide dismutase (SOD), catalase and peroxidases. Oxidative stress results from exposure to high levels of ROS, which are not detoxified by cellular antioxidizing agents, and produces cellular damage due to the oxidation of cellular constituents. ROS, however play not only a damaging role: recent studies have demonstrated that they also actively participate in a diverse array of biological processes, including normal cell growth, induction and maintenance of the transformed state, and cellular senescence. Moreover, ROS can also provide a signaling function, by acting as an intracellular messenger involved in the transduction of the signaling of cytokines such as TNF-α and IL-1β. We focused our attention on the effect of ROS in the activities of two proteins: PKCζ and p66Shc. On the one hand, PKCζ is a serine-threonine kinase belonging to the atypical subfamily of PKC proteins. We showed that in an in vitro model redox stress induces PKCζ translocation from the cytosol, where it is located in resting conditions, to the nucleus. Nuclear PKCζ protects cells from apoptotic stimuli such as H2O2 or ceramide and this protective effect is reverted by the selective inhibition of the nuclear pool of the protein. The protective effect of nuclear PKCζ is involved in the chemoresistance of tumor cells to chemotherapic drugs, as demonstrated by the fact that the selective inhibitor of nuclear PKCζ can revert the chemoresistance, suggesting nuclear PKCζ as a suitable target in anticancer therapies. On the other hand p66Shc is a Shc protein involved in stress responses, in particular it is activated by redox stress and it produces ROS itself. Our purpose is to investigate a possible involvement of p66Shc in two different phenomena: autophagy and adipogenic transdifferentiation of skeletal muscle cells by comparing wt mice with p66Shc KO mice. Autophagy is a general term referring to pathways for the degradation of cellular constituents (cytosol and organelles) by the autophagolysosome; it is activated mainly by nutrient starvation and it plays a dual role: it is primarly a surviving mechanism, but it also leads to cell death (called type II cell death) thus possibly acting as an alternative to apoptosis. Starting from this notion, and from the fact that p66Shc KO cells are protected from apoptosis, we investigated a possible role of p66shc as a key element in the switch from apoptosis to autophagy. We observed that, while in wt cells redox stress induces apoptosis, cells lacking p66Shc in the same condition activate the autophagic pathway. We are now trying to investigate the biological effect of these observation. The second aspect of our work is the investigation of a putative role of p66Shc in the adipogenic transdifferentiation of skeletal muscle precursor cells. To this purpose we used an in vivo model and we observed that mice lacking p66Shc exposed to muscle damage (e.g. freeze injury or redox stress) show lower adipocyte accumulation than wt mice, thus suggesting a role of p66 in the activation of adipogenic differentiation pathway. The key purpose of this work is the evaluation of many different effects of ROS production, looking for possible molecular targets to fight pathological processes such as chemoresistance and adipogenic degeneration of skeletal muscle.