Search

Reactive oxygen species (ROS) and insulin signaling in the adipose tissue are critical determinants of aging and age-associated diseases. It is not clear, however, if they represent independent factors or they are mechanistically linked. We investigated the effects of ROS on insulin signaling using as model system the p66Shc-null mice. p66Shc is a redox enzyme that generates mitochondrial ROS and promotes aging in mammals. We report that insulin activates the redox enzyme activity of p66Shc specifically in adipocytes and that p66Shc-generated ROS regulate insulin signaling through multiple mechanisms, including AKT phosphorylation, Foxo localization, and regulation of selected insulin target genes. Deletion of p66Shc resulted in increased mitochondrial uncoupling and reduced triglyceride accumulation in adipocytes and in vivo increased metabolic rate and decreased fat mass and resistance to diet-induced obesity. In addition, p66Shc-/- mice showed impaired thermo-insulation. These findings demonstrate that p66Shc-generated ROS regulate the effect of insulin on the energetic metabolism in mice and suggest that intracellular oxidative stress might accelerate aging by favoring fat deposition and fat-related disorders. [ABSTRACT FROM AUTHOR]

All-trans-retinoic acid (RA) is a potent inhibitor of leukemia cell proliferation and induces differentiation of acute promyelocytic leukemia cells in vitro and in vivo. For RA to induce its biological effects in target cells, binding to specific retinoic acid nuclear receptors is required. The resulting complexes bind to RA-responsive elements (RAREs) in the promoters of RA-inducible genes to initiate gene transcription and to generate protein products that mediate the biological effects of RA. In this report, we provide evidence that a member of the protein kinase C (PKC) family of proteins, PKC delta, is activated during RA treatment of the NB-4 and HL-60 acute myeloid leukemia cell lines as well as the MCF-7 breast cancer cell line. Such RA-dependent phosphorylation was also observed in primary acute promyelocytic leukemia cells and resulted in activation of the kinase domain of PKC delta. In studies aimed at understanding the functional relevance of PKC delta in the induction of RA responses, we found that pharmacological inhibition of PKC delta (but not of other PKC isoforms) diminished RA-dependent gene transcription via RAREs. On the other hand, overexpression of a constitutively active form of the kinase strongly enhanced RA-dependent gene transcription via RAREs. Gel shift assays and chromatin immunoprecipitation studies demonstrated that PKC delta associated with retinoic acid receptor-alpha and was present in an RA-inducible protein complex that bound to RAREs. Pharmacological inhibition of PKC delta activity abrogated the induction of cell differentiation and growth inhibition of NB-4 blast cells, demonstrating that its function is required for such effects. Altogether, our data provide strong evidence that PKC delta is activated in an RA-dependent manner and plays a critical role in the generation of the biological effects of RA in malignant cells.