ABSTRACT
Myc oncoproteins are commonly upregulated in human cancers of different organ origins, stabilized by Aurora A, degraded through ubiquitin-proteasome pathway-mediated proteolysis, and exert oncogenic effects by modulating gene and protein expression. Histone deacetylases are emerging as targets for cancer therapy. Here we demonstrated that the class III histone deacetylase SIRT2 was upregulated by N-Myc in neuroblastoma cells and by c-Myc in pancreatic cancer cells, and that SIRT2 enhanced N-Myc and c-Myc protein stability and promoted cancer cell proliferation. Affymetrix gene array studies revealed that the gene most significantly repressed by SIRT2 was the ubiquitin-protein ligase NEDD4. Consistent with this finding, SIRT2 repressed NEDD4 gene expression by directly binding to the NEDD4 gene core promoter and deacetylating histone H4 lysine 16. Importantly, NEDD4 directly bound to Myc oncoproteins and targeted Myc oncoproteins for ubiquitination and degradation, and small-molecule SIRT2 inhibitors reactivated NEDD4 gene expression, reduced N-Myc and c-Myc protein expression, and suppressed neuroblastoma and pancreatic cancer cell proliferation. Additionally, SIRT2 upregulated and small-molecule SIRT2 inhibitors decreased Aurora A expression. Our data reveal a novel pathway critical for Myc oncoprotein stability, and provide important evidences for potential application of SIRT2 inhibitors for the prevention and therapy of Myc-induced malignancies.
Subject(s)
Proto-Oncogene Proteins c-myc/metabolism , Sirtuin 2/metabolism , Aurora Kinases , Cell Line, Tumor , Cell Proliferation , Endosomal Sorting Complexes Required for Transport , Gene Expression , Humans , Naphthols/pharmacology , Nedd4 Ubiquitin Protein Ligases , Phenylpropionates/pharmacology , Phosphorylation , Protein Binding , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Protein Stability , Proto-Oncogene Proteins c-myc/antagonists & inhibitors , Proto-Oncogene Proteins c-myc/genetics , RNA Interference , RNA, Messenger/metabolism , RNA, Small Interfering/metabolism , Sirtuin 2/antagonists & inhibitors , Sirtuin 2/genetics , Ubiquitin-Protein Ligases , Ubiquitination , Up-Regulation/drug effectsABSTRACT
Brown recluse spider (loxosceles reclusa) venom has been demonstrated by a ferritin-labeled antibody technique to attach to human erythrocyte cell membranes. The number of individual attachment sites per cell is proportional to the concentration of the venom used to sensitize the erythrocytes. Structural changes in the red cell membrane are associated with the venom attachment. These sites may be related to the red cell hemolysis which sometimes occurs in the human as a result of the spider bite.
Subject(s)
Arthropod Venoms/immunology , Binding Sites, Antibody , Erythrocytes/immunology , Spider Venoms/immunology , Animals , Cell Membrane/immunology , Dose-Response Relationship, Immunologic , Erythrocytes/ultrastructure , Female , Ferritins , Humans , Immunologic Techniques , SpidersABSTRACT
Light and electron microscopic localization of parathyroid hormone (PTH) in human and bovine parathyroid tissue has been achieved using an indirect peroxidase labeled antibody method. Granular deposition of the reaction product was found throughout the chief cell cytoplasm. There was no nuclear staining. At the ultrastructural level, parathyroid hormone localized by this method appeared to be largely confined to the secretory granules in the cytoplasm of cells. Mitochondria and nuclei were free of reaction product. Aggregated sacs of granular endoplasmic reticulum were minimally reactive, and Golgi apparatuses did not show reaction product.
