ABSTRACT
Primitive neuroectodermal tumors (PNETs) are a family of primary malignant brain tumors that include medulloblastomas. Although genetic models of a subset of medulloblastomas are documented over the past decade, the molecular basis of other subclasses of PNET remains unclear. As elevated c-Myc expression, activation of Wnt/beta-catenin signaling and dysfunction of p53 are seen in human PNETs, we investigated what role these abnormalities have in the formation of PNETs. Incorporating these abnormalities, we generated supratentorial PNET (sPNET) in mice using somatic cell gene transfer. We show that sPNETs arise from GFAP-expressing cells by forced c-Myc expression combined with p53 inactivation. beta-catenin activation promotes tumor progression and induces divergent differentiation. These c-Myc+beta-catenin-induced PNETs are histologically similar to large cell/anaplastic medulloblastomas and can occur in both cerebrum and cerebellum. Furthermore, we have obtained one PNET with marked epithelial differentiation having histological resemblance to choroid plexus carcinoma in this series. Our results in mice suggest that sPNET with varied differentiation and large cell/anaplastic medulloblastomas may be two tumor groups with similar genetic foundations. These data provide insights into the biology and classification of human PNETs and suggest that multiple tumor types or variants can be generated from a fixed set of genetic abnormalities.
Subject(s)
Neuroectodermal Tumors, Primitive/etiology , Proto-Oncogene Proteins c-myc/physiology , Supratentorial Neoplasms/etiology , Tumor Suppressor Protein p53/physiology , beta Catenin/physiology , Animals , Cell Differentiation , Disease Models, Animal , Genes, myc , Medulloblastoma/etiology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Neuroectodermal Tumors, Primitive/classification , Neuroectodermal Tumors, Primitive/pathology , Signal Transduction , Tumor Suppressor Protein p53/geneticsABSTRACT
Although there is a binding site on the proteasome for the polyubiquitin chains attached to degradation substrates by the ubiquitination machinery, it is currently unclear whether in vivo the activities of the ubiquitination machinery and the proteasome are coupled. Here we show that two human homologs of the yeast ubiquitin-like Dsk2 protein, hPLIC-1 and hPLIC-2, physically associate with both proteasomes and ubiquitin ligases in large complexes. Overexpression of hPLIC proteins interferes with the in vivo degradation of two unrelated ubiquitin-dependent proteasome substrates, p53 and IkappaBalpha, but not a ubiquitin-independent substrate. Our findings raise the possibility that the hPLIC proteins, and possibly related ubiquitin-like family members, may functionally link the ubiquitination machinery to the proteasome to affect in vivo protein degradation.
Subject(s)
Carrier Proteins , Cell Cycle Proteins , Cysteine Endopeptidases/metabolism , Multienzyme Complexes/metabolism , Saccharomyces cerevisiae Proteins , Ubiquitins/metabolism , Adaptor Proteins, Signal Transducing , Amino Acid Sequence , Animals , Autophagy-Related Proteins , Cells, Cultured , Fungal Proteins/chemistry , Fungal Proteins/metabolism , Gene Expression Regulation/drug effects , Humans , Keratinocytes/cytology , Keratinocytes/metabolism , Male , Mice , Molecular Sequence Data , Proteasome Endopeptidase Complex , Recombinant Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Sequence Alignment , Sequence Homology, Amino Acid , Skin/cytology , Transfection , Tumor Necrosis Factor-alpha/pharmacology , Ubiquitins/chemistry , Ubiquitins/geneticsABSTRACT
In this study we identified and characterized the receptor related to the modulation of growth of human gastric cancer by gastrin. By performing receptor binding assays on human AGS gastric cancer cells with the selective CCK-B/gastrin receptor antagonist [3H]L-365,260, specific and saturable binding were determined. Binding was dependent on protein concentration, time, temperature, and the presence of protease inhibitors, and was located in the membrane fraction. Gastrin, as well as CCK, stimulated gastric cancer cell growth in a receptor-mediated fashion at a concentration consistent with the binding affinity. Receptor gene expression for the CCK-B/gastrin receptor, but not for the CCK-A receptor, was found by reverse transcription polymerase chain reaction. Receptor binding assays as well as transcriptional and growth studies provide evidence that gastrin-stimulated growth of human gastric cancer is mediated by CCK-B/gastrin-like receptors.
