title: Monoallelic loss of the imprinted gene Grb10 promotes tumor formation in irradiated Nf1+/- mice.
abstract: Imprinted genes are expressed from only one parental allele and heterozygous loss involving the expressed allele is sufficient to produce complete loss of protein expression. Genetic alterations are common in tumorigenesis but the role of imprinted genes in this process is not well understood. In earlier work we mutagenized mice heterozygous for the Neurofibromatosis I tumor suppressor gene (NF1) to model radiotherapy-associated second malignant neoplasms that arise in irradiated NF1 patients. Expression analysis of tumor cell lines established from our mouse models identified Grb10 expression as widely absent. Grb10 is an imprinted gene and polymorphism analysis of cell lines and primary tumors demonstrates that the expressed allele is commonly lost in diverse Nf1 mutant tumors arising in our mouse models. We performed functional studies to test whether Grb10 restoration or loss alter fundamental features of the tumor growth. Restoring Grb10 in Nf1 mutant tumors decreases proliferation, decreases soft agar colony formation and downregulates Ras signaling. Conversely, Grb10 silencing in untransformed mouse embryo fibroblasts significantly increased cell proliferation and increased Ras-GTP levels. Expression of a constitutively activated MEK rescued tumor cells from Grb10-mediated reduction in colony formation. These studies reveal that Grb10 loss can occur during in vivo tumorigenesis, with a functional consequence in untransformed primary cells. In tumors, Grb10 loss independently promotes Ras pathway hyperactivation, which promotes hyperproliferation, an early feature of tumor development. In the context of a robust Nf1 mutant mouse model of cancer this work identifies a novel role for an imprinted gene in tumorigenesis.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, California, United States of America.
authors.forename: Rana
authors.initials: R
authors.lastname: Mroue
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, California, United States of America.
authors.forename: Brian
authors.initials: B
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, California, United States of America.
authors.forename: Steve
authors.initials: S
authors.lastname: Braunstein
authors.affiliation: Department of Pediatrics, University of California, San Francisco, San Francisco, California, United States of America.
authors.forename: Ari J
authors.initials: AJ
authors.lastname: Firestone
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, California, United States of America.
authors.forename: Jean L
authors.initials: JL
authors.lastname: Nakamura
mesh_terms: D000483:Alleles; D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004195:Disease Models, Animal; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism; D051383:GRB10 Adaptor Protein / Q000235:genetics* / Q000378:metabolism; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D016514:Genes, Neurofibromatosis 1; D018392:Genomic Imprinting; D019656:Loss of Heterozygosity; D051379:Mice; D018345:Mice, Knockout; D009456:Neurofibromatosis 1 / Q000235:genetics*; D010766:Phosphorylation; D016283:Proto-Oncogene Proteins p21(ras); D011827:Radiation; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: C495959:Grb10 protein, mouse; D016159:Tumor Suppressor Protein p53; D051383:GRB10 Adaptor Protein; D016283:Proto-Oncogene Proteins p21(ras)