title: Undifferentiated State Induced by Rb-p53 Double Inactivation in Mouse Thyroid Neuroendocrine Cells and Embryonic Fibroblasts.
abstract: Retinoblastoma tumor suppressor protein (RB) is inactivated more frequently during tumor progression than during tumor initiation. However, its exact role in controlling the malignant features associated with tumor progression is poorly understood. We established in vivo and in vitro models to investigate the undifferentiated state induced by Rb inactivation. Rb heterozygous mice develop well-differentiated thyroid medullary carcinoma. We found that additional deletion of Trp53, without change in lineage, converted these Rb-deficient tumors to a poorly differentiated type associated with higher self-renewal activity. Freshly prepared mouse embryonic fibroblasts (MEFs) of Rb(-/-) ; Trp53(-/-) background formed stem cell-like spheres that expressed significant levels of embryonic genes despite of lacking the ability to form colonies on soft agar or tumors in immune-deficient mice. This suggested that Rb-p53 double inactivation resulted in an undifferentiated status but without carcinogenic conversion. We next established Rb(-/-) ; N-ras(-/-) MEFs that harbored a spontaneous carcinogenic mutation in Trp53. These cells (RN6), in an Rb-dependent manner, efficiently generated spheres that expressed very high levels of embryonic genes, and appeared to be carcinogenic. We then screened an FDA-approved drug library to search for agents that suppressed the spherogenic activity of RN6 cells. Data revealed that RN6 cells were sensitive to specific agents including ones those are effective against cancer stem cells. Taken together, all these findings suggest that the genetic interaction between Rb and p53 is a critical determinant of the undifferentiated state in normal and tumor cells.
authors.affiliation: Division of Oncology and Molecular Biology, Stem Cell Research Program, Cancer Research Institute, Kanazawa University, Kanazawa, Ishikawa, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kitajima
authors.forename: Susumu
authors.initials: S
authors.lastname: Kohno
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kondoh
authors.forename: Nobunari
authors.initials: N
authors.lastname: Sasaki
authors.forename: Yuuki
authors.initials: Y
authors.lastname: Nishimoto
authors.forename: Fengkai
authors.initials: F
authors.lastname: Li
authors.forename: Mohammed Salah
authors.initials: MS
authors.lastname: Abdallah Mohammed
authors.forename: Hayato
authors.initials: H
authors.lastname: Muranaka
authors.forename: Naoko
authors.initials: N
authors.lastname: Nagatani
authors.forename: Misa
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yukiharu
authors.initials: Y
authors.lastname: Kido
authors.forename: Chiaki
authors.initials: C
authors.lastname: Takahashi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001522:Behavior, Animal; D002454:Cell Differentiation; D002460:Cell Line; D004353:Drug Evaluation, Preclinical; D004622:Embryo, Mammalian / Q000166:cytology*; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D006579:Heterozygote; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D055099:Neuroendocrine Cells / Q000166:cytology*; D010641:Phenotype; D016160:Retinoblastoma Protein / Q000172:deficiency / Q000378:metabolism*; D018874:Spheroids, Cellular / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology*; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
chemical_list: D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D018631:ras Proteins
keywords: Cancer; Rb; Stem cell; Undifferentiated state; p53