title: Inorganic arsenic exposure induces E2F-dependent G0/G1 arrest via an increase in retinoblastoma family protein p130 in B-cell lymphoma A20 cells.
abstract: Inorganic arsenic exerts toxic effect on multiple systems including the immune system. We previously showed in a study on mouse thymocytes and B-cell lymphoma A20 cells that arsenite induces cell cycle arrest at G0/G1 by suppressing expression of E2F-target genes. In this study, we furthermore investigated the involvement of retinoblastoma (RB) family proteins in E2F-dependent cell cycle arrest by arsenite. Arsenite exposure of A20 cells was showed to increase the protein level of p130, a RB family member, without changing the mRNA level. Suppression of arsenite-induced p130 by siRNA reduced the G0/G1 phase, indicating that p130 accumulation is responsible for arsenite-induced G0/G1 arrest. The accumulated p130 was shown to increase the p130 complex with E2F4, a transcription-suppressing E2F. Comparison by Western blotting of arsenite-induced p130 and p130 accumulated by a proteasome inhibitor suggested that arsenite-induced p130 is hypophosphorylated and hypoubiquitinated and refractory to proteasome-dependent degradation. We also showed that arsenite increases mRNA and protein of p16(INK4a), an inhibitor of CDK4/6 that phosphorylates p130. Down-regulation of arsenite-induced p16(INK4a) by siRNA suppressed the p130 accumulation. We propose a novel mechanism in which arsenite inhibits phosphorylation/ubiquitin-dependent proteasome degradation of p130 by inducing p16(INK4a) and the accumulated p130 causes cell cycle arrest with E2F4.
authors.affiliation: Center for Environmental Health Sciences, National Institute for Environmental Studies, Tsukuba, 305-8506, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8577, Japan.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Okamura
authors.forename: Daisuke
authors.initials: D
authors.lastname: Miki
authors.forename: Keiko
authors.initials: K
authors.lastname: Nohara
mesh_terms: D000818:Animals; D018053:Arsenites / Q000494:pharmacology*; D059447:Cell Cycle Checkpoints / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050704:E2F4 Transcription Factor / Q000737:chemistry / Q000378:metabolism*; D005786:Gene Expression Regulation; D016393:Lymphoma, B-Cell / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D034741:RNA, Small Interfering; D050717:Retinoblastoma-Like Protein p130 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D018053:Arsenites; C493957:Cdkn1a protein, mouse; C417743:Cdkn2a protein, mouse; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050704:E2F4 Transcription Factor; C493763:E2f4 protein, mouse; D034741:RNA, Small Interfering; C493838:Rbl2 protein, mouse; D050717:Retinoblastoma-Like Protein p130; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C015001:arsenite