title: RASSF1A mediates p21Cip1/Waf1-dependent cell cycle arrest and senescence through modulation of the Raf-MEK-ERK pathway and inhibition of Akt.
abstract: Promoter hypermethylation preventing expression of the RAS association domain family 1 isoform A (RASSF1A) gene product is among the most abundant epigenetic deregulations in human cancer. Restoration of RASSF1A inhibits tumor cell growth in vitro and in murine xenograft models. Rassf1a-deficient mice feature increased spontaneous and carcinogen-induced tumor formation. Mechanistically, RASSF1A affects several cellular functions, such as microtubule dynamics, migration, proliferation, and apoptosis; however, its tumor-suppressive mechanism is incompletely understood. To study the functional consequences of RASSF1A expression in human cancer cells, we made use of a doxycycline-inducible expression system and a RASSF1A-deficient lung cancer cell line. We observed that RASSF1A induces cell cycle arrest in G(1) phase and senescence in vitro and in tumors established in immunodeficient mice. RASSF1A-mediated growth inhibition was accompanied by the up-regulation of the cyclin-dependent kinase inhibitor p21(Cip1/Waf1) and proceeded independently of p53, p14(Arf), and p16(Ink4a). Loss of p21(Cip1/Waf1) or coexpression of the human papilloma virus 16 oncoprotein E7 was found to override RASSF1A-induced cell cycle arrest and senescence. Conditional RASSF1A affected mitogen-activated protein kinase and protein kinase B/Akt signaling to up-regulate p21(Cip1/Waf1) and to facilitate its nuclear localization. In summary, RASSF1A can mediate cell cycle arrest and senescence in human cancer cells by p53-independent regulation of p21(Cip1/Waf1).
authors.affiliation: Center for Biomedicine and Medical Technology, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Thaler
authors.forename: Patricia S
authors.initials: PS
authors.lastname: Hähnel
authors.forename: Arno
authors.initials: A
authors.lastname: Schad
authors.forename: Reinhard
authors.initials: R
authors.lastname: Dammann
authors.forename: Martin
authors.initials: M
authors.lastname: Schuler
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002453:Cell Cycle; D016922:Cellular Senescence; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D006657:Histones / Q000502:physiology; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology*; D009856:Oncogene Proteins, Viral / Q000235:genetics; D050725:Papillomavirus E7 Proteins; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors*; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D048490:raf Kinases / Q000502:physiology*
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; C468783:H2AX protein, human; D006657:Histones; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; C411762:RASSF1 protein, human; C496882:RASSF1 protein, mouse; D025521:Tumor Suppressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D051057:Proto-Oncogene Proteins c-akt; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases