title: Loss of p21 disrupts p14 ARF-induced G1 cell cycle arrest but augments p14 ARF-induced apoptosis in human carcinoma cells.
abstract: The human INK4a locus encodes two structurally unrelated tumor suppressor proteins, p16 INK4a and p14 ARF (p19 ARF in the mouse), which are frequently inactivated in human cancer. Both the proapoptotic and cell cycle-regulatory functions of p14 ARF were initially proposed to be strictly dependent on a functional p53/mdm-2 tumor suppressor pathway. However, a number of recent reports have implicated p53-independent mechanisms in the regulation of cell cycle arrest and apoptosis induction by p14 ARF. Here, we show that the G1 cell cycle arrest induced by p14 ARF entirely depends on both p53 and p21 in human HCT116 and DU145 carcinoma cells. In contrast, neither loss of p53 nor p21 impaired apoptosis induction by p14 ARF as evidenced by nuclear DNA fragmentation, phosphatidyl serine exposure, and caspase activation, which included caspase-3/7- and caspase-9-like activities. However, lack of functional p21 resulted in the accumulation of cells in G2/M phase of the cell cycle and markedly enhanced p14 ARF-induced apoptosis that was, nevertheless, efficiently inhibited by the cell permeable broad-spectrum caspase inhibitor zVAD-fmk (valyl-alanyl-aspartyl-(O)-methyl)-fluoromethylketone). Thus, loss of cell cycle restriction point control in the absence of p21 may interfere with p14 ARF-induced apoptosis. Finally, these data indicate that the signaling events required for G1 cell cycle arrest and apoptosis induction by p14 ARF dissociate upstream of p53.
authors.affiliation: Department of Hematology, Oncology and Tumor Immunology, University Medical Center Charité, Campus Berlin-Buch, Berlin-Buch, Germany.
authors.forename: Philipp G
authors.initials: PG
authors.lastname: Hemmati
authors.forename: Guillaume
authors.initials: G
authors.lastname: Normand
authors.forename: Berlinda
authors.initials: B
authors.lastname: Verdoodt
authors.forename: Clarissa
authors.initials: C
authors.lastname: von Haefen
authors.forename: Anne
authors.initials: A
authors.lastname: Hasenjäger
authors.forename: Dilek
authors.initials: D
authors.lastname: Güner
authors.forename: Jana
authors.initials: J
authors.lastname: Wendt
authors.forename: Bernd
authors.initials: B
authors.lastname: Dörken
authors.forename: Peter T
authors.initials: PT
authors.lastname: Daniel
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis / Q000502:physiology*; D001973:Bromodeoxyuridine; D002277:Carcinoma; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics*; D002460:Cell Line; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016193:G1 Phase / Q000502:physiology*; D017353:Gene Deletion; D005822:Genetic Vectors; D006801:Humans; D007668:Kidney; D025803:Tumor Suppressor Protein p14ARF / Q000502:physiology*
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D025803:Tumor Suppressor Protein p14ARF; D020169:Caspases; D001973:Bromodeoxyuridine