title: Involvement of the Fanconi's anemia protein FAC in a pathway that signals to the cyclin B/cdc2 kinase.
abstract: Lymphoblastoid cell lines derived from patients with the chromosomal instability disorder Fanconi's anemia (FA) are hyperresponsive to G2 delay and apoptosis induced by cross-linking agents such as mitomycin C (MMC). Here, we investigated whether the protein defective in FA complementation group C (FA-C) cells functions in a pathway that signals to the cdc2 kinase complex, which controls mitotic progression. FA-C lymphoblasts treated with a low dose of MMC (1-5 microM, 1 h) exhibited a protracted G2-M arrest and subsequent apoptosis by 2 days after treatment. This G2-M arrest was mediated by persistent inactivation of the cyclin B1/cdc2 kinase complex characterized by both sustained accumulation of cyclin B1 and tyrosine phosphorylation of cdc2. In phenotypically corrected (wild-type) cells, the same treatment induced only temporal G2-M arrest, associated with a transient inactivation of the cyclin B1/cdc2 kinase complex, after which cells resumed cycling. Treatment with higher dosages (15-30 microM, 1 h) resulted in S-phase arrest and induced a similar high level of apoptosis in FA-C and wild-type cells, accompanied by degradation of cyclin B1 and dephosphorylation of cdc2. In low-dose treated G2-M-arrested FA-C cells, caffeine-dependent activation of cdc2 released the G2-M block but failed to protect against apoptosis, suggesting that apoptosis was not a direct consequence of persistent cdc2 kinase inactivation. Thus, at low doses of MMC, FA-C cells exhibit a unique cyclin B1/cdc2 response that is not observed in wild-type cells treated with an equitoxic high dosage of cross-linker. Although these results do not necessarily implicate a role for FAC in regulating cyclin B/cdc2 kinase activity, available evidence suggests that the FAC protein is involved in a cross-link damage avoidance pathway that signals to this kinase complex.
authors.affiliation: Department of Human Genetics, Free University, Amsterdam, the Netherlands. FAE.Kruyt.HumGen@med.vu.nl
authors.forename: F A
authors.initials: FA
authors.lastname: Kruyt
authors.forename: L M
authors.initials: LM
authors.lastname: Dijkmans
authors.forename: F
authors.initials: F
authors.lastname: Arwert
authors.forename: H
authors.initials: H
authors.lastname: Joenje
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D016213:Cyclins / Q000378:metabolism; D005199:Fanconi Anemia / Q000378:metabolism*; D052218:Fanconi Anemia Complementation Group C Protein; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D016685:Mitomycin / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects / Q000502:physiology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D011506:Proteins / Q000502:physiology*; D016196:S Phase / Q000187:drug effects; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
chemical_list: D016213:Cyclins; C497651:FANCC protein, human; D052218:Fanconi Anemia Complementation Group C Protein; D019384:Nucleic Acid Synthesis Inhibitors; D010726:Phosphodiesterase Inhibitors; D011506:Proteins; D002110:Caffeine; D014443:Tyrosine; D016685:Mitomycin; D018844:Cyclin-Dependent Kinases