Fanconi anemia genes act to suppress a cross-linker-inducible p53-independent apoptosis pathway in lymphoblastoid cell lines (original) (raw)

Hypersensitivity to cross-linking agents such as mitomycin C ("C) is characteristic of cells from patients suffering from the inherited bone marrow failure syndrome, Fanconi anemia (FA). Here, we link MMC hypersensitivity of Epstein-Barr virus (EBV)-immortalized FA lymphoblasts to a high susceptibility for apoptosis and p53 activation. In MMCtreated FA cells belonging to complementation group C (FA-C), apoptosis followed cell cycle arrest in the G2 phase. In stably transfected FA-C cells, plasmid-driven expression of the wild-type cytoplasmic FAC protein relieved MMC-dependent G2 arrest and suppressed p53 activation. However, in ANCON1 ANEMIA (FA) is an autosomal recessive disease characterized by developmental abnormalities (thumb and radius hypoplasia, microcephaly, growth delay, and kidney abnormalities), hyperpigmentation of the skin (cafk-au-lait spots), and life-threatening bone marrow failure.',' In addition, FA patients have a dramatically increased risk of developing malignancies, mainly acute myeloid leukemia and squamous cell carcinoma. Cultured FA cells exhibit an increased sensitivity to cross-linking agents such as mitomycin C ("C) and diepoxybutane.' Because of an increased level of spontaneous chromosomal aberrations in cultured cells, FA, like ataxia telangiectasia (AT) and Bloom syndrome (BS), is known as a chromosomal instability disorder. In FA, cell-fusion experiments have revealed four complementation groups, A to D'; recently, a fifth group was identified.4 In contrast to the UV-sensitivity diseases xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy, where disturbances in excision repair and transcription have been documented in detail,' the molecular bases of chromosomal instability disorders are still unknown. The FA group C gene, FAC (according to the nomenclature recommended by Lehmann et a16), cloned by Strathdee et al,7 is the first chromosomal instability disease gene isolated. The gene encodes a 63-kD polypeptide with no known sequence motifs that could provide a clue to its function. Since functionally active FAC protein apparently localizes to the cytoplasmic compartment of cells,8.' the protein is unlikely to be directly involved in DNA repair. Besides cross-linker hypersensitivity, cell cycle kinetic studies in primary fibroblasts and lymphocytes derived from FA patients revealed a characteristic spontaneous delay and arrest in G2."'.'' This phenomenon may explain the poor proliferative properties of primary FA cells. Since reduction F