Irene Garcia-Higuera

Interaction of the Fanconi Anemia Proteins and BRCA1 in a Common Pathway

Fanconi anemia (FA) is a human autosomal recessive cancer susceptibility disorder characterized by cellular sensitivity to mitomycin C and ionizing radiation. Although six FA genes (for subtypes A, C, D2, E, F, and G) have been cloned, their relationship to DNA repair remains unknown. In the current study, we show that a nuclear complex containing the FANCA, FANCC, FANCF, and FANCG proteins is required for the activation of the FANCD2 protein to a monoubiquitinated isoform. In normal (non-FA) cells, FANCD2 is monoubiquitinated in response to DNA damage and is targeted to nuclear foci (dots). Activated FANCD2 protein colocalizes with the breast cancer susceptibility protein, BRCA1, in ionizing radiation-induced foci and in synaptonemal complexes of meiotic chromosomes. The FANCD2 protein, therefore, provides the missing link between the FA protein complex and the cellular BRCA1 repair machinery. Disruption of this pathway results in the cellular and clinical phenotype common to all FA subtypes.

Convergence of the Fanconi Anemia and Ataxia Telangiectasia Signaling Pathways

Fanconi anemia (FA) and ataxia telangiectasia (AT) are clinically distinct autosomal recessive disorders characterized by spontaneous chromosome breakage and hematological cancers. FA cells are hypersensitive to mitomycin C (MMC), while AT cells are hypersensitive to ionizing radiation (IR). Here, we identify the Fanconi anemia protein, FANCD2, as a link between the FA and ATM damage response pathways. ATM phosphorylates FANCD2 on serine 222 in vitro. This site is also phosphorylated in vivo in an ATM-dependent manner following IR. Phosphorylation of FANCD2 is required for activation of an S phase checkpoint. The ATM-dependent phosphorylation of FANCD2 on S222 and the FA pathway-dependent monoubiquitination of FANCD2 on K561 are independent posttranslational modifications regulating discrete cellular signaling pathways. Biallelic disruption of FANCD2 results in both MMC and IR hypersensitivity.

Fanconi Anemia Proteins FANCA, FANCC, and FANCG/XRCC9 Interact in a Functional Nuclear Complex

ABSTRACT Fanconi anemia (FA) is an autosomal recessive cancer susceptibility syndrome with at least eight complementation groups (A to H). Three FA genes, corresponding to complementation groups A, C, and G, have been cloned, but their cellular function remains unknown. We have previously demonstrated that the FANCA and FANCC proteins interact and form a nuclear complex in normal cells, suggesting that the proteins cooperate in a nuclear function. In this report, we demonstrate that the recently cloned FANCG/XRCC9 protein is required for binding of the FANCA and FANCC proteins. Moreover, the FANCG protein is a component of a nuclear protein complex containing FANCA and FANCC. The amino-terminal region of the FANCA protein is required for FANCG binding, FANCC binding, nuclear localization, and functional activity of the complex. Our results demonstrate that the three cloned FA proteins cooperate in a large multisubunit complex. Disruption of this complex results in the specific cellular and clinical phenotype common to most FA complementation groups.

Complementation analysis in Fanconi anemia: Assignment of the reference FA-H patient to group A

Fanconi anemia (FA) is an autosomal recessive disorder with diverse clinical symptoms and extensive genetic heterogeneity. Of eight FA genes that have been implicated on the basis of complementation studies, four have been identified and two have been mapped to different loci; the status of the genes supposed to be defective in groups B and H is uncertain. Here we present evidence indicating that the patient who has been the sole representative of the eighth complementation group (FA-H) in fact belongs to group FA-A. Previous exclusion from group A was apparently based on phenotypic reversion to wild-type rather than on genuine complementation in fusion hybrids. To avoid the pitfall of reversion, future assignment of patients with FA to new complementation groups should conform with more-stringent criteria. A new group should be based on at least two patients with FA whose cell lines are excluded from all known groups and that fail to complement each other in fusion hybrids, or, if only one such cell line were available, on a new complementing gene that carries pathogenic mutations in this cell line. On the basis of these criteria, the current number of complementation groups in FA is seven.

A patient-derived mutant form of the Fanconi anemia protein, FANCA, is defective in nuclear accumulation

Fanconi anemia (FA) is an autosomal recessive cancer susceptibility syndrome with at least eight complementation groups (A-H). Three FA genes, corresponding to complementation groups A, C, and G, have been cloned, but the function of the encoded FA proteins remains unknown. We recently demonstrated that the FANCA and FANCC proteins bind and form a nuclear complex. In the current study, we identified a homozygous mutation in the FANCA gene (3329A>C) in an Egyptian FA patient from a consanguineous family. This mutant FANCA allele is predicted to encode a mutant FANCA protein, FANCA(H1110P), in which histidine 1110 is changed to proline. Initially, we characterized the FANCA(H1110P) protein, expressed in an Epstein Barr virus (EBV)-immortalized lymphoblast line derived from the patient. Unlike wild-type FANCA protein expressed in normal lymphoblasts, FANCA(H1110P) was not phosphorylated and failed to bind to FANCC. To test directly the effect of this mutation on FANCA function, we used retroviral-mediated transduction to express either wild-type FANCA or FANCA(H1110P) protein in the FA-A fibroblast line, GM6914. Unlike wild-type FANCA, the mutant protein failed to complement the mitomycin C sensitivity of these cells. In addition, the FANCA(H1110P) protein was defective in nuclear accumulation in the transduced cells. The characteristics of this mutant protein underscore the importance of FANCA phosphorylation, FANCA/FANCC binding, and nuclear accumulation in the function of the FA pathway.

The molecular and cellular biology of Fanconi anemia.

Fanconi anemia is a rare autosomal recessive disease characterized by multiple congenital abnormalities, bone marrow failure, and cancer susceptibility. The mean age of onset of anemia is 8 years, and the mean survival is 16 years. Death usually results from complications of bone marrow failure. Considerable progress in Fanconi anemia research has resulted from the recent identification and cloning of three Fanconi anemia genes. The current review describes the structure and function of the Fanconi anemia genes and describes the role of the encoded Fanconi anemia proteins in a cellular pathway controlling chromosome stability.

Fanconi Anemia Pathway and Cancer Susceptibility

Fanconi anemia (FA) is a rare autosomal recessive disease characterized by multiple congenital abnormalities, bone marrow failure (BMF), and cancer susceptibility. The mean age of onset of anemia is 8 years, and mean survival is 16 years. Death in FA usually results from complications of BMF. Considerable progress in the field of FA research has resulted from the recent identification and cloning of three FA genes. The purpose of this chapter is to describe the clinical and diagnostic features of FA, review the cellular phenotype of FA, review the structure and putative function of the cloned FA genes, and discuss the possible function of the FA genes as tumor suppressors.