The Fanconi anemia complementation group C gene product: structural evidence of multifunctionality

• Published in: Blood Vol. 98; no. 5; pp. 1392 - 1401
• Main Authors: Pang, Qishen, Christianson, Tracy A., Keeble, Winifred, Diaz, Jane, Faulkner, Gregory R., Reifsteck, Carol, Olson, Susan, Bagby, Grover C.
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 01.09.2001; The Americain Society of Hematology
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Amino Acid Substitution; Apoptosis - drug effects; Biological and medical sciences; Cell Cycle Proteins; Cell Line, Transformed - drug effects; Chromosome fragility (bloom syndrome, ataxia telangiectasia, fanconi anemia, x-linked mental retardation...); DNA-Binding Proteins - metabolism; Fanconi Anemia - genetics; Fanconi Anemia Complementation Group C Protein; Fanconi Anemia Complementation Group Proteins; Genetic Complementation Test; Humans; Interferon-gamma - pharmacology; Medical genetics; Medical sciences; Mitomycin - pharmacology; Molecular Sequence Data; Mutagenesis, Site-Directed; Nuclear Proteins; Phosphorylation; Protein Processing, Post-Translational; Proteins - chemistry; Proteins - genetics; Proteins - physiology; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - physiology; Sequence Alignment; Sequence Homology, Amino Acid; Signal Transduction; STAT1 Transcription Factor; Structure-Activity Relationship; Trans-Activators - metabolism; Tumor Necrosis Factor-alpha - pharmacology; Human; Fanconi anemia; Pathogenesis; Fanconi anemia group C; Clinical form; Structure function relationship; Symptomatology; Signal transduction; Transcription factor STAT1; Gene; Genetics; Mutation; Transduction factor STAT
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V98.5.1392

The Fanconi anemia (FA) group C gene product (FANCC) functions to protect cells from cytotoxic and genotoxic effects of cross-linking agents. FANCC is also required for optimal activation of STAT1 in response to cytokine and growth factors and for suppressing cytokine-induced apoptosis by modulating the activity of double-stranded RNA-dependent protein kinase. Because not all FANCC mutations affect STAT1 activation, the hypothesis was considered that cross-linker resistance function of FANCC depends on structural elements that differ from those required for the cytokine signaling functions of FANCC. Structure-function studies were designed to test this notion. Six separate alanine-substituted mutations were generated in 3 highly conserved motifs of FANCC. All mutants complemented mitomycin C (MMC) hypersensitive phenotype of FA-C cells and corrected aberrant posttranslational activation of FANCD2 in FA-C mutant cells. However, 2 of the mutants, S249A and E251A, failed to correct defective STAT1 activation. FA-C lymphoblasts carrying these 2 mutants demonstrated a defect in recruitment of STAT1 to the interferon γ (IFN-γ) receptor and GST-fusion proteins bearing S249A and E251A mutations were less efficient binding partners for STAT1 in stimulated lymphoblasts. These same mutations failed to complement the characteristic hypersensitive apoptotic responses of FA-C cells to tumor necrosis factor-α (TNF-α) and IFN-γ. Cells bearing a naturally occurring FANCC mutation (322delG) that preserves this conserved region showed normal STAT1 activation but remained hypersensitive to MMC. The conclusion is that a central highly conserved domain of FANCC is required for functional interaction with STAT1 and that structural elements required for STAT1-related functions differ from those required for genotoxic responses to cross-linking agents. Preservation of signaling capacity of cells bearing the del322G mutation may account for the reduced severity and later onset of bone marrow failure associated with this mutation.