The Fanconi anemia complementation group C gene product: structural evidence of multifunctionality.
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 gamma (IFN-gamma) 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-alpha (TNF-alpha) and IFN-gamma. 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.
Pang
Q
Q
Oregon Cancer Center, Department of Medicine (Division of Hematology and Medical Oncology), Oregon Health Sciences University, Portland, OR 97201, USA.
Christianson
T A
TA
Keeble
W
W
Diaz
J
J
Faulkner
G R
GR
Reifsteck
C
C
Olson
S
S
Bagby
G C
GC
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017209:Apoptosis / Q000187:drug effects; D018797:Cell Cycle Proteins; D002461:Cell Line, Transformed / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D005199:Fanconi Anemia / Q000235:genetics*; D052218:Fanconi Anemia Complementation Group C Protein; D051856:Fanconi Anemia Complementation Group Proteins; D005816:Genetic Complementation Test; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D016685:Mitomycin / Q000494:pharmacology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D050794:STAT1 Transcription Factor; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C497651:FANCC protein, human; D052218:Fanconi Anemia Complementation Group C Protein; D051856:Fanconi Anemia Complementation Group Proteins; D009687:Nuclear Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha; D016685:Mitomycin; D007371:Interferon-gamma