Gene-specific selection against experimental fanconi anemia gene inactivation in human cancer.
The Fanconi anemia (FA) gene family comprises at least 12 genes interacting in a common pathway involved in DNA repair. To gain insight into the role of FA gene inactivation occurring in tumors among the general population, we endogenously targeted in cancer cells four FA genes that act at different stages of the FA pathway. After successful mono-allelic deletion of all genes, the sequential homozygous deletion was achieved only for FANCC and FANCG, acting upstream, but not for BRCA2 or FANCD2, acting downstream in the FA pathway. Targeting of the second allele in in BRCA2 and FANCD2 heterozygote clones resulted in redeletion exclusively of the already defective allele in multiple instances (13x concerning BRCA2, 25x concerning FANCD2), strongly suggesting a detrimental phenotype. Unlike complete FANCD2 disruption, the mere reduction of FANCD2 protein levels had no discernible effect. In addition, we confirmed that human cancer cells harboring the Seckel ATR mutation display impaired FANCD2 monoubiquitination and FANCD2 nuclear focus formation, as well as an increased sensitivity to DNA interstrand-crosslinking agents. Nevertheless, these cells were viable, indicating an ATR-independent function of FANCD2, distinct from its major known functions, to be responsible for the detrimental effects of FANCD2 loss. In conclusion, we established the downstream FA genes FANCD2 and BRCA2 to represent particularly vulnerable parts of the FA pathway, providing direct evidence for the paradoxical assumption that their inactivation could be predominantly selected against in cancer cells. This would explain why certain FA gene defects, despite an apparent selection for FA pathway inactivation in cancer, are rarely observed in tumors among the general population.
Gallmeier
Eike
E
The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, Maryland, USA.
Hucl
Tomas
T
Calhoun
Eric S
ES
Cunningham
Steven C
SC
Bunz
Fred
F
Brody
Jonathan R
JR
Kern
Scott E
SE
D024682:BRCA2 Protein / Q000235:genetics*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004260:DNA Repair; D052218:Fanconi Anemia Complementation Group C Protein / Q000235:genetics*; D052236:Fanconi Anemia Complementation Group D2 Protein / Q000235:genetics*; D052241:Fanconi Anemia Complementation Group G Protein / Q000235:genetics*; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D020868:Gene Silencing / Q000502:physiology*; D018390:Gene Targeting; D006801:Humans; D015151:Immunoblotting; D017404:In Situ Hybridization, Fluorescence; D034741:RNA, Small Interfering / Q000494:pharmacology; D054875:Ubiquitination
D024682:BRCA2 Protein; C497651:FANCC protein, human; C499905:FANCD2 protein, human; C499909:FANCG protein, human; D052218:Fanconi Anemia Complementation Group C Protein; D052236:Fanconi Anemia Complementation Group D2 Protein; D052241:Fanconi Anemia Complementation Group G Protein; D034741:RNA, Small Interfering