The Cytoskeleton Protein Filamin-A Is Required for an Efficient Recombinational DNA Double Strand Break Repair

The human actin-binding protein filamin-A (also known as ABP-280) cross-links actin into a dynamic three-dimensional structure. It interacts with >45 proteins of diverse functions, serving as the scaffold in various signaling networks. BRCA2 is a protein that regulates RAD51-dependent recombinational repair of DNA double strand breaks (DSB). Proximate to the COOH terminus of the BRCA2 protein, a conserved and DNA binding domain (BRCA2-DBD) interacts with filamin-A and BCCIP. In this study, we sought to test the hypothesis that filamin-A influences homologous recombinational repair of DSB and the maintenance of genomic stability. We used three pairs of cell lines with normal and reduced filamin-A expression, including breast cancer and melanoma cells. We found that lack or reduction of filamin-A sensitizes cells to ionizing radiation, slows the removal of DNA damage-induced, gamma H2AX nuclear foci, reduces RAD51 nuclear focus formation and recruitment to chromatin in response to irradiation, and results in a 2-fold reduction of homologous recombinational repair of DSB. Furthermore, filamin-A-deficient cells have increased frequencies of micronucleus formation after irradiation. Our data illustrate the importance of the cytoskeleton structure in supporting the homologous recombinational DNA repair machinery and genome integrity, and further implicate a potential of filamin-A as a marker for prognosis in DNA damage-based cancer therapy. [Cancer Res 2009;69(20):7978-85]