Figure 1.

High levels of RAD51 increase genomic instability. Protein expression patterns in (A) U2OS cells transfected with a hormone-inducible RAD51 expression vector and (B) breast cancer cell lines. Induction of high RAD51 in U2OS cells was performed by addition of 1 µM Pon A for 24 h. (top) Protein was assessed by RAD51 immunoblotting with β-actin as loading control. (bottom) Quantification of RAD51 expression relative to levels of β-actin. Mean values of at least 3 independent protein extracts are shown. (C) RAD51 foci (left) and γH2AX-foci (right) in untreated U2OS cells with RAD51 overexpression. Exponentially growing cells were fixed 24 h after induction of RAD51 overexpression, immuno-stained for RAD51 or γH2AX, counterstained with DAPI and foci formation was quantified. Columns depict the mean number of RAD51 foci per cell and bars represent the standard error of the mean of at least 3 experiments. Statistical analysis was performed using Student's t-test. (D) Chromatid-type (left) and chromosome-type (right) aberrations in untreated U2OS cells with RAD51 overexpression. Representative examples for both types of chromosome aberrations are shown in the middle. Exponentially growing cells 24 h after induction of RAD51 overexpression were treated with 0.2 µM colcemid for 4 h and collected at metaphase. Giemsa stained chromatid-type or chromosome-type aberrations were scored and expressed as G2- or G1-aberrations per cell. Columns depict data of at least 3 experiments and statistical analysis was performed using Student's t-test.