TOPBP1 and triple-negative breast carcinoma: To determine how TopBP1 protein levels affect the intensity of Chk1 activation, we first knocked down TopBP1 in MDA-MB468, a triple-negative breast cancer cell line, and then reconstituted TopBP1 to different expression levels by infecting cells with a recombinant adenovirus Ad-TopBP1 at various multiplicity of infection (MOI).