TOP3B and breast cancer: Because TOP3B has been reported to be ubiquitylated and targeted for proteasomal degradation in MCF7 breast cancer cells in the absence of TDRD310, we measured the ubiquitylation of TOP3B in TDRD3-depleted cells (i.e., in siTDRD3-transfected HEK293 cells and in TDRD3KO HCT116 cells).