NUCLEOLIN and breast cancer: Notably, the effect of 4LB5-HP-RNase on intracellular levels of tumorigenic miR-21, -221, and -222 in breast cancer cells is greater than that of 4LB5, which indicates that the acquired enzymatic activity improves the antitumoral efficacy of 4LB5 due to its ability to be internalized by nucleolin, as shown by both cytosolic and nucleolar localization of the immunoRNase (see Figure 3C), which is in line with the natural distribution pathway of NCL [23].