ERBB2 and breast cancer: Furthermore, the expression level of Argonaute-2 (Ago2), the catalytic subunit of the RNA-induced silencing complex (RISC) that mediates miRNA-dependent cleavage/degradation, is higher in ERα-negative/human epidermal growth factor receptor 2 (HER2)-positive cells compared with ERα-positive/HER2 negative human breast cancer cell lines and tumors (52).