DICER1 and breast carcinoma: Lastly, in order to directly assess whether let7b-5p-mediated regulation of DICER is sufficient to account for the global upregulation in miRNAs observed through miRNA-seq, we transfected let-7b-5p or scramble control mimics into MCF10.AT1 cells and tested a panel of 12 randomly selected miRNAs that were noted from the sequencing data to be endogenously increased during breast cancer progression (Figure 2C).