MAPK3 and ductal breast carcinoma in situ: To define the specific roles of ERK1 and ERK2 in FGFR1-mediated TNFAIP3 expression, we co-expressed Cas9 with the sgRNA that specifically targets exon 2 of the human ERK1 gene or the sgRNA that specifically targets exon 2 of the human ERK2 gene in DCIS-iFGFR1 cells.