JUN and breast cancer: In particular, we were interested to study the role of c-Fos, c-Jun, Fra1 and JunB, AP-1 factors that have been implicated in promoting the invasive capabilities of breast cancer cells in response to TGF-β1.29 Gene expression analysis showed that among these AP-1 factors, c-Jun and JunB were significantly induced at the mRNA level after 24 h of TGF-β1-induced EMT in NMuMG cells (Figure 4e).