EIF4EBP1 and breast cancer: However, a recent study from Rutkovsky et al. found that 4EBP1, a well-established negative regulator of mTORC1 activity [100], is highly phosphorylated and overexpressed in a range of metastatic ER+ BC cell lines harbouring the 8p11-p12 amplicon, and contributes to BC cell proliferation [101].