CDKN1B and breast cancer: Consistent with the roles of 4E-BP1 and S6K1 inprotein synthesis, we employed PF-4708671 and 4E1Rcat to treat breast cancer cellsand found that these inhibitors had no effect on p27kip1 in cells without RP1. Interestingly, RIP assays illustrated that RP1 interacted with the complex p-4E-BP1/eIF4E.