RPS6KB1 and breast carcinoma: However when we investigated these findings in E-cadherin negative breast cancer cell lines, eg., MDA-MB-468, the levels of phosphorylated mTOR (Ser2448), phosphorylated p70-S6K and phosphorylated 4E-BP1 (Thr37/46) all increased throughout induced spheroidgenesis (Figure 3E).