RPS6KB1 and breast cancer: Moreover, siRNA against c-Src, Akt and mTOR was observed to inhibit the phosphorylation of 4E-BP1 and p70S6K (Figure 5C) as well as exhibited blunted HIF-1α expression (Figure 6B) in response to E2, suggesting the importance of mTOR signalling in the elevated HIF-1α levels in breast cancer cells.