HDAC1 phosphorylation at S421 and S423 was also related with the activity of p70 S6 kinase (S6K1) in breast cancer cells, occurring upon the activation of the phosphoinositide 3-kinase (PI3K)/ mammalian target of rapamycin (mTOR) pathway downstream of mitogenic stimulation. Here, MTOR is linked to breast carcinoma.