SIRT1 and squamous cell carcinoma: In addition, Back et al. demonstrated that mTOR activation caused phosphorylation of SIRT1 at the serine47 site, resulting in the inhibition of SIRT1 deacetylase activity in human squamous cell carcinoma (SCC) cells, although the pharmacologic and genetic inhibition of mTOR restored SIRT1 deacetylase activity [64].