Itorin 1 — an Active Site Inhibitor of Mtor , Suppresses Prostate Cancer Cell Growth Induced by Activated Α 2 M-Macroglobulin Ligation of Cell Surface GRP 78

In this study, we reported the effect of the ATP binding site competitive inhibitor Torin1 on activated α2-macroglobulin (α2M*)-induced cell proliferation and activation of mTORC1 and mTORC2 signaling in prostate cancer cells. Torin1 significantly inhibited α2M*-induced cellproliferation as measured by protein and DNA synthesis. Translational activity, a major cellular response in malignant cells, is coordinately regulated by the mTORC1-S6-kinaseand mTORC1-4EBP1 axes. Torin1 significantly inhibited α2M*and insulin-induced activation of mTORC1 as determined by phosphorylation of S6-kinaseat Thr and 4EBP1 at Thr compared to untreated cells employing Raptor immunoprecipitates. Torin1 also significantly inhibited α2M*and insulin-induced upregulation of p-Akt and p-Akt in prostate cancer cells. The effect was comparable to that of insulin employed as a positive control. Finally, Torin1 inhibited α2M*and insulin-induced activation of mTORC2 kinase assayas measured by phosphorylation of Akt at Ser in Rictor immunoprecipitates of prostate cancer cells.