Within the present examine we first of all demonstrated that curcumin also inhibited the phosphorylation of Akt substrates GSK3, FKHR1, TSC2, mTOR at the same time as mTOR downstream targets 4E-BP1, eIF4G, p70 S6K and S6 within a similar concentration-dependent manner as with Akt . In support within the part of Akt/mTOR signaling while in the management of protein synthesis, curcumin inhibited protein synthesis after which DNA synthesis in PC-3 cells , and these inhibitions may be partially but appreciably rescued by overexpression of Akt or by restoration of Akt/mTOR signaling by calyculin A . Cyclin D1, which is essential for cell proliferation, has become reported for being regulated by Akt/mTOR posttranscriptionally . In PC-3 cells the expression of cyclin D1 was also inhibited by curcumin and may be restored by overexpression of Akt or by calyculin A . These effects are consistent with the vital roles of Akt/mTOR signaling in cell survival and proliferation.
Curcumin continues to be reported to inhibit Akt/mTOR signaling in other cancer Vemurafenib cells , however the underlying mechanism remains unknown. A single major goal of this examine will be to delineate the molecular mechanism by which curcumin inhibits Akt/mTOR signaling. First of all we examined the result of curcumin within the p85 subunit of PI3K. The phosphorylation of p85 in PC-3 cells is barely detectable and was not impacted by curcumin treatment . LY294002, a specific PI3K inhibitor, inhibited the phosphorylation of Akt and mTOR, and this inhibition could be restored by addition of exogenous PIP3. In contrast, exogenous PIP3 failed to restore curcumin-mediated inhibition . Furthermore, it’s been very well documented that in many cancer cells including PC-3 cells, the activation of Akt/mTOR signaling axis is less dependent on upstream signals as a consequence of reduction of PTEN function .
Really, as reported by some others and confirmed in our lab, curcumin also inhibited Akt/mTOR signaling and proliferation in DU145 prostate cancer Tanshinone IIA cells which carry wt PTEN. Taken together, these evidences suggest that curcumin inhibits Akt/mTOR signaling at downstream of PI3K. As shown in inhibitors 1D, the phosphorylation of Akt at Thr308 was the very first to get inhibited. This led to the hypothesis that curcumin could directly inhibit PDK1-mediated phosphorylation of Akt and led to your inhibition of downstream signaling. Phosphorylation of PDK1 at Ser241 is necessary for its action, even though could possibly not be the main regulatory issue . On the other hand, curcumin didn’t inhibit the phosphorylation of PDK1 S241 .
Moreover, curcumin failed to inhibit the kinase activity of PDK1 to Akt the two in vitro and in vivo , suggesting that PDK1 just isn’t the direct target of curcumin. Related observations are already reported that Akt/mTOR signaling may be inhibited independent of PI3K/PDK1 . Upcoming we examined the purpose of Akt in curcumin-mediated inhibition.