Tyr705 phosphorylation was decreased by treatment with everolimus in the presence ACY-738 chemical structure of pretreatment with stattic. Moreover, to clarify how STAT3 and mTOR regulate cell toxicity whether in a parallel manner or in a downstream regulation, we examined if STAT3 activity varies in a time-dependent manner with treatment of everolimus (Figure 4B). Phosphorylation of STAT3 was decreased in short-term but increased in long-term incubated with Neuronal Signaling inhibitor low-dose everolimus. Phosphorylation of p70 S6K which is direct downstream of mTORC1 showed inhibition in a time-dependent manner based on the
mechanism of action of everolimus. This results show that STAT3 phosphorylation can be regulated indirectly 4SC-202 by mTOR. Figure 4 Effects of various STAT3 inhibitors on everolimus-mediated signal transduction in HaCaT cells. (A) Alteration in signal transduction of STAT3. HaCaT cells were incubated in medium containing everolimus at the indicated concentrations for 2 h (1): after pretreatment with 10 μM
stattic for 20 min or (2): coincubation with everolimus and 10 μM STA-21 or (3) vehicle alone (DMSO). (B) Alteration in signal transduction of STAT3. HaCaT cells were incubated in medium containing 10 μM everolimus at the indicated time. Total cell lysates were separated by SDS-PAGE and electrotransferred to PVDF membranes. Various proteins and phosphorylation levels were evaluated by immunoblotting assay with specific antibodies. Effects of everolimus on MAPKs activity in HaCaT cells and effects of MAPK inhibitors BCKDHA on everolimus-induced cell growth inhibition in HaCaT cells Previous studies demonstrated that the PI3K/Akt/mTOR and MAPK pathways represent a cross-linked signal network in various cell lines, and that STAT3 is an important downstream signaling factor of these pathways [25–27]. Therefore, we confirmed the differences in the phosphorylation of JNK, Erk1/2, and p38 MAPK after
treatment with everolimus in HaCaT cells (Figure 5A). The phosphorylation of Erk1/2 and p38 MAPK was increased after treatment with everolimus in a dose-dependent manner in HaCaT cells. Moreover, the phosphorylation of p38 MAPK was particularly increased in the presence of pretreatment with stattic. Figure 5B shows the everolimus-induced cell growth inhibition in HaCaT cells in the absence or presence of a MEK1/2 inhibitor (U0126), a p38 MAPK inhibitor (SB203580) or a JNK inhibitor (SP600125). Treatment with the p38 MAPK inhibitor reduced the efficacy of cell growth inhibition by everolimus in HaCaT cells. A MEK1/2 inhibitor also affect the everolimus-induced cell growth inhibition in HaCaT cells, slightly. Moreover, we examined a possibility that MAPKs inhibitors rescue the inhibition of phosphorylation of STAT3 by everolimus (Figure 5C). In the pretreatment of SB203580, STAT3 Tyr705 phosphorylation was enhanced comparing from treatment of everolimus alone.