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BACKGROUNDInhibition of mTOR complex 1 (mTORC1) with rapamycin leads to phosphorylation of AKT in some cancer cells, with unknown biological consequences. The role of this phosphorylation in melanoma is unknown, although preliminary clinical data indicate poor activity of rapalogues in melanoma.
OBJECTIVEWe aimed at elucidating the role of AKT phosphorylation after mTORC1 inhibition in melanoma cells.
METHODSWestern blotting, apoptosis assays, cell cycle analyses and viability assays were performed to analyse the effects of rapamycin and LY294002 treatment on melanoma cells. For suppression of mTOR complex 2 (mTORC2) an siRNA directed against rictor was used.
RESULTSRapamycin showed limited effects on cell viability but resulted in strong and lasting AKT phosphorylation in melanoma cells. Combined PI3K/mTOR inhibition with LY294002 had pronounced effects on viability but also led to increased AKT phosphorylation after prolonged treatment. In contrast, combination of rapamycin plus LY294002 suppressed AKT phosphorylation. Suppression of AKT phosphorylation did not correlate with decreases in cell viability. Inhibition of mTORC2 led to reduced levels of phosphorylated AKT.
CONCLUSIONSmTORC1 inhibition with rapamycin and with LY294002 can lead to AKT phosphorylation in melanoma cells via mTORC2. Combination of rapamycin and LY294002 suppresses AKT phosphorylation but without significant effect on treatment efficacy.