MTOR and breast cancer: However, although there is some evidence from human skin cells and breast cancer cells that indicates that TGFβR2 alone is able to mediate TGFβ signalling to ERK1/2 without participation of TGFβR1 [26,27], whether TGFβR2 alone is also able to mediate GDF15 signalling to ERK1/2 and mTOR activation in CGNs has yet to be determined.