A recent report on PTEN loss-induced senescence supports our choosing that senescence induced by PIK3CA/AKT activation is not really linked to activation of DNA injury signaling, but didn’t examine chromatin adjustments, autophagy plus the senescence secretome . On this study, by immediately evaluating activated RAS and PIK3CA/ AKT, we discover that the latter is not really an productive inducer of senescence. Especially, we show that inactivation of PTEN and activation of AKT is impaired in its skill to induce senescence, as recorded by several effectors of senescence, such as upregulation of p16, induction of DNA injury, recruitment of HIRA to PML bodies, formation of SAHF and upregulation of autophagy. Importantly, we also present that activation of PIK3CA/AKT is deficient in its ability to drive two practical outputs with the senescence system which are central to senescence-mediated tumor suppression, namely upregulation of your senescence secretome and productive proliferation arrest.
Most significant, concurrent activation of each RAS and PIK3CA/AKT impairs RAS-induced senescence, both in vitro and in vivo. Activated PIK3CA/AKT suppresses senescence induced by activated RAS via many routes. First, activated AKT1 reversed the upregulation of p16INK4a the original source induced by activated RAS. Second, GSK3| kinase is another critical nodal level at which signals from activated RAS and PIK3CA/AKT interact. We and others have previously proven that activation of GSK3| kinase contributes to onset of senescence . Exclusively, we showed that activation of GSK3| phosphorylates the HIRA histone chaperone, therefore localizing this protein to PML bodies and instigating the formation of SAHF .
Here OSI-930 we existing evidence that activated PIK3CA/AKT suppresses RASG12V-induced HIRA relocalization and formation of SAHF through its capability to phosphorylate and inhibit GS3K|. The significance on the PIK3CA/AKT-GSK3| signaling axis in human cancer is underscored by our locating that a large degree of AKTpS473 or GSK3|pS9 may be a predictor of poor survival in human pancreatic cancer, independent of other frequent prognostic indicators. Third, activated PIK3CA/AKT and activated RAS antagonize one another through mTOR signaling. mTOR is well-documented for being a potent repressor of autophagy . Whilst activated RAS inhibits mTOR action to upregulate autophagy and promote senescence , activated AKT1 was in a position to activate mTOR even while in the presence of activated RAS, probable explaining the potential of mAKT1 to inhibit RASG12V-induced autophagy.
To affirm this in vivo, in mice haboring activated RAS and activated PIK3CA/AKT signaling, the potent mTOR inhibitor, rapamycin, reactivated RAS-senescence. We conclude that activated PIK3CA/AKT suppresses RASinduced senescence via its ability to intersect with and antagonize several outputs of chronic activated RAS, such as upregulation of p16INK4a, activation of GSK3| and repression of mTOR.