07-1224 Sigma-AldrichAnti-PP6C Antibody

Amino acid deprivation promotes the inhibition of the kinase complex mTORC1 (mammalian target of rapamycin complex 1) and activation of the kinase GCN2 (general control nonrepressed 2). Signaling pathways downstream of both kinases have been thought to independently induce autophagy. We showed that these two amino acid-sensing systems are linked. We showed that pharmacological inhibition of mTORC1 led to activation of GCN2 and phosphorylation of the eukaryotic initiation factor 2α (eIF2α) in a mechanism dependent on the catalytic subunit of protein phosphatase 6 (PP6C). Autophagy induced by pharmacological inhibition of mTORC1 required PP6C, GCN2, and eIF2α phosphorylation. Although some of the PP6C mutants found in melanoma did not form a strong complex with PP6 regulatory subunits and were rapidly degraded, these mutants paradoxically stabilized PP6C encoded by the wild-type allele and increased eIF2α phosphorylation. Furthermore, these PP6C mutations were associated with increased autophagy in vitro and in human melanoma samples. Thus, these data showed that GCN2 activation and phosphorylation of eIF2α in response to mTORC1 inhibition are necessary for autophagy. Additionally, we described a role for PP6C in this process and provided a mechanism for PP6C mutations associated with melanoma.

We have recently shown that American ginseng (AG) prevents and treats mouse colitis. Because both mice and humans with chronic colitis have a high colon cancer risk, we tested the hypothesis that AG can be used to prevent colitis-driven colon cancer. Using the azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model of ulcerative colitis, we show that AG can suppress colon cancer associated with colitis. To explore the molecular mechanisms of the anticancer effects of AG, we also carried out antibody array experiments on colon cells isolated at a precancerous stage. We found there were 82 protein end points that were either significantly higher (41 proteins) or significantly lower (41 proteins) in the AOM + DSS group compared with the AOM-alone (control) group. In contrast, there were only 19 protein end points that were either significantly higher (10 proteins) or significantly lower (9 proteins) in the AOM + DSS + AG group compared with the AOM-alone (control) group. Overall, these results suggest that AG keeps the colon environment in metabolic equilibrium when mice are treated with AOM + DSS and gives insight into the mechanisms by which AG protects from colon cancer associated with colitis.