AGC Kinases in mTOR signaling

The mammalian target of rapamycin (mTOR), a protein kinase with homology to lipid kinases, orchestrates cellular responses to growth and stress signals. Various extracellular and intracellular inputs to mTOR are known. mTOR processes these inputs as part of two mTOR protein complexes, mTORC1 or mTORC2. Surprisingly, despite the many cellular functions that are linked to mTOR, there are very few direct mTOR substrates identified to date. With the recent discovery of mTORC2, mounting evidence point to mTOR as a central regulator of members of a family of protein kinases, the AGC (protein kinases A/PKG/PKC) family. The AGC kinases are one of the most well-characterized among the eukaryotic protein kinase family. A multitude of cellular functions and substrates has been ascribed to these kinases and their deregulation underlies numerous pathological conditions. mTOR phosphorylates common motifs in a number of these AGC kinases that could lead to their allosteric activation. AGC kinase activation triggers the phosphorylation of diverse targets that ultimately control cellular response to stimuli. This review will focus on the recent findings on how mTOR regulates AGC kinases. I will discuss how these kinases are wired to the mTOR signaling circuit, including examples of mTOR-dependent outputs consequent to AGC kinase activation.