Mammalian TOR controls one of two kinase pathways acting upon nPKC delta and nPKC epsilon

There are three conserved phosphorylation sites in protein kinase C (PKC) i sotypes that have been termed priming sites and play an important role in P KC function. The requirements and pathways involved in novel (nPKC) phospho rylation have been investigated here. The evidence presented for nPKC delta shows that there are two independent kinase pathways that act upon the act ivation loop (Thr-505) and a C-terminal hydrophobic site (Ser-662) and that the phosphorylation of the Ser-662 site is protected from dephosphorylatio n by the Thr-505 phosphorylation. Both phosphorylations require C1 domain-d ependent allosteric activation of PKC. The third site (Ser-643) appears to be an autophosphorylation site. The serum-dependent phosphorylation of the Thr-505 and Ser-662 sites increases nPKC delta activity up to 80-fold. Phos phorylation at the Ser-662 site is independently controlled by a pathway in volving mammalian TOR (mTOR) because the rapamycin-induced block of its pho sphorylation is overcome by co-expression of a rapamycin-resistant mutant o f mTOR. Consistent with this role of mTOR, amino acid deprivation selective ly inhibits the serum-induced phosphorylation of the Ser-662 site in nPKC d elta. It is established that nPKC epsilon behaves in a manner similar to nP KC delta with respect to phosphorylation at its C-terminal hydrophobic site , Ser-729. The results define the regulatory inputs to nPKC delta and nPKC epsilon and establish these PKC isotypes downstream of mTOR and on an amino acid sensing pathway. The multiple signals integrated in PKC are discussed .