Recent studies indicate that zinc activates p70 S6 kinase (p70S6k) by a mechanism involving phosphatidylinositol 3-kinase (PI 3-kinase) and Akt (protein kinase B). Here it is shown that phenanthroline, a zinc and heavy metal chelator, inhibited both amino acid- and insulin-stimulated phosphorylation of p70S6k. Both amino acid and insulin activations of p70S6k involve a rapamycin-sensitive step that involves the mammalian target of rapamycin (mTOR, also known as FRAP and RAFT). However, in contrast to insulin, amino acids activate p70S6k by an unknown PI 3-kinase- and Akt-independent mechanism. Thus the effects of chelator on amino acid activation of p70S6k were surprising. For this reason, we tested the hypothesis that zinc directly regulates mTOR activity, independently of PI 3-kinase activation. In support of this, basal and amino acid stimulation of p70S6k phosphorylation was increased by zinc addition to the incubation media. Furthermore, the protein kinase activities of mTOR immunoprecipitated from rat brain lysates were stimulated two- to fivefold by 10-300 μM Zn2+ in the presence of an excess of either Mn2+ or Mg2+, whereas incubation with 1,10-phenanthroline had no effect. These findings indicate that Zn2+ regulates, but is not absolutely required for, mTOR protein kinase activity. Zinc also stimulated a recombinant human form of mTOR. The stimulatory effects of Zn2+ were maximal at ∼100 μM but decreased and became inhibitory at higher physiologically irrelevant concentrations. Micromolar concentrations of other divalent cations, Ca2+, Fe2+, and Mn2+, had no effect on the protein kinase activity of mTOR in the presence of excess Mg2+. Our results and the results of others suggest that zinc acts at multiple steps in amino acid- and insulin cell-signaling pathways, including mTOR, and that the additive effects of Zn2+ on these steps may thereby promote insulin and nutritional signaling.
|Original language||English (US)|
|Journal||American Journal of Physiology - Endocrinology and Metabolism|
|Issue number||1 44-1|
|State||Published - Oct 10 2001|
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism
- Physiology (medical)