Activation of AMP-Activated Protein Kinase Leads to the Phosphorylation of Elongation Factor 2 and an Inhibition of Protein Synthesis

Abstract

Protein synthesis, in particular peptide-chain elongation, consumes cellular energy. Anoxia activates AMP-activated protein kinase (AMPK, see ), resulting in the inhibition of biosynthetic pathways to conserve ATP. In anoxic rat hepatocytes or in hepatocytes treated with 5-aminoimidazole-4-carboxamide (AICA) riboside, AMPK was activated and protein synthesis was inhibited. The inhibition of protein synthesis could not be explained by changes in the phosphorylation states of initiation factor 4E binding protein-1 (4E-BP1) or eukaryotic initiation factor 2alpha (eIF2alpha). However, the phosphorylation state of eukaryotic elongation factor 2 (eEF2) was increased in anoxic and AICA riboside-treated hepatocytes and in AICA riboside-treated CHO-K1 cells, and eEF2 phosphorylation is known to inhibit its activity. Incubation of CHO-K1 cells with increasing concentrations of 2-deoxyglucose suggested that the mammalian target of the rapamycin (mTOR) signaling pathway did not play a major role in controlling the level of eEF2 phosphorylation in response to mild ATP depletion. In HEK293 cells, transfection of a dominant-negative AMPK construct abolished the oligomycin-induced inhibition of protein synthesis and eEF2 phosphorylation. Lastly, eEF2 kinase, the kinase that phosphorylates eEF2, was activated in anoxic or AICA riboside-treated hepatocytes. Therefore, the activation of eEF2 kinase by AMPK, resulting in the phosphorylation and inactivation of eEF2, provides a novel mechanism for the inhibition of protein synthesis.

Lack of starvation-induced activation of AMP-activated protein kinase in the hypothalamus of the Lou/C rats resistant to obesity

“…The phosphorylation state of ACC and EF2, two known targets of AMPK, 25 was increased by starvation in control Wistar but not in the Lou/C rats, the total ACC and EF2 contents being not affected (Figures 2a-d). This result confirms the lack of AMPK activation by starvation in the hypothalamus of Lou/C rats ( Figure 1).…”

Hypoxia transiently affects skeletal muscle hypertrophy in a functional overload model

“…Consistent with previous data in vivo (16), the hypoxia-induced depression of mTOR signaling did not significantly influence 4E-BP1 activity. The elongation factor eEF2, is shown to be controlled by P70 S6K through eEF2 kinase (13) and inhibited by AMPK (23). The lack of change in AMPK phosphorylation in hypoxic rats suggests that the increased proportion of phosphorylated eEF2, and then decreased eEF2 activity in OvH muscles at day 5 could be rather explained by the impairment of P70 S6K activation.…”

Stress and mTORture signaling

“…AMPK, as a result of low energy levels, phosphorylates and thereby activates TSC2, resulting in TOR inhibition (Inoki et al, 2003a). Additional AMPK/eEF2 kinase-mediated stimulation of eEF2 phosphorylation by hypoxia (Horman et al, 2002) further contributes to inhibition of protein synthesis (Connolly et al, 2006;Liu et al, 2006).…”