Fig. 5.

Together, AMPK and HRI signal mitochondrial dysfunction to mTORC1. (A) Loss of HRI prevents activation of the ISR in response to mitochondrial distress and renders mTORC1 signaling resistant to the second phase of inhibition caused by oligomycin. Cell lysates were analyzed by immunoblotting and the levels of S6K1 phosphorylation quantified as in Fig. 4. Values are mean ± SEM for n = 3 biologically independent experiments. P values were determined using a two-sided Student’s t test. (B) HRI KO HEK293T cells have increased AMPK activity, which corresponds to an increase in AMP levels upon treatment with oligomycin. Metabolite extracts were analyzed by liquid chromatography-mass spectrometry (LC-MS) and relative AMP levels are shown as the mean ± SEM for n = 3 biologically independent experiments. (C) Loss of both HRI and AMPK prevents inhibition of mTORC1 by oligomycin. Time course experiments were performed and analyzed as in A in cells lacking AMPK and HRI (AMPK and HRI TKO). (D) In HEK293T cells lacking AMPK and HRI, mTORC1 signaling is resistant to the inhibition normally caused by a 6-h treatment with piericidin, antimycin, or oligomycin. (E) Model for pathway leading to mTORC1 inhibition in response to mitochondrial distress.