The Association of AMPK with ULK1 Regulates Autophagy

Abstract

Autophagy is a highly orchestrated intracellular bulk degradation process that is activated by various environmental stresses. The serine/threonine kinase ULK1, like its yeast homologue Atg1, is a key initiator of autophagy that is negatively regulated by the mTOR kinase. However, the molecular mechanism that controls the inhibitory effect of mTOR on ULK1-mediated autophagy is not fully understood. Here we identified AMPK, a central energy sensor, as a new ULK1-binding partner. We found that AMPK binds to the PS domain of ULK1 and this interaction is required for ULK1-mediated autophagy. Interestingly, activation of AMPK by AICAR induces 14-3-3 binding to the AMPK-ULK1-mTORC1 complex, which coincides with raptor Ser792 phosphorylation and mTOR inactivation. Consistently, AICAR induces autophagy in TSC2-deficient cells expressing wild-type raptor but not the mutant raptor that lacks the AMPK phosphorylation sites (Ser722 and Ser792). Taken together, these results suggest that AMPK association with ULK1 plays an important role in autophagy induction, at least in part, by phosphorylation of raptor to lift the inhibitory effect of mTOR on the ULK1 autophagic complex.

Anti-tumoral action of cannabinoids on hepatocellular carcinoma: role of AMPK-dependent activation of autophagy

“…35,36 Thus, under certain cellular settings, mTORC1 inhibition and AMPK activation may cooperate to trigger autophagy. [36][37][38] Although future research is needed to completely clarify this point, our data suggest that this could be the mechanism by which cannabinoids trigger autophagy in HCC cells. To note, it has been recently described that mTOR signaling has a critical role in the pathogenesis of HCC and that mTOR inhibitors have antineoplastic activity in experimental models of HCC.…”

Heat shock response and autophagy—cooperation and control

“…[60][61][62] Moreover, direct physical interaction between AMPK or MTOR and ULK1 (unc-51 like autophagy activating kinase 1) plays a crucial role in the regulation of mammalian autophagy. [63][64][65][66][67][68][69] Under conditions of nutrients abundance, the activated MTOR phosphorylates ULK1 and prevents its interaction with AMPK. Conversely, under starvation conditions, AMPK-induced MTOR inhibition prevents MTOR from binding to ULK1.…”

The Med1 Subunit of the Mediator Complex Induces Liver Cell Proliferation and Is Phosphorylated by AMP Kinase

“…4B). The reason that Med1 was not labeled in the absence of AICAR in hepatocytes may be insufficient levels of active AMPK, as studies have shown that AMPK needs to be phosphorylated at its ␣-subunit by upstream kinases before it phosphorylates the substrates (32,43). Med1 phosphorylation was also observed in HeLa cells (data not shown).…”

“…The generation of other GST fusion fragments used in this study, such as PPARbinding protein (PBP/Med1)-(1-6), and the full-length mouse Med1 containing a His tag at the N terminus and cloned into pShuttle-CMV vector (pShuttle-His-Med1) have been described previously (25). FLAG-AMPK␣ plasmid was a kind gift from Dr. Hong-Gang Wang (Penn State College of Medicine, Hershey, PA) (43). Anti-Med1 (sc-8998) and anti-His (sc-803) were from Santa Cruz Biotechnology, Santa Cruz, CA.…”