ER stress (PERK/eIF2alpha phosphorylation) mediates the polyglutamine-induced LC3 conversion, an essential step for autophagy formation

Expanded polyglutamine 72 repeat (polyQ72) aggregates induce endoplasmic reticulum (ER) stress-mediated cell death with caspase-12 activation and vesicular formation (autophagy). We examined this relationship and the molecular mechanism of autophagy formation. Rapamycin, a stimulator of autophagy, inhibited the polyQ72-induced cell death with caspase-12 activation. PolyQ72, but not polyQ11, stimulated Atg5-Atg12-Atg16 complex-dependent microtubule-associated protein 1 (MAP1) light chain 3 (LC3) conversion from LC3-I to -II, which plays a key role in autophagy. The eucaryotic translation initiation factor 2 alpha (eIF2alpha) A/A mutation, a knock-in to replace a phosphorylatable Ser51 with Ala51, and dominant-negative PERK inhibited polyQ72-induced LC3 conversion. PolyQ72 as well as ER stress stimulators upregulated Atg12 mRNA and proteins via eIF2alpha phosphorylation. Furthermore, Atg5 deficiency as well as the eIF2alpha A/A mutation increased the number of cells showing polyQ72 aggregates and polyQ72-induced caspase-12 activation. Thus, autophagy formation is a cellular defense mechanism against polyQ72-induced ER-stress-mediated cell death by degrading polyQ72 aggregates, with PERK/eIF2alpha phosphorylation being involved in polyQ72-induced LC3 conversion.