PPP2/PP2A-mediated dephosphorylation of LC3B links PINK1-PRKN/Parkin-mediated mitophagy to SCA12 pathogenesis

Atg8-family proteins are autophagosome-associated proteins and play important roles in macroautophagy/autophagy, a conserved process for degrading defective or excessive cellular components. Post-translational modifications of mammalian Atg8-family proteins, including phosphorylation, regulate multiple steps in the autophagic process. In this context, several Atg8-family protein-associated kinases have been found to regulate autophagy, yet the phosphatases in the dephosphorylation of Atg8-family proteins remain unknown. Here, we report that the heterotrimeric PPP2/PP2A (protein phosphatase 2) is a novel regulator in modulating LC3B dephosphorylation. Mechanistically, we find that PPP2-mediated LC3B dephosphorylation reduces the interaction between LC3B and the mitophagy receptor OPTN, thereby impeding the mitochondrial recruitment of phagophores during PINK1-PRKN/Parkin-mediated mitophagy. Interestingly, we find that overexpression of the β2 isoform of PPP2R2B (protein phosphatase 2 regulatory subunit Bbeta; PPP2R2Bβ2), which mimics the spinocerebellar ataxia type 12 (SCA12) pathological condition, harms neuronal survival by enhancing PPP2-mediated LC3B dephosphorylation and reducing mitochondrial recruitment of phagophores upon mitochondrial damage. Importantly, pharmacological induction of mitophagy by the small molecule compound deferiprone (DFP) relieves PPP2R2Bβ2-mediated neuronal toxicity. Overall, our results not only uncover a mechanism by which protein dephosphorylation negatively regulates mitophagy but also provide insights into the pathogenesis of PPP2R2Bβ2-mediated SCA12.Abbreviations: AO: antimycin A and oligomycin A; DFP: deferiprone; EGFP: enhanced green fluorescent protein; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; OPTN: optineurin; PINK1: PTEN induced kinase 1; PLA: proximity ligation assay; PPP2: protein phosphatase 2; PPP2CA: protein phosphatase 2 catalytic subunit alpha; PPP2CB: protein phosphatase 2 catalytic subunit beta; PPP2R2Bβ2: protein phosphatase 2 regulatory subunit B beta 2; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; SCA12: spinocerebellar ataxia type 12; WT: wild type.