A20 binding and inhibitor of nuclear factor kappa B (NF-κB)-1 (ABIN-1) - a novel modulator of mitochondrial autophagy

A20 binding inhibitor of nuclear factor kappa B (NF-κB)-1 (ABIN-1), a polyubiquitin-binding protein, is a signal-induced autophagy receptor that attenuates NF-κB-mediated inflammation and cell death. The present study aimed to elucidate the potential role of ABIN-1 in mitophagy, a biological process whose outcome is decisive in diverse physiological and pathological settings. Microtubule-associated proteins 1A/1B light chain 3B-II (LC3B-II) was found to be in complex with ectopically expressed hemagglutinin (HA)-tagged-full length (FL)-ABIN-1. Bacterial expression of ABIN-1 and LC3A and LC3B showed direct binding of ABIN-1 to LC3 proteins, while mutations in the LC3-interacting region (LIR) 1 and 2 motifs of ABIN-1 abrogated ABIN-1/LC3B-II complex formation. Importantly, induction of autophagy in HeLa cells resulted in co-localization of ABIN-1 with LC3B-II in autophagosomes and with lysosomal associated membrane protein 1 (LAMP-1) in autophagolysosomes, leading to co-degradation of ABIN-1 with p62. Interestingly, ABIN-1 was found to translocate to damaged mitochondria in HeLa-mCherry-Parkin cells. In line with this observation, CRISPR/Cas9-mediated deletion of ABIN-1 significantly inhibited the degradation of the mitochondrial outer membrane proteins voltage-dependent anion-selective channel 1 (VDAC-1), mitofusin-2 (MFN2), and translocase of outer mitochondrial membrane (TOM)20. Additionally, siRNA-mediated knockdown of ABIN-1 significantly decreased lysosomal uptake of mitochondria in HeLa cells expressing mCherry-Parkin and the fluorescence reporter mt-mKEIMA. Collectively, our results identify ABIN-1 as a novel and selective mitochondrial autophagy regulator that promotes mitophagy, thereby adding a new player to the complex cellular machinery regulating mitochondrial homeostasis.

• Merline, R.
• Rödig, H.
• Zeng-Brouwers, J.
• Poluzzi, C.
• Tascher, G.
• Michaelis, J.
• Lopez-Mosqueda, J.
• Rhiner, A.
• Huber, L. S.
• Diehl, V.
• Dikic, I.
• Kögel, D.
• Münch, C.
• Wygrecka, M.
• Schaefer, L.