LC3 subfamily in cardiolipin-mediated mitophagy: A comparison of the LC3A, LC3B and LC3C homologs

Abstract

Among the described indicators of mitochondrial damage, externalization of the phospholipid cardiolipin (CL) to the outer mitochondrial membrane has been proposed to trigger mitophagy, acting as a signal for binding the autophagy protein LC3B. However, the behavior of the other LC3 subfamily members has not been explored yet. In the present contribution, a comparative analysis of the interaction of LC3B, LC3A and LC3C with CL-containing model membranes, as well as their ability to translocate to mitochondria was assessed. Binding of LC3A to CL was higher than that of LC3B, and both proteins showed a similar ability to colocalize with mitochondria upon induction of CL externalization by rotenone in HeLa-NDPK-D or SH-SY5Y cells. Two residues located in the N-terminal region of LC3A were shown to be important for its recognition of damaged mitochondria. Moreover, the in vitro results suggested a possible role of LC3A, but not of LC3B, in oxidized-CL recognition as a counterweight to excessive apoptosis activation. In the case of LC3C, even if this protein showed a higher binding than LC3B or LC3A to CL, binding was less specific, and colocalization of LC3C with mitochondria was not rotenonedependent. These results suggest that, at variance with LC3A, LC3C does not participate in the rotenone-CL mitophagy mechanism. The data support the notion that the various LC3/GABARAP family members might play different roles during autophagy initiation, identifying LC3A as a novel stakeholder in CL-mediated mitophagy.