The inner mitochondrial membrane fission protein MTP18 serves as a mitophagy receptor to prevent apoptosis in oral cancer

Abstract

MTP18 (also known as MTFP1), an inner mitochondrial membrane protein, plays a vital role in maintaining mitochondrial morphology by regulating mitochondrial fission. Here, we found that MTP18 functions as a mitophagy receptor that targets dysfunctional mitochondria into autophagosomes for elimination. Interestingly, MTP18 interacts with members of the LC3 (also known as MAP1LC3) family through its LC3-interacting region (LIR) to induce mitochondrial autophagy. Mutation in the LIR motif (mLIR) inhibited that interaction, thus suppressing mitophagy. Moreover, Parkin or PINK1 deficiency abrogated mitophagy in MTP18-overexpressing human oral cancer-derived FaDu cells. Upon exposure to the mitochondrial oxidative phosphorylation uncoupler CCCP, MTP18[mLIR]-FaDu cells showed decreased TOM20 levels without affecting COX IV levels. Conversely, loss of Parkin or PINK1 resulted in inhibition of TOM20 and COX IV degradation in MTP18[mLIR]-FaDu cells exposed to CCCP, establishing Parkin-mediated proteasomal degradation of outer mitochondrial membrane as essential for effective mitophagy. We also found that MTP18 provides a survival advantage to oral cancer cells exposed to cellular stress and that inhibition of MTP18-dependent mitophagy induced cell death in oral cancer cells. These findings demonstrate that MTP18 is a novel mitophagy receptor and that MTP18-dependent mitophagy has pathophysiologic implications for oral cancer progression, indicating inhibition of MTP18-mitophagy could thus be a promising cancer therapy strategy.

Keywords: Apoptosis; MTP18; Mitochondrial fission; Mitophagy; Parkin.