The inner mitochondrial membrane fission protein MTP18 serves as a mitophagy receptor to prevent apoptosis in oral cancer
Debasna Pritimanjari Panigrahi, Prakash Priyadarshi Praharaj, Bishnu Prasad Behera, Srimanta Patra, Shankargouda Patil, Birija Sankar Patro, Sujit K. Bhutia
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.