Biology subjects

Kolitsida, P.

Publications and source records attributed to Kolitsida, P..

4 recordsLinked to original sources

bioRxiv2026

Dynamin-2 promotes Atg9A retrieval from phagophores during autophagy.

Autophagy involves the rapid growth of phagophores through membrane addition. This growth is triggered by vesicles containing the Atg9A protein. However, Atg9A is not incorporated into mature autophagosomes. We now demonstrate that Dynamin-2 (Dnm2) colocalizes with the BAR domain protein Endophilin-B1 (EndoB1/Bif-1/SH3GLB1) and other autophagy proteins when autophagy is induced. Our data suggest that Atg9A is retrieved from phagophores via fission, with Dnm2 acting as the membrane scission protein. Blocking Atg9A recycling, either by mutating Dnm2, using RNA interference, or applying chemical inhibitors, results in Atg9A remaining in autophagosomes and being degraded during autophagy. Overall, these findings provide new insights into the roles of membrane-scission proteins in autophagy.

cell biology↗

bioRxiv2024

Mfn2 induces NCLX-mediated calcium release from mitochondria.

Mfn2 is a mitochondrial outer-membrane fusion protein that also functions as a tether between mitochondria and the ER. Here, we identify a previously unrecognized role for Mfn2 in promoting mitochondrial Ca2+ release via the Na+/Ca2+ exchanger NCLX. This function was uncovered through studies with the fungal toxin phomoxanthone A (PXA), which induces NCLX-dependent Ca2+ release by directly targeting Mfn2. Mfn2-dependent Ca2+ release through NCLX is similarly triggered by ROS in respiring cells treated with oligomycin or mitoPQ. ROS enhances Ca2+ release by strengthening the interaction between Mfn2 and NCLX, an interaction that also requires the mitochondrial outer-membrane protein SLC25A46. Together, these proteins coordinate mitochondrial fission and Ca2+ release to initiate mitophagy. The antioxidant N-acetylcysteine blocks ROS-induced mitochondrial fission, but inhibition of Ca2+ release with the NCLX inhibitor CGP37157 does not, indicating that ROS-driven fission is independent of Ca2+ release. In contrast, Ca2+ release is required for efficient mitophagy, as NCLX inhibition arrests this process at a later stage. We further show that Ca2+ promotes mitophagy through NEDD4-1, which is a Ca2+-responsive E3 ubiquitin ligase. Together, these findings connect mitochondrial ROS production to Ca2+ signaling, mitochondrial remodeling, and mitophagy, providing new insight into how mitochondrial dysfunction may contribute to neurodegenerative and metabolic disease.

cell biology↗

bioRxiv2022

The pyruvate dehydrogenase complex regulates mitophagic selectivity independently of its catalytic activity

The mitophagic degradation of mitochondrial matrix proteins in S. cerevisiae was previously shown to be selective, reflecting a pre-engulfment sorting step within the mitochondrial network. This selectivity is regulated through phosphorylation of mitochondrial matrix proteins by the matrix kinases Pkp1 and Pkp2, which in turn appear to be regulated by the phosphatase Aup1/Ptc6. However, these same proteins also regulate the phosphorylation status and catalytic activity of the yeast pyruvate dehydrogenase complex, which is critical for mitochondrial metabolism. To understand the relationship between these two functions, we evaluated the role of the pyruvate dehydrogenase complex in mitophagic selectivity. Surprisingly, we identified a novel function of the complex in regulating mitophagic selectivity, which is independent of its enzymatic activity. Our data support a model in which the pyruvate dehydrogenase complex directly regulates the activity of its associated kinases and phosphatases. This regulatory interaction then determines the phosphorylation state of mitochondrial matrix proteins and their mitophagic fates.

cell biology↗

bioRxiv2019

Phosphorylation of mitochondrial matrix proteins regulates their selective mitophagic degradation

Mitophagy is an important quality control mechanism in eukaryotic cells, and defects in mitophagy correlate with aging phenomena and neurodegenerative disorders. It is known that different mitochondrial matrix proteins undergo mitophagy with very different rates, but to date the mechanism underlying this selectivity at the individual protein level has remained obscure. We now present evidence indicating that protein phosphorylation within the mitochondrial matrix plays a mechanistic role in regulating selective mitophagic degradation in yeast, via involvement of the Aup1 mitochondrial protein phosphatase, as well as two known matrix-localized protein kinases, Pkp1 and Pkp2. By focusing on a specific matrix phosphoprotein reporter, we also demonstrate that phospho-mimetic and non-phosphorylatable point mutations at known phosphosites in the reporter increased or decreased its tendency to undergo mitophagy. Finally, we show that phosphorylation of the reporter protein is dynamically regulated during mitophagy, in an Aup1-dependent manner. Our results indicate that structural determinants on a mitochondrial matrix protein can govern its mitophagic fate, and that protein phosphorylation regulates these determinants.\n\nSignificance statementMitochondrial dysfunction underlies many age-related human pathologies. In normal cells, defective mitochondria are often degraded by mitophagy, a process in which these mitochondria are engulfed in autophagosomes and sent for degradation in the lysosome/vacuole. Surprisingly, studies on mitophagy in diverse eukaryotic organisms reveal an unexpected dimension of protein-level selectivity, wherein individual protein species exhibit divergent rates of mitophagic degradation. In this manuscript, we show that this surprising intra-mitochondrial selectivity can be generated by differential phosphorylation of individual mitochondrial protein species, and we identify mitochondrial phosphatases and kinases which contribute to this regulation. By identifying a mechanism which regulates the intra-mitochondrial selectivity of mitophagic degradation, our findings open the door to potential manipulation of the quality control process in the future.

cell biology↗