bims-tricox 2025-06-22 papers

Issue of 2025–06–22
three papers selected by
Yash Verma, University of Zurich

EMBO J. 2025 Jun 16.

Dysfunctional mitochondria trap proteins in the intermembrane space.

Tamara Flohr, Markus Räschle, Johannes M Herrmann.

The accumulation of mitochondrial precursor proteins in the cytosol due to mitochondrial dysfunction compromises cellular proteostasis and is a hallmark of diseases. Why non-imported precursors are toxic and how eukaryotic cells prevent their accumulation in the cytosol is still poorly understood. Using a proximity labeling-based assay to globally monitor the intramitochondrial location of proteins, we show that, upon mitochondrial dysfunction, many mitochondrial matrix proteins are sequestered in the intermembrane space (IMS); something we refer to as "mitochondrial triage of precursor proteins" (MitoTraP). MitoTraP is not simply the result of a general translocation block at the level of the inner membrane, but specifically directs a subgroup of matrix proteins into the IMS, many of which are constituents of the mitochondrial ribosome. Using the mitoribosomal protein Mrp17 (bS6m) as a model, we found that IMS sequestration prevents its mistargeting to the nucleus, potentially averting interference with assembly of cytosolic ribosomes. Thus, MitoTraP represents a novel, so far unknown mechanism of the eukaryotic quality control system that protects the cellular proteome against the toxic effects of non-imported mitochondrial precursor proteins.

Keywords: Intermembrane Space; Mitochondria; Nucleolus; Protein Targeting; Ribosome

DOI: https://doi.org/10.1038/s44318-025-00486-1

Nat Commun. 2025 Jun 17. 16(1): 5328

Aneuploidy-induced proteostasis disruption impairs mitochondrial functions and mediates aggregation of mitochondrial precursor proteins through SQSTM1/p62.

Prince Saforo Amponsah, Jan-Eric Bökenkamp, Olha Kurpa, Svenja Lenhard, Anna Myronova, Daniel Osmar Vega Velazquez, Celina Hirschelmann, Christian Behrends, Johannes M Herrmann, Markus Räschle, Zuzana Storchová.

Aneuploidy, or aberrant chromosomal content, disrupts cellular proteostasis through altered expression of numerous proteins. Aneuploid cells accumulate SQSTM1/p62-positive cytosolic bodies, exhibit impaired protein folding, and show altered proteasomal and lysosomal activity. Here, we employ p62 proximity- and affinity-based proteomics to elucidate p62 interactors in aneuploid cells and observe an enrichment of mitochondrial proteins. Increased protein aggregation and colocalization of p62 with both novel interactors and mitochondrial proteins is further confirmed by microscopy. Compared to parental diploids, aneuploid cells suffer from mitochondrial defects, including perinuclearly-clustered mitochondrial networks, elevated reactive oxygen species levels, reduced mitochondrial DNA abundance, and impaired protein import, leading to cytosolic accumulation of mitochondrial precursor proteins. Overexpression of heat shock proteins in aneuploid cells mitigates protein aggregation and decreases the colocalization of p62 with the mitochondrial protein TOMM20. Thus, proteotoxic stress caused by chromosome gains results in the sequestration of mitochondrial precursor proteins into cytosolic p62-bodies, thereby compromising mitochondrial function.

DOI: https://doi.org/10.1038/s41467-025-60857-4

Life Sci Alliance. 2025 Sep;pii: e202403082. [Epub ahead of print]8(9):

Transcription arrest induces formation of RNA granules in mitochondria.

Katja G Hansen, Autum Baxter-Koenigs, Caroline Am Weiss, Erik McShane, L Stirling Churchman.

Mitochondrial gene expression regulation is required for the biogenesis of oxidative phosphorylation (OXPHOS) complexes, yet the spatial organization of mitochondrial RNAs (mt-RNAs) remains unknown. Here, we investigated the spatial distribution of mt-RNAs during various cellular stresses using single-molecule RNA-FISH. We discovered that transcription inhibition leads to the formation of distinct RNA granules within mitochondria, which we term inhibition granules. These structures differ from canonical mitochondrial RNA granules and form in response to multiple transcription arrest conditions, including ethidium bromide treatment, specific inhibition or stalling of the mitochondrial RNA polymerase, and depletion of the SUV3 helicase. Inhibition granules appear to stabilize certain mt-mRNAs during prolonged transcription inhibition. This phenomenon coincides with an imbalance in OXPHOS complex expression, where mitochondrial-encoded transcripts decrease while nuclear-encoded subunits remain stable. We found that cells recover from transcription inhibition via resolving the granules, restarting transcription, and repopulating the mitochondrial network with mt-mRNAs within hours. We suggest that inhibition granules may act as a reservoir to help overcome OXPHOS imbalance during recovery from transcription arrest.

DOI: https://doi.org/10.26508/lsa.202403082