Each human somatic cell typically harbors 23 pairs of chromosomes, ensuring the accurate distribution of genetic material during cell division. Aneuploidy refers to the condition where cells possess abnormal numbers of chromosomes, either as an addition or loss of entire chromosomes. This chromosomal imbalance is notorious in oncogenesis and certain genetic disorders such as Down syndrome. The RPTU research consortium spearheaded by Professor Zuzana Storchová has shed light on how even subtle numerical deviations in chromosomes initiate cascades of biochemical disturbances that severely impact cellular organelles, particularly mitochondria.

Previous knowledge has established that abnormal chromosome numbers induce an imbalance in protein synthesis, overwhelming cellular quality control systems that maintain proteome equilibrium. However, the specific downstream consequences of these proteostatic disruptions—especially on mitochondrial function—have remained elusive. Using sophisticated genetic engineering, the team generated colorectal cancer cell lines with one or two additional chromosomes by modifying the near-diploid HCT116 background, thereby creating controlled models of aneuploidy to dissect cellular consequences at high resolution.

Intriguingly, these aneuploid cell lines accumulated cytoplasmic protein aggregates lacking delimiting membranes. Central to these aggregates was SQSTM1, also known as p62, a multifunctional autophagy receptor known to bind ubiquitinated proteins and damaged organelles for degradation. The research demonstrated that the quantity of p62-containing aggregates positively correlated with the size of the extra chromosome, suggesting that chromosome dosage directly influences proteostasis stress levels. This finding highlights p62’s pivotal role in managing the cellular burden induced by superfluous protein synthesis due to aneuploidy.

Delving deeper, the study uncovered that mitochondrial precursor proteins—normally synthesized in the cytosol and imported into mitochondria for proper function—were sequestered within p62-positive aggregates. This sequestration effectively ‘confiscated’ these precursors, preventing their timely translocation into mitochondria. As a consequence, mitochondrial architecture and bioenergetics deteriorated, signifying a profound disruption of mitochondrial homeostasis triggered by chromosomal imbalances. This molecular crosstalk between nuclear genome instability and mitochondrial dysfunction marks a critical insight into aneuploidy pathology.

The researchers emphasize that their engineered cell lines mimic physiologically relevant aspects of human pathologies characterized by unbalanced genomic content, including cancer and trisomy syndromes. This experimental platform thus represents an invaluable tool for investigating how proteome imbalances translate into organelle dysfunction. The implications extend beyond basic biology, as the intersection of proteotoxic stress and impaired mitochondrial metabolism may underlie the remarkable adaptability and drug resistance observed in aneuploid cancer cells.

Interestingly, despite the inherent stress of chromosome number abnormalities, cancer cells often sustain viability and proliferative capacity by modulating mitochondrial functions. The team hypothesizes that alterations in mitochondrial metabolism may serve as an adaptive mechanism to withstand the detrimental consequences of proteotoxic stress, thereby conferring survival advantages under chemotherapeutic pressures. This paradigm challenges the traditional view of cancer cells as merely victims of proteome imbalance, instead highlighting their dynamic metabolic plasticity.

Professor Storchová articulates the broader significance of these findings by stating that they reveal a previously unappreciated linkage between genomic aberrations, protein aggregation stress, and mitochondrial function. Such insights underscore the intricate interdependence between cellular compartments and quality control systems in preserving cell viability amidst genetic disturbances. By delineating the molecular pathways involved, this research paves the way for exploring targeted interventions aimed at restoring mitochondrial import and alleviating proteotoxic aggregation in aneuploid conditions.

In addition to providing mechanistic clarity, the study emphasizes translational potential. The aggregation of mitochondrial precursor proteins via the SQSTM1/p62 axis could represent a druggable vulnerability in cancers harboring chromosomal abnormalities. Therapeutic strategies aimed at modulating p62-mediated pathways or enhancing mitochondrial protein import efficiency may sensitize tumor cells to existing treatments and overcome intrinsic drug resistance. As such, the work offers a promising framework for improving oncological outcomes by exploiting the mitochondrial adaptations of aneuploid cells.

This research was conducted as part of the graduate school program STRESSistance at RPTU, funded by the German Research Foundation, and benefited from collaborations with research groups specializing in molecular genetics, cell biology, and systems biology of neurodegenerative diseases. Cross-institutional cooperation facilitated a comprehensive approach, combining genetic engineering, biochemical assays, and advanced imaging techniques to unravel the cellular consequences of aneuploidy with unprecedented detail.

First author and postdoctoral researcher Prince Saforo Amponsah played a critical role in leading the project and conceptualizing the mitochondrial sequestration mechanisms. Supported by prestigious fellowships and grants, Amponsah’s work stands at the intersection of molecular genetics and cellular bioenergetics, spearheading efforts to understand how genomic instability impacts organelle function. His contributions highlight the importance of interdisciplinary research in tackling complex biological phenomena relevant to cancer and genetic disorders.

In conclusion, the pioneering study challenges existing notions about the biological repercussions of aneuploidy by linking protein homeostasis disturbances to mitochondrial dysfunction via p62-dependent protein aggregation. This nexus articulates a molecular pathway that may contribute significantly to disease progression and therapy resistance in cancers and other aneuploid conditions. Future research building upon these insights holds promise for innovative therapeutic strategies targeting mitochondrial adaptations in aberrant genomic contexts.

Subject of Research: Cells

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

News Publication Date: 17-Jun-2025

Web References: DOI: 10.1038/s41467-025-60857-4

Image Credits: Prince Saforo Amponsah

Keywords: Aneuploidy, Proteostasis, Mitochondrial Dysfunction, SQSTM1, p62, Protein Aggregation, Mitochondrial Precursor Proteins, Cancer, Chromosomal Imbalance, Proteotoxic Stress, Mitochondrial Import, Cellular Metabolism

Radiotherapy fundamentally operates by inflicting critical DNA lesions, predominantly double-strand breaks (DSBs), in target cancer cells. These lesions are inherently cytotoxic, and their efficient repair directly correlates with tumor cell survival post-treatment. However, many tumors, such as breast and lung cancers, express abnormally elevated levels of repair proteins, which enable brisk and robust repair of DNA damage, culminating in treatment resistance. The intricate network underlying this repair process is heavily influenced by epigenetic and post-translational modifications, realms that have remained partially opaque until now. Prof. ZHAO’s team delved deeply into this regulatory labyrinth, focusing on the role of SUMOylation, a small ubiquitin-like modifier process, in modulating DNA repair dynamics.

Central to their discovery is the zinc finger protein ZNF451, which the investigators identified as markedly overexpressed in multiple malignancies, including breast and lung cancers. Importantly, elevated ZNF451 levels were correlated with poorer prognostic outcomes in patient cohorts, signaling its potential clinical relevance. Upon exposure to ionizing radiation, ZNF451 rapidly localizes to DNA damage sites, initiating a catalytic event that post-translationally modifies the ubiquitin ligase RNF168 via conjugation with the SUMO2 modifier. This SUMOylation event acts as a stabilization mechanism for RNF168, preventing its proteasomal degradation and thereby augmenting its accumulation and retention at the sites of DNA lesions.

RNF168 itself is a pivotal E3 ubiquitin ligase responsible for propagating ubiquitin signaling cascades on chromatin, particularly on histone variants such as H2A and H2AX. These histone ubiquitinations are essential for recruiting downstream effector proteins that execute DNA repair through homologous recombination or non-homologous end joining. By enhancing RNF168 stability and localization, ZNF451 effectively amplifies the ubiquitin signal at damaged chromatin regions, thereby potentiating the cellular DNA repair response. This amplification mechanism is especially critical in the context of radiotherapy, where DNA damage must be resolved swiftly to facilitate tumor cell survival.

Intriguingly, the research also unveiled a sophisticated crosstalk between ZNF451 and RNF8, another canonical E3 ligase involved early in the DNA damage response cascade. Contrary to straightforward cooperative behavior, these two proteins exhibit a dynamic regulatory network characterized by competitive binding to RNF168, effectively regulating its recruitment and activity in a finely balanced manner. The study’s quantitative analyses revealed that ZNF451 and RNF8 exert mutually inhibitory influences on each other’s ability to recruit RNF168, yet paradoxically, simultaneous depletion of both proteins caused a severe deficiency in RNF168 accumulation at DNA damage sites. This underscores a complex equilibrium that maintains optimal ubiquitination signaling necessary for efficient DNA repair.

The sum of these findings led the authors to propose a novel model of “dynamic equilibrium regulation” in DNA damage repair, wherein opposing but complementary interactions between different ligases tune the amplitude and duration of ubiquitin signaling. Such a model has profound implications for understanding how tumor cells orchestrate DNA repair and resist genotoxic therapies. The elucidation of this balance between SUMOylation and ubiquitination at the molecular level opens potential avenues for therapeutic intervention by disrupting this equilibrium to sensitize tumors to radiation-induced damage.

This breakthrough also emphasizes the emerging importance of SUMOylation in the DNA damage response. While ubiquitination has been extensively studied in this context, SUMO modifications add an additional layer of regulation, influencing the stability, localization, and interactions of key repair factors. SUMO2 conjugation of RNF168 represents one such modification that stabilizes this integral repair protein, illustrating the nuanced interplay between different post-translational modifications in fine-tuning repair pathways.

The work by ZHAO et al. not only delineates the mechanistic insights into SUMO-mediated regulation of DNA repair but also highlights the translational potential of targeting the ZNF451-RNF8-RNF168 axis. Inhibiting the SUMOylation activity of ZNF451 or manipulating its interaction with RNF8 could render tumor cells more susceptible to radiotherapy, overcoming intrinsic radioresistance. This approach could revolutionize treatment paradigms for cancers characterized by DNA repair deregulation.

Furthermore, the identification of ZNF451’s overexpression as a biomarker linked to poor prognosis offers a clinical window for patient stratification. Patients with high ZNF451 expression may require more aggressive or alternative therapeutic regimes to counterbalance their tumors’ enhanced DNA repair capacity. This personalized medicine angle adds another valuable dimension to the research’s clinical impact.

In summary, this research unveiled a previously underappreciated regulatory axis centered on ZNF451’s SUMOylation of RNF168, modulated by the interplay with RNF8, that collectively amplifies ubiquitin signaling essential for DNA repair. This intricate regulatory schema redefines our comprehension of how cells dynamically control repair factor activities at DNA lesions and how disruptions in this system influence cancer radiotherapy sensitivity. As the field moves forward, targeting this finely tuned equilibrium holds promise as a novel therapeutic strategy to enhance the efficacy of DNA-damaging treatments.

This landmark study, set to transform the landscape of cancer biology and therapy, eloquently demonstrates the power of dissecting post-translational modification networks in revealing vulnerabilities within tumor DNA repair machinery. Through meticulous experimental work and mechanistic elucidation, Prof. ZHAO’s team has not only expanded the molecular vocabulary of DNA repair regulation but has also paved the way toward novel radiosensitization approaches critical for improving patient outcomes in oncology.

Subject of Research: Regulation of DNA damage repair mechanisms via SUMOylation and ubiquitination, focusing on the role of ZNF451, RNF8, and RNF168 in modulating radiotherapy sensitivity in cancer.

Article Title: ZNF451 collaborates with RNF8 to regulate RNF168 localization and amplify ubiquitination signaling to promote DNA damage repair and regulate radiosensitivity

News Publication Date: 7-Mar-2025

Web References: http://dx.doi.org/10.1038/s41418-025-01472-0

Image Credits: ZHAO Guoping

Keywords: Physical sciences