A p62-dependent rheostat dictates micronuclei catastrophe and chromosome rearrangements

Affiliations

• Department of Experimental Oncology at IEO, European Institute of Oncology IRCCS, Milan, Italy.
• Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
• IFOM ETS, The AIRC Institute of Molecular Oncology, Milan, Italy.
• Division of Basic Sciences and Human Biology, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.
• Human Oncology and Pathogenesis Program and Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA.
• Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
• The Blavatnik School of Computer Science, Tel Aviv University, Tel Aviv, Israel.
• Experimental Imaging Center, IRCCS Ospedale San Raffaele, Milan, Italy.
• Tumor Immunology Unit, Department of Sciences for Health Promotion and Mother-Child Care “G. D’Alessandro,” University of Palermo, Palermo, Italy.
• Department of Cell Biology, Harvard Medical School, Boston, MA, USA.
• Department of Oncology and Hemato-Oncology, University of Milan, Milan, Italy.

PMID: 39208097 DOI: 10.1126/science.adj7446

Abstract

Chromosomal instability (CIN) generates micronuclei—aberrant extranuclear structures that catalyze the acquisition of complex chromosomal rearrangements present in cancer. Micronuclei are characterized by persistent DNA damage and catastrophic nuclear envelope collapse, which exposes DNA to the cytoplasm. We found that the autophagic receptor p62/SQSTM1 modulates micronuclear stability, influencing chromosome fragmentation and rearrangements. Mechanistically, proximity of micronuclei to mitochondria led to oxidation-driven homo-oligomerization of p62, limiting endosomal sorting complex required for transport (ESCRT)–dependent micronuclear envelope repair by triggering autophagic degradation. We also found that p62 levels correlate with increased chromothripsis across human cancer cell lines and with increased CIN in colorectal tumors. Thus, p62 acts as a regulator of micronuclei and may serve as a prognostic marker for tumors with high CIN.

INTRODUCTION

A main feature of cancer cells is their high frequency of chromosome segregation errors, a condition known as chromosomal instability (CIN), which is associated with poor prognosis and chemoresistance. CIN leads to the formation of micronuclei—abnormal extranuclear bodies widely found in cancer cells.

The nuclear envelopes of micronuclei are often fragile and compromised, which causes irreparable ruptures and structural collapse. This exposes micronuclear DNA to the cytosol, resulting in DNA damage and extensive chromosomal rearrangements, which fuels genomic instability and cancer progression. In addition, rupture of the micronuclear membrane activates the cGAS-STING [cyclic guanosine monophosphate–adenosine monophosphate synthase (cGAS)–stimulator of interferon genes (STING)] pathway, triggering inflammatory responses that promote tumor invasion and metastasis.

RESULTS

We found that p62 localizes to micronuclei and is crucial for maintaining their integrity. The localization of p62 to micronuclei relied on its oxidation-driven homo-oligomerization, which was induced by reactive oxygen species (ROS) released by mitochondria proximal to micronuclei. We used electron tomography and quantitative imaging to analyze the proximity of mitochondria to micronuclei and found that p62-positive micronuclei were closer to mitochondria compared with those without p62. We tested how mitochondrial ROS affected p62 localization and found that reducing ROS decreased p62-positive micronuclei and prevented their rupture, whereas increasing ROS led to more p62-positive and ruptured micronuclei in both normal and cancer cells. Homo-oligomerization of p62 induced by ROS influenced micronuclear integrity by inhibiting the repair activity of the endosomal sorting complex required for transport–III (ESCRT-III), which is involved in envelope resealing. This control was achieved through the p62-mediated autophagic degradation of ESCRT components. The p62-dependent regulation of micronuclear integrity affected several features associated with micronuclei, such as chromosomal rearrangements and cGAS-STING–mediated inflammation. Furthermore, p62 levels correlated with chromothripsis status in cancer cells and tumor samples and were strongly linked to poor prognosis in colorectal cancer with high CIN.

CONCLUSION

In this work, we identified a critical mechanism by which p62 regulates micronuclear stability by influencing envelope repair. Given p62’s frequent deregulation in tumors and its control over micronuclear envelope integrity, our findings suggest that p62-mediated effects on micronuclear repair activities could influence cancer development and progression.

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