THE AUTOPHAGIC RECEPTOR P62 MODULATES MICRONUCLEUS STABILITY

Micronuclei are extranuclear bodies originated because of chromosome mis-segregation. In the past years, several studies identified the processes that are dysfunctional in micronuclei and described the structures that are disrupted within them, revealing how micronuclei differ from primary nuclei. Micronuclear membrane can undergo rupture and eventually collapse, causing defective nuclear protein import and impaired DNA replication. Micronuclei fail to repair damaged DNA and, if reincorporated into primary nuclei, may lead to the mutagenic event of chromothripsis. Through ruptures, the micronuclear DNA can be recognized by the cGAS-STING pathway which activates inflammation triggering innate immunity as well as promoting metastasis formation. Considering the defective features associated with micronuclei and the catastrophic consequences for the cells harboring them, I investigated the cellular mechanisms that may be responsible for sensing and recognizing these extranuclear bodies. Notably, I found that the autophagic receptor p62 recognizes micronuclei. p62 localizes to micronuclei spontaneously forming in colorectal cancer cell lines as well as those generated upon induction of chromosome mis-segregation in both untransformed and transformed cell lines. p62 can access micronuclei through nuclear envelope ruptures and diffuse within nuclear pores. On micronuclei, its presence correlates with DNA damage, membrane rupture and loss of compartmentalization and its recruitment depends on the ubiquitination of yet-to-be-identified micronuclear components. Importantly, the presence of p62 and other autophagic receptors does not produce the recruitment of downstream autophagic effector around micronuclei, nor induce the clearance of the whole-micronuclear structure, suggesting that p62 might be targeting specific micronuclear component(s) rather than the entire micronucleus. In line with this, I found that modulation of p62 levels has an impact on micronuclear membrane integrity. The molecular mechanism of this modulation is yet-to-be defined, and identifying p62 target will provide new insights in this respect. Importantly, elevating the level of p62 contributes to exacerbate micronuclear rupture and collapse, while decreasing its level limits these features. This, in turn, affects micronuclear DNA fragmentation and rearrangement accumulation, and might lead to chromothripsis modulation. Moreover, it contributes to micronuclear DNA spillage in the cytoplasm and to the cGAS-mediated inflammatory activation. With the ongoing experiments, I will assess if this modulation can eventually contribute to metastasis formation in vivo. Because p62 expression levels are deregulated in tumors, dissecting the molecular mechanism of p62 binding to micronuclei has the potential to provide crucial insights into the intricate relationship between chromosomal instability, autophagy and cancer development.