Breaking the vicious circle: Extrachromosomal circular DNA as an emerging player in tumour evolution.

Extrachromosomal circular DNA (ecDNA) or double minutes have gained renewed interest since its discovery more than five decades ago, emerging as potent drivers of tumour evolution. This has largely been motivated by recent discovery that the tumour-exclusive ecDNA are highly prevalent in almost all cancers unlike previously thought. EcDNAs contribute to elevated oncogene expression, intratumoural heterogeneity, tumour adaptation and therapy resistance independently of canonical chromosomal alterations. Importantly, ecDNAs play a critical role in patient survival as ecDNA-based oncogene amplification adversely affects clinical outcome to a significantly greater extent than intrachromosomal amplification. Chromothripsis, a major driver of ecDNA biogenesis and gene amplification, is a mutational process characterised by chromosomal shattering and localised complex genome rearrangement. Chemotherapeutic drugs can lead to chromothriptic rearrangements and therapy resistance. In this review, we examine how ecDNAs mediate oncogene overexpression, facilitate accelerated tumour malignancy and enhance rapid adaptation independently of linear chromosomes. We delve into discoveries pertaining to mechanisms of biogenesis, distinctive features of ecDNA, gene regulation and topological interactions with active chromatin. We also discuss the critical role of chromothripsis in engendering ecDNA amplification and evolution. One envisions that insights into ecDNA biology not only hold importance for the cancer genome and tumour evolutionary dynamics, but could also inform prognostication and clinical intervention, particularly for cancers characterised by high oncogene amplification.

Therapy-induced senescence through the redox lens.

Therapy-induced senescent tumor cells have emerged as significant drivers of tumor recurrence and disease relapse. Interestingly, reactive oxygen species (ROS) production and its associated redox signaling networks are intertwined with initiation and establishment of therapy-induced senescence. Therapy-induced senescent cells influence neighboring cells and the tumor microenvironment via their bioactive secretome known as the senescence-associated secretory phenotype (SASP). The intracellular effects of ROS are dose and context-dependent. Under normal physiological conditions, ROS is involved in various signalling pathways and cellular processes important for maintenance of cellular homeostasis, such as redox balance, stress response, inflammatory signalling, cell proliferation and cell death among others. However excess ROS accompanied by a pro-oxidant microenvironment can engender oxidative DNA damage, triggering cellular senescence. In this review, we discuss the role of ROS and the redox state dynamics in fine-tuning homeostatic processes that drive therapy-induced cell fate towards senescence establishment, as well as their influence in stimulating inflammatory signalling and SASP production. We also offer insights into interventional strategies, specifically senotherapeutics, that could potentially leverage on modulation of redox and antioxidant pathways. Lastly, we evaluate possible implications of redox rewiring during escape from therapy-induced senescence, an emerging area of research. We envision that examining therapy-induced senescence through the redox lens, integrated with time-resolved single-cell RNA sequencing combined with spatiotemporal multi-omics, could further enhance our understanding of its functional heterogeneity. This could aid identification of targetable signalling nodes to reduce disease relapse, as well as inform strategies for development of broad-spectrum senotherapeutics. Overall, our review aims to delineate redox-driven mechanisms which contribute to the biology of therapy-induced senescence and beyond, while highlighting implications for tumor initiation and recurrence.

CAMK2D serves as a molecular scaffold for RNF8-MAD2 complex to induce mitotic checkpoint in glioma.

MAD2 is a spindle assembly checkpoint protein that participates in the formation of mitotic checkpoint complex, which blocks mitotic progression. RNF8, an established DNA damage response protein, has been implicated in mitotic checkpoint regulation but its exact role remains poorly understood. Here, RNF8 proximity proteomics uncovered a role of RNF8-MAD2 in generating the mitotic checkpoint signal. Specifically, RNF8 competes with a small pool of p31comet for binding to the closed conformer of MAD2 via its RING domain, while CAMK2D serves as a molecular scaffold to concentrate the RNF8-MAD2 complex via transient/weak interactions between its p-Thr287 and RNF8's FHA domain. Accordingly, RNF8 overexpression impairs glioma stem cell (GSC) mitotic progression in a FHA- and RING-dependent manner. Importantly, low RNF8 expression correlates with inferior glioma outcome and RNF8 overexpression impedes GSC tumorigenicity. Last, we identify PLK1 inhibitor that mimics RNF8 overexpression using a chemical biology approach, and demonstrate a PLK1/HSP90 inhibitor combination that synergistically reduces GSC proliferation and stemness. Thus, our study has unveiled a previously unrecognized CAMK2D-RNF8-MAD2 complex in regulating mitotic checkpoint with relevance to gliomas, which is therapeutically targetable.