How p53 and MRE11 Dance in the Light of Disorder and Modification

DNA integrity is fundamental to cellular function and survival. The human genome faces continuous threats from both endogenous factors like replication errors and exogenous factors such as UV radiation. To counteract these damages, cells employ an array of repair mechanisms. The focus of this study is on the response to double-strand breaks (DSBs), one of the most lethal forms of DNA damage. DSBs are primarily repaired via two pathways: non-homologous end-joining and homologous recombination. The efficiency and accuracy of these repair processes are critical to prevent mutations and maintain genomic stability.

Tumor suppressor protein p53 and DNA repair protein MRE11 are crucial components in the cellular mechanisms that maintain genomic stability and prevent cancer. p53, often referred to as the “guardian of the genome,” is a tumor suppressor protein that plays a critical role in preventing cancer formation. It is activated in response to various stress signals, including DNA damage, oxidative stress, and oncogene activation. Upon activation, p53 can lead to cell cycle arrest, allowing for DNA repair, or it can induce apoptosis (programmed cell death) if the damage is irreparable. This prevents the propagation of cells with damaged DNA that could lead to cancer. Mutations in the p53 gene are one of the most common mutations in human cancers. When mutated, p53 loses its ability to control cell growth and division, leading to unregulated cell proliferation. On the other hand,  MRE11 is part of the MRE11-RAD50-NBS1 (MRN) complex, a key player in the DNA damage response. It is particularly involved in the repair of double-strand breaks, which are among the most lethal forms of DNA damage. MRE11 has both nuclease and DNA binding activities. It is involved in the detection of DNA damage and the initiation of DNA repair processes. MRE11 also plays a role in signaling the presence of DNA damage to the cell cycle checkpoints and other repair mechanisms. The interaction between p53 and MRE11 is critical in the cellular response to DNA damage. The MRN complex, including MRE11, is one of the first responders to double-strand breaks. It helps to activate ATM (Ataxia Telangiectasia Mutated), a kinase that phosphorylates p53 among other substrates. Activated p53 can halt the cell cycle, giving the cell time to repair the damage. If the damage is beyond repair, p53 can induce apoptosis. MRE11’s role in DNA repair is complementary to p53’s function in monitoring and responding to DNA integrity. Deficiencies in either p53 or MRE11 can compromise the DNA damage response, potentially leading to genomic instability and increased cancer risk. Indeed, p53 and MRE11 are essential for maintaining DNA integrity and preventing cancer. Their interaction is a vital part of the complex network of cellular responses to DNA damage. Defects in either of these proteins can disrupt this network and contribute to the development of cancer.

In a new study published in Biochimica et Biophysica Acta (BBA) – Molecular Cell Research led by Professor Tobias Madl and conducted by Sinem Usluer, Markus Galhuber, Yukti Khanna, Benjamin Bourgeois, Emil Spreitzer, Helene Michenthaler, and Andreas Prokesch from the Medical University of Graz in Austria conducted detailed investigation into the molecular interactions between the p53 protein, a key tumor suppressor, and MRE11, a critical component in DNA double-strand break repair. Their objective was to understand how these proteins interact at a molecular level, particularly focusing on the roles of specific protein regions and the impact of post-translational modifications (PTMs). Here’s a breakdown of what they did:

They discovered that the interaction between p53 and MRE11 is mediated by intrinsically disordered regions within these proteins. Specifically, they focused on the transactivation domain (TAD) of p53 and the glycine-arginine-rich (GAR) domain of MRE11. The authors investigated how phosphorylation and methylation, two common types of PTMs, affect the p53-MRE11 interaction. They found that phosphorylation of the p53 TAD enhances its binding to MRE11. Conversely, arginine methylation of the MRE11 GAR domain, while still allowing p53 binding, slightly reduces the interaction’s affinity. To uncover these molecular details, the team used sophisticated methods like nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC). These techniques allowed them to precisely map the interaction sites and quantify the changes in binding affinity due to PTMs. The research aimed to understand how the p53-MRE11 interaction contributes to the cellular response to DNA damage, particularly in the DNA repair process. By elucidating this interaction, they hoped to shed light on the broader mechanisms of DNA damage response and repair.

The central focus of the study is the interaction between p53, a key regulatory protein in DNA repair and cell cycle control, and MRE11, a component of the MRN complex crucial in DSB repair. The research uncovers that this interaction is mediated by intrinsically disordered regions within both proteins: the transactivation domain (TAD) of p53 and the glycine-arginine-rich (GAR) domain of MRE11. Intrinsically disordered proteins (IDPs) are known for their flexibility and ability to engage in various interactions, which is pivotal in the dynamic environment of DNA damage response. PTMs play a crucial role in modulating protein interactions. The study reveals that phosphorylation of the TAD of p53 enhances its binding to MRE11. Concurrently, arginine methylation of the MRE11 GAR domain, a modification known to occur in response to DNA damage, does not impede its binding to p53 but rather slightly reduces the affinity. These findings suggest that PTMs are not mere on-off switches but rather fine-tuners of protein-protein interactions, influencing the recruitment and assembly of repair complexes at DNA damage sites. The research team employed a range of biophysical techniques to elucidate the interaction between p53 and MRE11. These included nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC). These methods allowed for precise mapping of the interacting domains and the impact of PTMs on the binding affinity and kinetics. The interaction between p53 and MRE11 is crucial for the cellular response to DNA damage. The recruitment of p53 to DNA damage sites and its subsequent activation are essential steps in orchestrating the repair process. This study suggests that the p53-MRE11 interaction, modulated by PTMs, could be a critical factor in determining the cellular fate post-DNA damage, whether it leads to repair, apoptosis, or senescence.

Understanding the molecular details of protein interactions in DNA damage response opens new avenues for therapeutic interventions, particularly in cancer treatment where DNA repair mechanisms are often altered. Targeting specific protein interactions or modulating PTMs could be a strategy to enhance the efficacy of existing treatments or develop new therapeutic approaches. The study by Professor Madl and his team marks a significant advancement in our understanding of the DNA damage response. It highlights the complexity of protein interactions mediated by disordered regions and modulated by PTMs, underpinning the dynamic nature of the cellular response to DNA damage. This research not only provides valuable insights into fundamental biological processes but also has potential implications in the field of targeted cancer therapy.