Enhanced DNA repair through droplet formation and p53 oscillations

Nucleo-cytoplasmic environment modulates spatiotemporal p53 phase separation

Liquid-liquid phase separation of various transcription factors into biomolecular condensates plays an essential role in gene regulation. Here, using cellular models and in vitro studies, we show the spatiotemporal formation and material properties of p53 condensates that might dictate its function. In particular, p53 forms liquid-like condensates in the nucleus of cells, which can bind to DNA and perform transcriptional activity. However, cancer-associated mutations promote misfolding and partially rigidify the p53 condensates with impaired DNA binding ability. Irrespective of wild-type and mutant forms, the partitioning of p53 into cytoplasm leads to the condensate formation, which subsequently undergoes rapid solidification. In vitro studies show that abundant nuclear components such as RNA and nonspecific DNA promote multicomponent phase separation of the p53 core domain and maintain their liquid-like property, whereas specific DNA promotes its dissolution into tetrameric functional p53. This work provides mechanistic insights into how the life cycle and DNA binding properties of p53 might be regulated by phase separation.

Plausible, robust biological oscillations through allelic buffering

Biological oscillators can specify time- and dose-dependent functions via dedicated control of their oscillatory dynamics. However, how biological oscillators, which recurrently activate noisy biochemical processes, achieve robust oscillations remains unclear. Here, we characterize the long-term oscillations of p53 and its negative feedback regulator Mdm2 in single cells after DNA damage. Whereas p53 oscillates regularly, Mdm2 from a single MDM2 allele exhibits random unresponsiveness to ∼9% of p53 pulses. Using allelic-specific imaging of MDM2 activity, we show that MDM2 alleles buffer each other to maintain p53 pulse amplitude. Removal of MDM2 allelic buffering cripples the robustness of p53 amplitude, thereby elevating p21 levels and cell-cycle arrest. In silico simulations support that allelic buffering enhances the robustness of biological oscillators and broadens their plausible biochemical space. Our findings show how allelic buffering ensures robust p53 oscillations, highlighting the potential importance of allelic buffering for the emergence of robust biological oscillators during evolution. A record of this paper's transparent peer review process is included in the supplemental information.

Hydrochlorothiazide disrupts DNA damage response to exacerbate skin photosensitivity

Hydrochlorothiazide (HCTZ) is a widely utilized diuretic for the treatment of hypertension. The photosensitivity of HCTZ has been recognized for six decades, with UVA being considered the primary culprit. However, the precise molecular mechanism of HCTZ sensitizing skin to UV radiation remains unknown. In this study, we demonstrate that HCTZ exacerbates UVB-induced photosensitivity in normal skin by disrupting the DNA damage response, a crucial network responsible for maintaining epidermal homeostasis. Here, we found that HCTZ aggravates UVB-induced mouse skin damage. Through transcriptomic and proteomic profiling, we have found that the cell cycle and p53 signaling pathway may contribute to the photosensitivity caused by HCTZ. In keratinocytes, HCTZ promotes the transition from G1 to S phase and inhibits the p53 signaling pathway after exposure to UV radiation. We have found that HCTZ enhances the accumulation of DNA damage induced by UVB and impairs nucleotide excision repair (NER), which is responsible for repairing UVB-induced DNA lesions, by inhibiting the expression of NER-related genes and shortening the duration of G1 phase. Furthermore, pharmacologically inducing G1 arrest eliminates HCTZ-induced accumulation of damaged DNA. These findings unveil an unknown mechanism through which HCTZ impairs NER and interferes with UVB-induced cell cycle arrest, ultimately leading to improper response towards DNA damage and increased skin sensitivity.

Phase separation in DNA damage response: New insights into cancer development and therapy

Phase separation, a process in which biomolecules segregate into distinct liquid-like compartments within cells, has recently been identified as a crucial regulator of various cellular functions, including the DNA damage response (DDR). Dysregulation of phase separation may contribute to genomic instability, oncogenesis, and tumor progression. However, the specific roles and mechanisms underlying phase separation remain largely elusive. This comprehensive review aims to elucidate the complex relationship between phase separation and the DDR in the context of cancer biology. We focus on the molecular mechanisms underlying phase separation and its role in orchestrating DDR signaling and repair processes. Additionally, we discuss how the dysregulation of phase separation in cancer cells impacts genome stability, tumorigenesis, and therapeutic responses. By leveraging the unique properties of phase separation in the DDR, researchers can potentially advance basic research and develop personalized cancer therapies targeting the dysregulated biomolecular condensates that drive tumorigenesis.

Entrainment and multi-stability of the p53 oscillator in human cells

The tumor suppressor p53 responds to cellular stress and activates transcription programs critical for regulating cell fate. DNA damage triggers oscillations in p53 levels with a robust period. Guided by the theory of synchronization and entrainment, we developed a mathematical model and experimental system to test the ability of the p53 oscillator to entrain to external drug pulses of various periods and strengths. We found that the p53 oscillator can be locked and entrained to a wide range of entrainment modes. External periods far from p53's natural oscillations increased the heterogeneity between individual cells whereas stronger inputs reduced it. Single-cell measurements allowed deriving the phase response curves (PRCs) and multiple Arnold tongues of p53. In addition, multi-stability and non-linear behaviors were mathematically predicted and experimentally detected, including mode hopping, period doubling, and chaos. Our work revealed critical dynamical properties of the p53 oscillator and provided insights into understanding and controlling it. A record of this paper's transparent peer review process is included in the supplemental information.

Synthetic gene circuit evolution: Insights and opportunities at the mid-scale

Directed evolution focuses on optimizing single genetic components for predefined engineering goals by artificial mutagenesis and selection. In contrast, experimental evolution studies the adaptation of entire genomes in serially propagated cell populations, to provide an experimental basis for evolutionary theory. There is a relatively unexplored gap at the middle ground between these two techniques, to evolve in vivo entire synthetic gene circuits with nontrivial dynamic function instead of single parts or whole genomes. We discuss the requirements for such mid-scale evolution, with hypothetical examples for evolving synthetic gene circuits by appropriate selection and targeted shuffling of a seed set of genetic components in vivo. Implementing similar methods should aid the rapid generation, functionalization, and optimization of synthetic gene circuits in various organisms and environments, accelerating both the development of biomedical and technological applications and the understanding of principles guiding regulatory network evolution.

Liquid-liquid phase separation in subcellular assemblages and signaling pathways: Chromatin modifications induced gene regulation for cellular physiology and functions including carcinogenesis

Liquid-liquid phase separation (LLPS) describes many biochemical processes, including hydrogel formation, in the integrity of macromolecular assemblages and existence of membraneless organelles, including ribosome, nucleolus, nuclear speckles, paraspeckles, promyelocytic leukemia (PML) bodies, Cajal bodies (all exert crucial roles in cellular physiology), and evidence are emerging day by day. Also, phase separation is well documented in generation of plasma membrane subdomains and interplay between membranous and membraneless organelles. Intrinsically disordered regions (IDRs) of biopolymers/proteins are the most critical sticking regions that aggravate the formation of such condensates. Remarkably, phase separated condensates are also involved in epigenetic regulation of gene expression, chromatin remodeling, and heterochromatinization. Epigenetic marks on DNA and histones cooperate with RNA-binding proteins through their IDRs to trigger LLPS for facilitating transcription. How phase separation coalesces mutant oncoproteins, orchestrate tumor suppressor genes expression, and facilitated cancer-associated signaling pathways are unravelling. That autophagosome formation and DYRK3-mediated cancer stem cell modification also depend on phase separation is deciphered in part. In view of this, and to linchpin insight into the subcellular membraneless organelle assembly, gene activation and biological reactions catalyzed by enzymes, and the downstream physiological functions, and how all these events are precisely facilitated by LLPS inducing organelle function, epigenetic modulation of gene expression in this scenario, and how it goes awry in cancer progression are summarized and presented in this article.

Cell fate regulation governed by p53: Friends or reversible foes in cancer therapy

Cancer is a leading cause of death worldwide. Targeted therapies aimed at key oncogenic driver mutations in combination with chemotherapy and radiotherapy as well as immunotherapy have benefited cancer patients considerably. Tumor protein p53 (TP53), a crucial tumor suppressor gene encoding p53, regulates numerous downstream genes and cellular phenotypes in response to various stressors. The affected genes are involved in diverse processes, including cell cycle arrest, DNA repair, cellular senescence, metabolic homeostasis, apoptosis, and autophagy. However, accumulating recent studies have continued to reveal novel and unexpected functions of p53 in governing the fate of tumors, for example, functions in ferroptosis, immunity, the tumor microenvironment and microbiome metabolism. Among the possibilities, the evolutionary plasticity of p53 is the most controversial, partially due to the dizzying array of biological functions that have been attributed to different regulatory mechanisms of p53 signaling. Nearly 40 years after its discovery, this key tumor suppressor remains somewhat enigmatic. The intricate and diverse functions of p53 in regulating cell fate during cancer treatment are only the tip of the iceberg with respect to its equally complicated structural biology, which has been painstakingly revealed. Additionally, TP53 mutation is one of the most significant genetic alterations in cancer, contributing to rapid cancer cell growth and tumor progression. Here, we summarized recent advances that implicate altered p53 in modulating the response to various cancer therapies, including chemotherapy, radiotherapy, and immunotherapy. Furthermore, we also discussed potential strategies for targeting p53 as a therapeutic option for cancer.

Fluorogenic CRISPR for genomic DNA imaging

Genomic DNA exhibits high heterogeneity in terms of its dynamic within the nucleus, its structure and functional roles. CRISPR-based imaging approaches can image genomic loci in living cells. However, conventional CRISPR-based tools involve expressing constitutively fluorescent proteins, resulting in high background and nonspecific nucleolar signal. Here, we construct fluorogenic CRISPR (fCRISPR) to overcome these issues. fCRISPR is designed with dCas9, an engineered sgRNA, and a fluorogenic protein. Fluorogenic proteins are degraded unless they are bound to specific RNA hairpins. These hairpins are inserted into sgRNA, resulting in dCas9: sgRNA: fluorogenic protein ternary complexes that enable fluorogenic DNA imaging. With fCRISPR, we image various genomic DNA in different human cells with high signal-to-noise ratio and sensitivity. Furthermore, fCRISPR tracks chromosomes dynamics and length. fCRISPR also allows DNA double-strand breaks (DSBs) and repair to be tracked in real time. Taken together, fCRISPR offers a high-contrast and sensitive platform for imaging genomic loci.

Emerging role and therapeutic implications of p53 in intervertebral disc degeneration

Lower back pain (LBP) is a common degenerative musculoskeletal disease that imposes a huge economic burden on both individuals and society. With the aggravation of social aging, the incidence of LBP has increased globally. Intervertebral disc degeneration (IDD) is the primary cause of LBP. Currently, IDD treatment strategies include physiotherapy, medication, and surgery; however, none can address the root cause by ending the degeneration of intervertebral discs (IVDs). However, in recent years, targeted therapy based on specific molecules has brought hope for treating IDD. The tumor suppressor gene p53 produces a transcription factor that regulates cell metabolism and survival. Recently, p53 was shown to play an important role in maintaining IVD microenvironment homeostasis by regulating IVD cell senescence, apoptosis, and metabolism by activating downstream target genes. This study reviews research progress regarding the potential role of p53 in IDD and discusses the challenges of targeting p53 in the treatment of IDD. This review will help to elucidate the pathogenesis of IDD and provide insights for the future development of precision treatments.

Andrographolide causes p53-independent HCC cell death through p62 accumulation and impaired DNA damage repair

BACKGROUND

Hepatocellular carcinoma (HCC) is a highly lethal cancer characterized by dominant driver mutations, including p53. Consequently, there is an urgent need to search for novel therapeutic agents to treat HCC. Andrographolide (Andro), a clinically available anti-inflammatory phytochemical agent, has shown inhibitory effects against various types of cancer, including HCC. However, the underlying molecular mechanisms of its action remain poorly understood.

PURPOSE

This study aims to investigate the molecular mechanisms by which p53 and p62 collectively affect Andro-induced HCC cell death, using both in vitro and in vivo models.

METHODS

In vitro cellular experiments were conducted to examine the effects of Andro on cell viability and elucidate its mechanisms of action. In vivo xenograft experiments further validated the anti-cancer effects of Andro.

RESULTS

Andro induced dose- and time-dependent HCC cell death while sparing normal HL-7702 hepatocytes. Furthermore, Andro caused DNA damage through the generation of reactive oxygen species (ROS), a critical event leading to cell death. Notably, HCC cells expressing p53 exhibited greater resistance to Andro-induced cell death compared to p53-deficient cells, likely due to the ability of p53 to induce G2/M cell cycle arrest. Additionally, Andro-induced p62 aggregation led to the proteasomal degradation of RAD51 and 53BP1, two key proteins involved in DNA damage repair. Consequently, silencing or knocking out p62 facilitated DNA damage repair and protected HCC cells. Importantly, disruption of either p53 or p62 did not affect the expression of the other protein. These findings were further supported by the observation that xenograft tumors formed by p62-knockout HCC cells displayed increased resistance to Andro treatment.

CONCLUSION

This study elucidates the mechanistic basis of Andro-induced HCC cell death. It provides valuable insights for repurposing Andro for the treatment of HCC, regardless of the presence of functional p53.

Are physiological oscillations physiological?

Despite widespread and striking examples of physiological oscillations, their functional role is often unclear. Even glycolysis, the paradigm example of oscillatory biochemistry, has seen questions about its oscillatory function. Here, we take a systems approach to argue that oscillations play critical physiological roles, such as enabling systems to avoid desensitization, to avoid chronically high and therefore toxic levels of chemicals, and to become more resistant to noise. Oscillation also enables complex physiological systems to reconcile incompatible conditions such as oxidation and reduction, by cycling between them, and to synchronize the oscillations of many small units into one large effect. In pancreatic β-cells, glycolytic oscillations synchronize with calcium and mitochondrial oscillations to drive pulsatile insulin release, critical for liver regulation of glucose. In addition, oscillation can keep biological time, essential for embryonic development in promoting cell diversity and pattern formation. The functional importance of oscillatory processes requires a re-thinking of the traditional doctrine of homeostasis, holding that physiological quantities are maintained at constant equilibrium values, a view that has largely failed in the clinic. A more dynamic approach will initiate a paradigm shift in our view of health and disease. A deeper look into the mechanisms that create, sustain and abolish oscillatory processes requires the language of nonlinear dynamics, well beyond the linearization techniques of equilibrium control theory. Nonlinear dynamics enables us to identify oscillatory ('pacemaking') mechanisms at the cellular, tissue and system levels.

Targeting Biomolecular Condensation and Protein Aggregation against Cancer

Biomolecular condensates, membrane-less entities arising from liquid-liquid phase separation, hold dichotomous roles in health and disease. Alongside their physiological functions, these condensates can transition to a solid phase, producing amyloid-like structures implicated in degenerative diseases and cancer. This review thoroughly examines the dual nature of biomolecular condensates, spotlighting their role in cancer, particularly concerning the p53 tumor suppressor. Given that over half of the malignant tumors possess mutations in the TP53 gene, this topic carries profound implications for future cancer treatment strategies. Notably, p53 not only misfolds but also forms biomolecular condensates and aggregates analogous to other protein-based amyloids, thus significantly influencing cancer progression through loss-of-function, negative dominance, and gain-of-function pathways. The exact molecular mechanisms underpinning the gain-of-function in mutant p53 remain elusive. However, cofactors like nucleic acids and glycosaminoglycans are known to be critical players in this intersection between diseases. Importantly, we reveal that molecules capable of inhibiting mutant p53 aggregation can curtail tumor proliferation and migration. Hence, targeting phase transitions to solid-like amorphous and amyloid-like states of mutant p53 offers a promising direction for innovative cancer diagnostics and therapeutics.

The crisscross between p53 and metabolism in cancer

As the guardian of the genome, p53 is well known for its tumor suppressor function in humans, controlling cell proliferation, senescence, DNA repair and cell death in cancer through transcriptional and non-transcriptional activities. p53 is the most frequently mutated gene in human cancer, but how its mutation or depletion leads to tumorigenesis still remains poorly understood. Recently, there has been increasing evidence that p53 plays a vital role in regulating cellular metabolism as well as in metabolic adaptation to nutrient starvation. In contrast, mutant p53 proteins, especially those harboring missense mutations, have completely different functions compared to wild-type p53. In this review, we briefly summarize what is known about p53 mediating anabolic and catabolic metabolism in cancer, and in particular discuss recent findings describing how metabolites regulate p53 functions. To illustrate the variability and complexity of p53 function in metabolism, we will also review the differential regulation of metabolism by wild-type and mutant p53.

Targeting the p53 signaling pathway in cancers: Molecular mechanisms and clinical studies

Tumor suppressor p53 can transcriptionally activate downstream genes in response to stress, and then regulate the cell cycle, DNA repair, metabolism, angiogenesis, apoptosis, and other biological responses. p53 has seven functional domains and 12 splice isoforms, and different domains and subtypes play different roles. The activation and inactivation of p53 are finely regulated and are associated with phosphorylation/acetylation modification and ubiquitination modification, respectively. Abnormal activation of p53 is closely related to the occurrence and development of cancer. While targeted therapy of the p53 signaling pathway is still in its early stages and only a few drugs or treatments have entered clinical trials, the development of new drugs and ongoing clinical trials are expected to lead to the widespread use of p53 signaling-targeted therapy in cancer treatment in the future. TRIAP1 is a novel p53 downstream inhibitor of apoptosis. TRIAP1 is the homolog of yeast mitochondrial intermembrane protein MDM35, which can play a tumor-promoting role by blocking the mitochondria-dependent apoptosis pathway. This work provides a systematic overview of recent basic research and clinical progress in the p53 signaling pathway and proposes that TRIAP1 is an important therapeutic target downstream of p53 signaling.

Coupled oscillator cooperativity as a control mechanism in chronobiology

Control of dynamical processes is vital for maintaining correct cell regulation and cell-fate decisions. Numerous regulatory networks show oscillatory behavior; however, our knowledge of how one oscillator behaves when stimulated by two or more external oscillatory signals is still missing. We explore this problem by constructing a synthetic oscillatory system in yeast and stimulate it with two external oscillatory signals. Letting model verification and prediction operate in a tight interplay with experimental observations, we find that stimulation with two external signals expands the plateau of entrainment and reduces the fluctuations of oscillations. Furthermore, by adjusting the phase differences of external signals, one can control the amplitude of oscillations, which is understood through the signal delay of the unperturbed oscillatory network. With this we reveal a direct amplitude dependency of downstream gene transcription. Taken together, these results suggest a new path to control oscillatory systems by coupled oscillator cooperativity.