title: Deciphering Chronobiological Regulation of Cell Proliferation and Drug Responses: Insights from the Circadian Clock and p53-p21 Dynamics
Creators: name: Gutu Taralunga, Nica Nicoleta
Publisher: name: Humboldt-Universität zu Berlin
Year: 2025
Subjects: subject: circadian clock, cell cycle, biological oscillator, growth, proliferation, cancer, time-of-day assays, pharmacodynamics, drug sensitivity and resistance, signaling dynamics, DNA damage, p53, p21
subject: Circadiane Rhythmik
subject: Proliferation
subject: p53
subject: DNA-Schaden
subject: circadian clock
subject: proliferation
subject: p53
subject: DNA damage
subject: 570 Biologie

description: Temporal control, inherent in all biological processes, relies on intrinsic systems to govern periodical behaviors and physiological responses. The circadian clock, a vital timekeeper, enables organisms to anticipate and adjust to daily environmental changes. In mammals, the circadian clock is organized hierarchically, with a central master clock in the hypothalamic suprachiasmatic nucleus regulating peripheral clocks distributed across the body. To maintain coherent circadian rhythms at the tissue level, peripheral oscillators exchange intercellular coupling factors by paracrine signaling pathways to synchronize. At the individual cell scale, the circadian clock interacts with another periodical biological process: the cell cycle. However, the mechanisms governing this interplay remain poorly elucidated. Here, we explore the influence of extracellular circadian synchronization on the intracellular coordination between the circadian clock and the cell cycle. To do so, we combined a mathematical model and long-term live-imaging recordings at the single-cell and population level of a human cell line. We show that the global circadian and cell cycle coordination within individual cells is disrupted when the extracellular circadian synchronization is lost, obstructing collective tissue growth. Populations with coherent circadian rhythms display rhythmic growth oscillations, uncovering a novel global regulator of tissue dynamics. Knocking down core circadian elements abolished these effects, revealing the fundamental role of circadian clock control as a timing mechanism. These findings advance our understanding of how biological systems maintain equilibrium and regulate proliferation in normal and pathological conditions. The circadian clock plays a crucial role in orchestrating cell proliferation, impacting tumor initiation, growth, and treatment responses. Recent research has reported significant changes in drug response for different administration hours throughout the day, highlighting the benefits of aligning treatment strategies to the inherent circadian rhythm. However, chronotherapy is still omitted in clinical practice, primarily due to a lack of understanding of the underlying mechanisms driving time-dependent drug responses. Currrently, no standardized protocols exist for identifying these temporal factors. Therefore, we developed a combined mathematical and experimental approach to identify the factors influencing time-dependent drug sensitivity in human cells. Our results show how circadian and drug properties independently shape time-of-day drug responses, offering novel insights into the time-dependent treatment outcome. This framework holds potential for developing personalized treatment schedules aligned with the internal circadian clock, optimizing cancer therapeutical strategies. On the other hand, tissue growth masks heterogeneous proliferation patterns at the single-cell level, potentially jeopardizing the treatment outcome, which cannot be exclusively attributed to circadian clock regulation. Clustering the cells upon their overall number of divisions, the proliferative patterns remain strikingly constant across different tissues, a phenomenon reported by several recent studies. This consistency implies the existence of a common underlying mechanism that is currently unknown. Proliferation control relies on a set of checkpoint mechanisms that accurately and quickly detect DNA damage. The onset of cellular stress triggers the activation of the p53 protein, orchestrating the expression of hundreds of genes responsible for cell cycle regulation or apoptosis, among other functions. Here, we present evidence that changes in cellular stress levels contribute to the gradual proliferation variability. Specifically, different DNA damage levels are encoded quantitively into signal parameters of p53 and p21 proteins in a gradual manner, shaping proliferation activity proportionally. These results propose a novel function of the p53-p21 signaling network in deciphering and decoding the magnitude of DNA damage to adjust and control proliferation.
description: Diese Studie erforscht, wie extrazelluläre zirkadiane Synchronisation die Abstimmung zwischen der zirkadianen Uhr und dem Zellzyklus beeinflusst. Durch mathematische Modellierung und langfristige Live-Bildgebung an menschlichen Zellen zeigt sie, dass der Verlust der Synchronisation die zirkadiane und Zellzykluskoordination stört und Gewebewachstum hemmt. Bei kohärenten zirkadianen Rhythmen entstehen rhythmische Wachstumsoszillationen, die eine globale Steuerung der Gewebedynamik andeuten. Das Ausschalten zirkadianer Elemente beseitigt diese Effekte und verdeutlicht die zeitliche Rolle der zirkadianen Uhr. Diese Ergebnisse liefern Einblicke in die biologische Balance und Regulierung der Proliferation in normalen und pathologischen Zuständen. Die zirkadiane Uhr beeinflusst die Zellproliferation, das Tumorwachstum und die Wirkung von Behandlungen. Arzneimittelreaktionen variieren tageszeitabhängig, was die Relevanz der Chronotherapie unterstreicht – der Anpassung von Therapien an zirkadiane Rhythmen. Allerdings wird Chronotherapie selten klinisch genutzt, da die zugrundeliegenden Mechanismen nicht ausreichend verstanden sind. Diese Studie identifiziert Faktoren, die die zeitabhängige Arzneimittelempfindlichkeit beeinflussen, und bietet Perspektiven für personalisierte Therapien. Gewebewachstum verdeckt Proliferationsmuster einzelner Zellen, die für Behandlungen entscheidend sind. Durch Clusteranalysen der Zellteilungen zeigten sich konsistente Muster in Geweben, was auf unbekannte Mechanismen hindeutet. Das p53-p21-Signalnetzwerk reguliert die Proliferation, indem es DNA-Schäden bewertet und Zellzyklusreaktionen anpasst. Die Studie zeigt, wie dieses Netzwerk DNA-Schäden interpretiert, um Zellwachstum zu steuern.
description: This study examines how extracellular circadian synchronization affects the coordination between the circadian clock and the cell cycle. By combining mathematical modeling and long-term live imaging of human cells, we show that loss of synchronization disrupts global circadian and cell cycle coordination in individual cells, hindering tissue growth. When circadian rhythms are coherent, rhythmic growth oscillations occur, indicating a global tissue dynamics regulator. Knocking down key circadian elements abolished these effects, emphasizing the circadian clock's timing role. These findings enhance our understanding of biological balance and proliferation regulation in both normal and pathological states. The circadian clock is also vital in cell proliferation, influencing tumor growth and treatment responses. Drug responses vary depending on the time of day, highlighting the importance of aligning treatments with circadian rhythms. However, chronotherapy is not widely used in clinical practice due to insufficient understanding of the underlying mechanisms. Our approach identifies factors affecting time-dependent drug sensitivity, offering insights into personalized treatment schedules. Tissue growth masks single-cell proliferation patterns, essential for effective treatment. By clustering cells based on division numbers, we found consistent proliferation patterns across tissues, suggesting an unknown underlying mechanism. The p53-p21 signaling network regulates proliferation by quantifying DNA damage and adjusting cell cycle responses. This study reveals how p53-p21 signaling decodes DNA damage levels to control proliferation.