Biological clock regulation by the PER gene family: a new perspective on tumor development

The Period (PER) gene family is one of the core components of the circadian clock, with substantial correlations between the PER genes and cancers identified in extensive researches. Abnormal mutations in PER genes can influence cell function, metabolic activity, immunity, and therapy responses, thereby promoting the initiation and development of cancers. This ultimately results in unequal cancers progression and prognosis in patients. This leads to variable cancer progression and prognosis among patients. In-depth studies on the interactions between the PER genes and cancers can reveal novel strategies for cancer detection and treatment. In this review, we aim to provide a comprehensive overview of the latest research on the role of the PER gene family in cancer.


Introduction
With population aging, it is projected that by 2030, almost 20% of the world's population will be over 65, and by 2050, this figure is expected to reach 1.6 billion (Feng et al., 2023a).Cancers, closely associated with aging, are characterized by aberrant cellular proliferation and differentiation, continuing to pose a significant threat to global health (Hanahan, 2022;Shen et al., 2022;Feng et al., 2023b;Wang et al., 2023).In 2020, approximately 19 million new cancer cases and over 10 million cancer-related deaths were recorded worldwide (Sung et al., 2021).Specifically, in China, there were 4.57 million new cancer cases and 3.00 million cancer-specific deaths in the same year (He and Ke, 2023).Traditional cancer treatments include radiation therapy, chemotherapy, and surgery (Jin et al., 2022;Sirhan et al., 2022;Xing et al., 2022;Association, 2023), while molecularly targeted therapies and immune checkpoint inhibitors have transformed oncology (Chen et al., 2022;Chan et al., 2023;Yin et al., 2023;Yu et al., 2023).Despite advancements, the adverse effects of treatments on patient survival and quality of life remain pressing challenges in cancer therapy (Zhang and Zhang, 2020;Peng et al., 2022), complicating patient management (Wang YH. et al., 2020;Mokhtari-Hessari and Montazeri, 2020).High-throughput sequencing, a pioneering molecular biology technique, has fueled new oncology research directions (Walter et al., 2022;Larson et al., 2023).Contrasting with the conventional American Joint Committee on Cancer staging, which relies on tumor size, lymph node status, and metastasis, new classifications based on tumor genetic expression patterns have emerged, correlating more closely with clinical outcomes and patient survival (Yin et al., 2020;Park et al., 2022;de Jong et al., 2023).This shift signifies a move towards personalized precision medicine in oncology, with the potential to uncover new therapeutic targets and prognostic biomarkers through a deeper understanding of molecular mechanisms in cancer (Hong et al., 2020;Bao et al., 2023).
The Earth's rotation generates environmental variables with a 24-h periodicity, including temperature and light fluctuations (Hou et al., 2022;Laosuntisuk et al., 2023).Various life forms, including animals, plants, bacteria, fungi, have developed intricate internal timing mechanisms to synchronize their behavior and physiological processes with these cyclic environmental changes (Patton and Hastings, 2023).These mechanisms are known as "circadian rhythms," a term derived from the Latin "circa diem", meaning "about a day" (Allada and Bass, 2021).Thus, circadian rhythm denotes an organism's inherent rhythm-regulating system.In humans and other mammals, this 24-h rhythm is orchestrated by the circadian clock (Huang et al., 2023).The suprachiasmatic nucleus (SCN) of the hypothalamus, acting as the central clock, utilizes neuroendocrine pathways to coordinate peripheral clocks throughout the body (Starnes and Jones, 2023;Zhang-Sun et al., 2023).This network of clocks ensures the consistency of vital functions and numerous physiological activities.

Molecular circadian clock and cancer connection
From a molecular perspective, the circadian clock in mammals is governed by a transcription-translation feedback loop (TTFL), involving circadian genes and associated proteins (Patke et al., 2020;Li et al., 2023).This process begins when Brain and Muscle ARNT-Like Protein 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) proteins form a heterodimer that binds to the E-box in the promoter regions of various genes (Cox and Takahashi, 2019).This includes clockcontrolled genes (CCGs) and inhibitory elements like Period (PER) and Cryptochrome (CRY) proteins (Cao et al., 2021).As PER and CRY proteins levels rise, they eventually inhibit CLOCK-BMAL1 activity, thus regulating their own synthesis and setting the stage for a new circadian cycle.Additionally, RORα and REV-ERBs modulate BMAL1 expression through their interaction with REV-ERB-ROR response elements, creating a secondary loop (Preitner et al., 2002;Sato et al., 2004).D-box binding protein (DBP) and E4 promoter-binding protein 4 (E4BP4/NFIL3) also modulate gene expression and CCG activity via D-box promoters (Ripperger and Schibler, 2006).Furthermore, post-translational modifications (PTMs) by kinases/phosphatases and the ubiquitin-proteasome system, including Casein kinase Ⅰ epsilon (CKⅠε), β-transducin repeat-containing protein (β-TrCP), F-box and leucine-rich repeat protein 3 (FBXL3), and Tumor necrosis factor receptorassociated factor-2 (TRAF2) (Eide et al., 2005;Reischl et al., 2007;Siepka et al., 2007;Chen et al., 2018), maintain the stability and function of clock proteins.These mechanisms collectively create a delayed negative feedback loop, producing the roughly 24-h circadian rhythm.Our team has previously detailed this molecular mechanism in extensive studies (Feng et al., 2022;Zhu et al., 2023) (Figure 1).
Given the pivotal role of circadian rhythm in regulating diverse biological functions, extensive research has shown that its disruption is associated with a heightened risk of various diseases, including cardiovascular disorders, neurological conditions, and cancers (Crnko et al., 2019;Sancar and Van Gelder, 2021;Niu et al., 2022).In 2007, the World Health Organization identified shift work that disrupts circadian rhythms as a Group 2A carcinogen (Straif et al., 2007).Epidemiological studies have indicated that longterm night shift workers face increased risks of certain cancers, such as breast, prostate, and lung cancer (Cordina-Duverger et al., 2022;Berge et al., 2023;Schernhammer et al., 2023).Remarkably, about 43% of protein-coding genes in the mammalian genome are regulated by circadian clock genes, which are integral to various critical physiological and pathological processes (Zhang et al., 2014).Alterations in circadian clock genes or their functions can lead to disrupted cellular activities linked with cancer hallmarks, including cell cycle disruption (Lévi et al., 2007;Qu et al., 2023), genomic instability (Zhang et al., 2023), metabolic reprogramming (Chun et al., 2022), and immune system dysregulation (Chen et al., 2020;Zhang et al., 2024).As a result, the link between circadian clock genes and cancer has become a focal point in oncological research.In this review, we concentrate on the PER gene family, a central component of the circadian clock, explore its connection to cancer and summarize current research findings in the area.

Brief overview of the PER gene family
There are three homologous genes in mammals (PER1, PER2, and PER3) that are integral to the PER gene family, a key component of circadian clock genes (Deng and Yang, 2019).When Konopka and Benzer induced mutations in Drosophila melanogaster using ethyl methane sulfonate in 1971, they observed three distinct rhythm patterns in the mutants' eclosion and locomotor activities.The per gene was subsequently located on the X chromosome of D. melanogaster, with its variants (per o , per s , and per l ) associated with these rhythm changes (Konopka and Benzer, 1971).In 1984, the per gene was isolated and cloned by the teams of Jeffrey C. Hall (Zehring et al., 1984), Michael Rosbash (Reddy et al., 1984), and Michael Young (Bargiello and Young, 1984), who later received the 2017 Nobel Prize in Physiology or Medicine for their pioneering work on circadian rhythms.Further research by Hall and Rosbash demonstrated that the Per protein was a nuclear protein that oscillated between the cytoplasm and the nucleus, influencing the expression of its mRNA, leading to the hypothesis that the per gene acts as a transcription factor with feedback regulation (Zeng et al., 1994;Yildirim et al., 2022).Additionally, Young and his team found that the per gene's oscillation was synchronized with another clock gene, Timeless (tim), and that mutations in tim significantly affected the Per protein's synthesis, phosphorylation, and transport (Sehgal et al., 1995;Ahmad et al., 2021).These findings elucidated the interaction between Tim and Per proteins, supporting the TTFL model.Subsequent discoveries showed that CLOCK and BMAL1 proteins form a dimer that binds to the E-box to transcriptionally regulate the PER genes, confirming their role as positive regulators in the circadian rhythm (Vitaterna et al., 1994).The identification of other core clock genes, such as CLOCK (Allada et al., 1998), CYC (Rutila et al., 1998), andCRY (Todo et al., 1996), further elaborated the TTFL model, enhancing our understanding of circadian gene transcription regulation.These advancements propelled researches into circadian rhythms, underscoring the significance of clock genes in human physiology and diseases (Vitaterna et al., 2019) (Figure 2).
The PER gene family plays a pivotal role in maintaining circadian rhythms.Studies have demonstrated that Per2 homozygous mutant mice exhibit significantly shorter circadian rhythms than wild-type mice, which disappear in constant darkness (Zheng et al., 1999).Likewise, mice with homozygous Per1 mutations also display shorter rhythms, with Per2 influencing clock gene expression rhythm through transcriptional regulation (Zheng et al., 2001).Shiromani and colleagues found that Per1/ Per2 double mutant mice quickly experienced a decrease in core body temperature rhythm and a reduced circadian period, while Per3 mutants showed no notable rhythm alterations (Shiromani et al., 2004).Nakamura et al. (Nakamura et al., 2023) observed that the triple knockout of Per1/Per2/Per3 severely disrupted the estrous cycle in C57BL/6J mice (melatonin deficient), potentially due to compromised SCN amplitude stability.While the contribution of PER3 to circadian rhythm maintenance is less pronounced than PER1 and PER2, it has been linked to nocturnal preferences, psychiatric disorders, sleep patterns, and cognitive functions (Chen et al., 2023).The PER3 gene exhibits polymorphism in humans, with a variable number of tandem repeats (VNTR) consisting of a 54-base pair sequence in the 18th exon (Barragan et al., 2022).Aytac et al. (Aytac et al., 2022) identified an association between the VNTR variant at the rs57875989 locus of the PER3 gene and bipolar affective disorder risk, combining clinical scale assessments and blood analysis.The 4R/4R genotype appears to be protective against bipolar disorder, whereas the 5R/5R genotype is linked to a higher incidence of moderate manic symptoms in a study of 121 patients and controls (Yegin et al., 2021).Additionally, a significant correlation was found between the rs228697 SNP in PER3 and increased vulnerability to sleep-wake disturbances in Alzheimer's patients (Lozano-Tovar et al., 2023).Azevedo et al. (Azevedo et al., 2021) also noted a potential association between severe obesity and the rs228729 locus of the PER3 gene.

The PER gene family aberration and cancers
Emerging evidence suggests that alterations in clock genes, including the PER gene family (PER1, PER2, and PER3), play a significant role in cancer development and progression due to their regulatory functions in biological cycles and physiological processes.Researches have increasingly focused on comparing the PER genes The involvement of the PER gene family in the molecular mechanism of Circadian Clock.The core circadian transcriptional machinery consists of the positive transcription factors (CLOCK and BMAL1 proteins), and the repressors factors (PER and CRY proteins).Additionally, the nuclear receptors RORα, and REV-ERB compose the secondary circadian pathway.
expression levels in tumor and normal tissues to elucidate the potential link between PER genes aberrations and cancers.Downregulations of PER1, PER2, or PER3 have been observed in various cancers, including oral squamous cell carcinoma (Gong et al., 2021), head and neck squamous cell carcinoma (Li et al., 2019;Rahman et al., 2019), colorectal cancer (Orhan et al., 2019;Sahar et al., 2022), breast cancer (Liu et al., 2021;Liu et al., 2022a), ovarian cancer (Angelousi et al., 2019;Chen et al., 2021), melanoma (Lesicka et al., 2023), and hematological malignancies (Jiang et al., 2021).Studies have also highlighted the association between VNTR or SNPs polymorphism in the PER gene family and an increased risk of certain cancers, such as breast cancer (Fores-Martos et al., 2021;Song et al., 2023), colorectal cancer (Holipah and Kuroda, 2020), and prostate cancer (Wendeu-Foyet et al., 2019;Hinoura et al., 2021), through the analysis of tumor tissues or patient blood samples.To enhance our understanding of the prognostic significance of the PER gene family alterations in tumor progression, a growing body of research is exploring the relationship between these genetic changes and clinicopathological features.
A meta-analysis involving 7,476 cancer patients revealed that decreased PER1 gene expression was associated with poorer tumor differentiation and greater invasion depth, whereas reduced PER2 expression was correlated with advanced pathological stages and increased metastasis; furthermore, lower levels of both PER1 and PER2 were linked to shorter overall survivals (Zhang et al., 2020).Patients with advanced-stage head and neck squamous cell carcinoma exhibited markedly lower levels of PER1, PER2, and PER3 proteins compared to those with early-stage tumors, and higher levels of these proteins were associated with longer overall and recurrence-free survival.In oral squamous cell carcinoma, low PER2 expression was connected to poor prognosis, tumor grade progression, and lymph node metastasis (Xiong et al., 2018), whereas in lung cancer, increased PER2 expression was associated with less malignant differentiation and fewer lymph node metastases (Xiang et al., 2018).Transcriptome analysis from the GEO database indicated that PER3 gene expression could predict outcomes for ER+/HER2breast cancer patients through multifactor Cox analysis (Cadenas et al., 2014).The link between VNTR or SNP variations in the PER gene family and cancer risk has also attracted significant research interest (Morales-Santana et al., 2019).Lesicka et al. (Lesicka et al., 2019) identified that the dominant phenotype of PER1 rs2735611 and the recessive phenotype of PER2 rs934945 were associated with increased breast cancer risk.Additionally, the higher prevalence of the PER2 VNTR 4R/3R and 3R/3R genotypes in pancreatic cancer patients compared to healthy controls suggested that a greater proportion of the 3R allele in the PER2 VNTR may be a risk factor for pancreatic cancer (Dagmura et al., 2021).The period genes of Drosophila melanogaster and human.The discovery of the period gene can be traced back to 1971, when Konopka and Benzer identified three gene mutations (per o , per s , and per l ) on the X chromosome of Drosophila melanogaster; As for human, there are three homologous genes (PER1, PER2, and PER3).The PER1 and PER2 genes are primarily responsible for maintaining circadian rhythms of basic biological activities.And PER3 gene play an important role in mentality, sleep, and cognition.The relationships between alterations of the PER gene family and cancers.The aberrations, and VNTR or SNPs polymorphism of PER1, PER2, and PER3 gene were correlated with the development of various types of cancers, including BRCA (breast cancer), COAD/READ (colorectal cancer), HNSCC (head and neck squamous cell carcinoma), melanoma, NSCLC (non-small cell lung cancer), OSCC (oral squamous cell carcinoma), OV (ovarian cancer), PAAD (pancreatic adenocarcinoma), and PRAD (prostate cancer).

FIGURE 4
The potential mechanisms of PER1, PER2, and PER3 proteins affecting the hall markers of cancers.The PER1, PER2, and PER3 proteins influence the cell function, metabolism, TME, and therapy responses of cancers via a wide range of signal pathways and regulatory factors.Overall, the majority of previous cancer studies have consistently demonstrated significant downregulation of the PER gene family, often linked to reduced patient survival, poorer prognosis, and clinicopathological factors such as low tumor differentiation, advanced tumor stage, lymph node metastasis, and more aggressive tumor characteristics.Furthermore, researches into VNTR or SNPs polymorphisms of the PER gene family have established a connection between their anomalies and an increased risk of certain cancers (Figure 3).

The PER gene family and cell function
The cell cycle, which promotes cell division in a specific sequence and phases, exhibits a biological rhythm akin to the circadian clock.Cell cycle progression is governed by transient interactions between cyclins and cyclin-dependent kinases (CDKs), triggering phase transitions; While activities of the cyclin-CDK complexes are strictly regulated by CDK inhibitors like p16, p21, and WEE1, to halt the cell cycle under stress or damage conditions (Suski et al., 2021;Matthews et al., 2022).Consequently, there is growing interest in exploring the molecular interplay between the cell cycle and circadian rhythms, particularly regarding abnormal cell proliferation in cancers (Farshadi et al., 2020;Yao et al., 2021).For example, the PER1 protein has been shown to inhibit the cell cycle by interacting with checkpoint proteins ATM and CHK2 in colorectal cancer cells (Gery et al., 2006); similarly, NONO was found to influence the p16-Ink4A site by binding to PER1/ PER2 proteins during the G1 phase, linking the cell cycle with the circadian rhythm (Kowalska et al., 2013).Conversely, the TP53 gene can inhibit PER2 gene activation by interfering with BMAL1/ CLOCK-mediated E-box transcription, serving as a key cell cycle regulator (Miki et al., 2013;Zou et al., 2020;Engeland, 2022).Gao et al. (Gao et al., 2021) observed that IDH1 gene mutations in gliomas significantly reduced PER genes expression (PER1, PER2, and PER3) and altered the expression of cell cycle-related proteins like Cyclin A, CDK2, and Cyclin D3, resulting in increase of G1 phase cells and decrease of S phase cells.Overexpressing the PER2 gene in the chronic myelogenous leukemia cell line KCL22 led to G1 phase cell cycle arrest, while its downregulation expedited the transition to the S phase (Wang et al., 2020b;Basti et al., 2022).Recently, Han and colleagues integrated cell microarray analysis with experimental validation, revealing that overexpressing the PER1 gene affected the expression of cell cycle-related proteins such as Wee1, CRE-BP1, CDK1, and GADD45A, thereby inhibiting the cell cycle in cholangiocarcinoma cells (Han et al., 2016).
The epithelial-mesenchymal transition (EMT), marked by increased vimentin and decreased E-cadherin expression, is a critical process where cells transition from epithelial to mesenchymal traits (Bakir et al., 2020;Liu et al., 2022b;Huang et al., 2022;Lee et al., 2022).EMT is essential for tumor initiation, enhanced migration, metastasis, and treatment resistance (Pastushenko and Blanpain, 2019).Studies have shown that EMT in glioma C6 and breast cancer MCF-7 cells correlated with enhanced circadian rhythms and increased PER2 gene expression (De et al., 2020).Guo et al. (Guo et al., 2020) observed that elevated PER2 gene protected oral cancer cells from EMT via upregulation of TP53 protein.Conversely, PER2 knockdown in colorectal cancer cells activated the Snail/Slug-related EMT pathway, promoting proliferation and invasiveness of cancer cells (Xiong et al., 2022).Additionally, Lin et al. (Lin et al., 2020) reported that the mangiferin-induced EMT suppression in lung cancer cells was associated with decreased E-cadherin and increased PER1 protein expression.These findings suggest that the PER1 and PER2 genes play a role in inhibiting EMT, potentially reducing migration and invasion in cancer cells.6 The PER gene family and metabolism Metabolic reprogramming, a hallmark of cancer cells (Pavlova et al., 2022), involves altering cellular metabolism to manage different inputs and stressors (Wang et al., 2024).Cancer cells adapt their metabolic pathways to oncogenic mutations and external nutritional conditions, supporting their increased biosynthetic and energy needs while mitigating oxidative stress associated with survival and proliferation (Altea-Manzano et al., 2020;McGuirk et al., 2020;Schiliro and Firestein, 2021).An example is the Warburg effect, where cancer cells prefer glycolysis for energy production under aerobic conditions, highlighting their metabolic flexibility (Warburg et al., 1923;Warburg et al., 1924).Circadian rhythms regulate key biological processes associated with material and energy metabolism, including sleep-wake cycles (Daan et al., 1984;Wendrich et al., 2023), thermogenesis (Hasan et al., 2021), food intake (Teixeira et al., 2022), and glucose and lipid metabolism (Kalsbeek et al., 2010;Frazier et al., 2023;Small et al., 2023).Previous studies showed that mice lacking Bmal1 or Clock genes exhibit significant defects in gluconeogenesis, lipid, and glucose metabolism (Bolshette et al., 2023).In Drosophila, dietary restriction prolonged lifespan via promoting fat metabolism, which linked to increased oscillations and expressions of Per and Tim proteins (Katewa et al., 2016).Research on transgenic mice with the hPER2 S662G mutation revealed that derived lung cancer cells increased glucose, glutamine, and lactic acid consumption.Isotope tracing has also illustrated enhanced glucose utilization in cancer cell glycolysis and the tricarboxylic acid cycle (Papagiannakopoulos et al., 2016).Furthermore, Gong et al. (Gong et al., 2021) found that PER1 gene knockdown raised levels of key glycolytic enzymes, boosting glucose uptake and lactate production in oral squamous cell carcinoma cells.These studies indicate that disrupting PER1 or PER2 gene functions in cancer cells can lead to elevated metabolism and energy production, supporting their rapid proliferation and adaptability.

The PER gene family and tumor immune microenvironment
The tumor microenvironment (TME) comprises various cellular components (such as immune cells, fibroblasts, and endothelial cells) and acellular elements (including cytokines, growth factors, and the extracellular matrix) (Ribeiro Franco et al., 2020).Innate and adaptive immune cells within the TME interact with cancer cells directly or through chemokine and cytokine signaling (Liu et al., 2023a;Xiong et al., 2023;Zetrini et al., 2023).These interactions significantly influence the biological behavior and therapeutic responses of cancer cells, impacting patients' clinical outcomes and prognosis (Neophytou et al., 2021).For example, a comprehensive pan-cancer analysis demonstrated a strong association between the upregulation of immunosuppressive molecules like PD-L1 and CTLA-4, and the downregulation of PER1, PER2, and PER3 genes, underscoring the impact of disrupted clock genes on T cell exhaustion and immune evasion in the TME (Wu et al., 2019).In ovarian cancer, B lymphocyte, macrophage, and neutrophil infiltration levels were inversely correlated with PER1 gene expression (Chen et al., 2021).Recently, a colon cancer research indicated that the epigenetic regulator CBX4 was negatively associated with myeloid-derived suppressor cells and cancer-associated fibroblasts, and showed coordinated expression with PER1 and PER3 genes (Wei et al., 2021).Yang et al. (Yang et al., 2019) found a specific circadian rhythm in PD-L1 expression and a positive correlation between the PER1 gene and CD4 + and CD8 + T cell infiltration on lung cancer.Furthermore, in endometrial cancer, the PER1 gene is linked to immunological factors like PD-1/PD-L1 and inflammatory markers such as TNF-α and IL-6 (Wang et al., 2020c).Additionally, chronic shift-lag-induced suppression of Per1 and Per2 genes impaired natural killer (NK) cell-mediated immunosurveillance and promoted tumorigenesis in mice, potentially due to decreased expression of immune functional receptors like Ly49D, Ly49G2, and Ly49H (Zeng et al., 2020).These studies robustly support the PER gene family's regulatory role in immune cell function and tumor immune cell invasion.

The PER gene family and cancer therapy
To enhance patient prognosis, chemotherapy employs cytotoxic chemicals to eradicate cancer cells (van Stein et al., 2021).It may also serve as an adjuvant therapy alongside radiotherapy or surgery (Liu et al., 2022c).However, factors such as intratumor heterogeneity, adaptive mutations, epigenetic alterations, and metabolic changes enable some cancer cells to withstand clinical doses of medications, thereby escalating the challenge of medication resistance in cancer treatment (Vasan et al., 2019).Investigating the molecular mechanisms of drug resistance is crucial for improving therapeutic outcomes and introducing new treatment strategies (Nussinov et al., 2021;Liu et al., 2023b).Previous research revealed that oncogene-transformed mouse embryonic fibroblasts developed increased resistance to chemotherapeutic agents like methotrexate, gemcitabine, and etoposide, due to alterations of Per2 gene.Wang et al. (Wang et al., 2020d) found a link between the downregulation of PER2 gene expression in cisplatin-resistant ovarian cancer cells and the PI3K/AKT signaling pathway, which led to the activation of the multidrug resistance gene 1 (MDR1).Conversely, upregulating the PER2 gene in cervical cancer cells inhibited the PI3K/AKT pathway, diminishing multidrug resistance protein production and enhancing cisplatin's lethal effect on cancer cells (Wang et al., 2022).Additionally, Cai et al. (Cai et al., 2018) noted a downregulation of PER3 gene in prostate cancer patients with paclitaxel-resistant, while the paclitaxel sensitivity of cancer cells could be rescued by overexpressing the PER3 gene.Moreover, Redondo and colleagues observed that lower PER2 gene expression increased the susceptibility of esophageal cancer cells to cisplatin, promoting higher rates of cell apoptosis (Redondo et al., 2021).
Radiation therapy is a prevalent cancer treatment modality.Increasing research focuses on the link between circadian rhythm and radiotherapy, given that specific circadian clock genes are vital for DNA repair and apoptosis induced by ionizing radiation and influence cell sensitivity to radiation at different cell cycle stages (Amiama-Roig et al., 2022).In glioma research, Zhu et al. (Zhu et al., 2019) observed that the downregulation of the PER1 gene in U343 cells diminished X-ray-induced DNA damage and cell death through the CHK2-TP53 pathway.A comprehensive cohort study of 1,690 breast cancer patients demonstrated a significant association between the genotype variations of PER3 gene and radiotherapy side-effects, suggesting the potential of the PER3 gene as a predictor for radiotherapy response (Webb et al., 2022).Furthermore, studies have explored the impact of radiation timing on long-term prognosis and adverse patient outcomes, along with the predictive capacity of clock gene profiles for radiotherapy efficacy (Jin et al., 2021;Sapienza et al., 2021;Kong et al., 2022;Tang et al., 2023).
9 The PER gene family-related drugs Several studies have focused on the PER gene family in cell and animal models to augment cancer therapy.For instance, Yang et al. (Yang and Stockwell, 2008) demonstrated that IC261, a CKⅠε inhibitor, impedes fibrosarcoma cell proliferation by stabilizing PER2 protein.Oshima et al. (Oshima et al., 2019) conducted a proteomic analysis and identified that the CKⅡ inhibitor GO289 inhibited the PER2 phosphorylation sites, leading to extended circadian rhythms and suppressed growth in kidney cancer and acute myeloid leukemia cells.LY2857785, a CDK9 inhibitor, has been shown to decrease core clock protein levels including BMAL1 and PER2, by upregulating REV-ERBα expression (Ou et al., 2019).Additionally, mutations of PER2 could shorten circadian rhythms in mice induced by N-ethyl-N-nitrosourea (ENU) in the PAS domain, suggesting the PAS domain as target within the PER gene family for future interventions (Militi et al., 2016).These findings underscore the potential of targeting the PER gene family in cancer therapy.However, more clinical researches are necessary to elucidate their precise pharmacological effects and minimize unintended adverse impacts on healthy tissues.

Perspective and conclusion
As a crucial component of clock genes, the PER gene family in human (PER1, PER2, and PER3) plays a pivotal role in numerous significant pathological processes, including cancer initiation and development.These genes, by modulating downstream gene expression, are instrumental in regulating cell cycle and invasion processes, altering tumor cell metabolism, impacting the tumor immune environment, and influencing treatment responses (Figure 4; Table 1).This modulation leads to varied clinical and pathological features and prognostic outcomes in cancer patients.The dysregulated proliferative phenotype is a universally recognized hallmark of cancer.Consequently, research on the TP53 gene in cancer maintains a prominent and steadfast position, given its direct association with the cell cycle and proliferative phenotype, which may be intricately linked to circadian rhythms and the biological clock.Yet, the extent of the PER gene family's influence on cancer cell cycles remains incompletely elucidated.In our review, we thoroughly reviewed the discovery history, fundamental biological functions, and the interplay between the PER gene family and various tumor characteristics.We also anticipate further studies on the relationship between the PER gene family and TP53 to elucidate their connections.Our review advocates for in-depth investigations into the PER gene family's role in specific cancer types or stages, and their molecular mechanisms, to identify potential biomarkers for cancer risk and prognosis.
In future studies, our focus on the PER gene family will encompass several key areas (Feng et al., 2023a): Developing personalized treatment strategies: By harnessing a thorough comprehension of the PER genes' expression and functional disparities across different cancer types, we aim to craft more targeted treatment methodologies to improve patient responses and survival rates (Hanahan, 2022); Integrating immunotherapy: This involves exploring how immunotherapy can enhance the immune system's ability to detect and eliminate tumors, potentially including the creation of immunotherapeutic approaches directly linked to PER genes regulation (Shen et al., 2022); Deciphering treatment resistance mechanisms: Conducting detailed analyses of the resistance mechanisms associated with the PER genes to ascertain why some patients resist certain treatments, thereby providing insights for novel therapeutic development (Wang et al., 2023); Discovering early diagnostic and predictive biomarkers: Leveraging insights into the regulatory roles of PER genes in various biological processes to identify novel early diagnostic or predictive biomarkers, aiming to improve patient outcomes (Feng et al., 2023b); Fostering multidisciplinary collaboration and technological innovation: By enhancing collaboration across disciplines and integrating cutting-edge technologies from bioinformatics, molecular biology, and immunology, we plan to conduct an in-depth and comprehensive exploration of the mechanisms of action of PER genes in cancer.

FIGURE 3
FIGURE 3 The author(s) declare that financial support was received for the research, authorship, and/or publication of this article.This program was supported by the Chinese Scholarship Council (grant no.202206240086), National Key Research and Development Program of China (2021YFC2009303), Project of Health Commission of Sichuan Province (21PJ041), the Key Research and Development Support Plan of Chengdu Science and Technology Bureau (2022-YF05-01568-SN), 2023 Jiaxing Key Discipline of Medicine-Urology (Supporting Subject) (2023-ZC-013) and 2020 Jiaxing Key Laboratory of Precision Diagnosis and Treatment of Urological Tumors (2020-MNZDSYS).The funders had no role in the study design, data collection or analysis, preparation of the manuscript, or the decision to publish.

TABLE 1
Main studies of associations between the PER gene family and cancers