MLL1 is essential for the senescence-associated secretory phenotype

Multi-omics and single cell characterization of cancer immunosenescence landscape

Cellular senescence (CS) is closely related to tumor progression. However, the studies about CS genes across human cancers have not explored the relationship between cancer senescence signature and telomere length. Additionally, single-cell analyses have not revealed the evolutionary trends of malignant cells and immune cells at the CS level. We defined a CS-associated signature, called "senescence signature", and found that patients with higher senescence signature had worse prognosis. Higher senescence signature was related to older age, higher genomic instability, longer telomeres, increased lymphocytic infiltration, higher pro-tumor immune infiltrates (Treg cells and MDSCs), and could predict responses to immune checkpoint inhibitor therapy. Single-cell analysis further reveals malignant cells and immune cells share a consistent evolutionary trend at the CS level. MAPK signaling pathway and apoptotic processes may play a key role in CS, and senescence signature may effectively predict sensitivity of MEK1/2 inhibitors, ERK1/2 inhibitors and BCL-2 family inhibitors. We also developed a new CS prediction model of cancer survival and established a portal website to apply this model ( https://bio-pub.shinyapps.io/cs_nomo/ ).

The senescence-associated secretory phenotype and its physiological and pathological implications

Cellular senescence is a state of terminal growth arrest associated with the upregulation of different cell cycle inhibitors, mainly p16 and p21, structural and metabolic alterations, chronic DNA damage responses, and a hypersecretory state known as the senescence-associated secretory phenotype (SASP). The SASP is the major mediator of the paracrine effects of senescent cells in their tissue microenvironment and of various local and systemic biological functions. In this Review, we discuss the composition, dynamics and heterogeneity of the SASP as well as the mechanisms underlying its induction and regulation. We describe the various biological properties of the SASP, its beneficial and detrimental effects in different physiological and pathological settings, and its impact on overall health span. Finally, we discuss the use of the SASP as a biomarker and of SASP inhibitors as senomorphic interventions to treat cancer and other age-related conditions.

The senescence journey in cancer immunoediting

Cancer progression is continuously controlled by the immune system which can identify and destroy nascent tumor cells or inhibit metastatic spreading. However, the immune system and its deregulated activity in the tumor microenvironment can also promote tumor progression favoring the outgrowth of cancers capable of escaping immune control, in a process termed cancer immunoediting. This process, which has been classified into three phases, i.e. "elimination", "equilibrium" and "escape", is influenced by several cancer- and microenvironment-dependent factors. Senescence is a cellular program primed by cells in response to different pathophysiological stimuli, which is based on long-lasting cell cycle arrest and the secretion of numerous bioactive and inflammatory molecules. Because of this, cellular senescence is a potent immunomodulatory factor promptly recruiting immune cells and actively promoting tissue remodeling. In the context of cancer, these functions can lead to both cancer immunosurveillance and immunosuppression. In this review, the authors will discuss the role of senescence in cancer immunoediting, highlighting its context- and timing-dependent effects on the different three phases, describing how senescent cells promote immune cell recruitment for cancer cell elimination or sustain tumor microenvironment inflammation for immune escape. A potential contribution of senescent cells in cancer dormancy, as a mechanism of therapy resistance and cancer relapse, will be discussed with the final objective to unravel the immunotherapeutic implications of senescence modulation in cancer.

Subcellular structure, heterogeneity, and plasticity of senescent cells

Cellular senescence is a state of permanent growth arrest. It can be triggered by telomere shortening (replicative senescence) or prematurely induced by stresses such as DNA damage, oncogene overactivation, loss of tumor suppressor genes, oxidative stress, tissue factors, and others. Advances in techniques and experimental designs have provided new evidence about the biology of senescent cells (SnCs) and their importance in human health and disease. This review aims to describe the main aspects of SnCs phenotype focusing on alterations in subcellular compartments like plasma membrane, cytoskeleton, organelles, and nuclei. We also discuss the heterogeneity, dynamics, and plasticity of SnCs' phenotype, including the SASP, and pro-survival mechanisms. We advance on the multiple layers of phenotypic heterogeneity of SnCs, such as the heterogeneity between inducers, tissues and within a population of SnCs, discussing the relevance of these aspects to human health and disease. We also raise the main challenges as well alternatives to overcome them. Ultimately, we present open questions and perspectives in understanding the phenotype of SnCs from the perspective of basic and applied questions.

Autophagy and senescence facilitate the development of antiestrogen resistance in ER positive breast cancer

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer diagnosed annually in the US with endocrine-based therapy as standard-of-care for this breast cancer subtype. Endocrine therapy includes treatment with antiestrogens, such as selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). Despite the appreciable remission achievable with these treatments, a substantial cohort of women will experience primary tumor recurrence, subsequent metastasis, and eventual death due to their disease. In these cases, the breast cancer cells have become resistant to endocrine therapy, with endocrine resistance identified as the major obstacle to the medical oncologist and patient. To combat the development of endocrine resistance, the treatment options for ER+, HER2 negative breast cancer now include CDK4/6 inhibitors used as adjuvants to antiestrogen treatment. In addition to the dysregulated activity of CDK4/6, a plethora of genetic and biochemical mechanisms have been identified that contribute to endocrine resistance. These mechanisms, which have been identified by lab-based studies utilizing appropriate cell and animal models of breast cancer, and by clinical studies in which gene expression profiles identify candidate endocrine resistance genes, are the subject of this review. In addition, we will discuss molecular targeting strategies now utilized in conjunction with endocrine therapy to combat the development of resistance or target resistant breast cancer cells. Of approaches currently being explored to improve endocrine treatment efficacy and patient outcome, two adaptive cell survival mechanisms, autophagy, and "reversible" senescence, are considered molecular targets. Autophagy and/or senescence induction have been identified in response to most antiestrogen treatments currently being used for the treatment of ER+ breast cancer and are often induced in response to CDK4/6 inhibitors. Unfortunately, effective strategies to target these cell survival pathways have not yet been successfully developed. Thus, there is an urgent need for the continued interrogation of autophagy and "reversible" senescence in clinically relevant breast cancer models with the long-term goal of identifying new molecular targets for improved treatment of ER+ breast cancer.

Recent advances in senescence-associated secretory phenotype and osteoporosis

The worldwide elderly population is on the rise, and aging is a major osteoporosis risk factor. Senescent cells accumulation can have a detrimental effect the body as we age. The senescence-associated secretory phenotype (SASP), an essential cellular senescence hallmark, is an important mechanism connecting cellular senescence to osteoporosis. This review describes in detail the characteristics of SASPs and their regulatory agencies, and shed fresh light on how SASPs from different senescent cells contribute to osteoporosis development. Furthermore, we summarized various innovative therapy techniques that target SASPs to lower the burden of osteoporosis in the elderly and discussed the potential challenges of SASPs-based therapy for osteoporosis as a new clinical trial.

ΔNp63α-mediated epigenetic regulation in keratinocyte senescence

Keratinocyte senescence contributes to skin ageing and epidermal dysfunction. According to the existing knowledge, the transcription factor ΔNp63α plays pivotal roles in differentiation and proliferation of keratinocytes. It is traditionally accepted that ΔNp63α exerts its functions via binding to promoter regions to activate or repress gene transcription. However, accumulating evidence demonstrates that ΔNp63α can bind to elements away from promoter regions of its target genes, mediating epigenetic regulation. On the other hand, several epigenetic alterations, including DNA methylation, histone modification and variation, chromatin remodelling, as well as enhancer-promoter looping, are found to be related to cell senescence. To systematically elucidate how ΔNp63α affects keratinocyte senescence via epigenetic regulation, we comprehensively compiled the literatures on the roles of ΔNp63α in keratinocyte senescence, epigenetics in cellular senescence, and the relation between ΔNp63α-mediated epigenetic regulation and keratinocyte senescence. Based on the published data, we conclude that ΔNp63α mediates epigenetic regulation via multiple mechanisms: recruiting epigenetic enzymes to modify DNA or histones, coordinating chromatin remodelling complexes (CRCs) or regulating their expression, and mediating enhancer-promoter looping. Consequently, the expression of genes related to cell cycle is modulated, and proliferation of keratinocytes and renewal of stem cells are maintained, by ΔNp63α. During skin inflammaging, the decline of ΔNp63α may lead to epigenetic dysregulation, resultantly deteriorating keratinocyte senescence.

Insulin-like growth factor binding protein-3 induces senescence by inhibiting telomerase activity in MCF-7 breast cancer cells

Insulin-like growth factor binding protein-3 (IGFBP-3) has been known to inhibit cell proliferation and exert tumor-suppressing effects depending on the cell type. In this study, we aimed to show that IGFBP-3 induces cellular senescence via suppression of the telomerase activity, thereby inhibiting MCF-7 breast cancer cell proliferation. We found that the induction of IGFBP-3 in MCF-7 cells enhanced the loss of cell viability. Flow cytometry revealed a higher percentage of non-cycling cells among IGFBP-3-expressing cells than among controls. IGFBP-3 induction also resulted in morphological alterations, such as a flattened cytoplasm and increased granularity, suggesting that IGFBP-3 induces a senescence-like phenotype. The percentage of IGFBP-3 expressing cells with senescence-associated β-galactosidase activity was 3.4 times higher than control cells. Telomeric repeat amplification and real-time PCR showed that IGFBP-3 decreased telomerase activity by reducing the levels of the RNA component (hTR) and catalytic protein component with reverse transcriptase activity (hTERT) of telomerase in a dose-dependent manner. These results suggest that IGFBP-3 is a negative regulator of MCF-7 breast cancer cell growth by inducing senescence through telomerase suppression.

Induction of Hibernation and Changes in Physiological and Metabolic Indices in Pelodiscus sinensis

Pelodiscus sinensis (P. sinensis) is a commonly cultivated turtle species with a habit of hibernation. To study the changes in histone expression and methylation of P. sinensis during hibernation induction, a model was established by artificial induction. Physiological and metabolic indices were measured, and the expression and localization of histone (H1, H2A, H2B, H3, and H4) and methylation-related genes (ASH2L, KMT2A, KMT2E, KDM1A, KDM1B, and KDM5A) were measured by quantitative PCR, immunohistochemistry, and Western blot analysis. The results indicated that the metabolism, antioxidation index, and relative expression of histone methyltransferase were significantly decreased (p < 0.05), whereas the activity and expression of histone demethyltransferase were significantly increased (p < 0.05). Although our results showed significant changes in physiological and gene expression after hibernation induction, we could not confirm that P. sinensis entered deep hibernation. Therefore, for the state after cooling-induced hibernation, cold torpor might be a more accurate description. The results indicate that the P. sinensis can enter cold torpor through artificial induction, and the expression of histones may promote gene transcription. Unlike histones expressed under normal conditions, histone methylation may activate gene transcription during hibernation induction. Western blot analysis revealed that the ASH2L and KDM5A proteins were differentially expressed in the testis at different months (p < 0.05), which may perform a role in regulating gene transcription. The immunohistochemical localization of ASH2L and KDM5A in spermatogonia and spermatozoa suggests that ASH2L and KDM5A may perform a role in mitosis and meiosis. In conclusion, this study is the first to report changes in histone-related genes in reptiles, which provides insight for further studies on the physiological metabolism and histone methylation regulation of P. sinensis during the hibernation induction and hibernation period.

Emerging Therapeutic Approaches to Target the Dark Side of Senescent Cells: New Hopes to Treat Aging as a Disease and to Delay Age-Related Pathologies

Life expectancy has drastically increased over the last few decades worldwide, with important social and medical burdens and costs. To stay healthy longer and to avoid chronic disease have become essential issues. Organismal aging is a complex process that involves progressive destruction of tissue functionality and loss of regenerative capacity. One of the most important aging hallmarks is cellular senescence, which is a stable state of cell cycle arrest that occurs in response to cumulated cell stresses and damages. Cellular senescence is a physiological mechanism that has both beneficial and detrimental consequences. Senescence limits tumorigenesis, lifelong tissue damage, and is involved in different biological processes, such as morphogenesis, regeneration, and wound healing. However, in the elderly, senescent cells increasingly accumulate in several organs and secrete a combination of senescence associated factors, contributing to the development of various age-related diseases, including cancer. Several studies have revealed major molecular pathways controlling the senescent phenotype, as well as the ones regulating its interactions with the immune system. Attenuating the senescence-associated secretory phenotype (SASP) or eliminating senescent cells have emerged as attractive strategies aiming to reverse or delay the onset of aging diseases. Here, we review current senotherapies designed to suppress the deleterious effect of SASP by senomorphics or to selectively kill senescent cells by "senolytics" or by immune system-based approaches. These recent investigations are promising as radical new controls of aging pathologies and associated multimorbidities.

Multi-range ERK responses shape the proliferative trajectory of single cells following oncogene induction

Oncogene-induced senescence is a phenomenon in which aberrant oncogene expression causes non-transformed cells to enter a non-proliferative state. Cells undergoing oncogenic induction display phenotypic heterogeneity, with some cells senescing and others remaining proliferative. The causes of heterogeneity remain unclear. We studied the sources of heterogeneity in the responses of human epithelial cells to oncogenic BRAF^V600E expression. We found that a narrow expression range of BRAF^V600E generated a wide range of activities of its downstream effector ERK. In population-level and single-cell assays, ERK activity displayed a non-monotonic relationship to proliferation, with intermediate ERK activities leading to maximal proliferation. We profiled gene expression across a range of ERK activities over time and characterized four distinct ERK response classes, which we propose act in concert to generate the ERK-proliferation response. Altogether, our studies map the input-output relationships between ERK activity and proliferation, elucidating how heterogeneity can be generated during oncogene induction.

Mesenchymal stromal cell senescence in haematological malignancies

Acute myeloid leukaemia (AML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM) are age-related haematological malignancies with defined precursor states termed myelodysplastic syndrome (MDS), monoclonal B-cell lymphocytosis (MBL), and monoclonal gammopathy of undetermined significance (MGUS), respectively. While the progression from asymptomatic precursor states to malignancy is widely considered to be mediated by the accumulation of genetic mutations in neoplastic haematopoietic cell clones, recent studies suggest that intrinsic genetic changes, alone, may be insufficient to drive the progression to overt malignancy. Notably, studies suggest that extrinsic, microenvironmental changes in the bone marrow (BM) may also promote the transition from these precursor states to active disease. There is now enhanced focus on extrinsic, age-related changes in the BM microenvironment that accompany the development of AML, CLL, and MM. One of the most prominent changes associated with ageing is the accumulation of senescent mesenchymal stromal cells within tissues and organs. In comparison with proliferating cells, senescent cells display an altered profile of secreted factors (secretome), termed the senescence-associated-secretory phenotype (SASP), comprising proteases, inflammatory cytokines, and growth factors that may render the local microenvironment favourable for cancer growth. It is well established that BM mesenchymal stromal cells (BM-MSCs) are key regulators of haematopoietic stem cell maintenance and fate determination. Moreover, there is emerging evidence that BM-MSC senescence may contribute to age-related haematopoietic decline and cancer development. This review explores the association between BM-MSC senescence and the development of haematological malignancies, and the functional role of senescent BM-MSCs in the development of these cancers.

Cellular senescence in the tumor microenvironment and context-specific cancer treatment strategies

Cellular senescence in cancer development is known to have tumor-suppressive and tumor-promoting roles. Recent studies have revealed numerous molecular mechanisms of senescence followed by senescence-associated secretory phenotype induction and showed the significance of senescence on both sides. Cellular senescence in stromal cells is one of the reasons for therapeutic resistance in advanced cancer; thus, it is an inevitable phenomenon to address while seeking an effective cancer treatment strategy. This review summarizes the molecular mechanisms regarding cellular senescence, focusing on the dual roles played by senescence, and offers some direction toward successful treatments targeting harmful senescent cells.

Could senescence phenotypes strike the balance to promote tumor dormancy?

After treatment and surgery, patient tumors can initially respond followed by a rapid relapse, or respond well and seemingly be cured, but then recur years or decades later. The state of surviving cancer cells during the long, undetected period is termed dormancy. By definition, the dormant tumor cells do not proliferate to create a mass that is detectable or symptomatic, but also never die. An intrinsic state and microenvironment that are inhospitable to the tumor would bias toward cell death and complete eradication, while conditions that favor the tumor would enable growth and relapse. In neither case would clinical dormancy be observed. Normal cells and tumor cells can enter a state of cellular senescence after stress such as that caused by cancer therapy. Senescence is characterized by a stable cell cycle arrest mediated by chromatin modifications that cause gene expression changes and a secretory phenotype involving many cytokines and chemokines. Senescent cell phenotypes have been shown to be both tumor promoting and tumor suppressive. The balance of these opposing forces presents an attractive model to explain tumor dormancy: phenotypes of stable arrest and immune suppression could promote survival, while reversible epigenetic programs combined with cytokines and growth factors that promote angiogenesis, survival, and proliferation could initiate the emergence from dormancy. In this review, we examine the phenotypes that have been characterized in different normal and cancer cells made senescent by various stresses and how these might explain the characteristics of tumor dormancy.

Targeting Mitochondria to Control Ageing and Senescence

Ageing is accompanied by a progressive impairment of cellular function and a systemic deterioration of tissues and organs, resulting in increased vulnerability to multiple diseases. Here, we review the interplay between two hallmarks of ageing, namely, mitochondrial dysfunction and cellular senescence. The targeting of specific mitochondrial features in senescent cells has the potential of delaying or even reverting the ageing process. A deeper and more comprehensive understanding of mitochondrial biology in senescent cells is necessary to effectively face this challenge. Here, we discuss the main alterations in mitochondrial functions and structure in both ageing and cellular senescence, highlighting the differences and similarities between the two processes. Moreover, we describe the treatments available to target these pathways and speculate on possible future directions of anti-ageing and anti-senescence therapies targeting mitochondria.

The epigenetic regulation of cancer cell recovery from therapy exposure and its implications as a novel therapeutic strategy for preventing disease recurrence

The ultimate goal of cancer therapy is the elimination of disease from patients. Most directly, this occurs through therapy-induced cell death. Therapy-induced growth arrest can also be a desirable outcome, if prolonged. Unfortunately, therapy-induced growth arrest is rarely durable and the recovering cell population can contribute to cancer recurrence. Consequently, therapeutic strategies that eliminate residual cancer cells reduce opportunities for recurrence. Recovery can occur through diverse mechanisms including quiescence or diapause, exit from senescence, suppression of apoptosis, cytoprotective autophagy, and reductive divisions resulting from polyploidy. Epigenetic regulation of the genome represents a fundamental regulatory mechanism integral to cancer-specific biology, including the recovery from therapy. Epigenetic pathways are particularly attractive therapeutic targets because they are reversible, without changes in DNA, and are catalyzed by druggable enzymes. Previous use of epigenetic-targeting therapies in combination with cancer therapeutics has not been widely successful because of either unacceptable toxicity or limited efficacy. The use of epigenetic-targeting therapies after a significant interval following initial cancer therapy could potentially reduce the toxicity of combination strategies, and possibly exploit essential epigenetic states following therapy exposure. This review examines the feasibility of targeting epigenetic mechanisms using a sequential approach to eliminate residual therapy-arrested populations, that might possibly prevent recovery and disease recurrence.

Senescence of Tumor Cells in Anticancer Therapy—Beneficial and Detrimental Effects

Cellular senescence process results in stable cell cycle arrest, which prevents cell proliferation. It can be induced by a variety of stimuli including metabolic stress, DNA damage, telomeres shortening, and oncogenes activation. Senescence is generally considered as a process of tumor suppression, both by preventing cancer cells proliferation and inhibiting cancer progression. It can also be a key effector mechanism for many types of anticancer therapies such as chemotherapy and radiotherapy, both directly and through bioactive molecules released by senescent cells that can stimulate an immune response. Senescence is characterized by a senescence-associated secretory phenotype (SASP) that can have both beneficial and detrimental impact on cancer progression. Despite the negatives, attempts are still being made to use senescence to fight cancer, especially when it comes to senolytics. There is a possibility that a combination of prosenescence therapy—which targets tumor cells and causes their senescence—with senotherapy—which targets senescent cells, can be promising in cancer treatment. This review provides information on cellular senescence, its connection with carcinogenesis and therapeutic possibilities linked to this process.

Cellular senescence and abdominal aortic aneurysm: From pathogenesis to therapeutics

As China’s population enters the aging stage, the threat of abdominal aortic aneurysm (AAA) mainly in elderly patients is becoming more and more serious. It is of great clinical significance to study the pathogenesis of AAA and explore potential therapeutic targets. The purpose of this paper is to analyze the pathogenesis of AAA from the perspective of cellular senescence: on the basis of clear evidence of cellular senescence in aneurysm wall, we actively elucidate specific molecular and regulatory pathways, and to explore the targeted drugs related to senescence and senescent cells eliminate measures, eventually improve the health of patients with AAA and prolong the life of human beings.

Immunosenescence in atherosclerosis: A role for chronic viral infections

Immune system is a versatile and dynamic body organ which offers survival and endurance of human beings in their hostile living environment. However, similar to other cells, immune cells are hijacked by senescence. The ageing immune cells lose their beneficial functions but continue to produce inflammatory mediators which draw other immune and non-immune cells to the senescence loop. Immunosenescence has been shown to be associated with different pathological conditions and diseases, among which atherosclerosis has recently come to light. There are common drivers of both immunosenescence and atherosclerosis; e.g. inflammation, reactive oxygen species (ROS), chronic viral infections, genomic damage, oxidized-LDL, hypertension, cigarette smoke, hyperglycaemia, and mitochondrial failure. Chronic viral infections induce inflammaging, sustained cytokine signaling, ROS generation and DNA damage which are associated with atherogenesis. Accumulating evidence shows that several DNA and RNA viruses are stimulators of immunosenescence and atherosclerosis in an interrelated network. DNA viruses such as CMV, EBV and HBV upregulate p16, p21 and p53 senescence-associated molecules; induce inflammaging, metabolic reprogramming of infected cells, replicative senescence and telomere shortening. RNA viruses such as HCV and HIV induce ROS generation, DNA damage, induction of senescence-associated secretory phenotype (SASP), metabolic reprogramming of infected cells, G1 cell cycle arrest, telomere shortening, as well as epigenetic modifications of DNA and histones. The newly emerged SARS-CoV-2 virus is also a potent inducer of cytokine storm and SASP. The spike protein of SARS-CoV-2 promotes senescence phenotype in endothelial cells by augmenting p16, p21, senescence-associated β-galactosidase (SA-β-Gal) and adhesion molecules expression. The impact of SARS-CoV-2 mega-inflammation on atherogenesis, however, remains to be investigated. In this review we focus on the common processes in immunosenescence and atherogenesis caused by chronic viral infections and discuss the current knowledge on this topic.

Induction of senescence upon loss of the Ash2l core subunit of H3K4 methyltransferase complexes

Gene expression is controlled in part by post-translational modifications of core histones. Methylation of lysine 4 of histone H3 (H3K4), associated with open chromatin and gene transcription, is catalyzed by type 2 lysine methyltransferase complexes that require WDR5, RBBP5, ASH2L and DPY30 as core subunits. Ash2l is essential during embryogenesis and for maintaining adult tissues. To expand on the mechanistic understanding of Ash2l, we generated mouse embryo fibroblasts (MEFs) with conditional Ash2l alleles. Upon loss of Ash2l, methylation of H3K4 and gene expression were downregulated, which correlated with inhibition of proliferation and cell cycle progression. Moreover, we observed induction of senescence concomitant with a set of downregulated signature genes but independent of SASP. Many of the signature genes are FoxM1 responsive. Indeed, exogenous FOXM1 was sufficient to delay senescence. Thus, although the loss of Ash2l in MEFs has broad and complex consequences, a distinct set of downregulated genes promotes senescence.

Hexavalent chromium triggers hepatocytes premature senescence via the GATA4/NF-κB signaling pathway mediated by the DNA damage response

Hexavalent chromium [Cr(VI)] is a proven toxin, carcinogen and environmental pollutant. Oral intake of Cr(VI) has been shown to lead to an increasing incidence of primary hepatic carcinoma in the population. Cellular senescence is thought to be a natural barrier to malignant transformation of cells, but senescence-associated secretory phenotype (SASP) is secreted and regulated by senescent cells links cellular senescence to malignant transformation in a dynamic way. In the present research, we demonstrated novel mechanisms of premature hepatocytes senescence induced by Cr(VI). Continuous Cr(VI) stimulation led to DNA damaged in hepatocytes, and DNA damage response (DDR) signals were transmitted by ataxia telangiectasia-mutated gene (ATM)/ataxia telangiectasia and Rad-3-related protein (ATR), resulting in zinc finger transcription factor GATA4 escaping p62-mediated selective autophagy, thereby regulating nuclear factor kappa-B (NF-κB) to induce premature senescence in hepatocytes. In contrast to the classical senescence pathway p53-p21^{WAF1 /CIP1} and Rb/p16^INK4a, GATA4 can directly regulate the secretion of SASP during premature senescence. The results will provide valuable clues for targeted prevention and further individualized treatment of Cr(VI)-associated cancers.

Prognostic Ability of Enhancer RNAs in Metastasis of Non-Small Cell Lung Cancer

(1) Background: Non-small cell lung cancer (NSCLC) is the most common lung cancer. Enhancer RNA (eRNA) has potential utility in the diagnosis, prognosis and treatment of cancer, but the role of eRNAs in NSCLC metastasis is not clear; (2) Methods: Differentially expressed transcription factors (DETFs), enhancer RNAs (DEEs), and target genes (DETGs) between primary NSCLC and metastatic NSCLC were identified. Prognostic DEEs (PDEEs) were screened by Cox regression analyses and a predicting model for metastatic NSCLC was constructed. We identified DEE interactions with DETFs, DETGs, reverse phase protein arrays (RPPA) protein chips, immunocytes, and pathways to construct a regulation network using Pearson correlation. Finally, the mechanisms and clinical significance were explained using multi-dimensional validation unambiguously; (3) Results: A total of 255 DEEs were identified, and 24 PDEEs were selected into the multivariate Cox regression model (AUC = 0.699). Additionally, the NSCLC metastasis-specific regulation network was constructed, and six key PDEEs were defined (ANXA8L1, CASTOR2, CYP4B1, GTF2H2C, PSMF1 and TNS4); (4) Conclusions: This study focused on the exploration of the prognostic value of eRNAs in the metastasis of NSCLC. Finally, six eRNAs were identified as potential markers for the prediction of metastasis of NSCLC.

Targeting cellular senescence to combat cancer and aging

Senescence is a complex cellular process that is implicated in various physiological and pathological processes. It is characterized by a stable state of cell growth arrest and by a secretome of diverse pro‐inflammatory factors, chemokines and growth factors. In this review, we summarize the context‐dependent role of cellular senescence in ageing and in age‐related diseases, such as cancer. We discuss current approaches to targeting senescence to develop therapeutic strategies to combat cancer and to promote healthy ageing, and we outline our vision for future research directions for senescence‐based interventions in these fields.

Potential regulators of the senescence-associated secretory phenotype during senescence and ageing

Senescent cells express and secrete a variety of extracellular modulators that include cytokines, chemokines, proteases, growth factors and some enzymes associated with ECM remodeling, defined as the senescence-associated secretory phenotype (SASP). SASP reinforces senescent cell cycle arrest, stimulates and recruits immune cells for immune-mediated clearance of potentially tumorigenic cells, limits or induces fibrosis and promotes wound healing and tissue regeneration. On the other hand, SASP mediates chronic inflammation leading to destruction of tissue structure and function and stimulating the growth and survival of tumour cells. SASP is highly heterogeneous and the role of SASP depends on the context. The regulation of SASP occurs at multiple levels including chromatin remodelling, transcription, mRNA translation, intracellular trafficking and secretion. Several SASP modulators have already been identified setting the stage for future research on their clinical applications. In this review, we summarize in detail the potential signalling pathways that trigger and regulate SASP production during ageing and senescence.

Exploring the role of senescence inducers and senotherapeutics as targets for anticancer natural products

During the last few decades, cancer has remained one of the deadliest diseases that endanger human health, emphasizing urgent drug discovery. Cellular senescence has gained a great deal of attention in recent years because of its link to the development of cancer therapy. Senescent cells are incapable of proliferating due to irreversibly inhibited the initiation of the cell cycle pathways. However, senescent cells aggregate in tissues and produce a pro-inflammatory secretome called senescence-associated secretory phenotype (SASP) that can cause serious harmful effects if not managed properly. There is mounting evidence that senescent cells lead to various phases of tumorigenesis in various anatomical sites, owing mostly to the paracrine activities of the SASP. Therefore, a new treatment field called senotherapeutics has been established. Senotherapeutics are newly developed anticancer agents that have been demonstrated to inhibit cancer effectively. In light of recent findings, several promising natural products have been identified as senescence inducers and senotherapeutics, including, miliusanes, epigallocatechin gallate, phloretin, silybin, resveratrol, genistein, sulforaphane, quercetin, allicin, fisetin, piperlongumine, berberine, triptolide, tocotrienols and curcumin analogs. Several of them have already been validated through preclinical trials and exert an enormous potential for clinical trials. This review article focuses on and summarises the latest advances on cellular senescence and its potential as a target for cancer treatment and highlights the well-known natural products as senotherapeutics for cancer treatment.

Exploring Methods of Targeting Histone Methyltransferases and Their Applications in Cancer Therapeutics

Histone methyltransferases (HMTs) are enzymes that catalyze the methylation of lysine or arginine residues of histone proteins, a key post-translational modification (PTM). Aberrant expression or activity of these enzymes can lead to abnormal histone methylation of cancer-related genes and thus promote tumorigenesis. Histone methyltransferases have been implicated in chemotherapeutic resistance and immune stimulation, making these enzymes potential therapeutic targets of interest, and chemically targeting these proteins provides an avenue for novel drug development in cancer therapy. This Review aims to discuss the evolution of chemical approaches that have emerged in the past five years to design probes targeting these enzymes, including inhibition through noncovalent inhibitors, covalent inhibitors, and targeted protein degradation through proteolysis targeting chimeras (PROTACs). This Review also highlights how these compounds have been used to study the myriad of HMT functions in cancer progression and treatment response. The recent advancement of some of these drugs into human clinical investigation and even to regulatory approval highlights HMTs as a promising class of targets for chemical intervention and novel therapy development.

Epigenetic Regulation of Cellular Senescence

Senescence is a complex cellular stress response that abolishes proliferative capacity and generates a unique secretory pattern that is implicated in organismal aging and age-related disease. How a cell transitions to a senescent state is multifactorial and often requires transcriptional regulation of multiple genes. Epigenetic alterations to DNA and chromatin are powerful regulators of genome architecture and gene expression, and they play a crucial role in mediating the induction and maintenance of senescence. This review will highlight the changes in chromatin, DNA methylation, and histone alterations that establish and maintain cellular senescence, alongside the specific epigenetic regulation of the senescence-associated secretory phenotype (SASP).

Induction of senescence-associated secretory phenotype underlies the therapeutic efficacy of PRC2 inhibition in cancer

The methyltransferase Polycomb Repressive Complex 2 (PRC2), composed of EZH2, SUZ12, and EED subunits, is associated with transcriptional repression via tri-methylation of histone H3 on lysine 27 residue (H3K27me3). PRC2 is a valid drug target, as the EZH2 gain-of-function mutations identified in patient samples drive tumorigenesis. PRC2 inhibitors have been discovered and demonstrated anti-cancer efficacy in clinic. However, their pharmacological mechanisms are poorly understood. MAK683 is a potent EED inhibitor in clinical development. Focusing on MAK683-sensitive tumors with SMARCB1 or ARID1A loss, we identified a group of PRC2 target genes with high H3K27me3 signal through epigenomic and transcriptomic analysis. Multiple senescence-associated secretory phenotype (SASP) genes, such as GATA4, MMP2/10, ITGA2 and GBP1, are in this group besides previously identified CDKN2A/p16. Upon PRC2 inhibition, the de-repression of SASP genes is detected in multiple sensitive models and contributes to decreased Ki67+, extracellular matrix (ECM) reorganization, senescence associated inflammation and tumor regression even in CDKN2A/p16 knockout tumor. And the combination of PRC2 inhibitor and CDK4/6 inhibitor leads to better effect. The genes potential regulated by PRC2 in neuroblastoma samples exhibited significant enrichment of ECM and senescence associated inflammation, supporting the clinical relevance of our results. Altogether, our results unravel the pharmacological mechanism of PRC2 inhibitors and propose a combination strategy for MAK683 and other PRC2 drugs.

Chromatin basis of the senescence-associated secretory phenotype

Cellular senescence is a stable cell growth arrest. Senescent cells are metabolically active, as exemplified by the secretion of inflammatory cytokines, chemokines, and growth factors, which is termed senescence-associated secretory phenotype (SASP). The SASP exerts a range of functions in both normal health and pathology, which is possibly best characterized in cancers and physical aging. Recent studies demonstrated that chromatin is instrumental in regulating the SASP both through nuclear transcription and via the innate immune cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway in the cytoplasm. Here, we will review these regulatory mechanisms, with an emphasis on most recent developments in the field. We will highlight the challenges and opportunities in developing intervention approaches, such as targeting chromatin regulatory mechanisms, to alter the SASP as an emerging approach to combat cancers and achieve healthy aging.

MLL4 mediates differentiation and tumor suppression through ferroptosis

The epigenetic regulator, MLL4 (KMT2D), has been described as an essential gene in both humans and mice. In addition, it is one of the most commonly mutated genes in all of cancer biology. Here, we identify a critical role for Mll4 in the promotion of epidermal differentiation and ferroptosis, a key mechanism of tumor suppression. Mice lacking epidermal Mll4, but not the related enzyme Mll3 (Kmt2c), display features of impaired differentiation and human precancerous neoplasms, all of which progress with age. Mll4 deficiency profoundly alters epidermal gene expression and uniquely rewires the expression of key genes and markers of ferroptosis (Alox12, Alox12b, and Aloxe3). Beyond revealing a new mechanistic basis for Mll4-mediated tumor suppression, our data uncover a potentially much broader and general role for ferroptosis in the process of differentiation and skin homeostasis.

Epigenetic dysregulation in cardiovascular aging and disease

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity for all sexes, racial and ethnic groups. Age, and its associated physiological and pathological consequences, exacerbate CVD incidence and progression, while modulation of biological age with interventions track with cardiovascular health. Despite the strong link between aging and CVD, surprisingly few studies have directly investigated heart failure and vascular dysfunction in aged models and subjects. Nevertheless, strong correlations have been found between heart disease, atherosclerosis, hypertension, fibrosis, and regeneration efficiency with senescent cell burden and its proinflammatory sequelae. In agreement, senotherapeutics have had success in reducing the detrimental effects in experimental models of cardiovascular aging and disease. Aside from senotherapeutics, cellular reprogramming strategies targeting epigenetic enzymes remain an unexplored yet viable option for reversing or delaying CVD. Epigenetic alterations comprising local and global changes in DNA and histone modifications, transcription factor binding, disorganization of the nuclear lamina, and misfolding of the genome are hallmarks of aging. Limited studies in the aging cardiovascular system of murine models or human patient samples have identified strong correlations between the epigenome, age, and senescence. Here, we compile the findings in published studies linking epigenetic changes to CVD and identify clear themes of epigenetic deregulation during aging. Pending direct investigation of these general mechanisms in aged tissues, this review predicts that future work will establish epigenetic rejuvenation as a potent method to delay CVD.

The Contribution of Physiological and Accelerated Aging to Cancer Progression Through Senescence-Induced Inflammation

Senescent cells are found to accumulate in aged individuals, as well as in cancer patients that receive chemotherapeutic treatment. Although originally believed to halt cancer progression due to their characteristic growth arrest, senescent cells remain metabolically active and secrete a combination of inflammatory agents, growth factors and proteases, collectively known as the senescence-associated secretory phenotype (SASP). In this review, we discuss the contribution of senescent cells to cancer progression through their ability to alter cancer cells’ properties and to generate a microenvironment that promotes tumor growth. Furthermore, recent evidence suggests that senescent cells are able resume proliferation and drive cancer relapse, pointing to the use of senolytics and SASP modulators as a potential approach to prevent tumor resurgence following treatment cessation. Thus, a better understanding of the hallmarks of senescence and the impact of the SASP will allow the development of improved targeted therapeutic strategies to leverage vulnerabilities associated with this cellular state.

Roles of extracellular vesicles in the aging microenvironment and age-related diseases

Cellular senescence is a persistently hypoproliferative state with diverse stressors in a specific aging microenvironment. Senescent cells have a double-edged sword effect: they can be physiologically beneficial for tissue repair, organ growth, and body homeostasis, and they can be pathologically harmful in age-related diseases. Among the hallmarks of senescence, the SASP, especially SASP-related extracellular vesicle (EV) signalling, plays the leading role in aging transmission via paracrine and endocrine mechanisms. EVs are successful in intercellular and interorgan communication in the aging microenvironment and age-related diseases. They have detrimental effects on downstream targets at the levels of immunity, inflammation, gene expression, and metabolism. Furthermore, EVs obtained from different donors are also promising materials and tools for antiaging treatments and are used for regeneration and rejuvenation in cell-free systems. Here, we describe the characteristics of cellular senescence and the aging microenvironment, concentrating on the production and function of EVs in age-related diseases, and provide new ideas for antiaging therapy with EVs.

Long-term treatment with senolytic drugs Dasatinib and Quercetin ameliorates age-dependent intervertebral disc degeneration in mice

Intervertebral disc degeneration is highly prevalent within the elderly population and is a leading cause of chronic back pain and disability. Due to the link between disc degeneration and senescence, we explored the ability of the Dasatinib and Quercetin drug combination (D + Q) to prevent an age-dependent progression of disc degeneration in mice. We treated C57BL/6 mice beginning at 6, 14, and 18 months of age, and analyzed them at 23 months of age. Interestingly, 6- and 14-month D + Q cohorts show lower incidences of degeneration, and the treatment results in a significant decrease in senescence markers p16^INK4a, p19^ARF, and SASP molecules IL-6 and MMP13. Treatment also preserves cell viability, phenotype, and matrix content. Although transcriptomic analysis shows disc compartment-specific effects of the treatment, cell death and cytokine response pathways are commonly modulated across tissue types. Results suggest that senolytics may provide an attractive strategy to mitigating age-dependent disc degeneration.

Dissecting primary and secondary senescence to enable new senotherapeutic strategies

Cellular senescence is a state of stable cell cycle arrest that is known to be elicited in response to different stresses or forms of damage. Senescence limits the replication of old, damaged, and precancerous cells in the short-term but is implicated in diseases and debilities of aging due to loss of regenerative reserve and secretion of a complex combination of factors called the senescence-associated secretory phenotype (SASP). More recently, investigators have discovered that senescent cells induced by these methods (what we term "primary senescent cells") are also capable of inducing other non-senescent cells to undergo senescence - a phenomenon we call "secondary senescence." Secondary senescence has been demonstrated to occur via two broad types of mechanisms. First, factors in the SASP have been shown to be involved in spreading senescence; we call this phenomenon "paracrine senescence." Second, primary senescent cells can induce senescence via an additional group of mechanisms involving cell-to-cell contacts of different types; we term this phenomenon "juxtacrine senescence." "Secondary senescence" in our definition is thus the overarching term for both paracrine and juxtacrine senescence together. By allowing cells that are inherently small in number and incapable of replication to increase in number and possibly spread to anatomically distant locations, secondary senescence allows an initially small number of senescent cells to contribute further to age-related pathologies. We propose that understanding how primary and secondary senescent cells differ from each other and the mechanisms of their spread will enable the development of new rejuvenation therapies to target different senescent cell populations and interrupt their spread, extending human health- and potentially lifespan.

DOT1L modulates the senescence-associated secretory phenotype through epigenetic regulation of IL1A

Oncogene-induced senescence (OIS) is a stable cell cycle arrest that occurs in normal cells upon oncogene activation. Cells undergoing OIS express a wide variety of secreted factors that affect the senescent microenvironment termed the senescence-associated secretory phenotype (SASP), which is beneficial or detrimental in a context-dependent manner. OIS cells are also characterized by marked epigenetic changes. We globally assessed histone modifications of OIS cells and discovered an increase in the active histone marks H3K79me2/3. The H3K79 methyltransferase disruptor of telomeric silencing 1-like (DOT1L) was necessary and sufficient for increased H3K79me2/3 occupancy at the IL1A gene locus, but not other SASP genes, and was downstream of STING. Modulating DOT1L expression did not affect the cell cycle arrest. Together, our studies establish DOT1L as an epigenetic regulator of the SASP, whose expression is uncoupled from the senescence-associated cell cycle arrest, providing a potential strategy to inhibit the negative side effects of senescence while maintaining the beneficial inhibition of proliferation.

Inhibiting an RBM39/MLL1 epigenomic regulatory complex with dominant-negative peptides disrupts cancer cell transcription and proliferation

RBM39 is a known splicing factor and coactivator. Here, we report that RBM39 functions as a master transcriptional regulator that interacts with the MLL1 complex to facilitate chromatin binding and H3K4 trimethylation in breast cancer cells. We identify RBM39 functional domains required for DNA and complex binding and show that the loss of RBM39 has widespread effects on H3K4me3 and gene expression, including key oncogenic pathways. RBM39's RNA recognition motif 3 (RRM3) functions as a dominant-negative domain; namely, it disrupts the complex and H3K4me trimethylation and expression of RBM/MLL1 target genes. RRM3-derived cell-penetrating peptides phenocopy the effects of the loss of RBM39 to decrease growth and survival of all major subtypes of breast cancer and yet are nontoxic to normal cells. These findings establish RBM39/MLL1 as a major contributor to the abnormal epigenetic landscape in breast cancer and lay the foundation for peptide-mediated cancer-specific therapy based on disruption of RBM39 epigenomic functions.

Loss of p16: A Bouncer of the Immunological Surveillance?

p16INK4A (hereafter called p16) is an important tumor suppressor protein frequently suppressed in human cancer and highly upregulated in many types of senescence. Although its role as a cell cycle regulator is very well delineated, little is known about its other non-cell cycle-related roles. Importantly, recent correlative studies suggest that p16 may be a regulator of tissue immunological surveillance through the transcriptional regulation of different chemokines, interleukins and other factors secreted as part of the senescence-associated secretory phenotype (SASP). Here, we summarize the current evidence supporting the hypothesis that p16 is a regulator of tumor immunity.

Mechanisms of Cellular Senescence: Cell Cycle Arrest and Senescence Associated Secretory Phenotype

Cellular senescence is a stable cell cycle arrest that can be triggered in normal cells in response to various intrinsic and extrinsic stimuli, as well as developmental signals. Senescence is considered to be a highly dynamic, multi-step process, during which the properties of senescent cells continuously evolve and diversify in a context dependent manner. It is associated with multiple cellular and molecular changes and distinct phenotypic alterations, including a stable proliferation arrest unresponsive to mitogenic stimuli. Senescent cells remain viable, have alterations in metabolic activity and undergo dramatic changes in gene expression and develop a complex senescence-associated secretory phenotype. Cellular senescence can compromise tissue repair and regeneration, thereby contributing toward aging. Removal of senescent cells can attenuate age-related tissue dysfunction and extend health span. Senescence can also act as a potent anti-tumor mechanism, by preventing proliferation of potentially cancerous cells. It is a cellular program which acts as a double-edged sword, with both beneficial and detrimental effects on the health of the organism, and considered to be an example of evolutionary antagonistic pleiotropy. Activation of the p53/p21^WAF1/CIP1 and p16^INK4A/pRB tumor suppressor pathways play a central role in regulating senescence. Several other pathways have recently been implicated in mediating senescence and the senescent phenotype. Herein we review the molecular mechanisms that underlie cellular senescence and the senescence associated growth arrest with a particular focus on why cells stop dividing, the stability of the growth arrest, the hypersecretory phenotype and how the different pathways are all integrated.

Senescent cells as promising targets to tackle age-related diseases

As the world's population progressively ages, the burden on the socio-economic and health systems is escalating, demanding sustainable and lasting solutions. Cellular senescence, one of the hallmarks of ageing, is a state of irreversible cell cycle arrest that occurs in response to various genotoxic stressors and is considered an important factor in the development of many age-related diseases and therefore a potential therapeutic target. Here, the role of senescent cells in age-related diseases is discussed, focusing on their formation and main characteristics. The mechanisms leading to senescent cells are presented, including replicative and premature senescence as well as senescence that occurs in various physiological processes, such as wound healing. The second part comprises a comprehensive description of various biomarkers currently used for the detection of senescent cells along with the investigated therapeutic approaches, namely senolytics, senomorphics and the clearance of senescent cells by the immune system. Potential delivery systems suitable for such therapies and model organisms to study senescence are also briefly examined. This in-depth overview of cellular senescence contributes to a deeper understanding of a rapidly evolving area aimed to tackle the age-related diseases in a more mechanistic way, as well as highlights future research opportunities.

Suppression of p16 alleviates the senescence-associated secretory phenotype

Oncogene-induced senescence (OIS) is characterized by increased expression of the cell cycle inhibitor p16, leading to a hallmark cell cycle arrest. Suppression of p16 in this context drives proliferation, senescence bypass, and contributes to tumorigenesis. OIS cells are also characterized by the expression and secretion of a widely variable group of factors collectively termed the senescence-associated secretory phenotype (SASP). The SASP can be both beneficial and detrimental and affects the microenvironment in a highly context-dependent manner. The relationship between p16 suppression and the SASP remains unclear. Here, we show that knockdown of p16 decreases expression of the SASP factors and pro-inflammatory cytokines IL6 and CXCL8 in multiple models, including OIS and DNA damage-induced senescence. Notably, this is uncoupled from the senescence-associated cell cycle arrest. Moreover, low p16 expression in both cancer cell lines and patient samples correspond to decreased SASP gene expression, suggesting this is a universal effect of loss of p16 expression. Together, our data suggest that p16 regulates SASP gene expression, which has implications for understanding how p16 modulates both the senescent and tumor microenvironment.

Cellular senescence in ageing: from mechanisms to therapeutic opportunities

Cellular senescence, first described in vitro in 1961, has become a focus for biotech companies that target it to ameliorate a variety of human conditions. Eminently characterized by a permanent proliferation arrest, cellular senescence occurs in response to endogenous and exogenous stresses, including telomere dysfunction, oncogene activation and persistent DNA damage. Cellular senescence can also be a controlled programme occurring in diverse biological processes, including embryonic development. Senescent cell extrinsic activities, broadly related to the activation of a senescence-associated secretory phenotype, amplify the impact of cell-intrinsic proliferative arrest and contribute to impaired tissue regeneration, chronic age-associated diseases and organismal ageing. This Review discusses the mechanisms and modulators of cellular senescence establishment and induction of a senescence-associated secretory phenotype, and provides an overview of cellular senescence as an emerging opportunity to intervene through senolytic and senomorphic therapies in ageing and ageing-associated diseases.

Senescence in Post-Mitotic Cells: A Driver of Aging?

Significance: Cell senescence was originally defined by an acute loss of replicative capacity and thus believed to be restricted to proliferation-competent cells. More recently, senescence has been recognized as a cellular stress and damage response encompassing multiple pathways or senescence domains, namely DNA damage response, cell cycle arrest, senescence-associated secretory phenotype, senescence-associated mitochondrial dysfunction, autophagy/mitophagy dysfunction, nutrient and stress signaling, and epigenetic reprogramming. Each of these domains is activated during senescence, and all appear to interact with each other. Cell senescence has been identified as an important driver of mammalian aging. Recent Advances: Activation of all these senescence domains has now also been observed in a wide range of post-mitotic cells, suggesting that senescence as a stress response can occur in nondividing cells temporally uncoupled from cell cycle arrest. Here, we review recent evidence for post-mitotic cell senescence and speculate about its possible relevance for mammalian aging. Critical Issues: Although a majority of senescence domains has been found to be activated in a range of post-mitotic cells during aging, independent confirmation of these results is still lacking for most of them. Future Directions: To define whether post-mitotic senescence plays a significant role as a driver of aging phenotypes in tissues such as brain, muscle, heart, and others. Antioxid. Redox Signal. 34, 308-323.

The Jekyll and Hyde of Cellular Senescence in Cancer

Cellular senescence is a state of stable cell cycle arrest that can be triggered in response to various insults and is characterized by distinct morphological hallmarks, gene expression profiles, and the senescence-associated secretory phenotype (SASP). Importantly, cellular senescence is a key component of normal physiology with tumor suppressive functions. In the last few decades, novel cancer treatment strategies exploiting pro-senescence therapies have attracted considerable interest. Recent insight, however, suggests that therapy-induced senescence (TIS) elicits cell-autonomous and non-cell-autonomous implications that potentially entail detrimental consequences, reflecting the Jekyll and Hyde nature of cancer cell senescence. In essence, the undesirable manifestations that generally culminate in inflammation, cancer stemness, senescence reversal, therapy resistance, and disease recurrence are dictated by the persistent accumulation of senescent cells and the SASP. Thus, mitigating these pro-tumorigenic effects by eliminating these cells or inhibiting their SASP production holds great promise for developing innovative therapeutic strategies. In this review, we describe the fundamental aspects and dynamics of cancer cell senescence and summarize the comprehensive research on the adverse outcomes of TIS. Furthermore, we underline the rationale and motivation of emerging senotherapeutic modalities surrounding the removal of senescent cells and the SASP to help maximize the overall efficacy of cancer therapies.

The senescence-associated secretory phenotype as a driver of tumor growth: does G3BP1 hold the key?

Cellular senescence is a double-edged sword that, depending on the context, acts as either a potent tumor protective mechanism or an age-related driver of diseases such as cancer. Our recent findings show that the rasGAP SH3-binding protein 1 (G3BP1) activates the senescent-associated secretory phenotype (SASP) that, in turn, mediates cancer growth/progression.

The Senescence-Associated Secretory Phenotype (SASP) in the Challenging Future of Cancer Therapy and Age-Related Diseases

Simple Summary

A fundamental feature of cellular senescence is the emergence of the Senescence-Associated Secretory Phenotype (SASP), which represents a considerable source of inflammatory and tissue-remodeling cues. The pathophysiological relevance of senescence and SASP has generated a fertile area of research aimed at manipulating the SASP to fight cancer and age-related conditions. This review enlightens the most important mechanisms that regulate the SASP and summarizes the current evidence on the feasibility of intervening on its composition, providing a reading frame of the general potentialities of SASP modulation.

Abstract

Cellular senescence represents a robust tumor-protecting mechanism that halts the proliferation of stressed or premalignant cells. However, this state of stable proliferative arrest is accompanied by the Senescence-Associated Secretory Phenotype (SASP), which entails the copious secretion of proinflammatory signals in the tissue microenvironment and contributes to age-related conditions, including, paradoxically, cancer. Novel therapeutic strategies aim at eliminating senescent cells with the use of senolytics or abolishing the SASP without killing the senescent cell with the use of the so-called “senomorphics”. In addition, recent works demonstrate the possibility of modifying the composition of the secretome by genetic or pharmacological intervention. The purpose is not to renounce the potent immunostimulatory nature of SASP, but rather learning to modulate it for combating cancer and other age-related diseases. This review describes the main molecular mechanisms regulating the SASP and reports the evidence of the feasibility of abrogating or modulating the SASP, discussing the possible implications of both strategies.

Senescence and the SASP: many therapeutic avenues

Cellular senescence is a stress response that elicits a permanent cell cycle arrest and triggers profound phenotypic changes such as the production of a bioactive secretome, referred to as the senescence-associated secretory phenotype (SASP). Acute senescence induction protects against cancer and limits fibrosis, but lingering senescent cells drive age-related disorders. Thus, targeting senescent cells to delay aging and limit dysfunction, known as "senotherapy," is gaining momentum. While drugs that selectively kill senescent cells, termed "senolytics" are a major focus, SASP-centered approaches are emerging as alternatives to target senescence-associated diseases. Here, we summarize the regulation and functions of the SASP and highlight the therapeutic potential of SASP modulation as complimentary or an alternative to current senolytic approaches.

LSD1 Inhibition Promotes Epithelial Differentiation through Derepression of Fate-Determining Transcription Factors

Self-renewing somatic tissues depend upon the proper balance of chromatin-modifying enzymes to coordinate progenitor cell maintenance and differentiation, disruption of which can promote carcinogenesis. As a result, drugs targeting the epigenome hold significant therapeutic potential. The histone demethylase, LSD1 (KDM1A), is overexpressed in numerous cancers, including epithelial cancers; however, its role in the skin is virtually unknown. Here we show that LSD1 directly represses master epithelial transcription factors that promote differentiation. LSD1 inhibitors block both LSD1 binding to chromatin and its catalytic activity, driving significant increases in H3K4 methylation and gene transcription of these fate-determining transcription factors. This leads to both premature epidermal differentiation and the repression of squamous cell carcinoma. Together these data highlight both LSD1’s role in maintaining the epidermal progenitor state and the potential of LSD1 inhibitors for the treatment of keratinocyte cancers, which collectively outnumber all other cancers combined.

Egolf et al. demonstrate that inhibition of the epigenetic regulator and histone demethylase, LSD1, promotes activation of the epidermal differentiation transcriptional program and, in turn, represses the invasion of cutaneous squamous cell carcinoma, one of the most common of all human cancers.