To senesce or not to senesce: how primary human fibroblasts decide their cell fate after DNA damage

Current advances in the selection of adjuvant radiotherapy regimens for keloid

Keloid is a common benign skin tumor in the outpatient department, and patients are often accompanied by itching and pain. Since the pathogenesis is unknown, the effect of single method treatment is unsatisfactory, and therefore the recurrence rate is high. Therefore, comprehensive treatment is mostly used in clinical treatment. Adjuvant radiotherapy is currently one of the most effective treatments for keloid. After long-term clinical practice, brachytherapy and electron beam radiotherapy has increasingly become the gold standard of treatment, because brachytherapy provides more focused radiation treatment to focal tissue to significantly reduce recurrence rate, and better preserve normal tissue. With the development of new radiotherapy techniques, more options for the treatment of keloid. Currently, adjuvant radiotherapy has been widely recognized, but there is no consensus on the optimal protocol for adjuvant radiotherapy for keloids. This review provides a review of published treatment options and new radiotherapy techniques for adjuvant radiotherapy of keloids and gives a comprehensive evaluation for clinical treatment.

Gonadal sex patterns p21-induced cellular senescence in mouse and human glioblastoma

Males exhibit higher incidence and worse prognosis for the majority of cancers, including glioblastoma (GBM). Disparate survival may be related to sex-biased responses to treatment, including radiation. Using a mouse model of GBM, we show that female cells are more sensitive to radiation, and that senescence represents a major component of the radiation therapeutic response in both sexes. Correlation analyses revealed that the CDK inhibitor p21 and irradiation induced senescence were differentially regulated between male and female cells. Indeed, female cellular senescence was more sensitive to changes in p21 levels, a finding that was observed in wildtype and transformed murine astrocytes, as well as patient-derived GBM cell lines. Using a novel Four Core Genotypes model of GBM, we further show that sex differences in p21-induced senescence are patterned during early development by gonadal sex. These data provide a rationale for the further study of sex differences in radiation response and how senescence might be enhanced for radiation sensitization. The determination that p21 and gonadal sex are required for sex differences in radiation response will serve as a foundation for these future mechanistic studies.

Sex differences in cancer mechanisms

We now know that cancer is many different diseases, with great variation even within a single histological subtype. With the current emphasis on developing personalized approaches to cancer treatment, it is astonishing that we have not yet systematically incorporated the biology of sex differences into our paradigms for laboratory and clinical cancer research. While some sex differences in cancer arise through the actions of circulating sex hormones, other sex differences are independent of estrogen, testosterone, or progesterone levels. Instead, these differences are the result of sexual differentiation, a process that involves genetic and epigenetic mechanisms, in addition to acute sex hormone actions. Sexual differentiation begins with fertilization and continues beyond menopause. It affects virtually every body system, resulting in marked sex differences in such areas as growth, lifespan, metabolism, and immunity, all of which can impact on cancer progression, treatment response, and survival. These organismal level differences have correlates at the cellular level, and thus, males and females can fundamentally differ in their protections and vulnerabilities to cancer, from cellular transformation through all stages of progression, spread, and response to treatment. Our goal in this review is to cover some of the robust sex differences that exist in core cancer pathways and to make the case for inclusion of sex as a biological variable in all laboratory and clinical cancer research. We finish with a discussion of lab- and clinic-based experimental design that should be used when testing whether sex matters and the appropriate statistical models to apply in data analysis for rigorous evaluations of potential sex effects. It is our goal to facilitate the evaluation of sex differences in cancer in order to improve outcomes for all patients.

To control or to be controlled? Dual roles of CDK2 in DNA damage and DNA damage response

CDK2 (cyclin-dependent kinase 2), a member of the CDK family, has been shown to play a role in many cellular activities including cell cycle progression, apoptosis and senescence. Recently, accumulating evidence indicates that CDK2 is involved in DNA damage and DNA repair response (DDR). When DNA is damaged by internal or external genotoxic stresses, CDK2 activity is required for proper DNA repair in vivo and in vitro, whereas inactivation of CDK2 by siRNA techniques or by inhibitors could result in DNA damage and stimulate DDR. Hence, CDK2 seems to play dual roles in DNA damage and DDR. On one aspect, it is activated and stimulates DDR to repair DNA damage when DNA damage occurs; on the other hand, its inactivation directly leads to DNA damage and evokes DDR. Here, we describe the roles of CDK2 in DNA damage and DDR, and discuss the potential application of CDK2 inhibitors as anti-cancer agents.

Caloric restriction delays early phases of carcinogenesis via effects on the tissue microenvironment

Caloric restriction (CR) is an effective and consistent means to delay aging and the incidence of chronic diseases related to old age, including cancer. However, the precise mechanisms responsible for the beneficial effect of CR on carcinogenic process are yet to be identified.

In the present studies the hypothesis was tested that the CR might delay carcinogenesis via modulatory effects exerted on the age-associated, neoplastic-prone tissue microenvironment. Using a well characterized, orthotopic cell transplantation (Tx) system in the rat, preneoplastic hepatocytes isolated from liver nodules were injected into either old syngeneic rats fed ad libitum (AL) or animals of the same age given a CR diet (70% of AL feeding). Analysis of donor-derived cell clusters performed at 10 weeks post-Tx revealed a significant shift towards smaller class sizes in the group receiving CR diet. Clusters comprising more than 50 cells, including large hepatic nodules, were thrice more frequent in AL vs. CR animals. Incidence of spontaneous endogenous nodules was also decreased by CR. Markers of cell senescence were equally expressed in the liver of AL and CR groups. However, higher levels of SIRT1 and FOXO1 proteins were detected in CR-exposed livers, while expression of HDAC1 and C/EBPβ were decreased. These results are interpreted to indicate that CR delays the emergence of age-associated neoplastic disease through effects exerted, at least in part, on the tissue microenvironment. Nutrient-sensing pathways might mediate such modulatory effect.

Deficiency in DNA damage response of enterocytes accelerates intestinal stem cell aging in Drosophila

Stem cell dysfunction is closely linked to tissue and organismal aging and age-related diseases, and heavily influenced by the niche cells' environment. The DNA damage response (DDR) is a key pathway for tissue degeneration and organismal aging; however, the precise protective role of DDR in stem cell/niche aging is unclear. The Drosophila midgut is an excellent model to study the biology of stem cell/niche aging because of its easy genetic manipulation and its short lifespan. Here, we showed that deficiency of DDR in Drosophila enterocytes (ECs) accelerates intestinal stem cell (ISC) aging. We generated flies with knockdown of Mre11, Rad50, Nbs1, ATM, ATR, Chk1, and Chk2, which decrease the DDR system in ECs. EC-specific DDR depletion induced EC death, accelerated the aging of ISCs, as evidenced by ISC hyperproliferation, DNA damage accumulation, and increased centrosome amplification, and affected the adult fly's survival. Our data indicated a distinct effect of DDR depletion in stem or niche cells on tissue-resident stem cell proliferation. Our findings provide evidence of the essential role of DDR in protecting EC against ISC aging, thus providing a better understanding of the molecular mechanisms of stem cell/niche aging.

Senoptosis: non-lethal DNA cleavage as a route to deep senescence

DNA-damage-induced apoptosis and cellular senescence are perceived as two distinct cell fates. We found that after ionizing radiation (IR)-induced DNA damage the majority (up to 70 %) of senescent human diploid fibroblasts (HDFs) were subjected to controlled cleavage of DNA, resulting in the establishment of a viable and stable sub-G1 population, i.e. deeply senescent cells. We show that in senescent HDFs this DNA cleavage is triggered by modest loss of the mitochondrial membrane potential, which is not sufficient to activate caspases, but strong enough to release mitochondrial endonuclease G (EndoG). We demonstrate that upon γ-irradiation in HDFs EndoG translocates into the nucleus playing an essential role in the non-lethal cleavage of damaged DNA. Notably, the established sub-G1 cell population does not contribute to the senescence-associated secretory phenotype (SASP), however, it exhibits increased senescence-associated β-galactosidase activity. We show that EndoG knockdown causes an increase in DNA damage, indicating a role of this enzyme in DNA repair. Thus, we conclude that IR-induced deep senescence of HDFs exhibits features of both senescence, such as cell cycle arrest and viability, and apoptosis like reduced DNA content and no SASP, and, resembles uncomplete or stalled apoptosis, a phenomenon we term senoptosis.

Basics of Radiation Biology When Treating Hyperproliferative Benign Diseases

For decades, low- and moderate-dose radiation therapy (RT) has been shown to exert a beneficial therapeutic effect in a multitude of non-malignant conditions including painful degenerative muscoloskeletal and hyperproliferative disorders. Dupuytren and Ledderhose diseases are benign fibroproliferative diseases of the hand/foot with fibrotic nodules and fascial cords, which determine debilitating contractures and deformities of fingers/toes, while keloids are exuberant scar formations following burn damage, surgery, and trauma. Although RT has become an established and effective option in the management of these diseases, experimental studies to illustrate cellular composites and factors involved remain to be elucidated. More recent findings, however, indicate the involvement of radiation-sensitive targets like mitotic fibroblasts/myofibroblasts as well as inflammatory cells. Radiation-related molecular mechanisms affecting these target cells include the production of free radicals to hamper proliferative activity and interference with growth factors and cytokines. Moreover, an impairment of activated immune cells involved in both myofibroblast proliferative and inflammatory processes may further contribute to the clinical effects. We here aim at briefly describing mechanisms contributing to a modulation of proliferative and inflammatory processes and to summarize current concepts of treating hyperproliferative diseases by low and moderate doses of ionizing radiation.

Multiple functions of p21 in cell cycle, apoptosis and transcriptional regulation after DNA damage

An appropriate control over cell cycle progression depends on many factors. Cyclin-dependent kinase (CDK) inhibitor p21 (also known as p21(WAF1/Cip1)) is one of these factors that promote cell cycle arrest in response to a variety of stimuli. The inhibitory effect of P21 on cell cycle progression correlates with its nuclear localization. P21 can be induced by both p53-dependent and p53-independent mechanisms. Some other important functions attributed to p21 include transcriptional regulation, modulation or inhibition of apoptosis. These functions are largely dependent on direct p21/protein interactions and also on p21 subcellular localizations. In addition, p21 can play a role in DNA repair by interacting with proliferating cell nuclear antigen (PCNA). In this review, we will focus on the multiple functions of p21 in cell cycle regulation, apoptosis and gene transcription after DNA damage and briefly discuss the pathways and factors that have critical roles in p21 expression and activity.