Cell cycle arrest and apoptosis are not dependent on p53 prior to p53-dependent embryonic stem cell differentiation

Chromosome number alterations cause apoptosis and cellular hypertrophy in induced pluripotent stem cell models of embryonic epiblast cells

Chromosomal aneuploidies are a major cause of developmental failure and pregnancy loss. To investigate the possible consequences of aneuploidy on early embryonic development in vitro, we focused on primed pluripotent stem cells that are relatable to the epiblast of post-implantation embryos in vivo. We used human induced pluripotent stem cells (iPSCs) as an epiblast model and altered chromosome numbers by treating with reversine, a small-molecule inhibitor of monopolar spindle 1 kinase (MSP1) that inactivates the spindle assembly checkpoint, which has been strongly implicated in chromosome mis-segregation and aneuploidy generation. Upon reversine treatment, we obtained cells with varied chromosomal content that retained pluripotency and potential to differentiate into cells of three germ lineages. However, these cells displayed lagging chromosomes, increased micronuclei content, high p53 expression and excessive apoptotic activity. Cell proliferation was not affected. Prolonged in vitro culture of these cells resulted in a selective pool of cells with supernumerary chromosomes, which exhibited cellular hypertrophy, enlarged nuclei, and overproduction of total RNAs and proteins. We conclude that increased DNA damage responses, apoptosis, and improper cellular mass and functions are possible mechanisms that contribute to abnormal epiblast development.

Exploring the Anticancer Effect of Artemisia herba-alba on Colorectal Cancer: Insights From Eight Colorectal Cancer Cell Lines

Colorectal cancer (CRC) is a prevalent and deadly disease, necessitating the exploration of novel therapeutic strategies. Traditional chemotherapy often encounters drug resistance and adverse side effects, highlighting the need for alternative approaches. Artemisia herba-alba, a plant rich in phytochemical constituents, was investigated for its potential as an anticancer agent against colorectal cancer (CRC). The primary objective of this study was to investigate the cytotoxic effects of the methanolic extract of A. herba-alba on eight CRC cell lines including: Caco-2, DLD1, RKO+/+p53, RKO-/-p53, HCT+/+p53, HCT-/-p53, SW620, and SW480. Specifically, the study investigated the extract's impact on cell viability, apoptosis, cell cycle progression, and effects on the PI3K/AKT/mTOR signaling pathway. Chemical derivatization and Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed a diverse array of bioactive compounds, including ephedrine, hydroxyflavone, quinolinic acid, 4-hydroxybenzoic acid, borneol, β-eudesmol, and camphor, known for their cytotoxic properties. The methanolic extract of A. herba-alba exhibited varying degrees of cytotoxicity across a panel of CRC cell lines, with IC50 values indicating differential sensitivity. The extract triggered apoptosis in many cell lines, irrespective of p53 status. Importantly, A. herba-alba extract caused G2-M phase cell cycle arrest in CRC cells, accompanied by a decrease in Cyclin B1 and CDK1 expression. Furthermore, the extract demonstrated an inhibitory effect on the PI3K/AKT/mTOR pathway, crucial in cancer progression. These findings highlight the promising anticancer potential of Artemisia herba-alba as a valuable resource for innovative CRC treatments. Further research is warranted to elucidate its specific anticancer characteristics and explore its potential incorporation into future cancer therapy approaches.

Ionizing radiation inhibits zebrafish embryo hatching through induction of tissue inhibitors of metalloproteinases (TIMPs) expression

Ionizing radiation (IR) has garnered growing attention because of its biological effects on aquatic organisms and humans. Here, we identify the most impacted organs and uncover the molecular mechanisms causing the changes in the context of vertebrate development using single-cell RNA sequencing. Alterations in cellular composition and biological functions were explored using transcriptomic profiling of zebrafish embryos exposed to 5 Gy. Single-cell RNA sequencing analyses unveiled notable shifts in the proportions of brain/central nervous system and hatching gland clusters. Although IR exposure led to increased expression of hatching enzymes, a significant but mild delay in hatching was observed following 5 Gy IR exposure. Gene Ontology analysis showed an increased expression of tissue inhibitors of metalloproteinases (TIMPs), known as matrix metalloproteinase inhibitors, which was confirmed via whole-mount in situ hybridization. Correlation analysis linked TIMPs to transcription factors cebpb and cebpd, which were significantly correlated post-IR exposure. Although no morphological changes were observed in some organs, including the brain, the study reveals substantial alterations in developing vertebrates. Notably, despite increased hatching enzymes, elevated TIMPs in the hatching gland suggest a regulatory mechanism impacting hatching activity. This research contributes to comprehending the ecological repercussions of IR exposure, emphasizing the importance of safety measures for aquatic ecosystems and overall environmental health.

The molecular chronology of mammary epithelial cell fate switching

The adult mammary gland is maintained by lineage-restricted progenitor cells through pregnancy, lactation, involution, and menopause. Injury resolution, transplantation-associated mammary gland reconstitution, and tumorigenesis are unique exceptions, wherein mammary basal cells gain the ability to reprogram to a luminal state. Here, we leverage newly developed cell-identity reporter mouse strains, and time-resolved single-cell epigenetic and transcriptomic analyses to decipher the molecular programs underlying basal-to-luminal fate switching in vivo. We demonstrate that basal cells rapidly reprogram toward plastic cycling intermediates that appear to hijack molecular programs we find in bipotent fetal mammary stem cells and puberty-associatiated cap cells. Loss of basal-cell specifiers early in dedifferentiation coincides with activation of Notch and BMP, among others. Pharmacologic blockade of each pathway disrupts basal-to-luminal transdifferentiation. Our studies provide a comprehensive map and resource for understanding the coordinated molecular changes enabling terminally differentiated epithelial cells to transition between cell lineages and highlights the stunning rapidity by which epigenetic reprogramming can occur in response to disruption of tissue structure.

Apoptotic signaling pathways in bone metastatic lung cancer: a comprehensive analysis

This review provides a comprehensive analysis of apoptotic signaling pathways in the context of bone metastatic lung cancer, emphasizing the intricate molecular mechanisms and microenvironmental influences. Beginning with an overview of apoptosis in cancer, the paper explores the specific molecular characteristics of bone metastatic lung cancer, highlighting alterations in apoptotic pathways. Focused discussions delve into key apoptotic signaling pathways, including the intrinsic and extrinsic pathways, and the roles of critical molecular players such as Bcl-2 family proteins and caspases. Microenvironmental factors, such as the tumor microenvironment, extracellular matrix interactions, and immune cell involvement, are examined in depth. The review also addresses experimental approaches and techniques employed in studying apoptotic signaling, paving the way for a discussion on current therapeutic strategies, their limitations, and future prospects. This synthesis contributes a holistic understanding of apoptosis in bone metastatic lung cancer, offering insights for potential therapeutic advancements.

PIKFYVE inhibitors trigger interleukin-24-dependent cell death of autophagy-dependent melanoma

Inhibitors specifically targeting the 1-phosphatidylinositol 3-phosphate 5-kinase (PIKFYVE) disrupt lysosome homeostasis, thereby selectively terminating autophagy-dependent human cancer cells in vivo as well as in vitro without harming the viability of nonmalignant cells. To elucidate the mechanism by which PIKFYVE inhibition induces cell death, autophagy-dependent melanoma cells were compared with normal foreskin fibroblasts. RNA sequence profiling suggested that PIKFYVE inhibitors upregulated an endoplasmic reticulum (ER) stress response involving interleukin-24 (IL24; also known as MDA7) selectively in melanoma cells. Subsequent biochemical and genetic analyses confirmed these results and extended them to tumor xenografts in which tumor formation and expansion were inhibited. IL24 expression was upregulated by the DDIT3/CHOP/CEBPz transcription factor, a component of the PERK-dependent ER-stress response. Ectopic expression of IL24-induced cell death in melanoma cells, but not in foreskin fibroblasts, whereas ablation of the IL24 gene in melanoma cells prevented death. IL24 upregulation was triggered specifically by PIKFYVE inhibition. Thus, unlike thapsigargin and tunicamycin, which induce ER-stress indiscriminately, PIKFYVE inhibitors selectively terminated PIKFYVE-sensitive melanoma by inducing IL24-dependent ER-stress. Moreover, induction of cell death by a PIKFYVE inhibitor together with ectopic expression of IL24 protein was cumulative, thereby confirming the therapeutic potential of PIKFYVE inhibitors in the treatment of melanoma.

P53 and BCL-2 family proteins PUMA and NOXA define competitive fitness in pluripotent cell competition

Cell Competition is a process by which neighboring cells compare their fitness. As a result, viable but suboptimal cells are selectively eliminated in the presence of fitter cells. In the early mammalian embryo, epiblast pluripotent cells undergo extensive Cell Competition, which prevents suboptimal cells from contributing to the newly forming organism. While competitive ability is regulated by MYC in the epiblast, the mechanisms that contribute to competitive fitness in this context are largely unknown. Here, we report that P53 and its pro-apoptotic targets PUMA and NOXA regulate apoptosis susceptibility and competitive fitness in pluripotent cells. PUMA is widely expressed specifically in pluripotent cells in vitro and in vivo. We found that P53 regulates MYC levels in pluripotent cells, which connects these two Cell Competition pathways, however, MYC and PUMA/NOXA levels are independently regulated by P53. We propose a model that integrates a bifurcated P53 pathway regulating both MYC and PUMA/NOXA levels and determines competitive fitness.

The Role of ATP-Binding Cassette Proteins in Stem Cell Pluripotency

Pluripotent stem cells (PSCs) are highly proliferative cells that can self-renew indefinitely in vitro. Upon receiving appropriate signals, PSCs undergo differentiation and can generate every cell type in the body. These unique properties of PSCs require specific gene expression patterns that define stem cell identity and dynamic regulation of intracellular metabolism to support cell growth and cell fate transitions. PSCs are prone to DNA damage due to elevated replicative and transcriptional stress. Therefore, mechanisms to prevent deleterious mutations in PSCs that compromise stem cell function or increase the risk of tumor formation from becoming amplified and propagated to progenitor cells are essential for embryonic development and for using PSCs including induced PSCs (iPSCs) as a cell source for regenerative medicine. In this review, we discuss the role of the ATP-binding cassette (ABC) superfamily in maintaining PSC homeostasis, and propose how their activities can influence cellular signaling and stem cell fate decisions. Finally, we highlight recent discoveries that not all ABC family members perform only canonical metabolite and peptide transport functions in PSCs; rather, they can participate in diverse cellular processes from genome surveillance to gene transcription and mRNA translation, which are likely to maintain the pristine state of PSCs.

Specialized Circuitry of Embryonic Stem Cells Promotes Genomic Integrity

Embryonic stem cells (ESCs) give rise to all cell types of the organism. Given the importance of these cells in this process, ESCs must employ robust mechanisms to protect genomic integrity or risk catastrophic propagation of mutations throughout the organism. Should such an event occur in daughter cells that will eventually contribute to the germline, the overall species health could dramatically decline. This review describes several key mechanisms employed by ESCs that are unique to these cells, in order to maintain their genomic integrity. Additionally, the contributions of cell cycle regulators in modulating ESC differentiation, after DNA damage exposure, are also examined. Where data are available, findings reported in ESCs are extended to include observations described in induced pluripotent stem cells (IPSCs).

An Updated View of the Roles of p53 in Embryonic Stem Cells

The TP53 gene is unarguably one of the most studied human genes. Its encoded protein, p53, is a tumor suppressor and is often called the "guardian of the genome" due to its pivotal role in maintaining genome stability. Historically, most studies of p53 have focused on its roles in somatic cells and tissues, but in the last two decades, its functions in embryonic stem cells (ESCs) and induced pluripotent stem cells have attracted increasing attention. Recent studies have identified p53 as a critical regulator of pluripotency, self-renewal, differentiation, proliferation, and genome stability in mouse and human embryonic stem cells. In this article, we systematically review the studies on the functions of p53 in ESCs, provide an updated overview, attempt to reconcile controversial results described in the literature, and discuss the relevance of these cellular functions of p53 to its roles in tumor suppression.

P53-Related Anticancer Activities of Drimia calcarata Bulb Extracts Against Lung Cancer

Current lung cancer treatment strategies are ineffective, and lung cancer cases continue to soar; thus, novel anticancer drugs and targets are needed, and medicinal plants are promising to offer better alternatives. This study was aimed at analysing two p53 splice variants during the potential anticancer activities of Drimia calcarata (Dc) methanol and water extracts against different human lung cancer cell lines of varying p53 mutation status, and these included mutant H1573 and mutant H1437 and p53-wild type (A549) cells. The anticancer activities of the Dc extracts were assessed by establishing the cytotoxic effect and the apoptosis-inducing capacity of these extracts, using the MTT assay and Annexin V analysis, respectively, with the latter confirmed using fluorescence microscopy. The molecular mechanisms induced by these extracts were further evaluated using cell cycle analysis and RT-PCR. Both extracts demonstrated safety against noncancerous lung MRC-5 fibroblasts and exhibited significant anticancer potency (p < 0.001) against the H1437 (IC₅₀ values: 62.50 μg/ml methanol extract and 125 μg/ml WE), H1573 (IC₅₀ value: 125 μg/ml for both extracts) and A549 (IC₅₀ value: 500 μg/ml ME). The water extract had no effect on the viability of A549 cells. Treated H1437 cells underwent p53-dependent apoptosis and S-phase cell cycle arrest while H1573 treated cells underwent p53-independed apoptosis and G0/G1 cell cycle arrest through upregulation of p21 mRNA expression levels. The expression levels of STAT1, STAT3, STAT5A and STAT5B genes increased significantly (p < 0.001) following the treatment of H1573 cells with ME and WE. Treatment of H1437 cells with ME upregulated the STAT1, STAT3, STAT5A and STAT5B mRNAs. Our results indicate that the proliferative inhibitory effect of D. calcarata extracts on A549 and H1573 cells is correlated with the suppression of Bcl-2, STAT3 and STAT5B while that is not the case in H1437 cells. Thus, our results suggest that the dysregulation of anti-apoptotic molecules Bcl-2, STAT3, STAT5A and STAT5B in H1437 may play a role in cancer cell survival, which may consequently contribute to the development of p53-mutated non-small human lung cancer. Our results indicate that D. calcarata is a promising source of anticancer agents for the treatment of p53-mutant human non-small lung cancer cells than the p53-wild type human non-small lung cancer cells.

Cell Death and the p53 Enigma During Mammalian Embryonic Development

Twelve forms of programmed cell death (PCD) have been described in mammalian cells, but which of them occurs during embryonic development and the role played by the p53 transcription factor and tumor suppressor remains enigmatic. Although p53 is not required for mouse embryonic development, some studies conclude that PCD in pluripotent embryonic stem cells from mice (mESCs) or humans (hESCs) is p53-dependent whereas others conclude that it is not. Given the importance of pluripotent stem cells as models of embryonic development and their applications in regenerative medicine, resolving this enigma is essential. This review reconciles contradictory results based on the facts that p53 cannot induce lethality in mice until gastrulation and that experimental conditions could account for differences in results with ESCs. Consequently, activation of the G2-checkpoint in mouse ESCs is p53-independent and generally, if not always, results in noncanonical apoptosis. Once initiated, PCD occurs at equivalent rates and to equivalent extents regardless of the presence or absence of p53. However, depending on experimental conditions, p53 can accelerate initiation of PCD in ESCs and late-stage blastocysts. In contrast, DNA damage following differentiation of ESCs in vitro or formation of embryonic fibroblasts in vivo induces p53-dependent cell cycle arrest and senescence.

Selective elimination of pluripotent stem cells by PIKfyve specific inhibitors

Inhibition of PIKfyve phosphoinositide kinase selectively kills autophagy-dependent cancer cells by disrupting lysosome homeostasis. Here, we show that PIKfyve inhibitors can also selectively eliminate pluripotent embryonal carcinoma cells (ECCs), embryonic stem cells, and induced pluripotent stem cells under conditions where differentiated cells remain viable. PIKfyve inhibitors prevented lysosome fission, induced autophagosome accumulation, and reduced cell proliferation in both pluripotent and differentiated cells, but they induced death only in pluripotent cells. The ability of PIKfyve inhibitors to distinguish between pluripotent and differentiated cells was confirmed with xenografts derived from ECCs. Pretreatment of ECCs with the PIKfyve specific inhibitor WX8 suppressed their ability to form teratocarcinomas in mice, and intraperitoneal injections of WX8 into mice harboring teratocarcinoma xenografts selectively eliminated pluripotent cells. Differentiated cells continued to proliferate, but at a reduced rate. These results provide a proof of principle that PIKfyve specific inhibitors can selectively eliminate pluripotent stem cells in vivo as well as in vitro.

Noncanonical roles of p53 in cancer stemness and their implications in sarcomas

Impairment of the prominent tumor suppressor p53, well known for its canonical role as the "guardian of the genome", is found in almost half of human cancers. More recently, p53 has been suggested to be a crucial regulator of stemness, orchestrating the differentiation of embryonal and adult stem cells, suppressing reprogramming into induced pluripotent stem cells, or inhibiting cancer stemness (i.e., cancer stem cells, CSCs), which underlies the development of therapy-resistant tumors. This review addresses these noncanonical roles of p53 and their implications in sarcoma initiation and progression. Indeed, dysregulation of p53 family proteins is a common event in sarcomas and is associated with poor survival. Additionally, emerging studies have demonstrated that loss of wild-type p53 activity hinders the terminal differentiation of mesenchymal stem cells and leads to the development of aggressive sarcomas. This review summarizes recent findings on the roles of aberrant p53 in sarcoma development and stemness and further describes therapeutic approaches to restore normal p53 activity as a promising anti-CSC strategy to treat refractory sarcomas.

Developmental Acquisition of p53 Functions

Remarkably, the p53 transcription factor, referred to as “the guardian of the genome”, is not essential for mammalian development. Moreover, efforts to identify p53-dependent developmental events have produced contradictory conclusions. Given the importance of pluripotent stem cells as models of mammalian development, and their applications in regenerative medicine and disease, resolving these conflicts is essential. Here we attempt to reconcile disparate data into justifiable conclusions predicated on reports that p53-dependent transcription is first detected in late mouse blastocysts, that p53 activity first becomes potentially lethal during gastrulation, and that apoptosis does not depend on p53. Furthermore, p53 does not regulate expression of genes required for pluripotency in embryonic stem cells (ESCs); it contributes to ESC genomic stability and differentiation. Depending on conditions, p53 accelerates initiation of apoptosis in ESCs in response to DNA damage, but cell cycle arrest as well as the rate and extent of apoptosis in ESCs are p53-independent. In embryonic fibroblasts, p53 induces cell cycle arrest to allow repair of DNA damage, and cell senescence to prevent proliferation of cells with extensive damage.

Telomere erosion in human pluripotent stem cells leads to ATR-mediated mitotic catastrophe

It is well established that short telomeres activate an ATM-driven DNA damage response that leads to senescence in terminally differentiated cells. However, technical limitations have hampered our understanding of how telomere shortening is signaled in human stem cells. Here, we show that telomere attrition induces ssDNA accumulation (G-strand) at telomeres in human pluripotent stem cells (hPSCs), but not in their differentiated progeny. This led to a unique role for ATR in the response of hPSCs to telomere shortening that culminated in an extended S/G2 cell cycle phase and a longer period of mitosis, which was associated with aneuploidy and mitotic catastrophe. Loss of p53 increased resistance to death, at the expense of increased mitotic abnormalities in hPSCs. Taken together, our data reveal an unexpected dominant role of ATR in hPSCs, combined with unique cell cycle abnormalities and, ultimately, consequences distinct from those observed in their isogenic differentiated counterparts.

Novel Interplay between p53 and HO-1 in Embryonic Stem Cells

Stem cells genome safeguarding requires strict oxidative stress control. Heme oxygenase-1 (HO-1) and p53 are relevant components of the cellular defense system. p53 controls cellular response to multiple types of harmful stimulus, including oxidative stress. Otherwise, besides having a protective role, HO-1 is also involved in embryo development and in embryonic stem (ES) cells differentiation. Although both proteins have been extensively studied, little is known about their relationship in stem cells. The aim of this work is to explore HO-1-p53 interplay in ES cells. We studied HO-1 expression in p53 knockout (KO) ES cells and we found that they have higher HO-1 protein levels but similar HO-1 mRNA levels than the wild type (WT) ES cell line. Furthermore, cycloheximide treatment increased HO-1 abundance in p53 KO cells suggesting that p53 modulates HO-1 protein stability. Notably, H₂O₂ treatment did not induce HO-1 expression in p53 KO ES cells. Finally, SOD2 protein levels are also increased while Sod2 transcripts are not in KO cells, further suggesting that the p53 null phenotype is associated with a reinforcement of the antioxidant machinery. Our results demonstrate the existence of a connection between p53 and HO-1 in ES cells, highlighting the relationship between these stress defense pathways.