Tumor surveillance via the ARF-p53 pathway

A modelling framework for cancer ecology and evolution

Cancer incidence increases rapidly with age, typically as a polynomial. The somatic mutation theory explains this increase through the waiting time for enough mutations to build up to generate cells with the full set of traits needed to grow without control. However, lines of evidence ranging from tumour reversion and dormancy to the prevalence of presumed cancer mutations in non-cancerous tissues argue that this is not the whole story, and that cancer is also an ecological process, and that mutations only lead to cancer when the systems of control within and across cells have broken down. Aging thus has two effects: the build-up of mutations and the breakdown of control. This paper presents a mathematical modelling framework to unify these theories with novel approaches to model the mutation and diversification of cell lineages and of the breakdown of the layers of control both within and between cells. These models correctly predict the polynomial increase of cancer with age, show how germline defects in control accelerate cancer initiation, and compute how the positive feedback between cell replication, ecology and layers of control leads to a doubly exponential growth of cell populations.

p53 deficiency mediates cisplatin resistance by upregulating RRM2 and crotonylation of RRM2K283 through the downregulation of SIRT7

p53 deficiency plays a crucial role in chemotherapy resistance through various biological events, including posttranslational modifications (PTMs). Recently, lysine crotonylation (Kcr) has been shown to play a vital role in cancer progression. However, the global p53-regulated crotonylome and the function of these altered Kcr proteins after p53 deficiency remain unclear. In this study, we used a SILAC-based quantitative crotonylome to identify 3,520 Kcr in 1924 crotonylated proteins in response to p53 knockout. We found that increased crotonylation of RRM2 at K283 (RRM2K283Cr) in the presence of p53 deficiency promoted HCT116 cell resistance to cisplatin. We discovered that SIRT7 could be the decrotonylase of RRM2 and was downregulated after p53 knockout, resulting in increased RRM2K283Cr. Mechanistically, p53 deficiency inhibited cell apoptosis by upregulating RRM2 protein expression and RRM2K283Cr-mediated cleaved-PARP1 and cleaved-caspase3 expression, and SIRT7 was downregulated to upregulate crotonylation of RRM2 upon p53 deficiency. In conclusion, our results indicated that p53 deficiency plays a malignant role in colon cancer resistance to cisplatin therapy by regulating RRM2 protein and RRM2K283Cr expression. Our findings provide a novel therapeutic target against p53-deficient cancer.

Isoform-Directed Control of c-Myc Functions: Understanding the Balance from Proliferation to Growth Arrest

The transcription factor c-Myc, a key regulator of cellular processes, has long been associated with roles in cell proliferation and apoptosis. This review analyses the multiple functions of c-Myc by examining the different c-Myc isoforms in detail. The impact of different c-Myc isoforms, in particular p64 and p67, on fundamental biological processes remains controversial. It is necessary to investigate the different isoforms in the context of proto-oncogenesis. The current knowledge base suggests that neoplastic lesions may possess the means for self-destruction via increased c-Myc activity. This review presents the most relevant information on the c-Myc locus and focuses on a number of isoforms, including p64 and p67. This compilation provides a basis for the development of therapeutic approaches that target the potent growth arresting and pro-apoptotic functions of c-Myc. This information can then be used to develop targeted interventions against specific isoforms with the aim of shifting the oncogenic effects of c-Myc from pro-proliferative to pro-apoptotic. The research summarised in this review can deepen our understanding of how c-Myc activity contributes to different cellular responses, which will be crucial in developing effective therapeutic strategies; for example, isoform-specific approaches may allow for precise modulation of c-Myc function.

Expanding Roles of the E2F-RB-p53 Pathway in Tumor Suppression

The transcription factor E2F links the RB pathway to the p53 pathway upon loss of function of pRB, thereby playing a pivotal role in the suppression of tumorigenesis. E2F fulfills a major role in cell proliferation by controlling a variety of growth-associated genes. The activity of E2F is controlled by the tumor suppressor pRB, which binds to E2F and actively suppresses target gene expression, thereby restraining cell proliferation. Signaling pathways originating from growth stimulative and growth suppressive signals converge on pRB (the RB pathway) to regulate E2F activity. In most cancers, the function of pRB is compromised by oncogenic mutations, and E2F activity is enhanced, thereby facilitating cell proliferation to promote tumorigenesis. Upon such events, E2F activates the Arf tumor suppressor gene, leading to activation of the tumor suppressor p53 to protect cells from tumorigenesis. ARF inactivates MDM2, which facilitates degradation of p53 through proteasome by ubiquitination (the p53 pathway). P53 suppresses tumorigenesis by inducing cellular senescence or apoptosis. Hence, in almost all cancers, the p53 pathway is also disabled. Here we will introduce the canonical functions of the RB-E2F-p53 pathway first and then the non-classical functions of each component, which may be relevant to cancer biology.

Transcription factor E4F1 as a regulator of cell life and disease progression

E4F transcription factor 1 (E4F1), a member of the GLI-Kruppel family of zinc finger proteins, is now widely recognized as a transcription factor. It plays a critical role in regulating various cell processes, including cell growth, proliferation, differentiation, apoptosis and necrosis, DNA damage response, and cell metabolism. These processes involve intricate molecular regulatory networks, making E4F1 an important mediator in cell biology. Moreover, E4F1 has also been implicated in the pathogenesis of a range of human diseases. In this review, we provide an overview of the major advances in E4F1 research, from its first report to the present, including studies on its protein domains, molecular mechanisms of transcriptional regulation and biological functions, and implications for human diseases. We also address unresolved questions and potential research directions in this field. This review provides insights into the essential roles of E4F1 in human health and disease and may pave the way for facilitating E4F1 from basic research to clinical applications.

Senescence program and its reprogramming in pancreatic premalignancy

Tumor is a representative of cell immortalization, while senescence irreversibly arrests cell proliferation. Although tumorigenesis and senescence seem contrary to each other, they have similar mechanisms in many aspects. Pancreatic ductal adenocarcinoma (PDA) is highly lethal disease, which occurs and progresses through a multi-step process. Senescence is prevalent in pancreatic premalignancy, as manifested by decreased cell proliferation and increased clearance of pre-malignant cells by immune system. However, the senescent microenvironment cooperates with multiple factors and significantly contributes to tumorigenesis. Evidently, PDA progression requires to evade the effects of cellular senescence. This review will focus on dual roles that senescence plays in PDA development and progression, the signaling effectors that critically regulate senescence in PDA, the identification and reactivation of molecular targets that control senescence program for the treatment of PDA.

Identification of p53-target genes in human papillomavirus-associated head and neck cancer by integrative bioinformatics analysis

Introduction

Head and neck cancer (HNC) is a highly prevalent and heterogeneous malignancy. Although extensive efforts have been made to advance its treatment, the prognosis remained poor with increased mortality. Human papillomaviruses (HPV) have been associated with high risk in HNC. TP53, a tumor suppressor, is the most frequently altered gene in HNC, therefore, investigating its target genes for the identification of novel biomarkers or therapeutic targets in HPV-related HNC progression is highly recommended.

Methods

Transcriptomic profiles from three independent gene expression omnibus (GEO) datasets, including 44 HPV+ and 70 HPV- HNC patients, were subjected to integrative statistical and Bioinformatics analyses. For the top-selected marker, further in-silico validation in TCGA and GTEx databases and experimental validation in 65 (51 HPV- and 14 HPV+) subjects with histologically confirmed head and neck squamous cell carcinoma (HNSCC) have been performed.

Results

A total of 498 differentially expressed genes (DEGs) were identified including 291 up-regulated genes and 207 down-regulated genes in HPV+ compared to HPV- HNSCC patients. Functional annotations and gene set enrichment analysis (GSEA) showed that the up-regulated genes were significantly involved in p53-related pathways. The integrative analysis between the Hub-genes identified in the complex protein-protein network and the top frequent genes resulting from GSEA showed an intriguing correlation with five biomarkers which are EZH2, MDM2, PCNA, STAT5A and TYMS. Importantly, the MDM2 gene showed the highest gene expression difference between HPV+ and HPV- HNSCC (Average log2FC = 1.89). Further in-silico validation in a large HNSCC cohort from TCGA and GTEx databases confirmed the over-expression of MDM2 in HPV+ compared to HPV- HNSCC patients (p = 2.39E-05). IHC scoring showed that MDM2 protein expression was significantly higher in HPV+ compared to HPV- HNSCC patients (p = 0.031).

Discussion

Our findings showed evidence that over-expression of MDM2, proto-oncogene, may affect the occurrence and proliferation of HPV-associated HNSCC by disturbing the p53-target genes and consequently the p53-related pathways.

c-MYC-Induced AP4 Attenuates DREAM-Mediated Repression by p53

BACKGROUND

The deregulated expression of the c-MYC oncogene activates p53, which is presumably mediated by ARF/INK4, as well as replication-stress-induced DNA damage. Here, we aimed to determine whether the c-MYC-inducible AP4 transcription factor plays a role in this context using a genetic approach.

METHODS

We used a CRISPR/Cas9 approach to generate AP4- and/or p53-deficient derivatives of MCF-7 breast cancer cells harboring an ectopic, inducible c-MYC allele. Cell proliferation, senescence, DNA damage, and comprehensive RNA expression profiles were determined after activation of c-MYC. In addition, we analyzed the expression data from primary breast cancer samples.

RESULTS

Loss of AP4 resulted in elevated levels of both spontaneous and c-MYC-induced DNA damage, senescence, and diminished cell proliferation. Deletion of p53 in AP4-deficient cells reverted senescence and proliferation defects without affecting DNA damage levels. RNA-Seq analyses showed that loss of AP4 enhanced repression of DREAM and E2F target genes after p53 activation by c-MYC. Depletion of p21 or the DREAM complex component LIN37 abrogated this effect. These p53-dependent effects were conserved on the level of clinical and gene expression associations found in primary breast cancer tumors.

CONCLUSIONS

Our results establish AP4 as a pivotal factor at the crossroads of c-MYC, E2F, and p53 target gene regulation.

A common pathway to cancer: Oncogenic mutations abolish p53 oscillations

The tumor suppressor p53 oscillates in response to DNA double-strand breaks, a behavior that has been suggested to be essential to its anti-cancer function. Nearly all human cancers have genetic alterations in the p53 pathway; a number of these alterations have been shown to be oncogenic by experiment. These alterations include somatic mutations and copy number variations as well as germline polymorphisms. Intriguingly, they exhibit a mixed pattern of interactions in tumors, such as co-occurrence, mutual exclusivity, and paradoxically, mutual antagonism. Using a differential equation model of p53-Mdm2 dynamics, we employ Hopf bifurcation analysis to show that these alterations have a common mode of action, to abolish the oscillatory competence of p53, thereby, we suggest, impairing its tumor suppressive function. In this analysis, diverse genetic alterations, widely associated with human cancers clinically, have a unified mechanistic explanation of their role in oncogenesis.

Ubiquitin-specific peptidase 10, a deubiquitinating enzyme: Assessing its role in tumor prognosis and immune response

Ubiquitin-specific peptidase 10 (USP10) is a member of the ubiquitin-specific protease family that removes the ubiquitin chain from ubiquitin-conjugated protein substrates. We performed a literature search to evaluate the structure and biological activity of USP10, summarize its role in tumorigenesis and tumor progression, and discuss how USP10 may act as a tumor suppressor or a tumor-promoting gene depending on its mechanism of action. Subsequently, we elaborated further on these results through bioinformatics analysis. We demonstrated that abnormal expression of USP10 is related to tumorigenesis in various types of cancer, including liver, lung, ovarian, breast, prostate, and gastric cancers and acute myeloid leukemia. Meanwhile, in certain cancers, increased USP10 expression is associated with tumor suppression. USP10 was downregulated in kidney renal clear cell carcinoma (KIRC) and associated with reduced overall survival in patients with KIRC. In contrast, USP10 upregulation was associated with poor prognosis in head and neck squamous cell carcinoma (HNSC). In addition, we elucidated the novel role of USP10 in the regulation of tumor immunity in KIRC and HNSC through bioinformatics analysis. We identified several signaling pathways to be significantly associated with USP10 expression, such as ferroptosis, PI3K/AKT/mTOR, TGF-β, and G2/M checkpoint. In summary, this review outlines the role of USP10 in various forms of cancer, discusses the relevance of USP10 inhibitors in anti-tumor therapies, and highlights the potential function of USP10 in regulating the immune responses of tumors.

Impact of intravesical instillation of a novel biological response modifier (P-MAPA) on progress of non-muscle invasive bladder cancer treatment in a rat model

This work describes the effects of immunotherapy with Protein Aggregate Magnesium-Ammonium Phospholinoleate-Palmitoleate Anhydride in the treatment of non-muscle invasive bladder cancer in an animal model. NMIBC was induced by treating female Fischer 344 rats with N-methyl-N-nitrosourea. After treatment with MNU, the rats were distributed into four experimental groups: Control (without MNU) group, MNU (cancer) group, MNU-BCG (Bacillus Calmette-Guerin) group, and MNU-P-MAPA group. P-MAPA intravesical treatment was more effective in histopathological recovery from cancer state in relation to BCG treatment. Western blot assays showed an increase in the protein levels of c-Myc, COUP-TFII, and wild-type p53 in P-MAPA-treated rats in relation to BCG-treated rats. In addition, rats treated with P-MAPA intravesical immunotherapy showed the highest BAX protein levels and the lowest proliferation/apoptotic ratio in relation to BCG-treated rats, pointing out a preponderance of apoptosis. P-MAPA intravesical treatment increased the wild-type p53 levels and enhanced c-Myc/COUP-TFII-induced apoptosis mediated by p53. These alterations were fundamental for histopathological recovery from cancer and for suppress abnormal cell proliferation. This action of P-MAPA on apoptotic pathways may represent a new strategy for treating NMIBC.

CRL2-KLHDC3 E3 ubiquitin ligase complex suppresses ferroptosis through promoting p14ARF degradation

The cystine/glutamate antiporter SLC7A11 (commonly known as xCT) functions to import cystine for glutathione biosynthesis, thereby protecting cells from oxidative stress and ferroptosis, a regulated form of non-apoptotic cell death driven by the accumulation of lipid-based reactive oxygen species (ROS). p14^ARF, a well-established tumor suppressor, promotes ferroptosis by inhibiting NRF2-mediated SLC7A11 transcription. Here, we demonstrate the crucial role of Cullin 2 RING E3 ligase (CRL2)-KLHDC3 E3 ubiquitin ligase complex in regulating p14^ARF protein stability. KLHDC3 acts as a CRL2 adaptor that specifically recognizes a C-terminal degron in p14^ARF and triggers p14^ARF for ubiquitin-proteasomal degradation. This regulation mode is absent in the murine p14^ARF homolog, p19^arf which lacks the C-terminal degron. We also show that KLHDC3 suppresses ferroptosis in vitro and supports tumor growth in vivo by relieving p14^ARF-mediated suppression of SLC7A11 transcription. Overall, these findings reveal that the protein stability and pro-ferroptotic function of p14^ARF are controlled by a CRL2 E3 ubiquitin ligase complex, and suggest that suppression of the p14^ARF-NRF2-SLC7A11 regulatory pathway by KLHDC3 overexpression likely contributes to cancer progression.

Immune infiltration and a ferroptosis-associated gene signature for predicting the prognosis of patients with endometrial cancer

Ferroptosis, a form of programmed cell death induced by excess iron-dependent lipid peroxidation product accumulation, plays a critical role in cancer. However, there are few reports about ferroptosis in endometrial cancer (EC). This article explores the relationship between ferroptosis-related gene (FRG) expression and prognosis in EC patients. One hundred thirty-five FRGs were obtained by mining the literature, retrieving GeneCards and analyzing 552 malignant uterine corpus endometrial carcinoma (UCEC) samples, which were randomly assigned to training and testing groups (1:1 ratio), and 23 normal samples from The Cancer Genome Atlas (TCGA). We established a signature using eight screened FRGs (MDM2, GPX4, PRKAA2, PRNP, SLC11A2, ATP5MC3, PHKG2 and ACO1) related to overall survival using LASSO regression analysis. The samples were divided into low- and high-risk subgroups according to the median risk score. Kaplan-Meier survival curves showed that the low-risk group had better OS. ROC curves showed that this signature performed well in predicting OS (1-, 2-, 3-, and 5-year AUCs of 0.676, 0.775, 0.797, and 0.826, respectively). We systematically analyzed the immune infiltrating profile in UCEC samples from TCGA. Overall, our study identified a novel prognostic signature of 8 FRGs that can potentially predict the prognosis of EC.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Differential Expression of a Panel of Ten CNTN1-Associated Genes during Prostate Cancer Progression and the Predictive Properties of the Panel Towards Prostate Cancer Relapse

Contactin 1 (CNTN1) is a new oncogenic protein of prostate cancer (PC); its impact on PC remains incompletely understood. We observed CNTN1 upregulation in LNCaP cell-derived castration-resistant PCs (CRPC) and CNTN1-mediated enhancement of LNCaP cell proliferation. CNTN1 overexpression in LNCaP cells resulted in enrichment of the CREIGHTON_ENDOCRINE_THERAPY_RESISTANCE_3 gene set that facilitates endocrine resistance in breast cancer. The leading-edge (LE) genes (n = 10) of this enrichment consist of four genes with limited knowledge on PC and six genes novel to PC. These LE genes display differential expression during PC initiation, metastatic progression, and CRPC development, and they predict PC relapse following curative therapies at hazard ratio (HR) 2.72, 95% confidence interval (CI) 1.96–3.77, and p = 1.77 × 10⁻⁹ in The Cancer Genome Atlas (TCGA) PanCancer cohort (n = 492) and HR 2.72, 95% CI 1.84–4.01, and p = 4.99 × 10⁻⁷ in Memorial Sloan Kettering Cancer Center (MSKCC) cohort (n = 140). The LE gene panel classifies high-, moderate-, and low-risk of PC relapse in both cohorts. Additionally, the gene panel robustly predicts poor overall survival in clear cell renal cell carcinoma (ccRCC, p = 1.13 × 10⁻¹¹), consistent with ccRCC and PC both being urogenital cancers. Collectively, we report multiple CNTN1-related genes relevant to PC and their biomarker values in predicting PC relapse.

The Ins and Outs of HOPS/TMUB1 in biology and pathology

Liver regeneration represents an outstanding tool to study not only proliferation, but also other important processes such as inflammation, regenerative response or stem cell biology. Several novel genes have been identified as being involved in the proliferation of residual hepatocytes. One of them, HOPS/TMUB1, is proving to be a significant player in the control of proliferation, both contributing to genomic stability and as a partner of essential molecules. HOPS is an ubiquitin-like protein, shuttling from nucleus to cytoplasm, and it is engaged in a number of biological and physiopathological functions. HOPS overexpression in tumour cell lines strongly reduces proliferation, arresting cell cycle in G₀ /G₁ . HOPS is involved in centrosome assembly and maintenance, and its knockdown causes genomic instability. Moreover, a direct interaction of HOPS with nucleophosmin (NPM) and p19^Arf has been established, resulting in proper control of p19^Arf stability and localization. These data indicate that HOPS acts as a functional bridge in the interaction between NPM and p19^Arf , providing new mechanistic insight into how NPM and p19^Arf will oppose cell proliferation. HOPS exerts a control in p53 stability, directing p53 mitochondrial apoptosis and cytoplasmic localization. HOPS plays a direct role as novel post-translational modifier of p53, much like SUMO or NEDD. HOPS is overexpressed in a high number of human tumours in patients affected by large intestinal, CNS, liver and oesophageal tumours. This review highlights HOPS involvement in distinct cellular functions, establishing its role as a key player in cell biology and pathology in a broader context.

Characterization of porcine p53 and its regulation by porcine Mdm2

Pigs have been increasingly recognized as a relevant model for studying many human diseases. However, functions and regulations of numerous critical molecules involved in human diseases are not well characterized in pigs, including the prominent tumor suppressor p53, a transcription factor involved in various anti-proliferative processes. In this study, we systematically characterized porcine p53 (p-p53) in its transcriptional activity and regulation by the E3 ligase Mdm2, in comparison with that of human p53 (h-p53). p-p53 is highly homologous to h-p53 with the N-terminal region showing relative divergence. p-p53 exhibits a comparable transcriptional activity to that of h-p53 towards a diverse range of known target genes, and is subject to ubiquitination and degradation by both human and porcine Mdm2 (h-/p-Mdm2). Utilization of the h-Mdm2 targeting compound Nutlin-3 and protein RPL11 inhibits the negative effect of p-Mdm2 on p-p53. These results suggest that the transcription activity and regulation of p-p53 is very similar to that of h-p53, and that the developed agents targeting the h-p53 pathway could be used in the study of p53 related processes and diseases in pigs.

Loss of Both USP10 and p14ARF Protein Expression Is an Independent Prognostic Biomarker for Poor Prognosis in Patients With Epithelial Ovarian Cancer

BACKGROUND/AIM

The prognostic role of USP10 in epithelial ovarian cancer has been studied in various human cancers. Our aim was to evaluate the clinical and pathological significance of USP10 in epithelial ovarian cancer.

MATERIALS AND METHODS

Immunohistochemical analyses of the expression of USP10 and p14ARF by using tissue microarrays were performed in 336 ovarian tumours and the data were compared with clinicopathological variables. We examined their level of DNA methylation around the putative transcriptional start site in 5' CpG islands in fresh frozen tissues and ovarian cancer cells.

RESULTS

Expression of USP10 and p14ARF was significantly lower in cancer tissues than in normal epithelium. Low USP10 expression and a combined USP10/p14ARF low expression were revealed to be independent prognostic factors. A high degree of methylation in USP10 and p14ARF CpG islands was found by methylation specific PCR analysis in cancer than in normal tissues and cells.

CONCLUSION

Decreased expression of USP10 or combined USP10/p14ARF decreased expression is a strong indicator of poor prognosis in patients with ovarian cancer.

Contributions of DNA Damage to Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of neurodegenerative disease. Its typical pathology consists of extracellular amyloid-β (Aβ) plaques and intracellular tau neurofibrillary tangles. Mutations in the APP, PSEN1, and PSEN2 genes increase Aβ production and aggregation, and thus cause early onset or familial AD. Even with this strong genetic evidence, recent studies support AD to result from complex etiological alterations. Among them, aging is the strongest risk factor for the vast majority of AD cases: Sporadic late onset AD (LOAD). Accumulation of DNA damage is a well-established aging factor. In this regard, a large amount of evidence reveals DNA damage as a critical pathological cause of AD. Clinically, DNA damage is accumulated in brains of AD patients. Genetically, defects in DNA damage repair resulted from mutations in the BRAC1 and other DNA damage repair genes occur in AD brain and facilitate the pathogenesis. Abnormalities in DNA damage repair can be used as diagnostic biomarkers for AD. In this review, we discuss the association, the causative potential, and the biomarker values of DNA damage in AD pathogenesis.

UBR5 Is Coamplified with MYC in Breast Tumors and Encodes an Ubiquitin Ligase That Limits MYC-Dependent Apoptosis

For maximal oncogenic activity, cellular MYC protein levels need to be tightly controlled so that they do not induce apoptosis. Here, we show how ubiquitin ligase UBR5 functions as a molecular rheostat to prevent excess accumulation of MYC protein. UBR5 ubiquitinates MYC and its effects on MYC protein stability are independent of FBXW7. Silencing of endogenous UBR5 induced MYC protein expression and regulated MYC target genes. Consistent with the tumor suppressor function of UBR5 (HYD) in Drosophila, HYD suppressed dMYC-dependent overgrowth of wing imaginal discs. In contrast, in cancer cells, UBR5 suppressed MYC-dependent priming to therapy-induced apoptosis. Of direct cancer relevance, MYC and UBR5 genes were coamplified in MYC-driven human cancers. Functionally, UBR5 suppressed MYC-mediated apoptosis in p53-mutant breast cancer cells with UBR5/MYC coamplification. Furthermore, single-cell immunofluorescence analysis demonstrated reciprocal expression of UBR5 and MYC in human basal-type breast cancer tissues. In summary, UBR5 is a novel MYC ubiquitin ligase and an endogenous rheostat for MYC activity. In MYC-amplified, and p53-mutant breast cancer cells, UBR5 has an important role in suppressing MYC-mediated apoptosis priming and in protection from drug-induced apoptosis. SIGNIFICANCE: These findings identify UBR5 as a novel MYC regulator, the inactivation of which could be very important for understanding of MYC dysregulation on cancer cells. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/7/1414/F1.large.jpg.

Yinchenhao decoction attenuates obstructive jaundice-induced liver injury and hepatocyte apoptosis by suppressing protein kinase RNA-like endoplasmic reticulum kinase-induced pathway

BACKGROUND

Chronic biliary obstruction results in ischemia and hypoxia of hepatocytes, and leads to apoptosis. Apoptosis is very important in regulating the homeostasis of the hepatobiliary system. Endoplasmic reticulum (ER) stress is one of the signaling pathways that induce apoptosis. Moreover, the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-induced apoptotic pathway is the main way; but its role in liver injury remains unclear. Yinchenhao decoction (YCHD) is a traditional Chinese medicine formula that alleviates liver injury and apoptosis, yet its mechanism is unknown. We undertook this study to investigate the effects of YCHD on the expression of ER stress proteins and hepatocyte apoptosis in rats with obstructive jaundice (OJ).

AIM

To investigate whether YCHD can attenuate OJ-induced liver injury and hepatocyte apoptosis by inhibiting the PERK-CCAAT/enhancer-binding protein homologous protein (CHOP)-growth arrest and DNA damage-inducible protein 34 (GADD34) pathway and B cell lymphoma/leukemia-2 related X protein (Bax)/B cell lymphoma/leukemia-2 (Bcl-2) ratio.

METHODS

For in vivo experiments, 30 rats were divided into three groups: control group, OJ model group, and YCHD-treated group. Blood was collected to detect the indicators of liver function, and liver tissues were used for histological analysis. For in vitro experiments, 30 rats were divided into three groups: G1, G2, and G3. The rats in group G1 had their bile duct exposed without ligation, the rats in group G2 underwent total bile duct ligation, and the rats in group G3 were given a gavage of YCHD. According to the serum pharmacology, serum was extracted and centrifuged from the rat blood to cultivate the BRL-3A cells. Terminal deoxynucleotidyl transferase mediated dUTP nick end-labelling (TUNEL) assay was used to detect BRL-3A hepatocyte apoptosis. Alanine aminotransferase (ALT) and aspartate transaminase (AST) levels in the medium were detected. Western blot and quantitative real-time polymerase chain reaction (qRT-PCR) analyses were used to detect protein and gene expression levels of PERK, CHOP, GADD34, Bax, and Bcl-2 in the liver tissues and BRL-3A cells.

RESULTS

Biochemical assays and haematoxylin and eosin staining suggested severe liver function injury and liver tissue structure damage in the OJ model group. The TUNEL assay showed that massive BRL-3A rat hepatocyte apoptosis was induced by OJ. Elevated ALT and AST levels in the medium also demonstrated that hepatocytes could be destroyed by OJ. Western blot or qRT-PCR analyses showed that the protein and mRNA expression levels of PERK, CHOP, and GADD34 were significantly increased both in the rat liver tissue and BRL-3A rat hepatocytes by OJ. The Bax and Bcl-2 levels were increased, and the Bax/Bcl-2 ratio was also increased. When YCHD was used, the PERK, CHOP, GADD34, and Bax levels quickly decreased, while the Bcl-2 levels increased, and the Bax/Bcl-2 ratio decreased.

CONCLUSION

OJ-induced liver injury and hepatocyte apoptosis are associated with the activation of the PERK-CHOP-GADD34 pathway and increased Bax/Bcl-2 ratio. YCHD can attenuate these changes.

Identification of De Novo Enhancers Activated by TGFβ to Drive Expression of CDKN2A and B in HeLa Cells

Disruption of the CDKN2A (INK4A/ARF) and B (INK4B) genes, which encode three function-independent tumor suppressors, is one of the most common events in human cancer. Because their relative importance in tumor prevention appears to be species- and context-specific, studying their regulation can shed light on mechanisms by which they are bypassed in malignant transformation. We previously unveiled a new pathway in which TGFβ selectively induces Arf at mouse Cdkn2a in eye development and cultured fibroblasts. As TGFβ signaling is often derailed in cancer development or progression, we investigated its control of CDKN2A/B in human cancer. Computational analyses of sequencing and array data from nearly 11,000 patients with cancer in TCGA showed discordant expression of ARF and INK4A in most cancer subtypes, with gene copy-number loss and promoter methylation involved in only a subset. Using HeLa cells as a model, we found that exogenous TGFβ induced ARF mRNA and protein, and ARF knockdown limited TGFβ-mediated growth suppression. TGFβ-mediated ARF mRNA induction required SMAD2/3, p38MAPK, and SP1, and ARF mRNA was induced without added RNAPII recruitment. Chromatin immunoprecipitation unveiled a remote enhancer element engaged by TGFβ by a mechanism that partially depended on p38MAPK. CRISPR-based editing of this enhancer limited induction of ARF and INK4B by TGFβ, but not by oncogenic RAS. IMPLICATIONS: Our findings reveal new molecular mechanisms by which CDKN2A/B regulation is coupled to external cues, and those findings represent entry points to further explore pharmacologic strategies to restore their expression in cancer.

Two Pathways of p27Kip1 Degradation Are Required for Murine Lymphoma Driven by Myc and EBV Latent Membrane Protein 2A

Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A), expressed in EBV latency, contributes to Burkitt lymphoma (BL) development in a murine model by acting as a constitutively active B cell receptor (BCR) mimic. Mice expressing both LMP2A and MYC transgenes (LMP2A/λ-MYC) develop tumors significantly faster than mice only expressing MYC (λ-MYC). Previously, we demonstrated the cell cycle inhibitor p27Kip1 is present at significantly lower levels in LMP2A/λ-MYC mice due to increased posttranslational degradation. P27Kip1 degradation can occur in the cytoplasm following phosphorylation on serine 10 (S10) or in the nucleus via the SCFSkp2 complex, which depends on Cks1. We previously demonstrated an S10A knock-in of p27Kip1 (p27S10A/S10A) that prevented S10 phosphorylation failed to significantly delay tumor onset in LMP2A/λ-MYC mice. We also previously demonstrated that a Cks1 knockout partially delayed tumor onset in LMP2A/λ-MYC mice, but onset was still significantly faster than that in λ-MYC mice. Here, we have combined both genetic manipulations in what we call p27Super mice. LMP2A/λ-MYC/p27Super mice and λ-MYC/p27Super mice both displayed dramatic delays in tumor onset. Strikingly, tumor development in LMP2A/λ-MYC/p27Super mice was later than that in λ-MYC mice and not significantly different from that in λ-MYC/p27Super mice. The p27Super genotype also normalized G1-S-phase cell cycle progression, spleen size, and splenic architecture in LMP2A/λ-MYC mice. Our results reveal both major pathways of p27Kip1 degradation are required for the accelerated BL development driven by LMP2A in our BL model and that blocking both degradation pathways is sufficient to delay Myc-driven tumor development with or without LMP2A.IMPORTANCE BL is a cancer that primarily affects children. The side effects of chemotherapy highlight the need for better BL treatments. Many BL tumors contain EBV, and our goal is to determine what makes EBV-positive BL different from EBV-negative BL. This may lead to more specific treatments for both types. All cases of BL require overexpression of MYC Mice engineered to express EBV LMP2A along with MYC (LMP2A/λ-MYC mice) develop tumors much more quickly than mice only expressing MYC (λ-MYC mice). Blocking degradation of the cell cycle inhibitor protein p27Kip1 in LMP2A/λ-MYC mice causes tumors to develop later than in λ-MYC mice, showing that p27Kip1 degradation may play a larger role in EBV-positive BL than EBV-negative BL. Furthermore, our studies suggest the cell cycle is an attractive target as a treatment option for LMP2A-positive cancers in humans.

Dual Role of the Alternative Reading Frame ARF Protein in Cancer

The CDKN2a/ARF locus expresses two partially overlapping transcripts that encode two distinct proteins, namely p14ARF (p19Arf in mouse) and p16INK4a, which present no sequence identity. Initial data obtained in mice showed that both proteins are potent tumor suppressors. In line with a tumor-suppressive role, ARF-deficient mice develop lymphomas, sarcomas, and adenocarcinomas, with a median survival rate of one year of age. In humans, the importance of ARF inactivation in cancer is less clear whereas a more obvious role has been documented for p16INK4a. Indeed, many alterations in human tumors result in the elimination of the entire locus, while the majority of point mutations affect p16INK4a. Nevertheless, specific mutations of p14ARF have been described in different types of human cancers such as colorectal and gastric carcinomas, melanoma and glioblastoma. The activity of the tumor suppressor ARF has been shown to rely on both p53-dependent and independent functions. However, novel data collected in the last years has challenged the traditional and established role of this protein as a tumor suppressor. In particular, tumors retaining ARF expression evolve to metastatic and invasive phenotypes and in humans are associated with a poor prognosis. In this review, the recent evidence and the molecular mechanisms of a novel role played by ARF will be presented and discussed, both in pathological and physiological contexts.

Ironing out the role of the cyclin-dependent kinase inhibitor, p21 in cancer: Novel iron chelating agents to target p21 expression and activity

Iron (Fe) has become an important target for the development of anti-cancer therapeutics with a number of Fe chelators entering human clinical trials for advanced and resistant cancer. An important aspect of the activity of these compounds is their multiple molecular targets, including those that play roles in arresting the cell cycle, such as the cyclin-dependent kinase inhibitor, p21. At present, the exact mechanism by which Fe chelators regulate p21 expression remains unclear. However, recent studies indicate the ability of chelators to up-regulate p21 at the mRNA level was dependent on the chelator and cell-type investigated. Analysis of the p21 promoter identified that the Sp1-3-binding site played a significant role in the activation of p21 transcription by Fe chelators. Furthermore, there was increased Sp1/ER-α and Sp1/c-Jun complex formation in melanoma cells, suggesting these complexes were involved in p21 promoter activation. Elucidating the mechanisms involved in the regulation of p21 expression in response to Fe chelator treatment in neoplastic cells will further clarify how these agents achieve their anti-tumor activity. It will also enhance our understanding of the complex roles p21 may play in neoplastic cells and lead to the development of more effective and specific anti-cancer therapies.

Dual loss of USP10 and p14ARF protein expression is associated with poor prognosis in patients with small intestinal adenocarcinoma

Oncogene-induced senescence occurs following oncogene activation in normal cells and is considered as a critical tumor-suppressing mechanism. Ubiquitin-specific protease 10 (USP10) has been reported to play a vital role in oncogene-induced senescence via the deubiquitination-dependent stabilization of p14ARF. However, knowledge of the clinical significance of USP10 and p14ARF expression in patients with small intestinal adenocarcinoma is limited. To study the clinical significance of USP10 and p14ARF expression, we performed immunohistochemistry for USP10 and p14ARF on 195 surgically resected small intestinal adenocarcinoma specimens. Furthermore, we performed methylation analysis on five small intestinal adenocarcinoma samples and matched adjacent normal intestinal tissue samples. UPS10 ( p = 0.023) and p14ARF ( p = 0.007) expression were significantly decreased in adenocarcinoma in comparison with normal tissue. The loss of USP10 was observed in 124/194 (63.9%) of small intestinal adenocarcinoma samples and was correlated with a higher pT stage ( p = 0.044), lymphatic invasion ( p = 0.033), and the absence of sporadic adenoma ( p = 0.024) and peritumoral dysplasia ( p = 0.019). p14ARF expression was downregulated in 75/195 (38.5%) of small intestinal adenocarcinoma samples and was associated with vascular ( p = 0.011) and lymphatic ( p = 0.013) invasions. The loss of USP10 expression was associated with the loss of p14ARF expression ( r = 0.342, p < 0.001). Multivariate survival analysis revealed that the combined loss of USP10 and p14ARF expression could be an independent prognostic factor for overall survival in small intestinal adenocarcinoma. Furthermore, the aberrant hypermethylation of the USP10 and p14ARF promoter could be a key mechanism for the downregulation of USP10 and p14ARF proteins in small intestinal adenocarcinoma. These findings suggest that the dual loss of USP10 and p14ARF could be used as a prognostic indicator of small intestinal adenocarcinoma.

Dynamics of p14ARF and Focal Adhesion Kinase-Mediated Autophagy in Cancer

It has been widely shown that the focal adhesion kinase (FAK) is involved in nearly every aspect of cancer, from invasion to metastasis to epithelial–mesenchymal transition and maintenance of cancer stem cells. FAK has been shown to interact with p14ARF (alternative reading frame)—a well-established tumor suppressor—and functions in the negative regulation of cancer through both p53-dependent and -independent pathways. Interestingly, both FAK and ARF (human and mouse counterpart) proteins, as well as p53, are involved in autophagy—a process of “self-digestion”—whose main function is the recycling of cellular components and quality control of proteins and organelles. In the last years, an unexpected role of p14ARF in the survival of cancer cells has been underlined in different cellular contexts, suggesting a novel pro-oncogenic function of this protein. In this review, the mechanisms whereby ARF and FAK control autophagy are presented, as well as the role of autophagy in cell migration and spreading. Integrated investigation of these cell functions is extremely important to understand the mechanism of the basis of cell transformation and migration and thus cancer development.

Protective role of p53 in skin cancer: Carcinogenesis studies in mice lacking epidermal p53

p53 is a protein that causes cell cycle arrest, apoptosis or senescence, being crucial in the process of tumor suppression in several cell types. Different in vitro and animal models have been designed for the study of p53 role in skin cancer. These models have revealed opposing results, as in some experimental settings it appears that p53 protects against skin cancer, but in others, the opposite conclusion emerges. We have generated cohorts of mice with efficient p53 deletion restricted to stratified epithelia and control littermates expressing wild type p53 and studied their sensitivity to both chemically-induced and spontaneous tumoral transformation, as well as the tumor types originated in each experimental group. Our results indicate that the absence of p53 in stratified epithelia leads to the appearance, in two-stage skin carcinogenesis experiments, of a higher number of tumors that grow faster and become malignant more frequently than tumors arisen in mice with wild type p53 genotype. In addition, the histological diversity of the tumor type is greater in mice with epidermal p53 loss, indicating the tumor suppressive role of p53 in different epidermal cell types. Aging mice with p53 inactivation in stratified epithelia developed spontaneous carcinomas in skin and other epithelia. Overall, these results highlight the truly protective nature of p53 functions in the development of cancer in skin and in other stratified epithelia.

BMI1 reduces ATR activation and signalling caused by hydroxyurea

BMI1 facilitates DNA damage response (DDR) induced by double strand DNA breaks; however, it remains unknown whether BMI1 functions in single strand DNA (ssDNA) lesions-initiated DDR. We report here that BMI1 reduces hydroxyurea-elicited ATR activation, thereby reducing the S-phase checkpoints. Hydroxyurea induces ssDNA lesions, which activate ATR through binding TOPBP1 as evidenced by phosphorylation of ATR at threonine 1989 (ATRpT1989). ATR subsequently phosphorylates H2AX at serine 139 (γH2AX) and CHK1 at serine 345 (CHK1pS345), leading to phosphorylation of CDK1 at tyrosine 15 (CDK1pY15) and S-phase arrest. BMI1 overexpression reduced γH2AX, CHK1pS345, CDK1pY15, S-phase arrest, and ATR activation in HU-treated MCF7 and DU145 cells, whereas BMI1 knockdown enhanced these events. BMI1 contains a ring finger, helix-turn, proline/serine domain and two nuclear localization signals (NLS). Individual deletion of these domains did not abolish BMI1-derived reductions of CHK1pS345 in MCF7 cells following HU exposure, suggesting that these structural features are not essential for BMI1 to attenuate ATR-mediated CHK1pS345. BMI1 interacts with both TOPBP1 and ATR. Furthermore, all of our BMI1 mutants associate with endogenous TOPBP1. It has previously been established that association of TOPBP1 and ATR is required for ATR activation. Thus, our results suggest that BMI1 decreases ATR activation through a mechanism that involves binding to TOPBP1 and/or ATR.

Small mitochondrial Arf (smArf) protein corrects p53-independent developmental defects of Arf tumor suppressor-deficient mice

The mouse p19^Arf (human p14^ARF) tumor suppressor protein, encoded in part from an alternative reading frame of the Ink4a (Cdkn2a) gene, inhibits the Mdm2 E3 ubiquitin ligase to activate p53. Arf is not expressed in most normal tissues of young mice but is induced by high thresholds of aberrant hyperproliferative signals, thereby activating p53 in incipient tumor cells that have experienced oncogene activation. The single Arf mRNA encodes two distinct polypeptides, including full-length p19^Arf and N-terminally truncated and unstable p15^smArf ("small mitochondrial Arf") initiated from an internal in-frame AUG codon specifying methionine-45. Interactions of p19^Arf with Mdm2, or separately with nucleophosmin (NPM, B23) that localizes and stabilizes p19^Arf within the nucleolus, require p19^Arf N-terminal amino acids that are not present within p15^smArf We have generated mice that produce either smARF alone or M45A-mutated (smArf-deficient) full-length p19^Arf proteins. BCR-ABL-expressing pro/pre-B cells producing smArf alone are as oncogenic as their Arf-null counterparts in generating acute lymphoblastic leukemia when infused into unconditioned syngeneic mice. In contrast, smArf-deficient cells from mice of the Arf^M45A strain are as resistant as wild-type Arf^+/+ cells to comparable oncogenic challenge and do not produce tumors. Apart from being prone to tumor development, Arf-null mice are blind, and their male germ cells exhibit defects in meiotic maturation and sperm production. Although Arf^M45A mice manifest the latter defects, smArf alone remarkably rescues both of these p53-independent developmental phenotypes.

Genes coding for cyclin-dependent kinase inhibitors are fragile in Xenopus

Cell proliferation is strictly regulated by the dosage balance among cell-cycle regulators such as CDK/cyclin complexes and CDK-Inhibitors. Even in the allotetraploid genome of Xenopus laevis, the dosage balance must be maintained for animals to stay alive, and the duplicated homeologous genes seem to have gradually changed, through evolution, resulting in the best genes for them to thrive. In the Xenopus laevis genome, while homeologous gene pairs of CDKs are fundamentally maintained and a few cyclin genes are amplified, homeologous gene pairs of the important CDK-Inhibitors, CDKn1c and CDKn2a, are deleted from chromosomes L and S. Although losses of CDKn1c and CDKn2a can lead to diseases in humans, their loss in X. laevis does not affect the animals' health. Also, another gene coding CDKn1b is lost besides CDKn1c and CDKn2a in the genome of Xenopus tropicalis. These findings suggest a high resistance of Xenopus to diseases. We also found that CDKn2c.S expression is higher than that of CDKn2c.L, and a conserved noncoding sequence (CNS) of CDKn2c genomic loci on X. laevis chromosome S and X. tropicalis has an enhancement activity in regulating the different expression. These findings together indicate a surprising fragility of CDK inhibitor gene loci in the Xenopus genome in spite of their importance, and may suggest that factors other than CDK-inhibitors decelerate cell-cycling in Xenopus.

Modeling the response of a tumor-suppressive network to mitogenic and oncogenic signals

Intrinsic tumor-suppressive mechanisms protect normal cells against aberrant proliferation. Although cellular signaling pathways engaged in tumor repression have been largely identified, how they are orchestrated to fulfill their function still remains elusive. Here, we built a tumor-suppressive network model composed of three modules responsible for the regulation of cell proliferation, activation of p53, and induction of apoptosis. Numerical simulations show a rich repertoire of network dynamics when normal cells are subject to serum stimulation and adenovirus E1A overexpression. We showed that oncogenic signaling induces ARF and that ARF further promotes p53 activation to inhibit proliferation. Mitogenic signaling activates E2F activators and promotes Akt activation. p53 and E2F1 cooperate to induce apoptosis, whereas Akt phosphorylates p21 to repress caspase activation. These prosurvival and proapoptotic signals compete to dictate the cell fate of proliferation, cell-cycle arrest, or apoptosis. The cellular outcome is also impacted by the kinetic mode (ultrasensitivity or bistability) of p53. When cells are exposed to serum deprivation and recovery under fixed E1A, the shortest starvation time required for apoptosis induction depends on the terminal serum concentration, which was interpreted in terms of the dynamics of caspase-3 activation and cytochrome c release. We discovered that caspase-3 can be maintained active at high serum concentrations and that E1A overexpression sensitizes serum-starved cells to apoptosis. This work elucidates the roles of tumor repressors and prosurvival factors in tumor repression based on a dynamic network analysis and provides a framework for quantitatively exploring tumor-suppressive mechanisms.

Differing tumor-suppressor functions of Arf and p53 in murine basal cell carcinoma initiation and progression

Human basal cell carcinomas (BCCs) very frequently carry p53 mutations, and p53 loss markedly accelerates murine BCC carcinogenesis. We report here our studies of the mechanism by which p53 is activated to suppress BCC carcinogenesis. We find that aberrant hedgehog signaling in microscopic BCCs activates p53 in part via Arf (that is, the oncogene-induced stress pathway) but not via the DNA damage response pathway. However, Arf loss and p53 loss produce differing outcomes-loss of p53 promotes both tumor initiation and progression; loss of Arf promotes tumor progression but not initiation. Intriguingly, increased expression of Arf in tumor stromal cells, as in tumor keratinocytes themselves, contributes to suppression of BCC carcinogenesis.

CDK inhibitors for muscle stem cell differentiation and self-renewal

Regeneration of muscle is undertaken by muscle stem cell populations named satellite cells which are normally quiescent or at the G0 phase of the cell cycle. However, upon signals from damaged muscle, satellite cells lose their quiescence, and enter the G1 cell cycle phase to expand the population of satellite cell progenies termed myogenic precursor cells (MPCs). Eventually, MPCs stop their cell cycle and undergo terminal differentiation to form skeletal muscle fibers. Some MPCs retract to quiescent satellite cells as a self-renewal process. Therefore, cell cycle regulation, consisting of satellite cell activation, proliferation, differentiation and self-renewal, is the key event of muscle regeneration. In this review, we summarize up-to-date progress on research about cell cycle regulation of myogenic progenitor cells and muscle stem cells during embryonic myogenesis and adult muscle regeneration, aging, exercise and muscle diseases including muscular dystrophy and muscle fiber atrophy, especially focusing on cyclin-dependent kinase inhibitors (CDKIs).

RUNX3 and p53: How Two Tumor Suppressors Cooperate Against Oncogenic Ras?

RUNX family members play pivotal roles in both normal development and neoplasia. In particular, RUNX1 and RUNX2 are essential for determination of the hematopoietic and osteogenic lineages, respectively. RUNX3 is involved in lineage determination of various types of epithelial cells. Analysis of mouse models and human cancer specimens revealed that RUNX3 acts as a tumor suppressor via multiple mechanisms. p53-related pathways play central roles in tumor suppression through the DNA damage response and oncogene surveillance, and RUNX3 is involved in both processes. In response to DNA damage, RUNX3 facilitates p53 phosphorylation by the ATM/ATR pathway and p53 acetylation by p300. When oncogenes are activated, RUNX3 induces ARF, thereby stabilizing p53. Here, we summarize the molecular mechanisms underlying the p53-mediated tumor-suppressor activity of RUNX3.

Protein 4.1N acts as a potential tumor suppressor linking PP1 to JNK-c-Jun pathway regulation in NSCLC

Protein 4.1N is a member of protein 4.1 family and has been recognized as a potential tumor suppressor in solid tumors. Here, we aimed to investigate the role and mechanisms of 4.1N in non-small cell lung cancer (NSCLC). We confirmed that the expression level of 4.1N was inversely correlated with the metastatic properties of NSCLC cell lines and histological grade of clinical NSCLC tissues. Specific knockdown of 4.1N promoted tumor cell proliferation, migration and adhesion in vitro, and tumor growth and metastasis in mouse xenograft models. Furthermore, we identified PP1 as a novel 4.1N-interacting molecule, and the FERM domain of 4.1N mediated the interaction between 4.1N and PP1. Further, ectopic expression of 4.1N could inactivate JNK-c-Jun signaling pathway through enhancing PP1 activity and interaction between PP1 and p-JNK. Correspondingly, expression of potential downstream metastasis targets (ezrin and MMP9) and cell cycle targets (p53, p21 and p19) of JNK-c-Jun pathway were also regulated by 4.1N. Our data suggest that down-regulation of 4.1N expression is a critical step for NSCLC development and that repression of JNK-c-Jun signaling through PP1 is one of the key anti-tumor mechanisms of 4.1N.

Impact of loss of BH3-only proteins on the development and treatment of MLL-fusion gene-driven AML in mice

Inhibition of the apoptosis pathway controlled by opposing members of the Bcl-2 protein family plays a central role in cancer development and resistance to therapy. To investigate how pro-apoptotic Bcl-2 homology domain 3 (BH3)-only proteins impact on acute myeloid leukemia (AML), we generated mixed lineage leukemia (MLL)-AF9 and MLL-ENL AMLs from BH3-only gene knockout mice. Disease development was not accelerated by loss of Bim, Puma, Noxa, Bmf, or combinations thereof; hence these BH3-only proteins are apparently ineffectual as tumor suppressors in this model. We tested the sensitivity of MLL-AF9 AMLs of each genotype in vitro to standard chemotherapeutic drugs and to the proteasome inhibitor bortezomib, with or without the BH3 mimetic ABT-737. Loss of Puma and/or Noxa increased resistance to cytarabine, daunorubicin and etoposide, while loss of Bim protected against cytarabine and loss of Bmf had no impact. ABT-737 increased sensitivity to the genotoxic drugs but was not dependent on any BH3-only protein tested. The AML lines were very sensitive to bortezomib and loss of Noxa conveyed significant resistance. In vivo, several MLL-AF9 AMLs responded well to daunorubicin and this response was highly dependent on Puma and Noxa but not Bim. Combination therapy with ABT-737 provided little added benefit at the daunorubicin dose trialed. Bortezomib also extended survival of AML-bearing mice, albeit less than daunorubicin. In summary, our genetic studies reveal the importance of Puma and Noxa for the action of genotoxics currently used to treat MLL-driven AML and suggest that, while addition of ABT-737-like BH3 mimetics might enhance their efficacy, new Noxa-like BH3 mimetics targeting Mcl-1 might have greater potential.

Death Associated Protein Kinase 1 (DAPK1): A Regulator of Apoptosis and Autophagy

Death-Associated Protein Kinase 1 (DAPK1) belongs to a family of five serine/threonine (Ser/Thr) kinases that possess tumor suppressive function and also mediate a wide range of cellular processes, including apoptosis and autophagy. The loss and gain-of–function of DAPK1 is associated with various cancer and neurodegenerative diseases respectively. In recent years, mechanistic studies have broadened our knowledge of the molecular mechanisms involved in DAPK1-mediated autophagy/apoptosis. In the present review, we have discussed the structural information and various cellular functions of DAPK1 in a comprehensive manner.

A MYC-aurora kinase A protein complex represents an actionable drug target in p53-altered liver cancer

MYC oncoproteins are involved in the genesis and maintenance of the majority of human tumors but are considered undruggable. By using a direct in vivo shRNA screen, we show that liver cancer cells that have mutations in the gene encoding the tumor suppressor protein p53 (Trp53 in mice and TP53 in humans) and that are driven by the oncoprotein NRAS become addicted to MYC stabilization via a mechanism mediated by aurora kinase A (AURKA). This MYC stabilization enables the tumor cells to overcome a latent G2/M cell cycle arrest that is mediated by AURKA and the tumor suppressor protein p19(ARF). MYC directly binds to AURKA, and inhibition of this protein-protein interaction by conformation-changing AURKA inhibitors results in subsequent MYC degradation and cell death. These conformation-changing AURKA inhibitors, with one of them currently being tested in early clinical trials, suppressed tumor growth and prolonged survival in mice bearing Trp53-deficient, NRAS-driven MYC-expressing hepatocellular carcinomas (HCCs). TP53-mutated human HCCs revealed increased AURKA expression and a positive correlation between AURKA and MYC expression. In xenograft models, mice bearing TP53-mutated or TP53-deleted human HCCs were hypersensitive to treatment with conformation-changing AURKA inhibitors, thus suggesting a therapeutic strategy for this subgroup of human HCCs.

The Roles of MDM2 and MDMX in Cancer

For more than 25 years, MDM2 and its homolog MDMX (also known as MDM4) have been shown to exert oncogenic activity. These two proteins are best understood as negative regulators of the p53 tumor suppressor, although they may have additional p53-independent roles. Understanding the dysregulation of MDM2 and MDMX in human cancers and how they function either together or separately in tumorigenesis may improve methods of diagnosis and for assessing prognosis. Targeting the proteins themselves, or their regulators, may be a promising therapeutic approach to treating some forms of cancer.

MDM2 Associates with Polycomb Repressor Complex 2 and Enhances Stemness-Promoting Chromatin Modifications Independent of p53

The MDM2 oncoprotein ubiquitinates and antagonizes p53 but may also carry out p53-independent functions. Here we report that MDM2 is required for the efficient generation of induced pluripotent stem cells (iPSCs) from murine embryonic fibroblasts, in the absence of p53. Similarly, MDM2 depletion in the context of p53 deficiency also promoted the differentiation of human mesenchymal stem cells and diminished clonogenic survival of cancer cells. Most of the MDM2-controlled genes also responded to the inactivation of the Polycomb Repressor Complex 2 (PRC2) and its catalytic component EZH2. MDM2 physically associated with EZH2 on chromatin, enhancing the trimethylation of histone 3 at lysine 27 and the ubiquitination of histone 2A at lysine 119 (H2AK119) at its target genes. Removing MDM2 simultaneously with the H2AK119 E3 ligase Ring1B/RNF2 further induced these genes and synthetically arrested cell proliferation. In conclusion, MDM2 supports the Polycomb-mediated repression of lineage-specific genes, independent of p53.

Computer Simulations of Peptides from the p53 DNA Binding Domain

We have studied the dynamics and thermodynamics of two of the four evolutionarily conserved segments from the p53 DNA binding domain, using molecular dynamics and replica exchange simulations. These two regions contain well-defined elements of secondary structure (a β hairpin for region II and an α helix for region V) and bind to DNA in the intact protein. They are also mutational hot spots. The goal of our study was to determine the stability and folding propensity of these peptides in isolation. We used three force fields and solvent models (CHARMM19 with EEF1, CHARMM27 with GBMV, GROMOS96 with SPC). The predicted stability, folding propensity, and secondary structures depend upon the potential. Secondary structure predictors identify helical propensity for region II, in agreement with one of the force fields (CHARMM/GBMV). However, the other two potentials favor β structure for this peptide, although the conformations may differ from the crystal. For region V secondary structure predictions are unclear. Only one force field (CHARMM/GBMV) produces low-lying free energy minima that retain some of the α helical structure from the crystal structure. The other two potentials appear to favor β structure for this peptide.

A Novel Aspect of Tumorigenesis-BMI1 Functions in Regulating DNA Damage Response

BMI1 plays critical roles in maintaining the self-renewal of hematopoietic, neural, intestinal stem cells, and cancer stem cells (CSCs) for a variety of cancer types. BMI1 promotes cell proliferative life span and epithelial to mesenchymal transition (EMT). Upregulation of BMI1 occurs in multiple cancer types and is associated with poor prognosis. Mechanistically, BMI1 is a subunit of the Polycomb repressive complex 1 (PRC1), and binds the catalytic RING2/RING1b subunit to form a functional E3 ubiquitin ligase. Through mono-ubiquitination of histone H2A at lysine 119 (H2A-K119Ub), BMI1 represses multiple gene loci; among these, the INK4A/ARF locus has been most thoroughly investigated. The locus encodes the p16INK4A and p14/p19ARF tumor suppressors that function in the pRb and p53 pathways, respectively. Its repression contributes to BMI1-derived tumorigenesis. BMI1 also possesses other oncogenic functions, specifically its regulative role in DNA damage response (DDR). In this process, BMI1 ubiquitinates histone H2A and γH2AX, thereby facilitating the repair of double-stranded DNA breaks (DSBs) through stimulating homologous recombination and non-homologous end joining. Additionally, BMI1 compromises DSB-induced checkpoint activation independent of its-associated E3 ubiquitin ligase activity. We review the emerging role of BMI1 in DDR regulation and discuss its impact on BMI1-derived tumorigenesis.

p53/PUMA expression in human pulmonary fibroblasts mediates cell activation and migration in silicosis

Phagocytosis of SiO₂ into the lung causes an inflammatory cascade that results in fibroblast proliferation and migration, followed by fibrosis. Clinical evidence has indicated that the activation of alveolar macrophages by SiO₂ produces rapid and sustained inflammation characterized by the generation of monocyte chemotactic protein 1, which, in turn, induces fibrosis. However, the details of events downstream of monocyte chemotactic protein 1 activity in pulmonary fibroblasts remain unclear. Here, to elucidate the role of p53 in fibrosis induced by silica, both the upstream molecular mechanisms and the functional effects on cell proliferation and migration were investigated. Experiments using primary cultured adult human pulmonary fibroblasts led to the following results: 1) SiO₂ treatment resulted in a rapid and sustained increase in p53 and PUMA protein levels; 2) the MAPK and PI3K pathways were involved in the SiO₂-induced alteration of p53 and PUMA expression; and 3) RNA interference targeting p53 and PUMA prevented the SiO₂-induced increases in fibroblast activation and migration. Our study elucidated a link between SiO₂-induced p53/PUMA expression in fibroblasts and cell migration, thereby providing novel insight into the potential use of p53/PUMA in the development of novel therapeutic strategies for silicosis treatment.

Physiological Expression and Accumulation of the Products of Two Upstream Open Reading Frames mrtl and MycHex1 Along With p64 and p67 Myc From the Human c-myc Locus

In addition to the canonical c-Myc p64 and p67 proteins, the human c-myc locus encodes two distinct proteins, mrtl (myc-related translation/localization regulatory factor) and MycHex1 (Myc Human Exon 1), from the upstream open reading frames within the 5'-untranslated region of the c-myc P0 mRNA. The aim of this study is to examine simultaneously, for the first time, mrtl, MycHex1, c-Myc p64, and p67 in human tumor cell lines and pediatric brain tumor tissues. Western blot analysis demonstrated endogenous mrtl, MycHex1, c-Myc p64, and p67 simultaneously. The relative abundance of mrtl and MycHex1 were consistent among a variety of human tumor cell lines, and the relative intensities of mrtl and MycHex1 correlated positively. Confocal imaging revealed mrtl predominantly localized to the nuclear envelope, along with prominent reticular pattern in the cytoplasm. MycHex1 was observed as a series of bright foci located within the nucleus, a subset of which colocalized with fibrillarin. mrtl and MycHex1 co-immunoprecipitated with RACK1, c-Myc, fibrillarin, coilin, and with each other. These findings suggest that mrtl and MycHex1 have multiple interaction partners in both the nucleus and cytoplasm. Sequence analyses confirmed a known polymorphism of mrtl at base 1965 (G>T) and new mutations at bases 1900 (C>G) and 1798 (C>G). Evidence is presented for expression and stable accumulation of all four proteins encoded by three distinct non-overlapping open reading frames within the human c-myc locus. Additional work is warranted to further elucidate the functional or regulatory roles of these molecules in regulation of c-Myc and in oncogenesis.

Transcriptional control of stem cell fate by E2Fs and pocket proteins

E2F transcription factors and their regulatory partners, the pocket proteins (PPs), have emerged as essential regulators of stem cell fate control in a number of lineages. In mammals, this role extends from both pluripotent stem cells to those encompassing all embryonic germ layers, as well as extra-embryonic lineages. E2F/PP-mediated regulation of stem cell decisions is highly evolutionarily conserved, and is likely a pivotal biological mechanism underlying stem cell homeostasis. This has immense implications for organismal development, tissue maintenance, and regeneration. In this article, we discuss the roles of E2F factors and PPs in stem cell populations, focusing on mammalian systems. We discuss emerging findings that position the E2F and PP families as widespread and dynamic epigenetic regulators of cell fate decisions. Additionally, we focus on the ever expanding landscape of E2F/PP target genes, and explore the possibility that E2Fs are not simply regulators of general ‘multi-purpose’ cell fate genes but can execute tissue- and cell type-specific gene regulatory programs.

Phenotype specific analyses reveal distinct regulatory mechanism for chronically activated p53

The downstream functions of the DNA binding tumor suppressor p53 vary depending on the cellular context, and persistent p53 activation has recently been implicated in tumor suppression and senescence. However, genome-wide information about p53-target gene regulation has been derived mostly from acute genotoxic conditions. Using ChIP-seq and expression data, we have found distinct p53 binding profiles between acutely activated (through DNA damage) and chronically activated (in senescent or pro-apoptotic conditions) p53. Compared to the classical 'acute' p53 binding profile, 'chronic' p53 peaks were closely associated with CpG-islands. Furthermore, the chronic CpG-island binding of p53 conferred distinct expression patterns between senescent and pro-apoptotic conditions. Using the p53 targets seen in the chronic conditions together with external high-throughput datasets, we have built p53 networks that revealed extensive self-regulatory 'p53 hubs' where p53 and many p53 targets can physically interact with each other. Integrating these results with public clinical datasets identified the cancer-associated lipogenic enzyme, SCD, which we found to be directly repressed by p53 through the CpG-island promoter, providing a mechanistic link between p53 and the 'lipogenic phenotype', a hallmark of cancer. Our data reveal distinct phenotype associations of chronic p53 targets that underlie specific gene regulatory mechanisms.

Humanization of the mouse mammary gland by replacement of the luminal layer with genetically engineered preneoplastic human cells

Introduction

The cell of origin for estrogen receptor α (ERα) positive breast cancer is probably a luminal stem cell in the terminal duct lobular units. To model these cells we have used the murine myoepithelial layer in the mouse mammary ducts as a scaffold upon which to build a human luminal layer. To prevent squamous metaplasia, a common artifact in genetically engineered breast cancer models, we sought to limit activation of the epidermal growth factor receptor (EGFR) during in vitro cell culture before grafting the cells.

Methods

Human reduction mammoplasty cells were grown in vitro in WIT medium. Epidermal growth factor (EGF) in the medium was replaced with amphiregulin and neuregulin to decrease activation of EGFR and increase activation of EGFR homologs 3 and 4 (ERBB3 and ERBB4). Lentiviral vectors were used to express oncogenic transgenes and fluorescent proteins. Human mammary epithelial cells were mixed with irradiated mouse fibroblasts and matrigel, then injected through the nipple into the mammary ducts of immunodeficient mice. Engrafted cells were visualized by stereomicroscopy for fluorescent proteins and characterized by histology and immunohistochemistry.

Results

Growth of normal mammary epithelial cells in conditions favoring ERBB3/4 signaling prevented squamous metaplasia in vitro. Normal human cells were quickly lost after intraductal injection but cells infected with lentiviruses expressing CCND1, MYC, TERT, BMI1 and a short hairpin RNA targeting TP53 were able to engraft and progressively replace the luminal layer in the mouse mammary ducts, resulting in the formation of an extensive network of humanized ducts. Despite expressing multiple oncogenes, the human cells formed a morphologically normal luminal layer. Expression of a single additional oncogene, PIK3CA-H1047R, converted the cells into invasive cancer cells. The resulting tumors were ERα+, Ki67+ luminal B adenocarcinomas that were resistant to treatment with fulvestrant.

Conclusions

Injection of preneoplastic human mammary epithelial cells into the mammary ducts of immunodeficient mice leads to replacement of the murine luminal layer with morphologically normal human cells. Genetic manipulation of the injected cells makes it possible to study defined steps in the transformation of human mammary epithelial cells in a more physiological environment than has hitherto been possible.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0504-9) contains supplementary material, which is available to authorized users.

Relative genomic stability of adipose tissue derived mesenchymal stem cells: analysis of ploidy, H19 long non-coding RNA and p53 activity

Introduction

Mesenchymal stem cells (MSCs) are multipotent and have been derived from various tissues. Although MSCs share many basic features, they often display subtle tissue specific differences. We previously demonstrated that bone marrow (BM) MSCs frequently become polyploid in culture. This tendency was mediated by a reduction in the expression of H19 long non-coding RNA during the transition from a diploid to a polyploid state.

Methods

MSCs were derived from both BM and adipose tissue of mice and expanded under normoxic and hypoxic culture conditions. Cells were stained by propidium iodide and their ploidy was evaluated by FACS. Gene expression of independent MSC preparations was compared by quantitative real time PCR and protein expression levels by Western blot analysis. p53 silencing in MSCs was performed by a specific small hairpin RNA (shRNA).

Results

We set to examine whether genomic instability is common to MSCs originating from different tissues. It is demonstrated that adipose derived MSCs (ASCs) tend to remain diploid during culture while a vast majority of BM MSCs become polyploid. The diploid phenotype of ASCs is correlated with reduced H19 expression compared to BM MSCs. Under hypoxic conditions (3% oxygen) both ASCs and BM MSCs demonstrate increased RNA expression of H19 and Vascular endothelial growth factor A. Importantly, ASC gene expression is significantly less variable than BM MSCs under both oxygen conditions, indicating to their superior homogeneity. Gene expression analysis revealed that p53 target genes, often induced by DNA damage, are up-regulated in ASCs under basal conditions. However, p53 activation following treatment with DNA damaging agents was strongly elevated in BM MSCs compared to ASCs. We found that p53 is involved in maintaining the stable diploid state of ASCs as p53 shRNA induced ploidy changes in ASCs but not in BM MSCs.

Conclusions

The increased genomic stability of murine ASCs together with their lower H19 expression and relative homogeneity suggest a tissue specific higher stability of ASCs compared to BM MSCs, possibly due to higher activity of p53. The tissue specific differences between MSCs from a different tissue source may have important consequences on the use of various MSCs both in vitro and in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/scrt529) contains supplementary material, which is available to authorized users.

Downregulation of Kruppel-like factor 2 is associated with poor prognosis for nonsmall-cell lung cancer

Kruppel-like factor 2 (KLF2) expression is diminished in many malignancies. However, its expression and role in nonsmall-cell lung cancer (NSCLC) remain unknown. In this study, we found that KLF2 levels were decreased in NSCLC tissues compared with adjacent normal tissues. Its expression level was significantly correlated with TNM stages, tumor size, and lymph node metastasis. Moreover, patients with low levels of KLF2 expression had a relatively poor prognosis. Furthermore, knockdown of KLF2 expression by siRNA could promote cell proliferation, while ectopic expression of KLF2 inhibited cell proliferation and promoted apoptosis in NSCLC cells partly via regulating CDKN1A/p21 and CDKN2B/p15 protein expression. Our findings present that decreased KLF2 could be identified as a poor prognostic biomarker in NSCLC and regulate cell proliferation and apoptosis.