A p53-dependent mouse spindle checkpoint

2-Methoxyestradiol, an Endogenous 17β-Estradiol Metabolite, Induces Antimitogenic and Apoptotic Actions in Oligodendroglial Precursor Cells and Triggers Endoreduplication via the p53 Pathway

The abnormal growth of oligodendrocyte precursor cells (OPCs) significantly contributes to the progression of glioblastoma tumors. Hence, molecules that block OPC growth may be of therapeutic importance in treating gliomas. 2-Methoxyestradiol (2ME), an endogenous tubulin-interacting metabolite of estradiol, is effective against multiple proliferative disorders. Based on its anti-carcinogenic and anti-angiogenic actions, it is undergoing phase II clinical trials. We hypothesize that 2ME may prevent glioma growth by targeting OPC growth. Here, we tested this hypothesis by assessing the impact of 2ME on the growth of an OPC line, "Oli-neu", and dissected the underlying mechanism(s). Treatment with 2ME inhibited OPC growth in a concentration-dependent manner, accompanied by significant upregulation in the expression of p21 and p27, which are negative cell-cycle regulators. Moreover, treatment with 2ME altered OPC morphology from multi-arm processes to rounded cells. At concentrations of 1uM and greater, 2ME induced apoptosis, with increased expressions of caspase 3, PARP, and caspase-7 fragments, externalized phosphatidylserine staining/APOPercentage, and increased mitochondrial activity. Flow cytometry and microscopic analysis demonstrated that 2ME triggers endoreduplication in a concentration-dependent fashion. Importantly, 2ME induced cyclin E, JNK1/2, and p53 expression, as well as OPC fusion, which are key mechanisms driving endoreduplication and whole-genome duplication. Importantly, the inhibition of p53 with pifithrin-α rescued 2ME-induced endoreduplication. The pro-apoptotic and endoreduplication actions of 2ME were accompanied by the upregulation of survivin, cyclin A, Cyclin B, Cyclin D2, and ppRB. Similar growth inhibitory, apoptotic, and endoreduplication effects of 2ME were observed in CG4 cells. Taken together, our findings provide evidence that 2ME not only inhibits OPC growth and triggers apoptosis, but also activates OPCs into survival (fight or flight) mode, leading to endoreduplication. This inherent survival characteristic of OPCs may, in part, be responsible for drug resistance in gliomas, as observed for many tubulin-interacting drugs. Importantly, the fate of OPCs after 2ME treatment may depend on the cell-cycle status of individual cells. Combining tubulin-interfering molecules with drugs such as pifithrin-α that inhibit endoreduplication may help inhibit OPC/glioma growth and limit drug resistance.

Transcriptome profiles and chromatin states in mouse androgenetic haploid embryonic stem cells

Haploid embryonic stem cells (haESCs) are derived from the inner cell mass of the haploid blastocyst, containing only one set of chromosomes. Extensive and accurate chromatin remodelling occurs during haESC derivation, but the intrinsic transcriptome profiles and chromatin structure of haESCs have not been fully explored. We profiled the transcriptomes, nucleosome positioning, and key histone modifications of four mouse haESC lines, and compared these profiles with those of other closely-related stem cell lines, MII oocytes, round spermatids, sperm, and mouse embryonic fibroblasts. haESCs had transcriptome profiles closer to those of naïve pluripotent stem cells. Consistent with the one X chromosome in haESCs, Xist was repressed, indicating no X chromosome inactivation. haESCs and ESCs shared a similar global chromatin structure. However, a nucleosome depletion region was identified in 2056 promoters in ESCs, which was absent in haESCs. Furthermore, three characteristic spatial relationships were formed between transcription factor motifs and nucleosomes in both haESCs and ESCs, specifically in the linker region, on the nucleosome central surface, and nucleosome borders. Furthermore, the chromatin state of 4259 enhancers was off in haESCs but active in ESCs. Functional annotation of these enhancers revealed enrichment in regulation of the cell cycle, a predominantly reported mechanism of haESC self-diploidization. Notably, the transcriptome profiles and chromatin structure of haESCs were highly preserved during passaging but different from those of differentiated cell types.

Resistance to vincristine in DLBCL by disruption of p53-induced cell cycle arrest and apoptosis mediated by KIF18B and USP28

The frontline therapy R-CHOP for patients with diffuse large B-cell lymphoma (DLBCL) has remained unchanged for two decades despite numerous Phase III clinical trials investigating new alternatives. Multiple large studies have uncovered genetic subtypes of DLBCL enabling a targeted approach. To further pave the way for precision oncology, we perform genome-wide CRISPR screening to uncover the cellular response to one of the components of R-CHOP, vincristine, in the DLBCL cell line SU-DHL-5. We discover important pathways and subnetworks using gene-set enrichment analysis and protein-protein interaction networks and identify genes related to mitotic spindle organization that are essential during vincristine treatment. The inhibition of KIF18A, a mediator of chromosome alignment, using the small molecule inhibitor BTB-1 causes complete cell death in a synergistic manner when administered together with vincristine. We also identify the genes KIF18B and USP28 of which CRISPR/Cas9-directed knockout induces vincristine resistance across two DLBCL cell lines. Mechanistic studies show that lack of KIF18B or USP28 counteracts a vincristine-induced p53 response suggesting that resistance to vincristine has origin in the mitotic surveillance pathway (USP28-53BP1-p53). Collectively, our CRISPR screening data uncover potential drug targets and mechanisms behind vincristine resistance, which may support the development of future drug regimens.

Whole-Genome Doubling as a source of cancer: how, when, where, and why?

Chromosome instability is a well-known hallmark of cancer, leading to increased genetic plasticity of tumoral cells, which favors cancer aggressiveness, and poor prognosis. One of the main sources of chromosomal instability are events that lead to a Whole-Genome Duplication (WGD) and the subsequently generated cell polyploidy. In recent years, several studies showed that WGD occurs at the early stages of cell transformation, which allows cells to later become aneuploid, thus leading to cancer progression. On the other hand, other studies convey that polyploidy plays a tumor suppressor role, by inducing cell cycle arrest, cell senescence, apoptosis, and even prompting cell differentiation, depending on the tissue cell type. There is still a gap in understanding how cells that underwent WGD can overcome the deleterious effect on cell fitness and evolve to become tumoral. Some laboratories in the chromosomal instability field recently explored this paradox, finding biomarkers that modulate polyploid cells to become oncogenic. This review brings a historical view of how WGD and polyploidy impact cell fitness and cancer progression, and bring together the last studies that describe the genes helping cells to adapt to polyploidy.

Inactivation of RB1, CDKN2A, and TP53 have distinct effects on genomic stability at side-by-side comparison in karyotypically normal cells

Chromosomal instability is a common feature in malignant tumors. Previous studies have indicated that inactivation of the classical tumor suppressor genes RB1, CDKN2A, and TP53 may contribute to chromosomal aberrations in cancer by disrupting different aspects of the cell cycle and DNA damage checkpoint machinery. We performed a side-by-side comparison of how inactivation of each of these genes affected chromosomal stability in vitro. Using CRISPR-Cas9 technology, RB1, CDKN2A, and TP53 were independently knocked out in karyotypically normal immortalized cells, after which these cells were followed over time. Bulk RNA sequencing revealed a distinct phenotype with upregulation of pathways related to cell cycle control and proliferation in all three knockouts. Surprisingly, the RB1 and CDKN2A knocked out cell lines did not harbor more copy number aberrations than wild-type cells, despite culturing for months. The TP53-knocked out cells, in contrast, showed a massive amount of copy number alterations and saltatory evolution through whole genome duplication. This side-by-side comparison indicated that the effects on chromosomal stability from inactivation of RB1 and CDKN2A are negligible compared to inactivation of TP53, under the same conditions in a nonstressful environment, even though partly overlapping regulatory pathways are affected. Our data suggest that loss of RB1 and CDKN2A alone is not enough to trigger surviving detectable aneuploid clones while inactivation of TP53 on its own caused massive CIN leading to saltatory clonal evolution in vitro and clonal selection.

A comprehensive study of p53 protein

The protein p53 has been extensively investigated since it was found 43 years ago and has become a "guardian of the genome" that regulates the division of cells by preventing the growth of cells and dividing them, that is, inhibits the development of tumors. Initial proof of protein existence by researchers in the mid-1970s was found by altering and regulating the SV40 big T antigen termed the A protein. Researchers demonstrated how viruses play a role in cancer by employing viruses' ability to create T-antigens complex with viral tumors, which was discovered in 1979 following a viral analysis and cancer analog research. Researchers later in the year 1989 explained that in Murine Friend, a virus-caused erythroleukemia, commonly found that p53 was inactivated to suggest that p53 could be a "tumor suppressor gene." The TP53 gene, encoding p53, is one of human cancer's most frequently altered genes. The protein-regulated biological functions of all p53s include cell cycles, apoptosis, senescence, metabolism of the DNA, angiogenesis, cell differentiation, and immunological response. We tried to unfold the history of the p53 protein, which was discovered long back in 1979, that is, 43 years of research on p53, and how p53's function has been developed through time in this article.

Centrosome instability: when good centrosomes go bad

The centrosome is a tiny cytoplasmic organelle that organizes and constructs massive molecular machines to coordinate diverse cellular processes. Due to its many roles during both interphase and mitosis, maintaining centrosome homeostasis is essential to normal health and development. Centrosome instability, divergence from normal centrosome number and structure, is a common pathognomonic cellular state tightly associated with cancers and other genetic diseases. As novel connections are investigated linking the centrosome to disease, it is critical to understand the breadth of centrosome functions to inspire discovery. In this review, we provide an introduction to normal centrosome function and highlight recent discoveries that link centrosome instability to specific disease states.

MTHFR Knockdown Assists Cell Defense against Folate Depletion Induced Chromosome Segregation and Uracil Misincorporation in DNA

Folate depletion causes chromosomal instability by increasing DNA strand breakage, uracil misincorporation, and defective repair. Folate mediated one-carbon metabolism has been suggested to play a key role in the carcinogenesis and progression of hepatocellular carcinoma (HCC) through influencing DNA integrity. Methylenetetrahydrofolate reductase (MTHFR) is the enzyme catalyzing the irreversible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate that can control folate cofactor distributions and modulate the partitioning of intracellular one-carbon moieties. The association between MTHFR polymorphisms and HCC risk is inconsistent and remains controversial in populational studies. We aimed to establish an in vitro cell model of liver origin to elucidate the interactions between MTHFR function, folate status, and chromosome stability. In the present study, we (1) examined MTHFR expression in HCC patients; (2) established cell models of liver origin with stabilized inhibition of MTHFR using small hairpin RNA delivered by a lentiviral vector, and (3) investigated the impacts of reduced MTHFR and folate status on cell cycle, methyl group homeostasis, nucleotide biosynthesis, and DNA stability, all of which are pathways involved in DNA integrity and repair and are critical in human tumorigenesis. By analyzing the TCGA/GTEx datasets available within GEPIA2, we discovered that HCC cancer patients with higher MTHFR had a worse survival rate. The shRNA of MTHFR (shMTHFR) resulted in decreased MTHFR gene expression, MTHFR protein, and enzymatic activity in human hepatoma cell HepG2. shMTHFR tended to decrease intracellular S-adenosylmethionine (SAM) contents but folate depletion similarly decreased SAM in wildtype (WT), negative control (Neg), and shMTHFR cells, indicating that in cells of liver origin, shMTHFR does not exacerbate the methyl group supply in folate depletion. shMTHFR caused cell accumulations in the G2/M, and cell population in the G2/M was inversely correlated with MTHFR gene level (r = −0.81, p < 0.0001), MTHFR protein expression (r = −0.8; p = 0.01), and MTHFR enzyme activity (r = −0.842; p = 0.005). Folate depletion resulted in G2/M cell cycle arrest in WT and Neg but not in shMTHFR cells, indicating that shMTHFR does not exacerbate folate depletion-induced G2/M cell cycle arrest. In addition, shMTHFR promoted the expression and translocation of nuclei thymidine synthetic enzyme complex SHMT1/DHFR/TYMS and assisted folate-dependent de novo nucleotide biosynthesis under folate restriction. Finally, shMTHFR promoted nuclear MLH1/p53 expression under folate deficiency and further reduced micronuclei formation and DNA uracil misincorporation under folate deficiency. In conclusion, shMTHFR in HepG2 induces cell cycle arrest in G2/M that may promote nucleotide supply and assist cell defense against folate depletion-induced chromosome segregation and uracil misincorporation in the DNA. This study provided insight into the significant impact of MTHFR function on chromosome stability of hepatic tissues. Data from the present study may shed light on the potential regulatory mechanism by which MTHFR modulates the risk for hepatic malignancies.

Cytokinesis regulators as potential diagnostic and therapeutic biomarkers for human hepatocellular carcinoma

Cytokinesis, the final step of mitosis, is critical for maintaining the ploidy level of cells. Cytokinesis is a complex, highly regulated process and its failure can lead to genetic instability and apoptosis, contributing to the development of cancer. Human hepatocellular carcinoma is often accompanied by a high frequency of aneuploidy and the DNA ploidy pattern observed in human hepatocellular carcinoma results mostly from impairments in cytokinesis. Many key regulators of cytokinesis are abnormally expressed in human hepatocellular carcinoma, and their expression levels are often correlated with patient prognosis. Moreover, preclinical studies have demonstrated that the inhibition of key cytokinesis regulators can suppress the growth of human hepatocellular carcinoma. Here, we provide an overview of the current understanding of the signaling networks regulating cytokinesis, the key cytokinesis regulators involved in the initiation and development of human hepatocellular carcinoma, and their applications as potential diagnostic and therapeutic biomarkers.

The function of a heterozygous p53 mutation in a Li-Fraumeni syndrome patient

p53 is one of the most extensively studied proteins in cancer research. Mutations in p53 generally abolish normal p53 function, and some mutants can gain new oncogenic functions. However, the mechanisms underlying p53 mutation-driven cancer remains to be elucidated. Our study investigated the function of a heterozygous p53 mutation (p.Asn268Glufs*4) in a Li-Fraumeni syndrome (LFS) patient. We used episomal technology to perform somatic reprogramming, and used molecular and cell biology methods to determine the p53 mutation levels in patient-originated induced pluripotent stem (iPS) cells at the RNA and protein levels. We found that p53 protein expression was not increased in this patient’s somatic cells compared with those of a healthy control. p53 mutation facilitates the proliferation of tumor cells by inhibiting apoptosis and promoting cell division. It can inhibit the efficiency of somatic reprogramming by inhibiting OCT4 expression during reprogramming stage. Moreover, not all p53 mutant iPS cell lines have mutant p53 RNA sequences. A small percentage of mutant p53 mRNA is present in the somatic cells from the patient and his mother. In summary, this p53 mutation can promote tumor cell proliferation, inhibit somatic reprogramming, and exhibit random p53 allelic expression of heterozygous mutations in the patient and iPS cells which may be one of the reasons why the people with p53 mutations develop cancer at random. This finding suggested that mutant p53 allelic expression should be added to the risk forecasting of cancer.

Inhibition of Apoptosis Reduces Diploidization of Haploid Mouse Embryonic Stem Cells during Differentiation

Phenotypes of haploid embryonic stem cells (haESCs) are dominant for recessive traits in mice. However, one major obstacle to their use is self-diploidization in daily culture. Although haESCs maintain haploidy well by deleting p53, whether they can sustain haploidy in differentiated status and the mechanism behind it remain unknown. To address this, we induced p53-deficient haESCs into multiple differentiated lineages maintain haploid status in vitro. Haploid cells also remained in chimeric embryos and teratomas arising from p53-null haESCs. Transcriptome analysis revealed that apoptosis genes were downregulated in p53-null haESCs compared with that in wild-type haESCs. Finally, we knocked out p73, another apoptosis-related gene, and observed stabilization of haploidy in haESCs. These results indicated that the main mechanism of diploidization was apoptosis-related gene-triggered cell death in haploid cell cultures. Thus, we can derive haploid somatic cells by manipulating the apoptosis gene, facilitating genetic screens of lineage-specific development.

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haEpiLCs and haNSCLCs differentiated from p53-null haESCs in vitro

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p53-null haESCs contributed to chimeric embryos and teratoma

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Downregulation of apoptosis genes resulted in haploidy stabilization

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Deletion of p73 was also of benefit for haploidy sustenance

Derivation of Haploid Trophoblast Stem Cells via Conversion In Vitro

Owing to their single genome, haploid cells are powerful to uncover unknown genes by performing genetic screening in mammals. However, no haploid cell line from an extraembryonic lineage has been achieved yet, which limits the application of haploid cells in placental genetic screening. Here, we show that overexpression of Cdx2 can convert haploid embryonic stem cells to trophoblast stem cells (TSCs). p53 deletion reduces diploidization during the conversion and guarantees the generation of haploid-induced TSCs (haiTSCs). haiTSCs not only share the same molecular characterization with trophoderm-derived TSCs but also possess multipotency to placental lineages in various procedures. In addition, haiTSCs can maintain haploidy in the long term, assisted by periodic sorting and with reliance on FGF4 and heparin. Finally, we perform piggyBac-mediated high-throughput mutation in haiTSCs and use them in trophoblast lineage genetic screening. Deep sequencing analysis and validation experiments prove that Htra1 is a blocker for spongiotrophoblast specification.

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A haploid cell line of extraembryonic lineages with self-renewal ability

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haiTSCs have multipotency to functional trophoblast lineages both in vitro and in vivo

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High-throughput screening of spongiotrophoblast specification-related genes in haiTSCs

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Htra1 is a blocker for spongiotrophoblast-specific differentiation

Establishment of TP53-knockout canine cells using optimized CRIPSR/Cas9 vector system for canine cancer research

Background

Genetic engineering technology such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system provides a powerful tool for developing disease models and determining gene functions. Recent interests in canine cancer models have highlighted the necessity of developing genetic engineering tools for dogs. In this study, we attempted to generate optimized CRISPR/Cas9 system to target canine tumor protein 53 (TP53), one of the most crucial tumor suppressor genes, to establish TP53 knockout canine cells for canine cancer research.

Results

We constructed CRISPR/Cas9 vectors using each of three TP53 gene-targeting guide RNAs (gRNAs) with minimal off-target potential. After transfection, we obtained several clones of TP53 knockout cells containing “indel” mutations in the targeted locus which had infinite cellular life span, resistance to genotoxicity, and unstable genomic status in contrast to normal cells. Of the established TP53 knockout cells, TP53KO#30 cells targeted by TP53 gRNA #30 showed non-cancerous phenotypes without oncogenic activation both in vitro and in vivo. More importantly, no off-target alteration was detected in TP53KO#30 cells. We also tested the developmental capacity of TP53 knockout cells after application of the somatic cell nuclear transfer technique.

Conclusions

Our results indicated that TP53 in canine cells was effectively and specifically targeted by our CRISPR/Cas9 system. Thus, we suggest our CRISPR/Cas9-derived canine TP53 knockout cells as a useful platform to reveal novel oncogenic functions and effects of developing anti-cancer therapeutics.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0491-5) contains supplementary material, which is available to authorized users.

Cytokinesis defects and cancer

Whole-genome and centrosome duplication as a consequence of cytokinesis failure can drive tumorigenesis in experimental model systems. However, whether cytokinesis failure is in fact an important cause of human cancers has remained unclear. In this Review, we summarize evidence that whole-genome-doubling events are frequently observed in human cancers and discuss the contribution that cytokinesis defects can make to tumorigenesis. We provide an overview of the potential causes of cytokinesis failure and discuss how tetraploid cells that are generated through cytokinesis defects are used in cancer as a transitory state on the route to aneuploidy. Finally, we discuss how cytokinesis defects can facilitate genetic diversification within the tumour to promote cancer development and could constitute the path of least resistance in tumour evolution.

Activation of the apoptotic pathway during prolonged prometaphase blocks daughter cell proliferation

When untransformed human cells spend >1.5 h in prometaphase under standard culture conditions, all daughters arrest in G1 despite normal division of their mothers. We investigate what happens during prolonged prometaphase that leads to daughter cell arrest in the absence of DNA damage. We find that progressive loss of anti-apoptotic MCL-1 activity and oxidative stress act in concert to partially activate the apoptosis pathway, resulting in the delayed death of some daughters and senescence for the rest. At physiological oxygen levels, longer prometaphase durations are needed for all daughters to arrest. Partial activation of apoptosis during prolonged prometaphase leads to persistent caspase activity, which activates the kinase cascade mediating the post–mitotic activation of p38. This in turn activates p53, and the consequent expression of p21stops the cell cycle. This mechanism can prevent cells suffering intractable mitotic defects, which modestly prolong mitosis but allow its completion without DNA damage, from producing future cell generations that are susceptible to the evolution of a transformed phenotype.

Generation of Immortalised But Unstable Cells after hTERT Introduction in Telomere-Compromised and p53-Deficient vHMECs

Telomeres, the natural ends of chromosomes, hide the linear telomeric DNA from constitutive exposure to the DNA damage response with a lariat structure or t-loop. Progressive telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in t-loop collapse and unmasked telomeres. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptosis, but they can also promote tumour initiation when cell cycle checkpoints are disabled. In this setting, telomere dysfunction promotes increasing chromosome instability (CIN) through breakage-fusion-bridge cycles. Excessive instability may hamper cell proliferation but might allow for the appearance of some rare advantageous mutations that could be selected and ultimately favour neoplastic progression. With the aim of generating pre-malignant immortalised cells, we ectopically expressed telomerase in telomere-compromised variant human mammary epithelial cells (vHMECs), proficient and deficient for p53, and analysed structural and numerical chromosomal aberrations as well as abnormal nuclear morphologies. Importantly, this study provides evidence that while immortalisation of vHMECs at early stages results in an almost stable karyotype, a transient telomere-dependent CIN period—aggravated by p53 deficiency—and followed by hTERT overexpression serves as a mechanism for the generation of immortal unstable cells which, due to their evolving karyotype, could attain additional promoting properties permissive to malignancy.

Inhibition of histone deacetylases induces formation of multipolar spindles and subsequent p53-dependent apoptosis in nasopharyngeal carcinoma cells

Histone deacetylases (HDACs) play crucial roles in the initiation and progression of cancer, offering a promising target for cancer therapy. HDACs inhibitor MGCD0103 (MGCD) exhibits effective anti-tumor activity by blocking proliferation and inducing cell death in malignant cells. However, the molecular mechanisms of HDACs inhibition induces cell death have not been well elucidated. In this study, we showed that MGCD effectively restored histone acetylation, suppressed cell growth and induced apoptosis in two-dimensional (2D) and three-dimensional (3D) cultured CNE1 and CNE2 nasopharyngeal carcinoma (NPC) cells. Importantly, MGCD arrested cell cycle at mitosis (M) phase with formation of multipolar spindles, which was associated with activated p53-mediated postmitotic checkpoint pathway to induce apoptotic cell death. Moreover, MGCD-induced apoptosis was decreased by inhibition of p53 using short interfering RNA (siRNA), suggesting that p53 was required for MGCD-induced cell apoptosis. Consistently, MGCD in combination with Nutlin-3, a MDM2 inhibitor showed synergistic effect on inducing apoptosis in 2D and 3D cultured CNE2 cells. Collectively, our data revealed that MGCD induced p53-dependent cell apoptosis following formation of multipolar spindles in NPC cells, suggesting the therapeutic potential of combinations of HDACs and MDM2 inhibitors for NPC treatment.

Tea polyphenols for the prevention of UVB-induced skin cancer

Skin cancer is the most common type of cancer with increasing incidence rate and public health burden. Solar ultraviolet (UV) radiation causes an array of damaging cellular and molecular events that eventually lead to the development of skin cancer. Despite increased awareness about sun protection, the exposure rate remains high with less than 15% of men and 30% of women using sunscreen on a regular basis. Therefore, there is an imperative need for the development of novel preventive approaches. Skin cancer chemoprevention using phytochemicals either as dietary supplements or by topical applications has gained considerable attention due to their low toxicity, availability, and anticarcinogenic properties. Tea, the second most commonly consumed beverage in the world, is a rich source of promising phytochemicals known as polyphenols. In this review, we discuss the findings of various in vitro, in vivo and human studies signifying the chemopreventive effects of tea polyphenols against UVB-induced skin cancer. This is accomplished by exploring the role of tea polyphenols in DNA repair, inflammation, oxidative stress, signaling pathways, and epigenetics. Finally, this review discusses a variety of innovative delivery methods that enhance the photochemopreventive effects of tea polyphenols against skin cancer.

A p53-dependent response limits the viability of mammalian haploid cells

The recent development of haploid cell lines has facilitated forward genetic screenings in mammalian cells. These lines include near-haploid human cell lines isolated from a patient with chronic myelogenous leukemia (KBM7 and HAP1), as well as haploid embryonic stem cells derived from several organisms. In all cases, haploidy was shown to be an unstable state, so that cultures of mammalian haploid cells rapidly become enriched in diploids. Here we show that the observed diploidization is due to a proliferative disadvantage of haploid cells compared with diploid cells. Accordingly, single-cell-sorted haploid mammalian cells maintain the haploid state for prolonged periods, owing to the absence of competing diploids. Although the duration of interphase is similar in haploid and diploid cells, haploid cells spend longer in mitosis, indicative of problems in chromosome segregation. In agreement with this, a substantial proportion of the haploids die at or shortly after the last mitosis through activation of a p53-dependent cytotoxic response. Finally, we show that p53 deletion stabilizes haploidy in human HAP1 cells and haploid mouse embryonic stem cells. We propose that, similar to aneuploidy or tetraploidy, haploidy triggers a p53-dependent response that limits the fitness of mammalian cells.

Common Molecular Subtypes Among Asian Hepatocellular Carcinoma and Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) and hepatocellular carcinoma (HCC) are clinically disparate primary liver cancers with etiological and biological heterogeneity. We identified common molecular subtypes linked to similar prognosis among 199 Thai ICC and HCC patients through systems integration of genomics, transcriptomics, and metabolomics. While ICC and HCC share recurrently mutated genes, including TP53, ARID1A, and ARID2, mitotic checkpoint anomalies distinguish the C1 subtype with key drivers PLK1 and ECT2, whereas the C2 subtype is linked to obesity, T cell infiltration, and bile acid metabolism. These molecular subtypes are found in 582 Asian, but less so in 265 Caucasian patients. Thus, Asian ICC and HCC, while clinically treated as separate entities, share common molecular subtypes with similar actionable drivers to improve precision therapy.

Mutant p53 Protein and the Hippo Transducers YAP and TAZ: A Critical Oncogenic Node in Human Cancers

p53 protein is a well-known tumor suppressor factor that regulates cellular homeostasis. As it has several and key functions exerted, p53 is known as “the guardian of the genome” and either loss of function or gain of function mutations in the TP53 coding protein sequence are involved in cancer onset and progression. The Hippo pathway is a key regulator of developmental and regenerative physiological processes but if deregulated can induce cell transformation and cancer progression. The p53 and Hippo pathways exert a plethora of fine-tuned functions that can apparently be in contrast with each other. In this review, we propose that the p53 status can affect the Hippo pathway function by switching its outputs from tumor suppressor to oncogenic activities. In detail, we discuss: (a) the oncogenic role of the protein complex mutant p53/YAP; (b) TAZ oncogenic activation mediated by mutant p53; (c) the therapeutic potential of targeting mutant p53 to impair YAP and TAZ oncogenic functions in human cancers.

Phytochemicals for the Prevention of Photocarcinogenesis

Ultraviolet (UV) exposure has an array of damaging effects and is the main cause of skin cancer in humans. Nonmelanoma skin cancer (NMSC), including basal cell carcinoma and squamous cell carcinoma, is the most common type of cancer. Incidence of NMSC has increased due to greater UV radiation, increased life expectancy and other changes in lifestyle; the annual cost of skin cancer treatment in the United States has increased concurrently to around eight billion dollars. Because of these trends, novel approaches to skin cancer prevention have become an important area of research to decrease skin cancer morbidity and defray the costs associated with treatment. Chemoprevention aims to prevent or delay the development of skin cancer through the use of phytochemicals. Use of phytochemicals as chemopreventive agents has gained attention due to their low toxicity and anticarcinogenic properties. Phytochemicals also exhibit antioxidant, anti-inflammatory and antiproliferative effects which support their use as chemopreventive agents, particularly for skin cancer. Preclinical and human studies have shown that phytochemicals decrease UV-induced skin damage and photocarcinogenesis. In this review article, we discuss the selected phytochemicals that may prevent or delay UV-induced carcinogenesis and highlight their potential use for skin protection.

Links between DNA Replication, Stem Cells and Cancer

Cancers can be categorized into two groups: those whose frequency increases with age, and those resulting from errors during mammalian development. The first group is linked to DNA replication through the accumulation of genetic mutations that occur during proliferation of developmentally acquired stem cells that give rise to and maintain tissues and organs. These mutations, which result from DNA replication errors as well as environmental insults, fall into two categories; cancer driver mutations that initiate carcinogenesis and genome destabilizing mutations that promote aneuploidy through excess genome duplication and chromatid missegregation. Increased genome instability results in accelerated clonal evolution leading to the appearance of more aggressive clones with increased drug resistance. The second group of cancers, termed germ cell neoplasia, results from the mislocation of pluripotent stem cells during early development. During normal development, pluripotent stem cells that originate in early embryos give rise to all of the cell lineages in the embryo and adult, but when they mislocate to ectopic sites, they produce tumors. Remarkably, pluripotent stem cells, like many cancer cells, depend on the Geminin protein to prevent excess DNA replication from triggering DNA damage-dependent apoptosis. This link between the control of DNA replication during early development and germ cell neoplasia reveals Geminin as a potential chemotherapeutic target in the eradication of cancer progenitor cells.

An Observed Effect of p53 Status on the Bystander Response to Radiation-Induced Cellular Photon Emission

In this study, we investigated the potential influence of p53 on ultraviolet (UV) signal generation and response of bystander cells to the UV signals generated by beta-irradiated cells. Five cell lines of various p53 status (HaCaT, mutated; SW48, wild-type; HT29, mutated; HCT116^+/+, wild-type; HCT116^-/-, null) were irradiated with beta particles from tritium. Signal generation (photon emission at 340 ± 5 nm) was quantified from irradiated cells using a photomultiplier tube. Bystander response (clonogenic survival) was assessed by placing reporter cell flasks directly superior to irradiated signal-emitting cells. All cell lines emitted significant quantities of UV after tritium exposure. The magnitudes of HaCaT and HT29 photon emission at 340 nm were similar to each other while they were significantly different from the stronger signals emitted from SW48, HCT116^+/+ and HCT116^-/- cells. In regard to the bystander responses, HaCaT, HCT116^+/+ and SW48 cells demonstrated significant reductions in survival as a result of exposure to emission signals. HCT116^-/- and HT29 cells did not exhibit any changes in survival and thus were considered to be lacking the mechanisms or functions required to elicit a response. The survival response was found not to correlate with the observed signal strength for all experimental permutations; this may be attributed to varying emission spectra from cell line to cell line or differences in response sensitivity. Overall, these results suggest that the UV-mediated bystander response is influenced by the p53 status of the cell line. Wild-type p53 cells (HCT116^+/+ and SW48) demonstrated significant responses to UV signals whereas the p53-null cell line (HCT116^-/-) lacked any response. The two mutated p53 cell lines exhibited contrasting responses, which may be explained by unique modulation of functions by different point mutations. The reduced response (cell death) exhibited by p53-mutated cells compared to p53 wild-type cells suggests a possible role of the assessed p53 mutations in radiation-induced cancer susceptibility and reduced efficacy of radiation-directed therapy.

p38 MAPK-induced MDM2 degradation confers paclitaxel resistance through p53-mediated regulation of EGFR in human lung cancer cells

Paclitaxel (PTX) is a chemotherapeutic agent that is used to treat a variety of cancers, including non-small cell lung cancer (NSCLC). However, the emergence of drug resistance limits the utility of PTX. This study determined the signaling pathway that contributes to PTX resistance. We first established PTX resistant cell lines (H460/R and 226B/R) using a dose-escalating maintenance of PTX. We found that p38 MAPK and epidermal growth factor receptor (EGFR) were constitutively activated in these cell lines. The inhibition of p38 MAPK activity by SB203580 treatment or the transfection of dominant-negative p38 MAPK sensitized both cell lines to PTX treatment. Erlotinib, an EGFR inhibitor, also increased PTX-induced apoptosis in PTX resistant cells, which suggests a role for p38 MAPK and EGFR in the development of PTX resistance. We demonstrated that p38 MAPK enhanced EGFR expression via the induction of the rapid degradation of mouse double-minute 2 homolog (MDM2) and the consequent stabilization of p53, a transcription factor of EGFR. These results suggest for the first time that the p38 MAPK/p53/EGFR axis is crucial for the facilitation of PTX resistance in NSCLCs. We also propose a mechanism for the role of the tumor-suppressor p53 in drug resistance. These results provide a foundation for the future development of potential therapeutic strategies to regulate the p38 MAPK/p53/EGFR pathway for the treatment of lung cancer patients with PTX resistance.

Review : p53 in the pathogenesis, diagnosis, and treatment of cancer

Objective. The cellular functions of p53, the conse quences of the loss of p53 function, and the potential impact of p53 in oncology are reviewed within the framework of an overview of the molecular basis of cancer and cell cycle control.

Data Sources. A MEDLINE search of articles from 1976 to the present was conducted using the terms p53 protein and p53 gene. The search was restricted to the English language. Oncology and molecular biology textbooks were used as additional references.

Data Extraction. We reviewed the literature to discuss the cellular function of p53, the mechanisms of p53 inactivation, the cellular consequences of the loss of p53 function, the role of p53 loss in tumori genesis, and the potential applications of this knowl edge.

Data Synthesis. p53 mutations are found in ~ 50% of human cancers. Knowledge of p53 functions and defects provides the basis for potential applica tions in the areas of cancer epidemiology, cancer diagnosis, and determination of prognosis. An under standing of the functions and defects of p53 also presents a host of opportunities for the design of novel cancer therapies. Therapeutic approaches be ing studied include the restoration of p53 by gene therapy, the alteration of mutant p53 expression by antisense therapy, and the use of p53 mutations as a target for directing therapy to cancer cells; some of these approaches are already under phase I investiga tion. As knowledge of p53 unfolds, additional thera peutic approaches will certainly be developed. The story of p53 illustrates that the manipulation of mo lecular interactions is a new frontier in therapeutics and offers an additional role for oncology pharmacy specialists.

Genome Stability Requires p53

It is now clear that functional p53 is critical to protect the genome from alterations that lead to tumorigenesis. However, with the myriad of cellular stresses and pathways linked to p53 activation, much remains unknown about how p53 maintains genome stability and the proteins involved. The current understanding of the multiple ways p53 contributes to genome stability and how two of its negative regulators, Mdm2 and Mdmx, induce genome instability will be described.

The Cell-Cycle Arrest and Apoptotic Functions of p53 in Tumor Initiation and Progression

P53 is a transcription factor highly inducible by many stress signals such as DNA damage, oncogene activation, and nutrient deprivation. Cell-cycle arrest and apoptosis are the most prominent outcomes of p53 activation. Many studies showed that p53 cell-cycle and apoptosis functions are important for preventing tumor development. p53 also regulates many cellular processes including metabolism, antioxidant response, and DNA repair. Emerging evidence suggests that these noncanonical p53 activities may also have potent antitumor effects within certain context. This review focuses on the cell-cycle arrest and apoptosis functions of p53, their roles in tumor suppression, and the regulation of cell fate decision after p53 activation.

Minimal residual disease in cancer therapy--Small things make all the difference

Minimal residual disease (MRD) is a major hurdle in the eradication of malignant tumors. Despite the high sensitivity of various cancers to treatment, some residual cancer cells persist and lead to tumor recurrence and treatment failure. Obvious reasons for residual disease include mechanisms of secondary therapy resistance, such as the presence of mutant cells that are insensitive to the drugs, or the presence of cells that become drug resistant due to activation of survival pathways. In addition to such unambiguous resistance modalities, several patients with relapsing tumors do not show refractory disease and respond again when the initial therapy is repeated. These cases cannot be explained by the selection of mutant tumor cells, and the precise mechanisms underlying this clinical drug resistance are ill-defined. In the current review, we put special emphasis on cell-intrinsic and -extrinsic mechanisms that may explain mechanisms of MRD that are independent of secondary therapy resistance. In particular, we show that studying genetically engineered mouse models (GEMMs), which highly resemble the disease in humans, provides a complementary approach to understand MRD. In these animal models, specific mechanisms of secondary resistance can be excluded by targeted genetic modifications. This allows a clear distinction between the selection of cells with stable secondary resistance and mechanisms that result in the survival of residual cells but do not provoke secondary drug resistance. Mechanisms that may explain the latter feature include special biochemical defense properties of cancer stem cells, metabolic peculiarities such as the dependence on autophagy, drug-tolerant persisting cells, intratumoral heterogeneity, secreted factors from the microenvironment, tumor vascularization patterns and immunosurveillance-related factors. We propose in the current review that a common feature of these various mechanisms is cancer cell dormancy. Therefore, dormant cancer cells appear to be an important target in the attempt to eradicate residual cancer cells, and eventually cure patients who repeatedly respond to anticancer therapy but lack complete tumor eradication.

p53 checkpoint ablation exacerbates the phenotype of Hinfp dependent histone H4 deficiency

Histone Nuclear Factor P (HINFP) is essential for expression of histone H4 genes. Ablation of Hinfp and consequential depletion of histones alter nucleosome spacing and cause stalled replication and DNA damage that ultimately result in genomic instability. Faithful replication and packaging of newly replicated DNA are required for normal cell cycle control and proliferation. The tumor suppressor protein p53, the guardian of the genome, controls multiple cell cycle checkpoints and its loss leads to cellular transformation. Here we addressed whether the absence of p53 impacts the outcomes/consequences of Hinfp-mediated histone H4 deficiency. We examined mouse embryonic fibroblasts lacking both Hinfp and p53. Our data revealed that the reduced histone H4 expression caused by depletion of Hinfp persists when p53 is also inactivated. Loss of p53 enhanced the abnormalities in nuclear shape and size (i.e. multi-lobed irregularly shaped nuclei) caused by Hinfp depletion and also altered the sub-nuclear organization of Histone Locus Bodies (HLBs). In addition to the polyploid phenotype resulting from deletion of either p53 or Hinfp, inactivation of both p53 and Hinfp increased mitotic defects and generated chromosomal fragility and susceptibility to DNA damage. Thus, our study conclusively establishes that simultaneous loss of both Hinfp and the p53 checkpoint is detrimental to normal cell growth and may predispose to cellular transformation.

Activity of Andrographolide and Its Derivatives on HPV16 Pseudovirus Infection and Viral Oncogene Expression in Cervical Carcinoma Cells

Andrographolide (Androg) has been reported to contain antiviral and antitumor activities, but the effects of Androg on human papillomavirus (HPV) infection and cervical cancer have not been elucidated. This study investigated the effects of Androg and its derivatives, namely, 14-deoxy-11,12-didehydroandrographolide (14-DDA) and 3,19-isopropylidene andrographolide (IPAD), on HPV16 pseudovirus (HPV16PsV) infectivity, HPV16 E6 oncogene expression and cervical cancer cell apoptosis. The result demonstrated that all compounds inhibited HPV16PsV infection and that 14-DDA showed the highest potency. Only Androg suppressed long control region (LCR) transcription activity of HPV16 in transiently transfected C33A cells and significantly inhibited E6 oncogene expression in SiHa cells in a dose-dependent manner. A twofold subcytotoxic concentration of IPAD exhibited an inhibitory effect on E6 oncogene expression at 48-h posttreatment. Interestingly, p53 protein was restored in a downstream process and was detected earlier by IPAD treatment than by Androg treatment. This result corresponded to the level of cell apoptosis and cell cycle arrest at the G2/M phase. E6 oncogene expression was also suppressed in CaSki cells treated with Androg and IPAD leading to cell apoptosis. These findings imply that Androg and its derivatives have different activities and may be effective agents for HPV prevention and cervical cancer treatment.

Mechanisms of Photoaging and Cutaneous Photocarcinogenesis, and Photoprotective Strategies with Phytochemicals

Photoaging and photocarcinogenesis are primarily due to solar ultraviolet (UV) radiation, which alters DNA, cellular antioxidant balance, signal transduction pathways, immunology, and the extracellular matrix (ECM). The DNA alterations include UV radiation induced thymine-thymine dimers and loss of tumor suppressor gene p53. UV radiation reduces cellular antioxidant status by generating reactive oxygen species (ROS), and the resultant oxidative stress alters signal transduction pathways such as the mitogen-activated protein kinase (MAPK), the nuclear factor-kappa beta (NF-κB)/p65, the janus kinase (JAK), signal transduction and activation of transcription (STAT) and the nuclear factor erythroid 2-related factor 2 (Nrf2). UV radiation induces pro-inflammatory genes and causes immunosuppression by depleting the number and activity of the epidermal Langerhans cells. Further, UV radiation remodels the ECM by increasing matrixmetalloproteinases (MMP) and reducing structural collagen and elastin. The photoprotective strategies to prevent/treat photoaging and photocarcinogenesis include oral or topical agents that act as sunscreens or counteract the effects of UV radiation on DNA, cellular antioxidant balance, signal transduction pathways, immunology and the ECM. Many of these agents are phytochemical derivatives and include polyphenols and non-polyphenols. The flavonoids are polyphenols and include catechins, isoflavones, proanthocyanidins, and anthocyanins, whereas the non-flavonoids comprise mono phenolic acids and stilbenes. The natural sources of polyphenols include tea, cocoa, grape/wine, soy, pomegranate, and Polypodium leucotomos. The non-phenolic phytochemicals include carotenoids, caffeine and sulphoraphance (SFN). In addition, there are other phytochemical derivatives or whole extracts such as baicalin, flavangenol, raspberry extract, and Photomorphe umbellata with photoprotective activity against UVB radiation, and thereby carcinogenesis.

MDM4 overexpressed in acute myeloid leukemia patients with complex karyotype and wild-type TP53

Acute myeloid leukemia patients with complex karyotype (CK-AML) account for approximately 10–15% of adult AML cases, and are often associated with a poor prognosis. Except for about 70% of CK-AML patients with biallelic inactivation of TP53, the leukemogenic mechanism in the nearly 30% of CK-AML patients with wild-type TP53 has remained elusive. In this study, 15 cases with complex karyotype and wild-type TP53 were screened out of 140 de novo AML patients and the expression levels of MDM4, a main negative regulator of p53-signaling pathway, were detected. We ruled out mutations in genes associated with a poor prognosis of CK-AML, including RUNX1 or FLT3-ITD. The mRNA expression levels of the full-length of MDM4 (MDM4FL) and short isoform MDM4 (MDM4S) were elevated in CK-AML relative to normal karyotype AML (NK-AML) patients. We also explored the impact of MDM4 overexpression on the cell cycle, cell proliferation and the spindle checkpoint of HepG2 cells, which is a human cancer cell line with normal MDM4 and TP53 expression. The mitotic index and the expression of p21, BubR1 and Securin were all reduced following Nocodazole treatment. Moreover, karyotype analysis showed that MDM4 overexpression might lead to aneuploidy or polyploidy. These results suggest that MDM4 overexpression is related to CK-AML with wild-type TP53 and might play a pathogenic role by inhibiting p53-signal pathway.

Induction of giant cells by the synthetic food colorants viz. lemon yellow and orange red

Cytotoxicity and giant cell formation induced by lemon yellow and orange red synthetic food colorants were evaluated in the present study. The aqueous solutions of both the dye solutions were tested for cytotoxicity using Allium cepa assay. Frequency of giant cells were determined after treating the root tips with different concentrations of both food colorant solutions viz., 0.005, 0.01, 0.05, 0.1 % for varying time durations (1/2, 1, 2, 3 h). These colorants may cause giant cell formation primarily by interfering with the normal course of mitosis. Giant cells showing multiple aberrations viz. bridged and binucleate condition, cellular fragmentation, nuclear lesion, double and multiple nuclear lesions, double nuclear peaks and cellular breakage, elongated nucleus, nuclear budding, hyperchromasia, micronucleus, nuclear erosion, pulverized nucleus etc. were induced in root tips treated with both of the colorants. The synthetic food colorant treated cells showed inhibition of cell division and induction of giant cells. A dose dependant decrease in the mitotic index [88.20 % (c(-ve), 3h) to 81.54 % (Lx4, 3h) and 88.20 % (c(-ve), 3h) to 73.17 % (Ox4, 3h)] was observed. All mitotic phases show significant induction of giant cells when treated with both food colorants. Interphase stage shows higher percentage of giant cells, whereas in cytokinesis it was negligible. The orange red food colorant is observed to be more toxic because it recorded higher percentage of giant cell induction when compared with lemon yellow [27.93 % (Lx4, 3h) and 28.07 % (Ox4, 3h)].

Apc and p53 interaction in DNA damage and genomic instability in hepatocytes

Disruption of Apc within hepatocytes activates Wnt signaling, perturb differentiation and ultimately lead to neoplasia. Apc negatively regulates Wnt signaling but is also involved in organizing the cytoskeleton and may play a role in chromosome segregation. In vitro studies have implicated Apc in the control of genomic stability. However, the relevance of this data has been questioned in vivo as Apc is lost earlier than the onset of genomic instability. Here, we analyse the relationship between immediate loss of Apc and the acquisition of genomic instability in hepatocytes. We used Cre-lox technology to inactivate Apc and in combination with p53 in vivo, to define the consequences of gene loss upon cell-cycle regulation, proliferation, death and aneuploidy. We show that whilst Apc loss leads to increased proliferation, it also leads to increased apoptosis, the accumulation of p53, p21 and markers of DSBs and DNA repair. Flow cytometry revealed an increased 4N DNA content, consistent with a G2 arrest. Levels of anaphase bridges were also elevated, implicating failed chromosome segregation. This was accompanied by an increase in centrosome number which demonstrates a role for Apc in maintaining euploidy.

To address the role of p53 in these processes, we analyzed combined loss of Apc and p53, which led to a further increase in proliferation, cell death, DNA damages and repair and a bypass of G2 arrest than was observed with Apc loss. However we observed only a marginal effect on anaphase bridges and centrosome number which could be due to increased cell death. Our data therefore establishes, in an in vivo setting, that APC loss leads to a DNA damage signature and genomic instability in the liver and that additional loss of p53 leads to an increase in the DNA damage signal but not to an immediate increase in the genomic instability phenotype.

The ARF tumor suppressor prevents chromosomal instability and ensures mitotic checkpoint fidelity through regulation of Aurora B

The ARF tumor suppressor is best known for its role in stabilizing p53. This study identifies p53-independent functions of ARF in chromosome segregation and the mitotic checkpoint. Mitotic defects caused by loss of ARF are recapitulated by Aurora B overexpression and rescued by partial depletion of Aurora B.

The ARF tumor suppressor is part of the CDKN2A locus and is mutated or undetectable in numerous cancers. The best-characterized role for ARF is in stabilizing p53 in response to cellular stress. However, ARF has tumor suppressive functions outside this pathway that have not been fully defined. Primary mouse embryonic fibroblasts (MEFs) lacking the ARF tumor suppressor contain abnormal numbers of chromosomes. However, no role for ARF in cell division has previously been proposed. Here we demonstrate a novel, p53-independent role for ARF in the mitotic checkpoint. Consistent with this, loss of ARF results in aneuploidy in vitro and in vivo. ARF^−/− MEFs exhibit mitotic defects including misaligned and lagging chromosomes, multipolar spindles, and increased tetraploidy. ARF^−/− cells exhibit overexpression of Mad2, BubR1, and Aurora B, but only overexpression of Aurora B phenocopies mitotic defects observed in ARF^−/− MEFs. Restoring Aurora B to near-normal levels rescues mitotic phenotypes in cells lacking ARF. Our results define an unexpected role for ARF in chromosome segregation and mitotic checkpoint function. They further establish maintenance of chromosomal stability as one of the additional tumor-suppressive functions of ARF and offer a molecular explanation for the common up-regulation of Aurora B in human cancers.

Size Does Matter: Why Polyploid Tumor Cells are Critical Drug Targets in the War on Cancer

Tumor evolution presents a formidable obstacle that currently prevents the development of truly curative treatments for cancer. In this perspective, we advocate for the hypothesis that tumor cells with significantly elevated genomic content (polyploid tumor cells) facilitate rapid tumor evolution and the acquisition of therapy resistance in multiple incurable cancers. We appeal to studies conducted in yeast, cancer models, and cancer patients, which all converge on the hypothesis that polyploidy enables large phenotypic leaps, providing access to many different therapy-resistant phenotypes. We develop a flow-cytometry based method for quantifying the prevalence of polyploid tumor cells, and show the frequency of these cells in patient tumors may be higher than is generally appreciated. We then present recent studies identifying promising new therapeutic strategies that could be used to specifically target polyploid tumor cells in cancer patients. We argue that these therapeutic approaches should be incorporated into new treatment strategies aimed at blocking tumor evolution by killing the highly evolvable, therapy-resistant polyploid cell subpopulations, thus helping to maintain patient tumors in a drug sensitive state.

The p53-PUMA axis suppresses iPSC generation

Mechanisms underlying the reprogramming process of induced pluripotent stem cells remain poorly defined. Like tumorigenesis, generation of induced pluripotent stem cells was shown to be suppressed by the Trp53 (p53) pathway, at least in part via p21Cdkn1a (p21)-mediated cell cycle arrest. Here we examine the role of PUMA, a pro-apoptotic mediator of p53, during somatic reprogramming in comparison to p21 in the p53 pathway. Using mouse strains deficient in these molecules, we demonstrate that PUMA is an independent mediator of the negative effect of p53 on induced pluripotent stem cell induction. PUMA deficiency leads to a better survival rate associated with reduced DNA damage and fewer chromosomal aberrations in induced pluripotent stem cells, whereas loss of p21 or p53 results in an opposite outcome. Given these new findings, PUMA may serve as a distinct and more desirable target in the p53 pathway for induced pluripotent stem cell generation, thereby having important implications for potential therapeutic applications of induced pluripotent stem cells.

Prognostic biomarkers in renal cell carcinoma

A hallmark of renal cell carcinoma is its variable prognosis. Surgical resection of primary renal cell carcinoma can be curative when the disease is localized. However, approximately 20% of patients with early stages of localized renal cell carcinomas subsequently develop metastasis after the primary tumor is removed. The median survival for patients with metastatic disease is approximately 13 months. Therefore, there is a great need for biomarkers to predict metastasis and prognosis. Many prognostic biomarkers were studied in the past decade. In recent years, several promising biomarkers, including CAIX, B7-H1 and IMP3, have also been identified by large retrospective studies. Further validation of these biomarkers is essential to transfer the research data into clinical practice. Eventually, an outcome prediction model with biomarkers, staging system and other risk factors will identify high-risk patients with likelihood of progression and formulate different follow-up protocols or systematic treatments for these patients.

AMG 900, pan-Aurora kinase inhibitor, preferentially inhibits the proliferation of breast cancer cell lines with dysfunctional p53

Aurora kinases play important roles in cell division and are frequently overexpressed in human cancer. AMG 900 is a novel pan-Aurora kinase inhibitor currently being tested in Phase I clinical trials. We aimed to evaluate the in vitro activity of AMG 900 in a panel of 44 human breast cancer and immortalized cell lines and identify predictors of response. AMG 900 inhibited proliferation at low nanomolar concentrations in all cell lines tested. Response was further classified based on the induction of lethality. 25 cell lines were classified as highly sensitive (lethality at 10 nM of AMG 900 >10 %), 19 cell lines as less sensitive to AMG 900 (lethality at 10 nM of AMG 900 <10 %). Traditional molecular subtypes of breast cancer did not predict for this differential response. There was a weak association between AURKA amplification and response to AMG 900 (response ratio = 2.53, p = 0.09). mRNA expression levels of AURKA, AURKB, and AURKC and baseline protein levels of Aurora kinases A and B did not significantly associate with response. Cell lines with TP53 loss of function mutations (RR = 1.86, p = 0.004) and low baseline p21 protein levels (RR = 2.28, p = 0.0004) were far more likely to be classified as highly sensitive to AMG 900. AMG 900 induced p53 and p21 protein expression in cell lines with wt TP53. AMG 900 caused the accumulation of cells with >4 N DNA content in a majority of cell lines independently of sensitivity and p53 status. AMG 900 induced more pronounced apoptosis in highly sensitive p53-dysfunctional cell lines. We have found that AMG 900 is highly active in breast cancer cell lines and that TP53 loss of function mutations as well as low baseline expression of p21 protein predict strongly for increased sensitivity to this compound in vitro.

A Comparison of Signaling Activities Induced by Taxol and Desoxyepothilone B

Desoxyepothilone B (dEpoB), currently in clinical trials, is a novel microtubule inhibitor with similar mode-of-action to paclitaxel (Taxol). Intriguingly, it is effective in some cell lines and tumor xenografts refractory to Taxol. The purpose of this study is to compare signaling induced by the two drugs and identify a molecular basis for increased efficacy of dEpoB in resistant lines. The importance of ERK signaling, already established for Taxol, was shown for dEpoB and other G2-blocking agents. However, a role in differential sensitivity was not observed. Affymetrix analysis shows similar gene modulation by either agent, alone or in combination with MEK inhibitor. Differential sensitivity in a set of Taxol-resistant lines correlated to the expression of P-glycoprotein (P-gp), and its importance was demonstrated directly. These results suggest that Taxol and dEpoB elicit similar cell death pathways, and the increased efficacy of dEpoB in resistant tumor lines lies in differential susceptibility to P-gp.

Battle of the eternal rivals: restoring functional p53 and inhibiting Polo-like kinase 1 as cancer therapy

Polo-like kinase 1, a pivotal regulator of mitosis and cytokinesis, is highly expressed in a broad spectrum of tumors and its expression correlates often with poor prognosis, suggesting its potential as a therapeutic target. p53, the guardian of the genome, is the most important tumor suppressor. In this review, we address the intertwined relationship of these two key molecules by fighting each other as eternal rivals in many signaling pathways. p53 represses the promoter of Polo-like kinase 1, whereas Polo-like kinase 1 inhibits p53 and its family members p63 and p73 in cancer cells lacking functional p53. Plk1 inhibitors target all rapidly dividing cells irrespective of tumor cells or non-transformed normal but proliferating cells. Upon treatment with Plk1 inhibitors, p53 in tumor cells is activated and induces strong apoptosis, whereas tumor cells with inactive p53 arrest in mitosis with DNA damage. Thus, inactive p53 is not associated with a susceptible cytotoxicity of Polo-like kinase 1 inhibition and could rather foster the induction of polyploidy/aneuploidy in surviving cells. In addition, compared to the mono-treatment, combination of Polo-like kinase 1 inhibition with anti-mitotic or DNA damaging agents boosts more severe mitotic defects, effectually triggers apoptosis and strongly inhibits proliferation of cancer cells with functional p53. In this regard, restoration of p53 in tumor cells with loss or mutation of p53 will reinforce the cytotoxicity of combined Polo-like kinase 1 therapy and provide a proficient strategy for combating relapse and metastasis of cancer.

Sperm-associated antigen 4, a novel hypoxia-inducible factor 1 target, regulates cytokinesis, and its expression correlates with the prognosis of renal cell carcinoma

Hypoxia plays a crucial role in many pathophysiological conditions, including cancer biology, and hypoxia-inducible factor (HIF) regulates transcriptional responses under hypoxia. To elucidate the cellular responses to hypoxia, we performed chromatin immunoprecipitation with deep sequencing in combination with microarray analysis and identified HIF-1 targets. We focused on one of the novel targets, sperm-associated antigen 4 (SPAG4), whose function was unknown. SPAG4, an HIF-1-specific target, is up-regulated in various cultured cells under hypoxia. Examination of SPAG4 expression using a tissue microarray consisting of 190 human renal cell carcinoma (RCC) samples revealed that SPAG4 is an independent prognostic factor of cancer-specific mortality. Live-cell imaging revealed localization of SPAG4 at the intercellular bridge in telophase. We also studied cells in which SPAG4 was knocked down. Hypoxia enhances tetraploidy, which disturbs cell proliferation, and knockdown of SPAG4 increased tetraploid formation and decreased cell proliferation under both normoxic and hypoxic conditions. Studies using deletion mutants of SPAG4 also suggested the involvement of SPAG4 in cytokinesis. Microarray analysis confirmed dysregulation of cytokinesis-related genes by knockdown of SPAG4. In conclusion, SPAG4 is an independent prognostic factor in RCC and plays a crucial role in cytokinesis to defend against hypoxia-induced tetraploid formation. This defensive mechanism may promote survival of cancer cells under hypoxic conditions, thus leading to poor prognosis.