p21WAF1 and tumourigenesis: 20 years after. Curr Opin Oncol. 2013;25:52-58. [PMID: 23159848 DOI: 10.1097/cco.0b013e32835b639e]

Targeting DYRK1B suppresses the proliferation and migration of liposarcoma cells

Liposarcoma is a common subtype of soft tissue sarcoma and accounts for 20% of all sarcomas. Conventional chemotherapeutic agents have limited efficacy in liposarcoma patients. Expression and activation of serine/threonine-protein kinase dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1B (DYRK1B) is associated with growth and survival of many types of cancer cells. However, the role of DYRK1B in liposarcoma remains unknown. In this study, we investigated the functional and therapeutic relevance of DYRK1B in liposarcoma. Tissue microarray and immunohistochemistry analysis showed that higher expression levels of DYRK1B correlated with a worse prognosis. RNA interference-mediated knockdown of DYRK1B or targeting DYRK1B with the kinase inhibitor AZ191 inhibited liposarcoma cell growth, decreased cell motility, and induced apoptosis. Moreover, combined AZ191 with doxorubicin demonstrated an increased anti-cancer effect on liposarcoma cells. These findings suggest that DYRK1B is critical for the growth of liposarcoma cells. Targeting DYRK1B provides a new rationale for treatment of liposarcoma.

Development of a genetic sensor that eliminates p53 deficient cells

The TP53 gene fulfills a central role in protecting cells from genetic insult. Given this crucial role it might be surprising that p53 itself is not essential for cell survival. Indeed, TP53 is the single most mutated gene across different cancer types. Thus, both a theoretical and a question of significant practical applicability arise: can cells be programmed to make TP53 an essential gene? Here we present a genetic p53 sensor, in which the loss of p53 is coupled to the rise of HSV-TK expression. We show that the sensor can distinguish both p53 knockout and cells expressing a common TP53 cancer mutation from otherwise isogenic TP53 wild-type cells. Importantly, the system is sensitive enough to specifically target TP53 loss-of-function cells with the HSV-TK pro-drug Ganciclovir both in vitro and in vivo. Our work opens new ways to programming cell intrinsic transformation protection systems that rely on endogenous components.

TP53 is mutated in many cancers, a system to detect and selectively eliminate p53 mutant cells is an attractive therapeutic strategy. Here, the authors present a genetic sensor that can detect p53 activity and is coupled to the thymidine kinase gene, which can activate the drug Ganciclovir, resulting in cell death.

ADAM10 as a therapeutic target for brain diseases: from developmental disorders to Alzheimer's disease

INTRODUCTION

In the central nervous system a disintegrin and metalloproteinase 10 (ADAM10) controls several functions such as neurodevelopment, synaptic plasticity and dendritic spine morphology thanks to its activity towards a high number of substrates, including the synaptic cell adhesion molecules as the Amyloid Precursor Protein, N-cadherin, Notch and Ephrins. In particular, ADAM10 plays a key role in the modulation of the molecular mechanisms responsible for dendritic spine formation, maturation and stabilization and in the regulation of the molecular organization of the glutamatergic synapse. Consequently, an alteration of ADAM10 activity is strictly correlated to the onset of different types of synaptopathies, ranging from neurodevelopmental disorders, i.e. autism spectrum disorders, to neurodegenerative diseases, i.e. Alzheimer's Disease. Areas covered: We describe the most recent discoveries in understanding of the role of ADAM10 activity at the glutamatergic excitatory synapse and its involvement in the onset of neurodevelopmental and neurodegenerative disorders. Expert opinion: A progress in the understanding of the molecular mechanisms driving ADAM10 activity at synapses and its alterations in brain disorders is the first step before designing a specific drug able to modulate ADAM10 activity.

Downregulation of Pin1 in human atherosclerosis and its association with vascular smooth muscle cell senescence

OBJECTIVE

Pin1 is prevalently overexpressed in human cancers and implicated to regulate cell growth and apoptosis. Thus far, however, no role for Pin1 has been described in modulating vascular smooth muscle cell (VSMC) senescence.

METHODS

Immunohistochemistry and Western blotting were used to assess Pin1 protein level in human normal and atherosclerotic tissues. β-galactosidase staining, cumulative population doubling level, telomerase activity, and relative telomere length measurement were used to confirm VSMC senescence. The expressions of Pin1 and other genes involved in this research were analyzed by quantitative reverse-transcription polymerase chain reaction and Western blotting in VSMCs. Apolipoprotein E gene-deleted mice (ApoE^-/-) fed a high-fat diet were treated with juglone or 10% ethanol, respectively, for 3 weeks. The extent of atherosclerosis was evaluated by Oil Red O, Masson trichrome staining, and immunohistology.

RESULTS

Pin1 protein level decreased in human atherosclerotic tissues and VSMCs, synchronously with increased VSMC senescence. Adenoviral-mediated Pin1 overexpression rescued cellular senescence in atherosclerotic VSMCs, with concurrent down-regulation of P53, p21, growth arrest and DNA-damage-inducible protein 45-alpha (Gadd45a), phosphorylated retinoblastoma (p-pRb), p65 and upregulation of cyclin subfamilies (cyclin B, D, and E), and cyclin-dependent kinase subfamilies (2, 4, and 6), whereas Pin1 knockdown resulted in the converse effects, indicating that VSMC senescence mediated by Pin1 is an integrated response to diverse signals. In vivo data from ApoE^-/- mice showed that treatment of juglone led to accelerated atherosclerosis development.

CONCLUSIONS

Altogether this work supports a role for Pin1 as a vital modulator of VSMC senescence, thereby providing a novel target for regulation and control of atherosclerosis.

Trichostatin A induces bladder cancer cell death via intrinsic apoptosis at the early phase and Sp1‑survivin downregulation at the late phase of treatment

Histone deacetylase (HDAC) inhibitors have been widely shown to result in cancer cell death. The present study investigated the mechanisms underlying the antitumor effects of the phytochemical trichostatin A (TSA), a classic pan-HDAC inhibitor, in 5,637 urinary bladder cancer cells. It was found that TSA caused cell cycle arrest at the G2/M and G1 phase accompanied by reduced expression of cyclin D1 and upregulated induction of p21. In addition, TSA induced morphological changes, reduced cell viability and apoptotic cell death in 5,637 cells through caspase-3 activation followed by PARP cleavage. The loss of mitochondrial membrane potential (MMP) indicated that TSA induced apoptosis in 5,637 cells through the intrinsic mitochondrial pathway. TSA significantly suppressed Akt activity at 12 h after treatment, suggesting that the apoptosis in the early phase was mediated by Akt inhibition. In addition, the protein level of transcription factor Sp1 was decreased at 24 h after TSA treatment, which likely led to the downregulation of survivin gene expression, and then contributed to the antitumor activity of TSA. Taken together, the present study delineated that TSA-induced growth inhibition and apoptosis in 5,637 cells was associated with pAKT inhibition and MMP loss at the early phase, followed by downregulation of Sp1 and survivin at the late phase of treatment.

MicroRNA-22 may promote apoptosis and inhibit the proliferation of hypertrophic scar fibroblasts by regulating the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase/p21 pathway

Hypertrophic scarring (HS) is a common skin disorder that occurs during the wound healing process, and the pathogenesis of HS remains unclear. Increasing evidence indicated that specific microRNAs (miRs) may be involved in the onset and progression of HS. In the present study, the association between miR-22 and HS was investigated. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to examine the expression of miR-22 in 30 HS and matched normal skin tissues. In addition, human hypertrophic scar fibroblasts (HSFBs) were cultured and transfected with miR-22 mimics, and MTT and Annexin V apoptosis assays were performed to investigate the role of miR-22 in the proliferation and apoptosis of the human HSFBs. Next, RT-qPCR and western blot assays were performed to compare the expression levels of mitogen-activated protein kinase kinase (MEK), extracellular signal-regulated kinase (ERK) and p21 in untransfected and miR-22 mimic-transfected skin fibroblasts. The results identified that miR-22 was significantly downregulated in HS tissues as compared with the normal skin. Furthermore, transfection with miR-22 mimics in human HSFBs led to inhibited cell proliferation, increased apoptosis, as well as to decreased MEK expression and ERK1/2 phosphorylation, and increased expression of p21. In conclusion, the present study was the first to prove that aberrant expression of miR-22 may serve an important role in the pathogenesis of HS by regulating the MEK/ERK/p21 pathway, thus suggesting that miR-22 has the potential to become a therapeutic target for the treatment of HS.

IGF2 mRNA binding protein-2 is a tumor promoter that drives cancer proliferation through its client mRNAs IGF2 and HMGA1

The gene encoding the Insulin-like Growth Factor 2 mRNA binding protein 2/IMP2 is amplified and overexpressed in many human cancers, accompanied by a poorer prognosis. Mice lacking IMP2 exhibit a longer lifespan and a reduced tumor burden at old age. Herein we show in a diverse array of human cancer cells that IMP2 overexpression stimulates and IMP2 elimination diminishes proliferation by 50–80%. In addition to its known ability to promote the abundance of Insulin-like Growth Factor 2/IGF2, we find that IMP2 strongly promotes IGF action, by binding and stabilizing the mRNA encoding the DNA binding protein HMGA1, a known oncogene. HMGA1 suppresses the abundance of IGF binding protein 2/IGFBP2 and Grb14, inhibitors of IGF action. IMP2 stabilization of HMGA1 mRNA plus IMP2 stimulated IGF2 production synergistically drive cancer cell proliferation and account for IMP2’s tumor promoting action. IMP2’s ability to promote proliferation and IGF action requires IMP2 phosphorylation by mTOR.

Some types of cancers develop when genes known as oncogenes or tumor promoters become faulty, and are present at abnormally high levels or inappropriately turned on. For example, cancer cells often have extra copies of the gene IMP2 and therefore produce too much the IMP2 protein. Previous research has shown that mice that lack the IMP2 protein develop fewer cancers and live longer, while patients whose cancers make too much IMP2 have a poorer prognosis.

In healthy cells, the IMP2 protein normally helps to make new gene products by stabilising certain newly produced RNA molecules – the precursors of proteins, and in some cases by promoting the translation of these RNAs into proteins. For example, IMP2 binds to the mRNA that encodes the protein IGF2, which is a protein that helps cells to grow and is commonly produced in large quantities by cancer cells. However, until now it was not clear whether IMP2 only acts by increasing the production of IGF2 or also contributes to cancer growth in other ways.

Using a range of human cancer cell lines, and healthy mouse cells, Dai et al. first confirmed that without IMP2, cancer cells made less IGF2 and grew less quickly. When IGF2 was added to the cells lacking IMP2, it only partially restored their ability to grow. Further experiments revealed that cells without IMP2 had increased levels of proteins that counteract the effects of IGF2. Usually, IMP2 binds and stabilizes the mRNA that encodes the oncogenic protein HMGA1, which is known to regulate the number of ‘anti-IGF2 proteins’. However, without IMP2, the HMGA1 levels drop, which causes an increase of the anti-IGF2 proteins.

This indicates that IMP2 promotes cancer cell growth both by enabling cells to produce more IGF2 and by suppressing inhibitors of IGF2 action. This suggests that cancer patients whose tumors have abnormally high levels of IMP2 may be especially sensitive to drugs that target and inhibit IGF2.

Development of Therapeutic dsP21-322 for Cancer Treatment

Small activating RNAs (saRNAs) are a class of artificially designed short duplex RNAs targeted at the promoter of a particular gene to upregulate its expression via a mechanism known as RNA activation (RNAa) and hold great promise for treating a wide variety of diseases including those undruggable by conventional therapies. The therapeutic benefits of saRNAs have been demonstrated in a number of preclinical studies carried out in different disease models including cancer. With many tumor suppressor genes (TSGs) downregulated due to either epigenetic mechanisms or haploinsufficiency resulting from deletion/mutation, cancer is an ideal disease space for saRNA therapeutics which can restore the expression of TSGs via epigenetic reprogramming. The p21^WAF1/CIP gene is a TSG frequently downregulated in cancer and an saRNA for p21^WAF1/CIP known as dsP21-322 has been identified to be a sequence-specific p21^WAF1/CIP activator in a number of cancer types. In this chapter, we review preclinical development of medicinal dsP21-322 for cancer, especially prostate cancer and bladder cancer, and highlight its potential for further clinical development.

Expression and Therapeutic Potential of SOX9 in Chordoma

Purpose: Conventional chemotherapeutic agents are ineffective in the treatment of chordoma. We investigated the functional roles and therapeutic relevance of the sex-determining region Y (SRY)-box 9 (SOX9) in chordoma.Experimental Design: SOX9 expression was examined by immunohistochemistry (IHC) using 50 chordoma tissue samples. SOX9 expression in chordoma cell lines was examined by Western blot and immunofluorescent assays. We used synthetic human SOX9 siRNA to inhibit the expression of SOX9. Cell proliferation ability and cytotoxicity of inhibiting SOX9 were assessed by 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) and clonogenic assays. The effect of SOX9 knockdown on chordoma cell motility was evaluated by a wound-healing assay and a Transwell invasion chamber assay. Knockdown of SOX9 induced apoptosis, cell-cycle arrest, as well as decreased expression of cancer stem cell markers were determined by Western blot and flow cytometric assays. The effect of the combination of SOX9 siRNA and the chemotherapeutic drug doxorubicin/cisplatin on chordoma cells was assessed by an MTT assay.Results: Tissue microarray and IHC analysis showed that SOX9 is broadly expressed in chordomas and that higher expression levels of SOX9 correlated with a poor prognosis. RNA interference (RNAi)-mediated knockdown of SOX9 inhibited chordoma cell growth, decreased cell motility, and induced apoptosis as well as cell-cycle arrest. Moreover, the combination of SOX9 inhibition and chemotherapeutic drugs had an enhanced anti-cancer effect on chordoma cells.Conclusions: Our results demonstrate that SOX9 plays a crucial role in chordoma. Targeting SOX9 provides a new rationale for treatment of chordoma. Clin Cancer Res; 23(17); 5176-86. ©2017 AACR.

Teng-Long-Bu-Zhong-Tang induces p21-dependent cell senescence in colorectal carcinoma LS174T cells via histone acetylation

Teng-Long-Bu-Zhong-Tang (TLBZT) is a Chinese herbal formula for colorectal carcinoma treatment. TLBZT effectively induces cell senescence in colorectal carcinoma, accompanied by p21 upregulation. In this study, we further explored the role of p21 in TLBZT-induced cell senescence, as well as the mechanism by which TLBZT upregulates p21. Specific knockdown of p21 expression by small interfering RNA significantly attenuated TLBZT-induced cell senescence in human colorectal carcinoma LS174T cells. Silencing of p53 by small interfering RNA did not affect TLBZT-induced p21 upregulation. Meanwhile, TLBZT inhibited histone deacetylase activity. Furthermore, TLBZT increased acetylation levels of histone H3 and H4, enhancing their binding to the p21 promoter. These data suggested that TLBZT induces cell senescence in LS174T cells through a mechanism involving p21 upregulation via histone H3 and H4 acetylation. This study provides new insights into the application of TLBZT for colorectal carcinoma treatment.

ROCK2/rasHa co-operation induces malignant conversion via p53 loss, elevated NF-κB and tenascin C-associated rigidity, but p21 inhibits ROCK2/NF-κB-mediated progression

To study ROCK2 activation in carcinogenesis, mice expressing 4-hydroxytamoxifen (4HT)-activated ROCK2 (K14.ROCKer) were crossed with mice expressing epidermal-activated rasHa (HK1.ras1205). At 8 weeks, 4HT-treated K14.ROCKer/HK1.ras1205 cohorts exhibited papillomas similar to HK1.ras1205 controls; however, K14.ROCKer/HK1.ras1205 histotypes comprised a mixed papilloma/well-differentiated squamous cell carcinoma (wdSCC), exhibiting p53 loss, increased proliferation and novel NF-κB expression. By 12 weeks, K14.ROCKer/HK1.ras1205 wdSCCs exhibited increased NF-κB and novel tenascin C, indicative of elevated rigidity; yet despite continued ROCK2 activities/p-Mypt1 inactivation, progression to SCC required loss of compensatory p21 expression. K14.ROCKer/HK1.ras1205 papillomatogenesis also required a wound promotion stimulus, confirmed by breeding K14.ROCKer into promotion-insensitive HK1.ras1276 mice, suggesting a permissive K14.ROCKer/HK1.ras1205 papilloma context (wound-promoted/NF-κB+/p53-/p21+) preceded K14.ROCKer-mediated (p-Mypt1/tenascin C/rigidity) malignant conversion. Malignancy depended on ROCKer/p-Mypt1 expression, as cessation of 4HT treatment induced disorganized tissue architecture and p21-associated differentiation in wdSCCs; yet tenascin C retention in connective tissue extracellular matrix suggests the rigidity laid down for conversion persists. Novel papilloma outgrowths appeared expressing intense, basal layer p21 that confined endogenous ROCK2/p-Mypt1/NF-κB to supra-basal layers, and was paralleled by restored basal layer p53. In later SCCs, 4HT cessation became irrelevant as endogenous ROCK2 expression increased, driving progression via p21 loss, elevated NF-κB expression and tenascin C-associated rigidity, with p-Mypt1 inactivation/actinomyosin-mediated contractility to facilitate invasion. However, p21-associated inhibition of early-stage malignant progression and the intense expression in papilloma outgrowths, identifies a novel, significant antagonism between p21 and rasHa/ROCK2/NF-κB signalling in skin carcinogenesis. Collectively, these data show that ROCK2 activation induces malignancy in rasHa-initiated/promoted papillomas in the context of p53 loss and novel NF-κB expression, whereas increased tissue rigidity and cell motility/contractility help mediate tumour progression.

Significance of Wild-Type p53 Signaling in Suppressing Apoptosis in Response to Chemical Genotoxic Agents: Impact on Chemotherapy Outcome

Our genomes are subject to potentially deleterious alterations resulting from endogenous sources (e.g., cellular metabolism, routine errors in DNA replication and recombination), exogenous sources (e.g., radiation, chemical agents), and medical diagnostic and treatment applications. Genome integrity and cellular homeostasis are maintained through an intricate network of pathways that serve to recognize the DNA damage, activate cell cycle checkpoints and facilitate DNA repair, or eliminate highly injured cells from the proliferating population. The wild-type p53 tumor suppressor and its downstream effector p21^WAF1 (p21) are key regulators of these responses. Although extensively studied for its ability to control cell cycle progression, p21 has emerged as a multifunctional protein capable of downregulating p53, suppressing apoptosis, and orchestrating prolonged growth arrest through stress-induced premature senescence. Studies with solid tumors and solid tumor-derived cell lines have revealed that such growth-arrested cancer cells remain viable, secrete growth-promoting factors, and can give rise to progeny with stem-cell-like properties. This article provides an overview of the mechanisms by which p53 signaling suppresses apoptosis following genotoxic stress, facilitating repair of genomic injury under physiological conditions but having the potential to promote tumor regrowth in response to cancer chemotherapy.

Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication

Gain-of-function (GOF) p53 mutations are observed frequently in most intractable human cancers and establish dependency for tumor maintenance and progression. While some of the genes induced by GOF p53 have been implicated in more rapid cell proliferation compared with p53-null cancer cells, the mechanism for dependency of tumor growth on mutant p53 is unknown. This report reveals a therapeutically targetable mechanism for GOF p53 dependency. We have shown that GOF p53 increases DNA replication origin firing, stabilizes replication forks, and promotes micronuclei formation, thus facilitating the proliferation of cells with genomic abnormalities. In contrast, absence or depletion of GOF p53 leads to decreased origin firing and a higher frequency of fork collapse in isogenic cells, explaining their poorer proliferation rate. Following genome-wide analyses utilizing ChIP-Seq and RNA-Seq, GOF p53-induced origin firing, micronuclei formation, and fork protection were traced to the ability of GOF p53 to transactivate cyclin A and CHK1. Highlighting the therapeutic potential of CHK1's role in GOF p53 dependency, experiments in cell culture and mouse xenografts demonstrated that inhibition of CHK1 selectively blocked proliferation of cells and tumors expressing GOF p53. Our data suggest the possibility that checkpoint inhibitors could efficiently and selectively target cancers expressing GOF p53 alleles.

Decreased RNA-binding motif 5 expression is associated with tumor progression in gastric cancer

RNA-binding motif 5 is a putative tumor suppressor gene that modulates cell cycle arrest and apoptosis. We recently demonstrated that RNA-binding motif 5 inhibits cell growth through the p53 pathway. This study evaluated the clinical significance of RNA-binding motif 5 expression in gastric cancer and the effects of altered RNA-binding motif 5 expression on cancer biology in gastric cancer cells. RNA-binding motif 5 protein expression was evaluated by immunohistochemistry using the surgical specimens of 106 patients with gastric cancer. We analyzed the relationships of RNA-binding motif 5 expression with clinicopathological parameters and patient prognosis. We further explored the effects of RNA-binding motif 5 downregulation with short hairpin RNA on cell growth and p53 signaling in MKN45 gastric cancer cells. Immunohistochemistry revealed that RNA-binding motif 5 expression was decreased in 29 of 106 (27.4%) gastric cancer specimens. Decreased RNA-binding motif 5 expression was correlated with histological differentiation, depth of tumor infiltration, nodal metastasis, tumor-node-metastasis stage, and prognosis. RNA-binding motif 5 silencing enhanced gastric cancer cell proliferation and decreased p53 transcriptional activity in reporter gene assays. Conversely, restoration of RNA-binding motif 5 expression suppressed cell growth and recovered p53 transactivation in RNA-binding motif 5-silenced cells. Furthermore, RNA-binding motif 5 silencing reduced the messenger RNA and protein expression of the p53 target gene p21. Our results suggest that RNA-binding motif 5 downregulation is involved in gastric cancer progression and that RNA-binding motif 5 behaves as a tumor suppressor gene in gastric cancer.

Identification of Key Candidate Genes and Pathways in Colorectal Cancer by Integrated Bioinformatical Analysis

Colorectal cancer (CRC) is one of the most common malignant diseases worldwide, but the involved signaling pathways and driven-genes are largely unclear. This study integrated four cohorts profile datasets to elucidate the potential key candidate genes and pathways in CRC. Expression profiles GSE28000, GSE21815, GSE44076 and GSE75970, including 319 CRC and 103 normal mucosa, were integrated and deeply analyzed. Differentially expressed genes (DEGs) were sorted and candidate genes and pathways enrichment were analyzed. DEGs-associated protein–protein interaction network (PPI) was performed. Firstly, 292 shared DEGs (165 up-regulated and 127 down-regulated) were identified from the four GSE datasets. Secondly, the DEGs were clustered based on functions and signaling pathways with significant enrichment analysis. Thirdly, 180 nodes/DEGs were identified from DEGs PPI network complex. Lastly, the most significant 2 modules were filtered from PPI, 31 central node genes were identified and most of the corresponding genes are involved in cell cycle process, chemokines and G protein-coupled receptor signaling pathways. Taken above, using integrated bioinformatical analysis, we have identified DEGs candidate genes and pathways in CRC, which could improve our understanding of the cause and underlying molecular events, and these candidate genes and pathways could be therapeutic targets for CRC.

The DEAD-box RNA helicase DDX41 is a novel repressor of p21WAF1/CIP1 mRNA translation

The cyclin-dependent kinase inhibitor p21 is an important player in stress pathways exhibiting both tumor-suppressive and oncogenic functions. Thus, expression of p21 has to be tightly controlled, which is achieved by numerous mechanisms at the transcriptional, translational, and posttranslational level. Performing immunoprecipitation of bromouridine-labeled p21 mRNAs that had been incubated before with cytoplasmic extracts of untreated HCT116 colon carcinoma cells, we identified the DEAD-box RNA helicase DDX41 as a novel regulator of p21 expression. DDX41 specifically precipitates with the 3'UTR, but not with the 5'UTR, of p21 mRNA. Knockdown of DDX41 increases basal and γ irradiation-induced p21 protein levels without affecting p21 mRNA expression. Conversely, overexpression of DDX41 strongly inhibits expression of a FLAG-p21 and a luciferase construct, but only in the presence of the p21 3'UTR. Together, these data suggest that this helicase regulates p21 expression at the translational level independent of the transcriptional activity of p53. However, knockdown of DDX41 completely fails to increase p21 protein levels in p53-deficient HCT116 cells. Moreover, posttranslational up-regulation of p21 achieved in both p53^+/+ and p53^-/- HCT116 cells in response to pharmaceutical inhibition of the proteasome (by MG-132) or p90 ribosomal S6 kinases (by BI-D1870) is further increased by knockdown of DDX41 only in p53-proficient but not in p53-deficient cells. Although our data demonstrate that DDX41 suppresses p21 translation without disturbing the function of p53 to directly induce p21 mRNA expression, this process indirectly requires p53, perhaps in the form of another p53 target gene or as a still undefined posttranscriptional function of p53.

HDAC4 and HDAC6 sustain DNA double strand break repair and stem-like phenotype by promoting radioresistance in glioblastoma cells

The role of histone deacetylase (HDAC) 4 and 6 in glioblastoma (GBM) radioresistance was investigated. We found that tumor samples from 31 GBM patients, who underwent temozolomide and radiotherapy combined treatment, showed HDAC4 and HDAC6 expression in 93.5% and 96.7% of cases, respectively. Retrospective clinical data analysis demonstrated that high-intensity HDAC4 and/or HDAC6 immunostaining was predictive of poor clinical outcome. In vitro experiments revealed that short hairpin RNA-mediated silencing of HDAC4 or HDAC6 radiosensitized U87MG and U251MG GBM cell lines by promoting DNA double-strand break (DSBs) accumulation and by affecting DSBs repair molecular machinery. We found that HDAC6 knock-down predisposes to radiation therapy-induced U251MG apoptosis- and U87MG autophagy-mediated cell death. HDAC4 silencing promoted radiation therapy-induced senescence, independently by the cellular context. Finally, we showed that p53^WT expression contributed to the radiotherapy lethal effects and that HDAC4 or HDAC6 sustained GBM stem-like radioresistant phenotype. Altogether, these observations suggest that HDAC4 and HDAC6 are guardians of irradiation-induced DNA damages and stemness, thus promoting radioresistance, and may represent potential prognostic markers and therapeutic targets in GBM.

Depletion of oxaloacetate decarboxylase FAHD1 inhibits mitochondrial electron transport and induces cellular senescence in human endothelial cells

In this study we report the identification of FAH domain containing protein 1 (FAHD1), a recently described member of the fumarylacetoacetate hydrolase (FAH) superfamily of metabolic enzymes, as a novel player in the regulation of cellular senescence. FAHD1 was found in a proteomic screen searching for mitochondrial proteins, which are differentially regulated in mitochondria from young and senescent human endothelial cells, and subsequently identified as oxaloacetate decarboxylase. We report here that depletion of FAHD1 from human endothelial cells inhibited mitochondrial energy metabolism and subsequently induced premature senescence. Whereas senescence induced by FAHD1 depletion was not associated with DNA damage, we noted a reduction of mitochondrial ATP-coupled respiration associated with upregulation of the cdk inhibitor p21. These results indicate that FAHD1 is required for mitochondrial function in human cells and provide additional support to the growing evidence that mitochondrial dysfunction can induce cellular senescence by metabolic alterations independent of the DNA damage response pathway.

The B6 -vitamer Pyridoxal is a Sensitizer of UVA-induced Genotoxic Stress in Human Primary Keratinocytes and Reconstructed Epidermis

UVA-driven photooxidative stress in human skin may originate from excitation of specific endogenous chromophores acting as photosensitizers. Previously, we have demonstrated that 3-hydroxypyridine-derived chromophores including B₆ -vitamers (pyridoxine, pyridoxamine and pyridoxal) are endogenous photosensitizers that enhance UVA-induced photooxidative stress in human skin cells. Here, we report that the B₆ -vitamer pyridoxal is a sensitizer of genotoxic stress in human adult primary keratinocytes (HEKa) and reconstructed epidermis. Comparative array analysis indicated that exposure to the combined action of pyridoxal and UVA caused upregulation of heat shock (HSPA6, HSPA1A, HSPA1L, HSPA2), redox (GSTM3, EGR1, MT2A, HMOX1, SOD1) and genotoxic (GADD45A, DDIT3, CDKN1A) stress response gene expression. Together with potentiation of UVA-induced photooxidative stress and glutathione depletion, induction of HEKa cell death occurred only in response to the combined action of pyridoxal and UVA. In addition to activational phosphorylation indicative of genotoxic stress [p53 (Ser15) and γ-H2AX (Ser139)], comet analysis indicated the formation of Fpg-sensitive oxidative DNA lesions, observable only after combined exposure to pyridoxal and UVA. In human reconstructed epidermis, pyridoxal preincubation followed by UVA exposure caused genomic oxidative base damage, procaspase 3 cleavage and TUNEL positivity, consistent with UVA-driven photooxidative damage that may be relevant to human skin exposed to high concentrations of B₆ -vitamers.

Long noncoding AGAP2-AS1 is activated by SP1 and promotes cell proliferation and invasion in gastric cancer

BACKGROUND

Long noncoding RNAs (lncRNAs) have emerged as important regulators of tumorigenesis and cancer progression. Recently, the lncRNA AGAP2-AS1 was identified as an oncogenic lncRNA in human non-small cell lung cancer (NSCLC) and its elevated expression was linked to NSCLC development and progression. However, the expression pattern and molecular mechanism of AGAP2-AS1 in gastric cancer (GC) have not been characterized.

METHODS

Bioinformatic analysis was performed to determine AGAP2-AS1 expression levels in the GC and normal tissues using gene profiling data from the Gene Expression Omnibus. Quantitative real-time polymerase chain reaction was used to validate AGAP2-AS1 expression in the GC tissues/cell lines compared with that in the adjacent nontumorous tissues/normal epithelial cells. Loss- and gain-of-function approaches were performed to investigate the effect of AGAP2-AS1 on GC cell phenotypes. The effect of AGAP2-AS1 on cell proliferation was evaluated by MTT, colony formation, flow cytometry, and in vivo tumor formation assays. The effects of AGAP2-AS1 on cell migration and invasion were examined using Transwell assays. Chromatin immunoprecipitation, luciferase reporter assays, RNA pull-down, and RNA immunoprecipitation were used to investigate the factors involved in AGAP2-AS1 dysregulation and the mechanism of action of AGAP2-AS1 in the GC cells.

RESULTS

AGAP2-AS1 was highly expressed in the GC tissues and cell lines, and patients with higher AGAP2-AS1 expression had a poorer prognosis and shorter overall survival. Furthermore, knockdown of AGAP2-AS1 significantly inhibited GC cell proliferation, migration, and invasion in vitro and tumor growth in vivo. AGAP2-AS1 overexpression promoted cell growth and invasion. In addition, the transcription factor SP1 activated AGAP2-AS1 expression in the GC cells. AGAP2-AS1 functions as an oncogenic lncRNA by interacting with LSD1 and EZH2 and suppressing CDKN1A (P21) and E-cadherin transcription.

CONCLUSIONS

Taken together, these findings imply that AGAP2-AS1 upregulated by SP1 plays an important role in GC development and progression by suppressing P21 and E-cadherin, which suggests that AGAP2-AS1 is a potential diagnostic marker and therapeutic target for GC patients.

Multinucleated Giant Cancer Cells Produced in Response to Ionizing Radiation Retain Viability and Replicate Their Genome

Loss of wild-type p53 function is widely accepted to be permissive for the development of multinucleated giant cells. However, whether therapy-induced multinucleation is associated with cancer cell death or survival remains controversial. Herein, we demonstrate that exposure of p53-deficient or p21^WAF1 (p21)-deficient solid tumor-derived cell lines to ionizing radiation (between 2 and 8 Gy) results in the development of multinucleated giant cells that remain adherent to the culture dish for long times post-irradiation. Somewhat surprisingly, single-cell observations revealed that virtually all multinucleated giant cells that remain adherent for the duration of the experiments (up to three weeks post-irradiation) retain viability and metabolize 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT), and the majority (>60%) exhibit DNA synthesis. We further report that treatment of multinucleated giant cells with pharmacological activators of apoptosis (e.g., sodium salicylate) triggers their demise. Our observations reinforce the notion that radiation-induced multinucleation may reflect a survival mechanism for p53/p21-deficient cancer cells. With respect to evaluating radiosensitivity, our observations underscore the importance of single-cell experimental approaches (e.g., single-cell MTT) as the creation of viable multinucleated giant cells complicates the interpretation of the experimental data obtained by commonly-used multi-well plate colorimetric assays.

Epigenetic modulators of thyroid cancer

There are some well known factors involved in the etiology of thyroid cancer, including iodine deficiency, radiation exposure at early ages, or some genetic changes. However, epigenetic modulators that may contribute to development of these tumors and be helpful to for both their diagnosis and treatment have recently been discovered. The currently known changes in DNA methylation, histone modifications, and non-coding RNAs in each type of thyroid carcinoma are reviewed here.

Integrative analysis for the role of long non-coding RNAs in radiation-induced mouse thymocytes responses

Long non-coding RNAs (lncRNAs) are a critical class of regulatory molecules involved in a variety of biological functions; however, their role in immune cells response to radiation is unknown. Therefore, in this study we used integrative analysis to determine the expression profile of lncRNAs in mouse thymocytes and the potential functions of lncRNAs in response to radiation. Microarray data profiling indicated that 53 lncRNAs (36 up-regulated and 17 down-regulated) and 74 coding genes (39 up-regulated and 35 down-regulated) were highly differentially expressed in the high dose radiation (HDR) group compared with the control group. In the low dose radiation (LDR) group, only one lncRNA was down-regulated. Moreover, as compared with the control group, 109 lncRNA pathways in the HDR group and 14 lncRNA pathways in the LDR group were differentially expressed. Our data revealed the expression pattern of lncRNAs in mouse thymocytes and predicted their potential functions in response to LDR and HDR. In the HDR group, GO analysis showed that the role of lncRNAs in damage responses of thymocytes to HDR mainly involved chromatin organization and cell death. These findings might improve our understanding of the role of lncRNAs in LDR- and HDR-induced immune cells and provide a new experimental basis for further investigation.

MicroRNA-93-5p increases multidrug resistance in human colorectal carcinoma cells by downregulating cyclin dependent kinase inhibitor 1A gene expression

Multidrug resistance (MDR) impedes successful chemotherapy in colorectal carcinoma (CRC) and emerging evidence suggests that microRNAs (miRs) are involved in the development of MDR. In the present study, the role of miR-93-5p in the modulation of drug resistance in CRC was investigated using HCT-8 and MDR HCT-8/vincristine (VCR) cell lines. The results demonstrated upregulated expression of miR-93-5p and MDR protein 1 (MDR1) in HCT-8/VCR cells, compared with the parental HCT-8 cells. Furthermore, cyclin-dependent kinase inhibitor 1A (CDKN1A) was identified as a potential target of miR-93-5p using miR target analysis tools, including PicTar, TargetScan and miRanda. In addition, inhibition of miR-93-5p expression in HCT-8/VCR cells markedly downregulated MDR1 gene expression, upregulated CDKN1A gene expression and induced cell cycle arrest in G₁. Conversely, the overexpression of miR-93-5p in HCT-8/VCR cells upregulated MDR1 gene expression, downregulated CDKN1A gene expression and promoted G₁/S transition. Furthermore, the in vitro drug sensitivity assay performed suggested that downregulation of miR-93-5p enhanced the sensitivity of HCT-8/VCR cells to VCR, while the upregulation of miR-93-5p decreased the sensitivity of HCT-8 cells to VCR. In conclusion, the results of the present study suggest that miR-93-5p serves a role in the development of MDR through downregulating CDKN1A gene expression in CRC.

Olaparib, Monotherapy or with Ionizing Radiation, Exacerbates DNA Damage in Normal Tissues: Insights from a New p21 Reporter Mouse

Many drugs targeting the DNA damage response are being developed as anticancer therapies, either as single agents or in combination with ionizing radiation (IR) or other cytotoxic agents. Numerous clinical trials in this area are either in progress or planned. However, concerns remain about the potential of such treatments to increase toxicity to normal tissues. In order to address this issue, a novel reporter mouse line was created through the simultaneous incorporation of multiple reporters, β-galactosidase, and firefly luciferase, into the DNA damage-inducible p21 (CDKN1A) locus. The data demonstrate that in situ β-galactosidase staining facilitates high fidelity mapping of p21 expression across multiple organs and tissues at single-cell resolution, whereas the luciferase reporter permits noninvasive bioluminescent imaging of p21 expression. This model was used to determine the capacity of a number of DNA-damaging agents, including IR, cisplatin, and etoposide to induce p21 expression in normal tissues. In addition, the PARP inhibitor olaparib was examined alone or in combination with IR as well as cisplatin. A single exposure to olaparib alone caused DNA damage to cells in the mucosal layer lining mouse large intestine. It also exacerbated DNA damage induced in this organ and the kidney by coadministered IR. These studies suggest that olaparib has carcinogenic potential and illustrate the power of this new model to evaluate the safety of new therapeutic regimens involving combination therapies.

IMPLICATIONS

Olaparib causes DNA damage to normal tissues and might be a carcinogen. Mol Cancer Res; 14(12); 1195-203. ©2016 AACR.

The interaction of adenovirus E1A with the mammalian protein Ku70/XRCC6

Human adenovirus infects terminally differentiated cells and to replicate it must induce S-phase. The chief architects that drive adenovirus-infected cells into S-phase are the E1A proteins, with 5 different isoforms expressed during infection. E1A remodels the infected cell by associating with cellular factors and modulating their activity. The C-terminus of E1A is known to bind to only a handful of proteins. We have identified a novel E1A C-terminus binding protein, Ku70 (XRCC6), which was found to bind directly within the CR4 of E1A from human adenovirus type 5. Depletion of Ku70 reduced virus growth, possibly by activating the DNA damage response pathway. Ku70 was found to localize to viral replication centers and associate with the viral genome. Ku70 was also recruited to cellular cell cycle regulated promoters following viral infection. Our study has identified, for the first time, Ku70 as a novel E1A-binding protein which affects virus life cycle.

Cyclin Kinase-independent role of p21CDKN1A in the promotion of nascent DNA elongation in unstressed cells

The levels of the cyclin-dependent kinase (CDK) inhibitor p21 are low in S phase and insufficient to inhibit CDKs. We show here that endogenous p21, instead of being residual, it is functional and necessary to preserve the genomic stability of unstressed cells. p21depletion slows down nascent DNA elongation, triggers permanent replication defects and promotes the instability of hard-to-replicate genomic regions, namely common fragile sites (CFS). The p21’s PCNA interacting region (PIR), and not its CDK binding domain, is needed to prevent the replication defects and the genomic instability caused by p21 depletion. The alternative polymerase kappa is accountable for such defects as they were not observed after simultaneous depletion of both p21 and polymerase kappa. Hence, in CDK-independent manner, endogenous p21 prevents a type of genomic instability which is not triggered by endogenous DNA lesions but by a dysregulation in the DNA polymerase choice during genomic DNA synthesis.

DOI:http://dx.doi.org/10.7554/eLife.18020.001

Cancer develops when cells in the body mutate in ways that allow them to rapidly grow and divide. To protect cells from becoming cancerous, various molecules act like guardians to prevent cells from dividing when their DNA is damaged, or if they are short of energy. Other guardian molecules monitor the DNA copying process to ensure that the newly-made DNA is as identical as possible to the original DNA template.

A protein called p21 belongs to the first group of guardian molecules: DNA damage triggers the production of p21, which prevents the cell from copying its DNA. This role relies on a section of the protein called the CDK binding domain. Cells that have already started to copy their genetic material also have low levels of p21.

Mansilla et al. used human cells to investigate whether p21 is also involved in the process of copying DNA. The experiments show that the low levels of p21 act to increase the speed at which the DNA is copied. This activity helps to ensure that all of the cell’s DNA is copied within the time available, including sections of DNA that are harder to copy because they are more fragile and prone to damage. This newly identified role does not involve the CDK binding domain, but instead requires a different section of the p21 protein known as the PCNA interacting region.

Mansilla et al. propose that p21 plays a dual role in protecting us from developing cancer. The PCNA interacting region is also found in other proteins that are involved in copying DNA. Therefore, a future challenge is to find out how these proteins interact with each other to ensure that cells accurately copy their DNA in a timely fashion.

DOI:http://dx.doi.org/10.7554/eLife.18020.002

Demystifying the mechanistic and functional aspects of p21 gene activation with double-stranded RNAs in human cancer cells

BACKGROUND

The recently identified phenomenon of double-stranded RNA (dsRNA)-mediated gene activation (RNAa) has been studied extensively, as it is present in humans, mice, and Caenorhabditis elegans, suggesting that dsRNA-mediated RNAa is an evolutionarily conserved mechanism. Previous studies have shown that dsP21-322 can induce tumor suppressor gene p21 expression in several human cancer cells. Nonetheless, the role of dsRNAs in the activation of gene expression, including their target molecules and associated key factors, remains poorly understood.

METHODS

Oligonucleotides were used to overexpress dsRNAs and dsControl. Real-time PCR and Western blotting were used to detect corresponding mRNA and protein expression, respectively. Fluorescence microscopy was used to examine the kinetics of dsRNA subcellular distribution. Luciferase reporter assays were performed to verify dsRNA target molecules. Chromatin immunoprecipitation (ChIP) assays were carried out to determine whether histone modification and other associated key factors are involved in saRNA-mediated p21 expression.

RESULTS

We demonstrated that dsRNA-mediated p21 induction in human cell lines is a common phenomenon. This process occurs at the transcriptional level, and the complementary p21 promoter is the intended dsRNA target. Additionally, ChIP assays indicated that p21 activation was accompanied by an increased enrichment of AGO1 and the trimethylation of histone H3K4 at dsRNA-targeted genomic sites.

CONCLUSION

These data systematically reveal the mechanistic and functional aspects of ncRNA-mediated p21 activation in human cancer cells, which may be a useful tool to analyze gene function and aid in the development of novel drug targets for cancer therapeutics.

Inhibition of Aurora kinases induces apoptosis and autophagy via AURKB/p70S6K/RPL15 axis in human leukemia cells

Leukemia is a common malignancy of blood cells with poor prognosis in many patients. Aurora kinases, a family of serine/threonine kinases, play a key role in regulating cell division and mitosis and are linked to tumorigenesis, metastasis, and poor prognosis in many human cancers including leukemia and lymphoma. Danusertib (Danu) is a pan-inhibitor of Aurora kinases with few data available in leukemia therapy. This study aimed to identify new molecular targets for Aurora kinase inhibition in human leukemia cells using quantitative proteomic analysis followed by verification experiments. There were at least 2932 proteins responding to Danu treatment, including AURKB, p70S6K, and RPL15, and 603 functional proteins and 245 canonical signaling pathways were involved in regulating cell proliferation, metabolism, apoptosis, and autophagy. The proteomic data suggested that Danu-regulated RPL15 signaling might contribute to the cancer cell killing effect. Our verification experiments confirmed that Danu negatively regulated AURKB/p70S6K/RPL15 axis with the involvement of PI3K/Akt/mTOR, AMPK, and p38 MAPK signaling pathways, leading to the induction of apoptosis and autophagy in human leukemia cells. Further studies are warranted to verify the feasibility via targeting AURKB/p70S6K/RPL15 axis for leukemia therapy.

Emerging links among Chromosome Instability (CIN), cancer, and aging

Aneuploidy was predicted to cause cancer. To test the prediction, various Chromosome Instability (CIN) mice models that carry transgenic mutations in mitotic regulators have been created. The availability of these mice has aided researchers in discovering connections between CIN, cancer, and aging. This review will focus on recent interdisciplinary findings regarding how CIN and aneuploidy affect carcinogenesis, immune dysfunction, and aging. High CIN can be generated in vivo by various intrinsic alterations (e.g., gene mutation, epigenetic modification) and extrinsic/environmental challenges (e.g., biological, chemical, biophysical), while immune surveillance, cell death, and natural turnover can remove cells with CIN. CIN itself is mutagenic and may cause further cellular mutations, which can be carcinogenic. Mitotically damaged cells can activate senescence-related tumor suppressors (e.g., p21^WAF1 , p27^KIP1 , p16^INK4A ), which may lead to tissue-level senescence/aging through inflammatory paracrine mechanisms called Senescence-Associated Secretory Phenotype (SASP) and Senescence Inflammatory Response (SIR). Organs with high CIN show altered gene expressions in both organ-specific and non-specific manners. Organ-specific gene expression signatures include activation of oncogenic pathways. Non-organ-specific gene expression signatures include metabolic changes and downregulations in immune functions. Immune surveillance normally targets senescent cells and tetraploid cells, a form of aneuploidy, for elimination. However, with partial immune dysfunction, immune surveillance is weakened with systemic CIN. In this case, more senescent cells and aneuploid cells survive, which further leads to an inflammatory, pro-tumorigenic, and senescent/aging microenvironment. We also discuss how we may intervene in this sequence of events to prevent CIN- or age-related carcinogenesis and/or some aspects of tissue aging. © 2016 Wiley Periodicals, Inc.

Calcitriol Inhibits Cervical Cancer Cell Proliferation Through Downregulation of HCCR1 Expression

Calcitriol (1α,25-dihydroxyvitamin D3) has demonstrated anticancer activity against several tumors. However, the underlying mechanism for this activity is not yet fully understood. Our experiment was designed and performed to address one aspect of this issue in cervical cancer. HeLa S3 cells were cultured in media with various concentrations of calcitriol. Cell proliferation and cell cycle were assessed by spectrophotometry and flow cytometry, respectively. The mRNA and protein expression levels of human cervical cancer oncogene (HCCR-1) and p21 were determined by RT-PCR and Western blot, respectively. Results indicated that calcitriol inhibited HeLa S3 cell proliferation and induced cell cycle arrest at the G₁ phase. Calcitriol decreased HCCR-1 protein expression in a dose- and time-dependent manner. Furthermore, promoter activity analyses revealed that transcriptional regulation was involved in the inhibition of HCCR-1 expression. Overexpression of HCCR-1 in HeLa S3 cells reversed the inhibition of cell proliferation and G₁ phase arrest that resulted from calcitriol treatment. In addition, calcitriol increased p21 expression and promoter activity. HCCR-1 overexpression decreased p21 expression and promoter activity. Thus, our results suggested that calcitriol inhibited HeLa S3 cell proliferation by decreasing HCCR-1 expression and increasing p21 expression.

Non genomic loss of function of tumor suppressors in CML: BCR-ABL promotes IκBα mediated p53 nuclear exclusion

Tumor suppressor function can be modulated by subtle variation of expression levels, proper cellular compartmentalization and post-translational modifications, such as phosphorylation, acetylation and sumoylation. The non-genomic loss of function of tumor suppressors offers a challenging therapeutic opportunity. The reactivation of a tumor suppressor could indeed promote selective apoptosis of cancer cells without affecting normal cells. The identification of mechanisms that affect tumor suppressor functions is therefore essential. In this work, we show that BCR-ABL promotes the accumulation of the NFKBIA gene product, IκBα, in the cytosol through physical interaction and stabilization of the protein. Furthermore, BCR-ABL/IκBα complex acts as a scaffold protein favoring p53 nuclear exclusion. We therefore identify a novel BCR-ABL/IκBα/p53 network, whereby BCR-ABL functionally inactivates a key tumor suppressor.

Effects of irreversible electroporation on cervical cancer cell lines in vitro

The effects of irreversible electroporation (IRE) on the proliferation, migration, invasion and adhesion of human cervical cancer cell lines HeLa and SiHa were investigated in the present study. HeLa and SiHa cells were divided into a treatment group and control group. The treatment group cells were exposed to electric pulses at 16 pulses, 1 Hz frequency for 100 µsec with 1,000 V/cm strength. Cellular proliferation was determined 24 h after treatment using a Cell Counting Kit‑8 (CCK‑8) assay and carboxyfluorescein diacetate‑succinimidyl ester (CFDA‑SE) labeling assay. The different phases of the cell cycle were detected using flow cytometry. Wound healing, Transwell invasion and Matrigel adhesion assays were performed to evaluate the migration, invasion and adhesion abilities of HeLa and SiHa cells. The expression levels of metastasis‑associated proteins were determined by western blot analysis. CCK‑8 and CFSE labeling assays indicated that the inhibition of cellular proliferation occurs in cells treated with IRE. Additionally, cell cycle progression was arrested at the G1/S phase. A western blot analysis indicated that the expression levels of p53 and p21 proteins were increased, whilst those of cyclin‑dependent kinase 2 (CDK2) and proliferating cell nuclear antigen (PCNA) proteins were decreased. However, wound healing, invasion and adhesion assays indicated that cellular migration, invasion and adhesion abilities were not significantly altered following exposure to IRE. IRE was not observed to promote the migration, invasion or adhesion capacity of HeLa and SiHa cells. However, IRE may inhibit the capacity of cells to proliferate and their progression through the cell cycle in vitro. Preliminary evidence suggests that the underlying mechanism involves increased expression levels of p53 and p21 and decreased expression levels of CDK2 and PCNA.

SAHA-induced loss of tumor suppressor Pten gene promotes thyroid carcinogenesis in a mouse model

Thyroid cancer is on the rise. Novel approaches are needed to improve the outcome of patients with recurrent and advanced metastatic thyroid cancers. FDA approval of suberoylanilide hydroxamic acid (SAHA; vorinostat), an inhibitor of histone deacetylase, for the treatment of hematological malignancies led to the clinical trials of vorinostat for advanced thyroid cancer. However, patients were resistant to vorinostat treatment. To understand the molecular basis of resistance, we tested the efficacy of SAHA in two mouse models of metastatic follicular thyroid cancer: Thrb(PV/PV) and Thrb(PV/PV)Pten(+/-) mice. In both, thyroid cancer is driven by overactivation of PI3K-AKT signaling. However, the latter exhibit more aggressive cancer progression due to haplodeficiency of the tumor suppressor, the Pten gene. SAHA had no effects on thyroid cancer progression in Thrb(PV/PV) mice, indicative of resistance to SAHA. Unexpectedly, thyroid cancer progressed in SAHA-treated Thrb(PV/PV)Pten(+/-) mice with accelerated occurrence of vascular invasion, anaplastic foci, and lung metastasis. Molecular analyses showed further activated PI3K-AKT in thyroid tumors of SAHA-treated Thrb(PV/PV)Pten(+/-) mice, resulting in the activated effectors, p-Rb, CDK6, p21(Cip1), p-cSrc, ezrin, and matrix metalloproteinases, to increase proliferation and invasion of tumor cells. Single-molecule DNA analysis indicated that the wild-type allele of the Pten gene was progressively lost, whereas carcinogenesis progressed in SAHA-treated Thrb(PV/PV)Pten(+/-) mice. Thus, this study has uncovered a novel mechanism by which SAHA-induced loss of the tumor suppressor Pten gene to promote thyroid cancer progression. Effectors downstream of the Pten loss-induced signaling may be potential targets to overcome resistance of thyroid cancer to SAHA.

Chronic p53-independent p21 expression causes genomic instability by deregulating replication licensing

The cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (p21) is a cell-cycle checkpoint effector and inducer of senescence, regulated by p53. Yet, evidence suggests that p21 could also be oncogenic, through a mechanism that has so far remained obscure. We report that a subset of atypical cancerous cells strongly expressing p21 showed proliferation features. This occurred predominantly in p53-mutant human cancers, suggesting p53-independent upregulation of p21 selectively in more aggressive tumour cells. Multifaceted phenotypic and genomic analyses of p21-inducible, p53-null, cancerous and near-normal cellular models showed that after an initial senescence-like phase, a subpopulation of p21-expressing proliferating cells emerged, featuring increased genomic instability, aggressiveness and chemoresistance. Mechanistically, sustained p21 accumulation inhibited mainly the CRL4-CDT2 ubiquitin ligase, leading to deregulated origin licensing and replication stress. Collectively, our data reveal the tumour-promoting ability of p21 through deregulation of DNA replication licensing machinery-an unorthodox role to be considered in cancer treatment, since p21 responds to various stimuli including some chemotherapy drugs.

Carnosic acid induces proteasomal degradation of Cyclin B1, RB and SOX2 along with cell growth arrest and apoptosis in GBM cells

BACKGROUND

Carnosic acid (CA) is a diterpenoid found in Rosmarinus officinalis L. and Salvia officinalis L. as well as in many other Lamiaceae. This compound is reported to have antioxidant and antimicrobial properties. In addition, a number of reports showed that CA has a cytotoxic activity toward several cancer cell lines.

PURPOSE

The aim of this study was to establish whether CA has any specific antiproliferative effect toward human glioblastoma (GBM) cells and to analyze the molecular mechanisms involved.

METHODS

We evaluated cell survival by MTT assay, apoptosis and DNA content by flow cytometry, protein expression and phosphorylation by immunoblot analyses.

RESULTS

Our results showed that CA inhibited cell survival on both normal astrocytes and GBM cells. In GBM cells, in particular, CA caused an early G2 block, a reduction in the percentage of cells expressing Ki67, an enhanced expression of p21(WAF) and induced apoptosis. Furthermore, we showed that CA promoted proteasomal degradation of several substrate proteins, including Cyclin B1, retinoblastoma (RB), SOX2, and glial fibrillary acid protein (GFAP), whereas MYC levels were not modified. In addition, CA dramatically reduced the activity of CDKs.

CONCLUSION

In conclusion, our findings strongly suggest that CA promotes a profound deregulation of cell cycle control and reduces the survival of GBM cells via proteasome-mediated degradation of Cyclin B1, RB and SOX2.

Downregulation of the Deiminase PADI2 Is an Early Event in Colorectal Carcinogenesis and Indicates Poor Prognosis

Peptidyl arginine deiminases (PADI) are a family of enzymes that catalyze the poorly understood posttranslational modification converting arginine residues into citrullines. In this study, the role of PADIs in the pathogenesis of colorectal cancer was investigated. Specifically, RNA expression was analyzed and its association with survival in a cohort of 98 colorectal cancer patient specimens with matched adjacent mucosa and 50 controls from donors without cancer. Key results were validated in an independent collection of tumors with matched adjacent mucosa and by mining of a publicly available expression data set. Protein expression was analyzed by immunoblotting for cell lines or IHC for patient specimens that further included 24 cases of adenocarcinoma with adjacent dysplasia and 11 cases of active ulcerative colitis. The data indicate that PADI2 is the dominantly expressed PADI enzyme in colon mucosa and is upregulated during differentiation. PADI2 expression is low or absent in colorectal cancer. Frequently, this occurs already at the stage of low-grade dysplasia. Mucosal PADI2 expression is also low in ulcerative colitis. The expression level of PADI2 in tumor and adjacent mucosa correlates with differential survival: low levels associate with poor prognosis.

IMPLICATIONS

Downregulation of PADI2 is an early event in the pathogenesis of colorectal cancer associated with poor prognosis and points toward a possible role of citrullination in modulating tumor cells and their microenvironment. Mol Cancer Res; 14(9); 841-8. ©2016 AACR.

SUV39H2 methylates and stabilizes LSD1 by inhibiting polyubiquitination in human cancer cells

LSD1 is a histone lysine demethylase, which is highly expressed in multiple types of human cancer. Although its roles in transcriptional regulation have been well-studied, functional regulation of LSD1 by post-translational modifications still remains unknown. Here, we demonstrate that the histone lysine methyltransferase SUV39H2 trimethylated LSD1 on lysine 322. Knockdown of SUV39H2 resulted in a decrease of LSD1 protein even though the mRNA levels were unchanged. SUV39H2-induced LSD1 methylation suppresses LSD1 polyubiquitination and subsequent degradation. In addition, we also observed indirect effect of SUV39H2 overexpression on LSD1-target genes. Our results reveal the regulatory mechanism of LSD1 protein through its lysine methylation by SUV39H2 in human cancer cells.

A new mechanism of regulation of p21 by the mTORC1/4E-BP1 pathway predicts clinical outcome of head and neck cancer

We have identified a novel mechanism of regulation of the protein CDKN1A (also known as p21) by the serine/threonine kinase complex mammalian target of rapamycin complex 1 (mTORC1). Our results demonstrate that the mTORC1 substrate EIF4E-binding protein 1 (4E-BP1) in its non-phosphorylated state interacts with p21 and promotes p21 degradation. In addition, we demonstrate the prevalence of this mechanism in head and neck squamous cell carcinomas and show that it strongly and significantly associates with improved disease-specific survival, providing evidence for its clinical relevance.

The Growing Complexity of Cancer Cell Response to DNA-Damaging Agents: Caspase 3 Mediates Cell Death or Survival?

It is widely stated that wild-type p53 either mediates the activation of cell cycle checkpoints to facilitate DNA repair and promote cell survival, or orchestrates apoptotic cell death following exposure to cancer therapeutic agents. This reigning paradigm has been challenged by numerous discoveries with different human cell types, including solid tumor-derived cell lines. Thus, activation of the p53 signaling pathway by ionizing radiation and other DNA-damaging agents hinders apoptosis and triggers growth arrest (e.g., through premature senescence) in some genetic backgrounds; such growth arrested cells remain viable, secrete growth-promoting factors, and give rise to progeny with stem cell-like properties. In addition, caspase 3, which is best known for its role in the execution phase of apoptosis, has been recently reported to facilitate (rather than suppress) DNA damage-induced genomic instability and carcinogenesis. This observation is consistent with an earlier report demonstrating that caspase 3 mediates secretion of the pro-survival factor prostaglandin E₂, which in turn promotes enrichment of tumor repopulating cells. In this article, we review these and related discoveries and point out novel cancer therapeutic strategies. One of our objectives is to demonstrate the growing complexity of the DNA damage response beyond the conventional “repair and survive, or die” hypothesis.

Controlled diesel exhaust and allergen coexposure modulates microRNA and gene expression in humans: Effects on inflammatory lung markers

BACKGROUND

Air pollution's association with asthma may be due to its augmentation of allergenic effects, but the role of microRNA (miRNA) and gene expression in this synergy is unknown.

OBJECTIVE

We sought to determine whether exposure to allergen, exposure to diesel exhaust (DE), or coexposures modulate miRNA, gene expression, or inflammatory pathways and whether these measurements are correlated.

METHODS

Fifteen participants with atopy completed this controlled study of 2 hours of filtered air or DE (300 μg PM_2.5/m³) exposure, followed by saline-controlled segmental bronchial allergen challenge. Gene and miRNA expression in bronchial brushings and lung inflammatory markers were measured 48 hours later, in study arms separated by approximately 4 weeks. Expression of miRNAs, messenger RNAs, and inflammatory markers and their interrelationships were determined using regression.

RESULTS

Robust linear models indicated that DE plus saline and DE plus allergen significantly modulated the highest number of miRNAs and messenger RNAs, respectively, relative to control (filtered air plus saline). In mixed models, allergen exposure modulated (q ≤ 0.2) miRNAs including miR-183-5p, miR-324-5p, and miR-132-3p and genes including NFKBIZ and CDKN1A, but DE did not significantly modify this allergenic effect. Repression of CDKN1A by allergen-induced miR-132-3p may contribute to shedding of bronchial epithelial cells.

CONCLUSIONS

Expression of specific miRNAs and genes associated with bronchial immune responses were significantly modulated by DE or allergen. However, DE did not augment the effect of allergen at 48 hours, suggesting that adjuvancy may be transient or require higher or prolonged exposure. In silico analysis suggested a possible mechanism contributing to epithelial wall damage following allergen exposure.

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

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

Novel cinnamohydroxamic acid derivatives as HDAC inhibitors with anticancer activity in vitro and in vivo

A novel series of cinnamohydroxamic acid derivatives were synthesized and their biological activities against HDAC were assessed. Our results showed that the compound with more strong inhibitory activity to HDAC would exhibited more significant anti-proliferative effect on tumor cells. Among these compounds, 7e displayed clearly inhibitory effects on HDAC and tumor cell growth. Furthermore, HDAC isoforms enzyme data indicated that, compared to HDAC pan-inhibitor SAHA, 7e owned an enhanced inhibitory effect on HDAC1, 3 and 6 isoforms. Meanwhile, it also significantly suppressed cell growth of lung cancer cells compared to SAHA, but with lower toxicity in normal cells. Mechanistically, 7e prompted acetylation of histone3 and histone4, led to up-regulation of p21, and then mediated cell cycle arrest and pro-apoptosis. Moreover, the in vivo study indicated that compound 7e could retard tumor growth of A549 xenograft models. These findings support the further investigation on the anti-tumor potential of this class of compounds as HDAC inhibitor.

Oncogene-Induced Senescence in Pituitary Adenomas--an Immunohistochemical Study

Oncogene-induced senescence (OIS) serves as an initial barrier to cancer development, being proposed as a possible explanation for the usually benign behavior of the pituitary adenomas. We aimed to explore the immunohistochemical expression of the OIS markers, senescence-associated lysosomal β-galactosidase (SA-β-GAL), p16, and p21 in different types of 345 pituitary adenomas and compared it with the expression in the normal pituitary and in the specimens from the repeated surgeries. SA-β-GAL was overexpressed in the pituitary adenomas, compared to the normal pituitaries. Growth hormone (GH) producing adenomas showed the strongest SA-β-GAL, with densely granulated (DG)-GH adenomas more reactive than the sparsely granulated (SG). Nuclear p21 was decreased in the adenomas, except for the SG-GH adenomas that had higher p21 than the normal pituitaries and the other adenomas. p16 was significantly lower in the adenomas, without type-related differences. SA-β-GAL was slightly lower and p16 slightly higher in the recurrences. Our findings indicate alterations of the senescence program in the different types of pituitary adenomas. Activation of senescence in the pituitary adenomas presents one possible explanation for their usually benign behavior, at least in the GH adenomas that show a synchronous increase of two OIS markers. However, subdivision into GH adenoma subtypes reveals differences that reflect complex regulatory mechanisms influenced by the interplay between the granularity pattern and the hormonal factors, with possible impact on the different clinical behavior of the SG- and DG-GH adenoma subtypes. p16 seems to have a more prominent role in the pituitary tumorigenesis than in the senescence. Recurrent growth in a subset of the pituitary adenomas is not associated with consistent changes in the senescence pattern.

Correlation between cell cycle proteins and hMSH2 in actinic cheilitis and lip cancer

This study aims to evaluate and verify the relationship between the immunoexpression of hMSH2, p53 and p21 in actinic cheilitis (AC) and lower lip squamous cell carcinoma (SCC) cases. Forty AC and 40 SCC cases were submitted to immunoperoxidase method and quantitatively analyzed. Expression was compared by Mann-Whitney test, Student t test or one-way ANOVA. To correlate the variables, Pearson's correlation coefficient was calculated. The expression of p53 and p21 showed no significant differences between histopathological grades of AC or lower lip SCC (p > 0.05). Immunoexpression of p53 was higher in SCC than in AC (p < 0.001), while p21 expression was more observed in AC when compared to SCC group (p = 0.006). The AC group revealed an inverse correlation between p53 and hMSH2 expression (r = -0.30, p = 0.006). Alterations in p53 and p21 expression suggest that these proteins are involved in lower lip carcinogenesis. Moreover, p53 and hMSH2 seem to be interrelated in early events of this process.

Stabilization of p21 by mTORC1/4E-BP1 predicts clinical outcome of head and neck cancers

The levels, regulation and prognostic value of p21 in head and neck squamous cell carcinomas (HNSCC) has been puzzling for years. Here, we report a new mechanism of regulation of p21 by the mTORC1/4E-BP1 pathway. We find that non-phosphorylated 4E-BP1 interacts with p21 and induces its degradation. Accordingly, hyper-activation of mTORC1 results in phosphorylation of 4E-BP1 and stabilization of p21. In HNSCC, p21 levels strongly correlate with mTORC1 activity but not with p53 status. Finally, clinical data indicate that HNSCC patients with p21 and phospho-S6-double-positive tumours present a better disease-specific survival. We conclude that over-activation of the mTORC1/4E-BP1/p21 pathway is a frequent and clinically relevant alteration in HNSCC.

The molecular pathways involving p21 and mTORC1 are frequently deregulated in head and neck squamous cell carcinomas (HNSCC). Here, Llanos et al. report a mechanism that regulates p21 stability through the mTORC1/4E-BP1 pathway independently of p53, and show that the mechanism is prevalent in HNSCC.