SHP-2 tyrosine phosphatase inhibits p73-dependent apoptosis and expression of a subset of p53 target genes induced by EGCG

Context-dependent activation of p53 target genes and induction of apoptosis by actinomycin D in aerodigestive tract cancers

Actinomycin D (ActD) was the first anticancer antibiotic approved for the management of human cancers. However, the notorious toxicity profile limits its widespread application in cancers, including cancers of the aerodigestive tract. Recent studies show that combining low-dose ActD with existing chemotherapies could potentially protect normal cells from the toxicity of chemotherapy drugs through p53 activation (cyclotherapy). An understanding of ActD's effect on p53 signaling is critical for the meaningful application of ActD in cyclotherapy-based combinations. This study evaluated the anti-tumor efficacy and mechanism of action of ActD in aerodigestive tract cancers. We found that ActD strongly inhibited the growth of a panel of aerodigestive tract cancer cell lines and induced efficient apoptosis, although the sensitivity varies among cell lines. The IC₅₀ values of ActD spanned between 0.021 and 2.96 nM. Mechanistic studies revealed that ActD increased the expression of total and phosphorylated p53 (ser15) in a time- and dose-dependent manner. Moreover, ActD-induced apoptosis is dependent on p53 in cells expressing wild-type p53 and that ActD induced context-dependent differential expression of downstream targets p21 and PUMA without significant effects on p27. In the final analysis, this study revealed that p53-p21 is the predominant pathway activated by low-dose ActD, supporting further development of ActD in cyclotherapy.

CENPE Inhibition Leads to Mitotic Catastrophe and DNA Damage in Medulloblastoma Cells

Simple Summary

Medulloblastoma (MB) is the most frequent brain tumor in children. The standard treatment consists in surgery, followed by radiotherapy and chemotherapy. These therapies are only partially effective, since many patients still die and those who survive suffer from neurological and endocrine disorders. Therefore, more effective therapies are needed. CENPE is a gene critical for normal proliferation and survival of neural progenitors. Since there is evidence that MB cells are very similar to neural progenitors, we hypothesized that CENPE could be an effective target for MB treatment. In MB cell lines, CENPE depletion induced defects in division and resulted in cell death. To consolidate CENPE as a target for MB treatment, we tested GSK923295, a specific inhibitor already in clinical trials for other cancer types. GSK923295 induced effects similar to CENPE depletion at low nM levels, supporting the idea that CENPE’s inhibition could be a viable strategy for MB treatment.

Abstract

Medulloblastoma (MB) is the most frequent brain tumor in children. The standard treatment consists in surgery, followed by radiotherapy and chemotherapy. These therapies are only partially effective since many patients still die and those who survive suffer from neurological and endocrine disorders. Therefore, more effective therapies are needed. Primary microcephaly (MCPH) is a rare disorder caused by mutations in 25 different genes. Centromere-associated protein E (CENPE) heterozygous mutations cause the MCPH13 syndrome. As for other MCPH genes, CENPE is required for normal proliferation and survival of neural progenitors. Since there is evidence that MB shares many molecular features with neural progenitors, we hypothesized that CENPE could be an effective target for MB treatment. In ONS-76 and DAOY cells, CENPE knockdown induced mitotic defects and apoptosis. Moreover, CENPE depletion induced endogenous DNA damage accumulation, activating TP53 or TP73 as well as cell death signaling pathways. To consolidate CENPE as a target for MB treatment, we tested GSK923295, an allosteric inhibitor already in clinical trial for other cancer types. GSK923295, induced effects similar to CENPE depletion with higher penetrance, at low nM levels, suggesting that CENPE’s inhibition could be a therapeutic strategy for MB treatment.

Reactive oxygen species generation and increase in mitochondrial copy number: new insight into the potential mechanism of cytotoxicity induced by aurora kinase inhibitor, AZD1152-HQPA

Aurora-B kinase overexpression plays important roles in the malignant progression of prostate cancer (PCa). AZD1152-HQPA, as an inhibitor of Aurora-B, has recently emerged as a promising agent for cancer treatment. In this study, we aimed to investigate the effects of AZD1152-HQPA on reactive oxygen species (ROS) generation and mitochondrial function in PCa. We used AZD1152-HQPA (Barasertib), a highly potent and selective inhibitor of Aurora-B kinase. The effects of AZD1152-HQPA on cell viability, DNA content, cell morphology, and ROS production were studied in the androgen-independent PC-3 PCa cell line. Moreover, the mitochondrial copy number and the expression of genes involved in cell survival and cancer stem cell maintenance were investigated. We found that AZD1152-HQPA treatment induced defective cell survival, polyploidy, micronuclei formation, cell enlargement, and cell death by significant overexpression of p73, p21 and downregulation of cell cycle-regulatory genes in a drug concentration-dependent manner. Moreover, AZD1152 treatment led to an excessive ROS generation and an increase in the mitochondrial copy number not only in PC-3 but also in several other malignant cells. AZD1152 treatment also led to downregulation of genes involved in the maintenance of cancer stem cells. Our results showed a functional relationship between the aurora kinase inhibition, an increase in mitochondrial copy number, and ROS generation in therapeutic modalities of cancer. This study suggests that the excessive ROS generation may be a novel mechanism of cytotoxicity induced by the aurora kinase inhibitor, AZD1152-HQPA.

A Review of the Antiviral Role of Green Tea Catechins

Over the centuries, infectious diseases caused by viruses have seriously threatened human health globally. Viruses are responsible not only for acute infections but also many chronic infectious diseases. To prevent diseases caused by viruses, the discovery of effective antiviral drugs, in addition to vaccine development, is important. Green tea catechins (GTCs) are polyphenolic compounds from the leaves of Camelliasinensis. In recent decades, GTCs have been reported to provide various health benefits against numerous diseases. Studies have shown that GTCs, especially epigallocatechin-3-gallate (EGCG), have antiviral effects against diverse viruses. The aim of this review is to summarize the developments regarding the antiviral activities of GTCs, to discuss the mechanisms underlying these effects and to offer suggestions for future research directions and perspectives on the antiviral effects of EGCG.

The NAD(+) salvage pathway modulates cancer cell viability via p73

The involvement of the nicotinamide adenine dinucleotide (NAD(+)) salvage pathway in cancer cell survival is poorly understood. Here we show that the NAD(+) salvage pathway modulates cancer cell survival through the rarely mutated tumour suppressor p73. Our data show that pharmacological inhibition or knockdown of nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in the NAD(+) salvage pathway, enhances autophagy and decreases survival of cancer cells in a p53-independent manner. Such NAMPT inhibition stabilizes p73 independently of p53 through increased acetylation and decreased ubiquitination, resulting in enhanced autophagy and cell death. These effects of NAMPT inhibition can be effectively reversed using nicotinamide mononucleotide (NMN), the enzymatic product of NAMPT. Similarly, knockdown of p73 also decreases NAMPT inhibition-induced autophagy and cell death, whereas overexpression of p73 alone enhances these effects. We show that the breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) harbour significantly higher levels of NAMPT and lower levels of p73 than does the normal cell line (MCF-10A), and that NAMPT inhibition is cytotoxic exclusively to the cancer cells. Furthermore, data from 176 breast cancer patients demonstrate that higher levels of NAMPT and lower levels of p73 correlate with poorer patient survival, and that high-grade tumours have significantly higher NAMPT/p73 mRNA ratios. Therefore, the inverse relationship between NAMPT and p73 demonstrable in vitro is also reflected from the clinical data. Taken together, our studies reveal a new NAMPT-p73 nexus that likely has important implications for cancer diagnosis, prognosis and treatment.

A multi-targeted approach to suppress tumor-promoting inflammation

Cancers harbor significant genetic heterogeneity and patterns of relapse following many therapies are due to evolved resistance to treatment. While efforts have been made to combine targeted therapies, significant levels of toxicity have stymied efforts to effectively treat cancer with multi-drug combinations using currently approved therapeutics. We discuss the relationship between tumor-promoting inflammation and cancer as part of a larger effort to develop a broad-spectrum therapeutic approach aimed at a wide range of targets to address this heterogeneity. Specifically, macrophage migration inhibitory factor, cyclooxygenase-2, transcription factor nuclear factor-κB, tumor necrosis factor alpha, inducible nitric oxide synthase, protein kinase B, and CXC chemokines are reviewed as important antiinflammatory targets while curcumin, resveratrol, epigallocatechin gallate, genistein, lycopene, and anthocyanins are reviewed as low-cost, low toxicity means by which these targets might all be reached simultaneously. Future translational work will need to assess the resulting synergies of rationally designed antiinflammatory mixtures (employing low-toxicity constituents), and then combine this with similar approaches targeting the most important pathways across the range of cancer hallmark phenotypes.

Functions of Shp2 in cancer

Diagnostics and therapies have shown evident advances. Tumour surgery, chemotherapy and radiotherapy are the main techniques in treat cancers. Targeted therapy and drug resistance are the main focus in cancer research, but many molecular intracellular mechanisms remain unknown. Src homology region 2-containing protein tyrosine phosphatase 2 (Shp2) is associated with breast cancer, leukaemia, lung cancer, liver cancer, gastric cancer, laryngeal cancer, oral cancer and other cancer types. Signalling pathways involving Shp2 have also been discovered. Shp2 is related to many diseases. Mutations in the ptpn11 gene cause Noonan syndrome, LEOPARD syndrome and childhood leukaemia. Shp2 is also involved in several cancer-related processes, including cancer cell invasion and metastasis, apoptosis, DNA damage, cell proliferation, cell cycle and drug resistance. Based on the structure and function of Shp2, scientists have investigated specific mechanisms involved in cancer. Shp2 may be a potential therapeutic target because this phosphatase is implicated in many aspects. Furthermore, Shp2 inhibitors have been used in experiments to develop treatment strategies. However, conflicting results related to Shp2 functions have been presented in the literature, and such results should be resolved in future studies.

Curcumin induces apoptosis of upper aerodigestive tract cancer cells by targeting multiple pathways

Curcumin, a natural compound isolated from the Indian spice "Haldi" or "curry powder", has been used for centuries as a traditional remedy for many ailments. Recently, the potential use of curcumin in cancer prevention and therapy urges studies to uncover the molecular mechanisms associated with its anti-tumor effects. In the current manuscript, we investigated the mechanism of curcumin-induced apoptosis in upper aerodigestive tract cancer cell lines and showed that curcumin-induced apoptosis is mediated by the modulation of multiple pathways such as induction of p73, and inhibition of p-AKT and Bcl-2. Treatment of cells with curcumin induced both p53 and the related protein p73 in head and neck and lung cancer cell lines. Inactivation of p73 by dominant negative p73 significantly protected cells from curcumin-induced apoptosis, whereas ablation of p53 by shRNA had no effect. Curcumin treatment also strongly inhibited p-AKT and Bcl-2 and overexpression of constitutively active AKT or Bcl-2 significantly inhibited curcumin-induced apoptosis. Taken together, our findings suggest that curcumin-induced apoptosis is mediated via activating tumor suppressor p73 and inhibiting p-AKT and Bcl-2.

FLLL12 induces apoptosis in lung cancer cells through a p53/p73-independent but death receptor 5-dependent pathway

Unlike chemotherapy drugs, the safety of natural compounds such as curcumin has been well established. However, the potential use of curcumin in cancer has been compromised by its low bioavailability, limited tissue distribution and rapid biotransformation leading to low in vivo efficacy. To circumvent these problems, more potent and bioavailable analogs have been synthesized. In the current study, we investigated the mechanism of anti-tumor effect of one such analog, FLLL12, in lung cancers. IC50 values measured by sulforhodamine B (SRB) assay at 72 h and apoptosis assays (annexin V staining, cleavage of PARP and caspase-3) suggest that FLLL12 is 5-10-fold more potent than curcumin against a panel of premalignant and malignant lung cancer cell lines, depending on the cell line. Moreover, FLLL12 induced the expression of death receptor-5 (DR5). Ablation of the expression of the components of the extrinsic apoptotic pathway (DR5, caspase-8 and Bid) by siRNA significantly protected cells from FLLL12-induced apoptosis (p < 0.05). Analysis of mRNA expression revealed that FLLL-12 had no significant effect on the expression of DR5 mRNA expression. Interestingly, inhibition of global phosphatase activity as well as protein tyrosine phosphatases (PTPs), but not of alkaline phosphatases, strongly inhibited DR5 expression and significantly inhibited apoptosis (p < 0.05), suggesting the involvement of PTPs in the regulation of DR5 expression and apoptosis. We further showed that the apoptosis is independent of p53 and p73. Taken together, our results strongly suggest that FLLL12 induces apoptosis of lung cancer cell lines by posttranscriptional regulation of DR5 through activation of protein tyrosine phosphatase(s).

T cell activation is reduced by the catalytically inactive form of protein tyrosine phosphatase SHP-2

Src-homology 2 domain-containing tyrosine phosphatase-2 (SHP-2) is a ubiquitously expressed cytosolic tyrosine phosphatase implicated in many different signaling pathways involving cytokine receptors and T and B cell receptors; however, the precise functional role of SHP-2 in T cell signaling is not entirely clear. In this study, we overexpressed a catalytically inactive form of SHP-2 with a classic cysteine 459-to-serine mutation (dnSHP-2) to elucidate the in vivo effects of SHP-2 on T cells. We found that mice overexpressing dnSHP-2 showed reduced T cell activation, presumably due to increased tyrosine phosphorylation of Grb2-binding protein (Gab2) and inhibition of mitogen-activated protein kinase (MAPK) activity. SHP-2 appears to be a positive regulator of the MAPK pathway in T cells, likely through coupling of the multimeric complex to the Ras/MAPK pathway. However, SHP-2 does not appear to affect T cell antigen receptor (TCR)-evoked calcium mobilization, stress-activated protein kinase/c-jun N-terminal kinases (SAPK/JNKs) activation, or overall tyrosine phosphorylation.

Evasion of anti-growth signaling: A key step in tumorigenesis and potential target for treatment and prophylaxis by natural compounds

The evasion of anti-growth signaling is an important characteristic of cancer cells. In order to continue to proliferate, cancer cells must somehow uncouple themselves from the many signals that exist to slow down cell growth. Here, we define the anti-growth signaling process, and review several important pathways involved in growth signaling: p53, phosphatase and tensin homolog (PTEN), retinoblastoma protein (Rb), Hippo, growth differentiation factor 15 (GDF15), AT-rich interactive domain 1A (ARID1A), Notch, insulin-like growth factor (IGF), and Krüppel-like factor 5 (KLF5) pathways. Aberrations in these processes in cancer cells involve mutations and thus the suppression of genes that prevent growth, as well as mutation and activation of genes involved in driving cell growth. Using these pathways as examples, we prioritize molecular targets that might be leveraged to promote anti-growth signaling in cancer cells. Interestingly, naturally occurring phytochemicals found in human diets (either singly or as mixtures) may promote anti-growth signaling, and do so without the potentially adverse effects associated with synthetic chemicals. We review examples of naturally occurring phytochemicals that may be applied to prevent cancer by antagonizing growth signaling, and propose one phytochemical for each pathway. These are: epigallocatechin-3-gallate (EGCG) for the Rb pathway, luteolin for p53, curcumin for PTEN, porphyrins for Hippo, genistein for GDF15, resveratrol for ARID1A, withaferin A for Notch and diguelin for the IGF1-receptor pathway. The coordination of anti-growth signaling and natural compound studies will provide insight into the future application of these compounds in the clinical setting.

Chemoprevention of oral cancer: Green tea experience

Oral cancer has a well characterized progression from premalignant oral epithelial changes to invasive cancer, making oral squamous cell carcinoma an optimal disease for chemoprevention interventions prior to malignant transformation. The primary goal of chemoprevention here is to reverse, suppress, or inhibit the progression of premalignant lesions to cancer. Due to the extended duration of oral pathogenesis, its chemoprevention using natural products has been found promising due to their decreased dose and limited toxicity profiles. This review discusses with an emphasis on the clinical trials using green tea extract (GTE) in chemoprevention of oral premalignant lesions along with use of GTE as a chemopreventive agent in various other cancers as well. It is worthwhile to include green tea extract in an oral screening program for evaluating the premalignant lesions comparing the results between the treated and untreated group. Given the wide acceptance of green tea, its benefits may help in effective chemoprevention oral cancer.

Multivariate signaling regulation by SHP2 differentially controls proliferation and therapeutic response in glioma cells

Information from multiple signaling axes is integrated in the determination of cellular phenotypes. Here, we demonstrate this aspect of cellular decision making in glioblastoma multiforme (GBM) cells by investigating the multivariate signaling regulatory functions of the protein tyrosine phosphatase SHP2 (also known as PTPN11). Specifically, we demonstrate that the ability of SHP2 to simultaneously drive ERK1/2 and antagonize STAT3 pathway activities produces qualitatively different effects on the phenotypes of proliferation and resistance to EGFR and c-MET co-inhibition. Whereas the ERK1/2 and STAT3 pathways independently promote proliferation and resistance to EGFR and c-MET co-inhibition, SHP2-driven ERK1/2 activity is dominant in driving cellular proliferation and SHP2-mediated antagonism of STAT3 phosphorylation prevails in the promotion of GBM cell death in response to EGFR and c-MET co-inhibition. Interestingly, the extent of these SHP2 signaling regulatory functions is diminished in glioblastoma cells that express sufficiently high levels of the EGFR variant III (EGFRvIII) mutant, which is commonly expressed in GBM. In cells and tumors that express EGFRvIII, SHP2 also antagonizes the phosphorylation of EGFRvIII and c-MET and drives expression of HIF-1α and HIF-2α, adding complexity to the evolving understanding of the regulatory functions of SHP2 in GBM.

Anti-cancer potential of flavonoids: recent trends and future perspectives

Cancer is a major public health concern in both developed and developing countries. Several plant-derived anti-cancer agents including taxol, vinblastine, vincristine, the campothecin derivatives, topotecan, irinotecan and etoposide are in clinical use all over the world. Other promising anti-cancer agents include flavopiridol, roscovitine, combretastatin A-4, betulinic acid and silvestrol. From this list one can well imagine the predominance of polyphenols, flavonoids and their synthetic analogs in the treatment of ovarian, breast, cervical, pancreatic and prostate cancer. Flavonoids present in human diet comprise many polyphenolic secondary metabolites with broad-spectrum pharmacological activities including their potential role as anti-cancer agents. A positive correlation between flavonoids-rich diet (from vegetables and fruits) and lower risk of colon, prostate and breast cancers lead to a question that whether flavonoids mediate the protective effects as chemopreventive agents or can interact with different genes and proteins to play role in chemotherapy. The current review emphasizes onto the therapeutic potential of flavonoids and their synthetic analogs as anti-cancer agents by providing new insights into the factors, regulation and molecular mechanisms along with their significant protein interactions.

RRM2 regulates Bcl-2 in head and neck and lung cancers: a potential target for cancer therapy

PURPOSE

Ribonucleotide reductase subunit M2 (RRM2) plays an active role in tumor progression. Recently, we reported that depletion of RRM2 by systemic delivery of a nanoparticle carrying RRM2-specific siRNA suppresses head and neck tumor growth. The aim of this study is to clarify the underlying mechanism by which RRM2 depletion inhibits tumor growth.

EXPERIMENTAL DESIGN

siRNA-mediated gene silencing was carried out to downregulate RRM2. Immunoblotting, reverse-transcriptase PCR, confocal microscopy, tissue fractionation, gene overexpression and knockdown were employed to analyze critical apoptosis signaling. Conventional immunohistochemistry and quantum dot-based immunofluorescence were applied to detect RRM2 and Bcl2 expression and localization in tissue samples from patients and mice.

RESULTS

Knockdown of RRM2 led to apoptosis through the intrinsic pathway in head and neck squamous cell carcinoma (HNSCC) and non-small cell lung cancer (NSCLC) cell lines. We showed that Bcl-2 is a key determinant controlling apoptosis, both in vitro and in vivo, and that RRM2 depletion significantly reduces Bcl-2 protein expression. We observed that RRM2 regulates Bcl-2 protein stability, with RRM2 suppression leading to increased Bcl-2 degradation, and identified their colocalization in HNSCC and NSCLC cells. In a total of 50 specimens each from patients with HNSCC and NSCLC, we identified the colocalization of Bcl-2 and RRM2 and found a significant positive correlation between their expression in HNSCC (R = 0.98; P < 0.0001) and NSCLC (R = 0.92; P < 0.0001) tumor tissues.

CONCLUSIONS

Our novel findings add to the knowledge of RRM2 in regulating expression of the antiapoptotic protein Bcl-2 and reveal a critical link between RRM2 and Bcl-2 in apoptosis signaling.

Going Green: The Role of the Green Tea Component EGCG in Chemoprevention

Tea is one of the most consumed beverages worldwide, and green tea is the least processed from the buds of the Camellia sinensis plant. The most abundant component of green tea is (-)-epigallocatechin-3-gallate (EGCG), which has been the focus of many cell culture, animal and clinical trials, revealing that EGCG possesses antiproliferative, antimutagenic, antioxidant, antibacterial, antiviral and chemopreventive effects. In this review we briefly summarize the mechanism of action(s) of the green tea component EGCG, highlighting recent advances in the epigenetic regulation by EGCG. Additionally, we provide an overview of mouse chemoprevention studies and EGCG chemoprevention clinical trials.

Novel functions of the phosphatase SHP2 in the DNA replication and damage checkpoints

Replication stress- and DNA damage-induced cell cycle checkpoints are critical for maintaining genome stability. To identify protein phosphatases involved in the activation and maintenance of the checkpoints, we have carried out RNA interference-based screens with a human phosphatome shRNA library. Several phosphatases, including SHP2 (also called PTPN11) were found to be required for cell survival upon hydroxyurea-induced replicative stress in HeLa cells. More detailed studies revealed that SHP2 was also important for the maintenance of the checkpoint after DNA damage induced by cisplatin or ionizing radiation in HeLa cells. Furthermore, SHP2 was activated after replicative stress and DNA damage. Although depletion of SHP2 resulted in a delay in cyclin E accumulation and an extension of G₁ phase, these cell cycle impairments were not responsible for the increase in apoptosis after DNA damage. Depletion of SHP2 impaired CHK1 activation, checkpoint-mediated cell cycle arrest, and DNA repair. These effects could be rescued with a shRNA-resistant SHP2. These results underscore the importance of protein phosphatases in checkpoint control and revealed a novel link between SHP2 and cell cycle checkpoints.

The chemopreventive and chemotherapeutic potentials of tea polyphenols

Tea is the second most consumed beverage in the world reported to have multiple health benefits. Preventive and therapeutic benefits of tea polyphenols include enhanced general well being and anti-neoplastic effects. The pharmacologic action of tea is often attributed to various catechins present therein. Experiments conducted in cancer cell lines and animal models demonstrate that tea polyphenols protect against cellular damage caused by oxidative stress and altered immunity. Tea polyphenols modify various metabolic and signaling pathways in the regulation of proliferation, apoptosis, angiogenesis, and metastasis and therefore restrict clonal expansion of cancer cells. Tea polyphenols have been shown to reactivate tumor suppressors, block the unlimited replicative potential of cancer cells, and physically bind to nucleic acids involved in epigenetic alterations of gene regulation. Remarkable interest in green tea as a potential chemopreventive agent has been generated since recent epigenetic data showed that tea polyphenols have the potential to reverse epigenetic modifications which might otherwise be carcinogenic. Like green tea, black tea may also possess chemopreventive and chemotherapeutic potential; however, there is still not enough evidence available to make any conclusive statements. Here we present a brief description of tea polyphenols and discuss the findings of various in vitro and in vivo studies of the anticancer effects of tea polyphenols. Detailed discussion of various studies related to epigenetic changes caused by tea polyphenols leading to prevention of oncogenesis or cancer progression is included. Finally, we discuss on the scope and development of tea polyphenols in cancer prevention and therapy.

Overexpression of Shp-2 attenuates apoptosis in neonatal rat cardiac myocytes through the ERK pathway

During cardiac ischemia and end-stage heart disease, a large number of cardiac cells are apoptotic, and therefore, heart function is impaired. Although the role of Shp-2 in cell survival has been reported, its regulation of cardiac apoptosis is still undetermined. To better understand the potential role of Shp-2 in apoptosis, cell death was determined in serum-depleted cardiomyocytes. Shp-2 was inhibited by NSC87877, and apoptosis, Cyt C release and caspase 3 activation were determined. To evaluate the notion that Shp-2 plays a role in survival stimulation, wild-type and gain-of-function mutant Shp-2 adenoviruses were infected into neonatal cardiomyocytes, and ERK activation was examined. Finally, the MEK inhibitor U0126 was utilized to block the ERK pathway and determine the role of Shp-2 in this pathway. We found that Shp-2 inhibition enhanced apoptosis via regulation of mitochondrial Cyt C release and activation of caspase 3. Overexpression of Shp-2 inhibited apoptosis through activation of ERK. The MEK inhibitor U0126 abolished Shp-2's effect on apoptosis in cardiomyocytes. Our results have revealed that Shp-2 functions as an intracellular inhibitor of apoptosis. These data provide insight into the pathogenesis and the therapeutic strategies of heart diseases.

N-(phosphonacetyl)-L-aspartate induces TAp73-dependent apoptosis by modulating multiple Bcl-2 proteins: potential for cancer therapy

p53 is essential for the cellular responses to DNA damage that help to maintain genomic stability. However, the great majority of human cancers undergo disruption of the p53-network. Identification and characterization of molecular components important in both p53-dependent and -independent apoptosis might be useful in developing novel therapies for cancers. In the complete absence of p53, cells treated with N-(phosphonacetyl)-L-aspartate (PALA) continue to synthesize DNA slowly and eventually progress through S phase, suffering severe DNA damage that in turn triggers apoptosis, whereas cells with functional p53 undergo growth arrest. In the present study, we investigated apoptotic signaling in response to PALA and the role of p53 expression in this pathway. We found that treatment of cells lacking p53 with PALA induced TAp73, Noxa, and Bim and inactivation of these proteins with dominant negative plasmids or siRNAs significantly inhibited apoptosis, suggesting that PALA-induced apoptosis was mediated via TAp73-dependent expression of Noxa and Bim. However, PALA treatment inhibited the expression of ΔNp73 only in cells lacking p53 but not in cells expressing p53. In addition, PALA treatment inhibited Bcl-2, and overexpression of Bcl-2 significantly inhibited PALA-induced apoptosis. Moreover, expression of p53 in these cells protected them from PALA-induced apoptosis by activating p21, sustaining the expression of ΔNp73 and inhibiting the induction of Noxa and Bim. Taken together, our study identifies novel but opposing roles for the p53 and TAp73 in the induction of Noxa and Bim and regulation of apoptosis. Our data will help to develop strategies to eliminate cancer cells lacking p53 while protecting normal cells with wild-type p53.

Essential role for Ptpn11 in survival of hematopoietic stem and progenitor cells

Src homology 2 domain-containing phosphatase 2 (Shp2), encoded by Ptpn11, is a member of the nonreceptor protein-tyrosine phosphatase family, and functions in cell survival, proliferation, migration, and differentiation in many tissues. Here we report that loss of Ptpn11 in murine hematopoietic cells leads to bone marrow aplasia and lethality. Mutant mice show rapid loss of hematopoietic stem cells (HSCs) and immature progenitors of all hematopoietic lineages in a gene dosage-dependent and cell-autonomous manner. Ptpn11-deficient HSCs and progenitors undergo apoptosis concomitant with increased Noxa expression. Mutant HSCs/progenitors also show defective Erk and Akt activation in response to stem cell factor and diminished thrombopoietin-evoked Erk activation. Activated Kras alleviates the Ptpn11 requirement for colony formation by progenitors and cytokine/growth factor responsiveness of HSCs, indicating that Ras is functionally downstream of Shp2 in these cells. Thus, Shp2 plays a critical role in controlling the survival and maintenance of HSCs and immature progenitors in vivo.

Cancer prevention with natural compounds

Botanical and nutritional compounds have been used for the treatment of cancer throughout history. These compounds also may be useful in the prevention of cancer. Population studies suggest that a reduced risk of cancer is associated with high consumption of vegetables and fruits. Thus, the cancer chemopreventive potential of naturally occurring phytochemicals is of great interest. There are numerous reports of cancer chemopreventive activity of dietary botanicals, including cruciferous vegetables such as cabbage and broccoli, Allium vegetables such as garlic and onion, green tea, Citrus fruits, soybeans, tomatoes, berries, and ginger, as well as medicinal plants. Several lead compounds, such as genistein (from soybeans), lycopene (from tomatoes), brassinin (from cruciferous vegetables), sulforaphane (from asparagus), indole-3-carbinol (from broccoli), and resveratrol (from grapes and peanuts) are in preclinical or clinical trials for cancer chemoprevention. Phytochemicals have great potential in cancer prevention because of their safety, low cost, and oral bioavailability. In this review, we discuss potential natural cancer preventive compounds and their mechanisms of action.

Chemoprevention of head and neck cancer with green tea polyphenols

Recently, squamous cell carcinoma of the head and neck chemoprevention research has made major advances with novel clinical trial designs suited for the purpose, use of biomarkers to identify high-risk patients, and the emergence of numerous molecularly targeted agents and natural dietary compounds. Among many natural compounds, green tea polyphenols, particularly (-)-epigallocatechin-3-gallate (EGCG), possess remarkable potential as chemopreventive agents. EGCG modulates several key molecular signaling pathways at multiple levels and has synergistic or additive effects when combined with many other natural or synthetic compounds. This review will provide an update of the potential of green tea polyphenols, particularly EGCG, for the chemoprevention of squamous cell carcinoma of the head and neck.

p53-Dependent p21-mediated growth arrest pre-empts and protects HCT116 cells from PUMA-mediated apoptosis induced by EGCG

The tumor suppressor protein p53 plays a key role in regulation of negative cellular growth in response to EGCG. To further explore the role of p53 signaling and elucidate the molecular mechanism, we employed colon cancer HCT116 cell line and its derivatives in which a specific transcriptional target of p53 is knocked down by homologous recombination. Cells expressing p53 and p21 accumulate in G1 upon treatment with EGCG. In contrast, same cells lacking p21 traverse through the cell cycle and eventually undergo apoptosis as revealed by TUNEL staining. Treatment with EGCG leads to induction of p53, p21 and PUMA in p21 wild-type, and p53 and PUMA in p21(-/-) cells. Ablation of p53 by RNAi protects p21(-/-) cells, thus indicating a p53-dependent apoptosis by EGCG. Furthermore, analysis of cells lacking PUMA or Bax with or without p21 but with p53 reveals that all the cells expressing p53 and p21 survived after EGCG treatment. More interestingly, cells lacking both PUMA and p21 survived ECGC treatment whereas those lacking p21 and Bax did not. Taken together, our results present a novel concept wherein p21-dependent growth arrest pre-empts and protects cells from otherwise, in its absence, apoptosis which is mediated by activation of pro-apoptotic protein PUMA. Furthermore, we find that p53-dependent activation of PUMA in response to EGCG directly leads to apoptosis with out requiring Bax as is the case in response to agents that induce DNA damage. p21, thus can be used as a molecular switch for therapeutic intervention of colon cancer.

Inhibition of the insulin-like growth factor I receptor by epigallocatechin gallate blocks proliferation and induces the death of Ewing tumor cells

The insulin-like growth factor I receptor (IGFIR) has emerged as a key therapeutic target in many human malignancies, including childhood cancers such as Ewing family tumors (EFT). In this study, we show that IGFIR is constitutively activated in EFTs and that the major catechin derivative found in green tea, (-)-epigallocatechin gallate (EGCG), can inhibit cell proliferation and survival of EFT cells through the inhibition of IGFIR activity. Treatment of EFT cell lines with EGCG blocked the autophosphorylation of IGFIR tyrosine residues and inhibited its downstream pathways including phosphoinositide 3-kinase-Akt, Ras-Erk, and Jak-Stat cascades. EGCG treatment was associated with dose- and time-dependent inhibition of cellular proliferation, viability, and anchorage-independent growth, as well as with the induction of cell cycle arrest and apoptosis. Apoptosis in EFT cells by EGCG correlated with altered expression of Bcl-2 family proteins, including increased expression of proapoptotic Bax and decreased expression of prosurvival Bcl2, Bcl-XL, and Mcl-1 proteins. Our results provide further evidence that IGFIR is an attractive therapeutic target in EFTs and that EGCG is an effective inhibitor of this receptor tyrosine kinase. EGCG may be a useful agent for targeting IGFIR, either alone or in combination, with other potentially more toxic IGFIR inhibitors for the management of EFTs.

Oral cancer prevention advances with a translational trial of green tea

This perspective on Tsao et al. (beginning on p. 931 in this issue of the journal) discusses green tea extract, which was shown for the first time to have dose-dependent effects in a clinical chemopreventive setting (oral premalignant lesions). This translational trial provides important data on angiogenesis and other biomarkers on which to base future clinical research, which should include trials of green tea extract or polyphenols combined with other natural or synthetic compounds to enhance chemopreventive effects.

Arsenic trioxide induces apoptosis in NB-4, an acute promyelocytic leukemia cell line, through up-regulation of p73 via suppression of nuclear factor kappa B-mediated inhibition of p73 transcription and prevention of NF-kappaB-mediated induction of XIAP, cIAP2, BCL-XL and survivin

The purpose of the present study is to evaluate the effects of arsenic trioxide (ATO) on human acute promyelocytic leukemia NB-4 cells. Microculture tetrazolium test, bromodeoxyuridine (BrdU) cell proliferation assay, caspase 3 activity assay, cell-based nuclear factor kappa B (NF-kappaB) phosphorylation measurement by ELISA and real-time RT-PCR were employed to appraise the effects of ATO on metabolic activity, DNA synthesis, induction of programmed cell death and NF-kappaB activation. The suppressive effects of ATO on metabolic potential, cell proliferation and NF-kappaB activation were associated with induction of apoptosis in NB-4 cells. In addition, an expressive enhancement in mRNA levels of p73, cyclin-dependent kinase inhibitor 1A (p21), tumor protein 53-induced nuclear protein 1 (TP53INP1), WNK lysine deficient protein kinase 2 (WNK2) and lipocalin 2 coupled with a significant reduction in transcriptional levels of NF-kappaB inhibitor beta (IKK2), Nemo, BCL2-like 1 (BCL-X(L)), inhibitor of apoptosis protein 1 (cIAP2), X-linked inhibitor of apoptosis protein (XIAP), survivin, Bcl-2, TIP60, ataxia telangiectasia (ATM), SHP-2 and sirtuin (SIRT1) were observed. Altogether, these issues show for the first time that ATO treatment could trammel cell growth and proliferation as well as induces apoptosis in NB-4 cells through induction of transcriptional levels of p73, TP53INP1, WNK2, lipocalin 2 as well as suppression of NF-kappaB-mediated induction of BCL-X(L), cIAP2, XIAP and survivin. Furthermore, the inductionary effects of ATO on transcriptional stimulation of p73 might be through cramping the NF-kappaB module (through suppression of p65 phosphorylation as well as transcriptional hindering of IKK2, ATM and Nemo) along with diminishing the mRNA expression of TIP60, SHP-2 and SIRT1.

Perspectives for cancer prevention with natural compounds

Cancer is the second leading cause of death in the United States. Despite the estimated 565,650 deaths in 2008 of Americans as a result of cancer, it is mostly a preventable disease. Simply by modification of diet, maintenance of optimum body weight, and regular physical activity, 30% to 40% of all instances of cancer could be prevented. Modification of diet alone by increasing vegetable and fruit intake could prevent 20% or more of all cases of cancer and may potentially prevent approximately 200,000 cancer-related deaths annually. Because of their safety, low toxicity, antioxidant properties, and general acceptance as dietary supplements, fruits, vegetables, and other dietary elements (phytochemicals and minerals) are being investigated for the prevention of cancer. Extensive research over the past several decades has identified numerous dietary and botanical natural compounds that have chemopreventive potential. In this review, we discuss promising natural chemopreventive compounds, their molecular targets, and their mechanisms, which may help the further design and conduct of preclinical and clinical trials.

Synergistic growth inhibition of squamous cell carcinoma of the head and neck by erlotinib and epigallocatechin-3-gallate: the role of p53-dependent inhibition of nuclear factor-kappaB

We have previously reported that the green tea polyphenol epigallocatechin-3-gallate (EGCG) and the epidermal growth factor receptor-tyrosine kinase inhibitor erlotinib had synergistic growth-inhibitory effects in cell culture and a nude mouse xenograft model of squamous cell carcinoma of the head and neck. However, the mechanism of their antitumor synergism is not fully understood. In the current study, we investigate the mechanism of their synergistic growth-inhibitory effects. The treatment of squamous cell carcinoma of the head and neck cell lines with erlotinib time-dependently increased the expression of cell cycle regulatory proteins p21 and p27 and apoptosis regulatory protein Bim. EGCG alone had very little or no effect on the expression of these proteins among the cell lines. However, simultaneous treatment with EGCG and erlotinib strongly inhibited erlotinib-induced expression of p21 and p27 without affecting the expression of Bim. Moreover, erlotinib increased the expression of p53 protein, the ablation of which by short hairpin RNA strongly inhibited EGCG- and erlotinib-mediated growth inhibition and the expression of p21, p27, and Bim. In addition, combined treatment with erlotinib and EGCG inhibited the protein level of p65 subunit of nuclear factor-kappaB and its transcriptional target Bcl-2, but failed to do so in cells with ablated p53. Taken together, our results, for the first time, suggest that erlotinib treatment activates p53, which plays a critical role in synergistic growth inhibition by erlotinib and EGCG via inhibiting nuclear factor-kappaB signaling pathway. Characterizing the underlying mechanisms of EGCG and erlotinib synergism will provide an important rationale for chemoprevention or treatment trials using this combination.

Inhibition of BCL2 expression and activity increases H460 sensitivity to the growth inhibitory effects of polyphenon E

The anti-cancer properties of the green tea-derived mixture Polyphenon E (Poly E) have been demonstrated in a variety of cell culture and animal models. We recently discovered that the H460 lung cancer cell line is markedly resistant to the growth inhibitory effects of Poly E compared with SW480 colon and Flo-1 esophageal cancer cells. We investigated the mechanism of H460 resistance by comparing gene expression profiles of Poly E-sensitive and -resistant cells. Unsupervised hierarchical clustering revealed that Poly E-sensitive cells clustered separately from Poly E-resistant cells, and 6,242 genes were differentially expressed between the two groups at the 0.01 level of significance. We discovered that BCL2 gene and protein expression were significantly higher in H460 cells compared with SW480 and Flo-1 cells (10.60-fold higher gene expression; P < 0.0001). Inhibition of BCL2 expression and activity, using siRNA and the small molecule inhibitor HA14-1 respectively, restored sensitivity to Poly E and induced BCL2-related apoptosis by decreasing mitochondrial membrane potential and inducing PARP cleavage. Our results suggest that increased BCL2 expression may contribute to H460 resistance to the growth inhibitory effects of Poly E. If validated in additional laboratory and clinical models, BCL2 could ultimately be used as a marker of Poly E resistance.

Nitric oxide as a target of complementary and alternative medicines to prevent and treat inflammation and cancer

Nitric oxide (NO) and associated reactive nitrogen species (RNS) are involved in many physiological functions. There has been an ongoing debate to whether RNS can inhibit or perpetuate chronic inflammation and associated carcinogenesis. Although the final outcome depends on the genetic make-up of its target, the surrounding microenvironment, the activity and localization of nitric oxide synthase (NOS) isoforms, and overall levels of NO/RNS, evidence is accumulating that in general, RNS drive inflammation and cancers associated with inflammation. To this end, many complementary and alternative medicines (CAMs) that work in chemoprevention associated with chronic inflammation, are inhibitors of excessive NO observed in inflammatory conditions. Here, we review recent literature outlining a role of NO/RNS in chronic inflammation and cancer, and point toward NO as one of several targets for the success of CAMs in treating chronic inflammation and cancer associated with this inflammation.

Adamantyl-substituted retinoid-derived molecules that interact with the orphan nuclear receptor small heterodimer partner: effects of replacing the 1-adamantyl or hydroxyl group on inhibition of cancer cell growth, induction of cancer cell apoptosis, and inhibition of SRC homology 2 domain-containing protein tyrosine phosphatase-2 activity

(E)-4-[3-(1-Adamantyl)-4'-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC) induces the cell-cycle arrest and apoptosis of leukemia and cancer cells. Studies demonstrated that 3-Cl-AHPC bound to the atypical orphan nuclear receptor small heterodimer partner (SHP). Although missing a DNA-binding domain, SHP heterodimerizes with the ligand-binding domains of other nuclear receptors to repress their abilities to induce or inhibit gene expression. 3-Cl-AHPC analogues having the 1-adamantyl and phenolic hydroxyl pharmacophoric elements replaced with isosteric groups were designed, synthesized, and evaluated for their inhibition of proliferation and induction of human cancer cell apoptosis. Structure-anticancer activity relationship studies indicated the importance of both groups to apoptotic activity. Docking of 3-Cl-AHPC and its analogues to an SHP computational model that was based on the crystal structure of ultraspiracle complexed with 1-stearoyl-2-palmitoylglycero-3-phosphoethanolamine suggested why these 3-Cl-AHPC groups could influence SHP activity. Inhibitory activity against Src homology 2 domain-containing protein tyrosine phosphatase 2 (Shp-2) was also assessed. The most active Shp-2 inhibitor was found to be the 3'-(3,3-dimethylbutynyl) analogue of 3-Cl-AHPC.

Small-molecule RETRA suppresses mutant p53-bearing cancer cells through a p73-dependent salvage pathway

Identification of unique features of cancer cells is important for defining specific and efficient therapeutic targets. Mutant p53 is present in nearly half of all cancer cases, forming a promising target for pharmacological reactivation. In addition to being defective for the tumor-suppressor function, mutant p53 contributes to malignancy by blocking a p53 family member p73. Here, we describe a small-molecule RETRA that activates a set of p53-regulated genes and specifically suppresses mutant p53-bearing tumor cells in vitro and in mouse xenografts. Although the effect is strictly limited to the cells expressing mutant p53, it is abrogated by inhibition with RNAi to p73. Treatment of mutant p53-expressing cancer cells with RETRA results in a substantial increase in the expression level of p73, and a release of p73 from the blocking complex with mutant p53, which produces tumor-suppressor effects similar to the functional reactivation of p53. RETRA is active against tumor cells expressing a variety of p53 mutants and does not affect normal cells. The results validate the mutant p53-p73 complex as a promising and highly specific potential target for cancer therapy.

A Novel Role for p73 in the Regulation of Akt-Foxo1a-Bim Signaling and Apoptosis Induced by the Plant Lectin, Concanavalin A

Virtually all human cancers encounter disruption of the "p53 network." From a therapeutic point of view, it is important to devise strategies that eliminate cancer cells, which are often defective in functional p53 and protect p53-expressing normal cells. By comparing the response of a pair of isogenic cell lines, we identify a plant-derived compound, Concanavalin A (Con A), which differentially kills p53-null cells. Further, we find that p53 family member, p73, plays a critical role that is unmasked in the absence of p53. Con A treatment leads to induction of p73 and several others that are important mediators of apoptosis and act downstream, such as p21, Bax, Foxo1a, and Bim. Inactivation of p73 reverses the expression of these proteins and apoptosis. Inhibition of Akt activation sensitizes otherwise resistant cells. These observations thus reveal a novel role for p73 in the regulation of Akt-Foxo1a-Bim signaling and apoptosis especially when p53 is absent.

Cancer preventive mechanisms of the green tea polyphenol (-)-epigallocatechin-3-gallate

Accumulating evidence indicates that consumption of tea, especially green tea, is good for preventing cancer. To elucidate the cancer preventive mechanisms of green tea, much effort has been devoted to investigating the anticancer effects of (-)-epigallocatechin-3-gallate (EGCG), the major component of green tea. It has been revealed that EGCG restrained carcinogenesis in a variety of tissues through inhibition of mitogen-activated protein kinases (MAPK), growth factor-related cell signaling, activation of activator protein 1 (AP-1) and nuclear factor-B (NF-kappaB), topoisomerase I, matrix metalloproteinases and other potential targets. Therefore, EGCG is a multipotent anticancer agent, which not only provides solid evidence to support the anticancer potential of green tea, but also offers new clues for discovering multiple-targeted anticancer drugs.