The reaction of flavanols with nitrous acid protects against N-nitrosamine formation and leads to the formation of nitroso derivatives which inhibit cancer cell growth

Studies have suggested that diets rich in polyphenols Such as flavonoids may lead to a reduced risk of gastrointestinal cancers. We demonstrate the ability of monomeric and dimeric flavanols to scavenge reactive nitrogen species derived from nitrous acid. Both epicatechin and dimer B2 (epicatechin dimer) inhibited nitrous acid-induced formation of 3-nitrotyrosine and the formation of the carcinogenic N-nitrosamine, N-nitrosodimethylamine. The reaction of monomeric and dimeric epicatechin with nitrous acid led to the formation of mono- and di-nitroso flavanols, whereas the reaction with hesperetin resulted primarily in the formation of nitrated products. Although, epicatechin was transferred across the jejunum of the small intestine yielding metabolites, its nitroso form was not absorbed. Dimer B2 but not epicatechin monomer inhibited the proliferation of, and triggered apoptosis in, Caco-2 cells. The latter was accompanied by caspase-3 activation and reductions in Akt phosphorylation, suggesting activation of apoptosis via inhibition of prosurvival signaling. Furthermore, the dinitroso derivative of dimer B2, and to a lesser extent the dinitroso-epicatechin, also induced significant toxic effects in Caco-2 cells. The inhibitory effects on cellular proliferation were paralleled by early inhibition of ERK 1/2 phosphorylation and later reductions in cyclin D I levels, indicating modulation of cell cycle regulation in Caco-2 cells. These effects highlight multiple routes in which dietary derived flavanols may exert beneficial effects in the gastrointestinal tract. (c) 2005 Elsevier Inc. All rights reserved.

Specific, Reversible Cytostatic Protection of Normal Cells Against Negative Effects of Chemotherapy

Chemotherapy is a common and effective method to treat many forms of cancer. However, treatment of cancer with chemotherapy has severe side effects which often limit the doses of therapy administered. Because some cancer chemotherapeutics target proliferating cells and tissues, all dividing cells, whether normal or tumor, are affected. Cell culture studies have demonstrated that UCN-01 is able to reversibly and selectively arrest normal dividing cells; tumor cells lines do not undergo this temporary arrest. Following UCN-01 treatment, normal cells displayed a 50-fold increase in IC50 for camptothecin; tumor cells showed no such increased tolerance. We have examined the response of the proliferating tissues of the mouse to UCN- 01 treatment, using the small bowel epithelium as a model system. Our results indicate that UCN-01 treatment can cause a cell cycle arrest in the gut epithelium, beginning 24 hours following UCN-01 administration, with cell proliferation remaining suppressed for one week. Two weeks post-UCN-01 treatment the rate of proliferation returns to normal levels. 5-FU administered during this period demonstrates that UCN-01 is able to provide protection to normal cells of the mouse within a narrow window of efficacy, from three to five days post-UCN-01. UCN-01 pretreated mice displayed improved survival, weight status and blood markers following 5-FU compared to control mice, indicating that UCN-01 can protect normal dividing tissues. The mechanism by which UCN-01 arrests normal cells in vivo was also examined. We have demonstrated that UCN-01 treatment in mice causes an increase in the G1 phase cell cycle proteins cdk4 and cyclin D, as well as the inhibitor p27. Phosphorylated Rb was also elevated in the arrested cells. These results are a departure from cell culture studies, in which inhibition of G1 phase cyclin dependent kinases led to hyposphosphorylation of Rb. Future investigation will be required to understand the mechanism of UCN-01 action. This is important information, especially for identification of alternate compounds which could provide the protection afforded by UCN-01.

Human DMTF1β antagonizes DMTF1α regulation of the p14(ARF) tumor suppressor and promotes cellular proliferation

The human DMTF1 (DMP1) transcription factor, a DNA binding protein that interacts with cyclin D, is a positive regulator of the p14ARF (ARF) tumor suppressor. Our earlier studies have shown that three differentially spliced human DMP1 mRNAs, α, β and γ, arise from the human gene. We now show that DMP1α, β and γ isoforms differentially regulate ARF expression and promote distinct cellular functions. In contrast to DMP1α, DMP1β and γ did not activate the ARF promoter, whereas only β resulted in a dose-dependent inhibition of DMP1α-induced transactivation of the ARF promoter. Ectopic expression of DMP1β reduced endogenous ARF mRNA levels in human fibroblasts. The DMP1β- and γ-isoforms share domains necessary for the inhibitory function of the β-isoform. That DMP1β may interact with DMP1α to antagonize its function was shown in DNA binding assays and in cells by the close proximity of DMP1α/β in the nucleus. Cells stably expressing DMP1β, as well as shRNA targeting all DMP1 isoforms, disrupted cellular growth arrest induced by serum deprivation or in PMA-derived macrophages in the presence or absence of cellular p53. DMP1 mRNA levels in acute myeloid leukemia samples, as compared to granulocytes, were reduced. Treatment of acute promyelocytic leukemia patient samples with all-trans retinoic acid promoted differentiation to granulocytes and restored DMP1 transcripts to normal granulocyte levels. Our findings imply that DMP1α- and β-ratios are tightly regulated in hematopoietic cells and DMP1β antagonizes DMP1α transcriptional regulation of ARF resulting in the alteration of cellular control with a gain in proliferation.

Integrin mediated growth and apoptosis in human gastric adenocarcinoma

Integrins are important as the primary cell adhesion molecule providing information about the extracellular microenvironment to the interior of the cell to influence cellular behavior such as differentiation, proliferation and apoptosis. Apoptotic death due to loss of adhesion is termed anoikis. In this study we have obtained a parental human gastric adenocarcinoma cell line that yielded two variant lines that had differing responses to lack of adhesion. The STAD.APO cell line undergoes apoptosis when denied adherence and the STAD.ARR cell line enters into cell cycle arrest under the identical suspended conditions. We have shown that cyclin A and cyclin D mRNA and protein are down regulated when cells are denied adherence for 24 hours in tissue culture wells previously coated with poly-HEMA. To test whether cyclin A was able to rescue cells from cell cycle arrest and/or anoikis by overriding the cell cycle machinery we transfected the full length cDNA in to each cell type. Surprisingly we found that anoikis and cell cycle arrest due to suspended conditions was not affected by overexpression of cyclin A protein, but that growth under adhered conditions was reduced compared to vector alone control transfectants. Further, we transfected other cell lines; ST7, gastric cancer, MDA-MB-4.35, breast cancer, and HPB T-cell leukemic and in no case were suspended culturing conditions overcome by cyclin A. This result indicates an additional level of regulation for the cell cycle machinery. Additionally, soluble collagen was shown to be able to save from anoikis and also from cell cycle arrest while the β1 specific mAb 33B6 was only able to save from anoikis. Immunofluorescent studies show that soluble collagen creates clusters of β1 with FAK and also β1 with actin in the STAD.ARR cells but does not in the STAD.APO cells. This result indicates that the phenotypes under suspended conditions between these cell lines may diverge at their requirements for integrin ligation. Additionally we characterized the nature of anoikis by showing cytochrome c release, caspase 3, p21 and p53 activation in STAD.APO cells. Thus, our results have implications in the understanding of integrin biology and neoplastic progression. ^

Characterization of E2F1's oncogenic, apoptotic and tumor-suppressive activities utilizing the K5 mouse model

Though E2F1 is deregulated in most human cancers by mutations of the p16-cyclin D-Rb pathway, it also exhibits tumor suppressive activity. A transgenic mouse model overexpressing E2F1 under the control of the bovine keratin 5 (K5) promoter exhibits epidermal hyperplasia and spontaneously develops tumors in the skin and other epithelial tissues after one year of age. In a p53-deficient background, aberrant apoptosis in K5 E2F1 transgenic epidermis is reduced and tumorigenesis is accelerated. In sharp contrast, K5 E2F1 transgenic mice are resistant to papilloma formation in the DMBA/TPA two-stage carcinogenesis protocol. K5 E2F4 and K5 DP1 transgenic mice were also characterized and both display epidermal hyperplasia but do not develop spontaneous tumors even in cooperation with p53 deficiency. These transgenic mice do not have increased levels of apoptosis in their skin and are more susceptible to papilloma formation in the two-stage carcinogenesis model. These studies show that deregulated proliferation does not necessarily lead to tumor formation and that the ability to suppress skin carcinogenesis is unique to E2F1. E2F1 can also suppress skin carcinogenesis when okadaic acid is used as the tumor promoter and when a pre-initiated mouse model is used, demonstrating that E2F1's tumor suppressive activity is not specific for TPA and occurs at the promotion stage. E2F1 was thought to induce p53-dependent apoptosis through upregulation of p19ARF tumor suppressor, which inhibits mdm2-mediated p53 degradation. Consistent with in vitro studies, the overexpression of E2F1 in mouse skin results in the transcriptional activation of the p19ARF and the accumulation of p53. Inactivation of either p19ARF or p53 restores the sensitivity of K5 E2F1 transgenic mice to DMBA/TPA carcinogenesis, demonstrating that an intact p19ARF-p53 pathway is necessary for E2F1 to suppress carcinogenesis. Surprisingly, while p53 is required for E2F1 to induce apoptosis in mouse skin, p19ARF is not, and inactivation of p19ARF actually enhances E2F1-induced apoptosis and proliferation in transgenic epidermis. This indicates that ARF is important for E2F1-induced tumor suppression but not apoptosis. Senescence is another potential mechanism of tumor suppression that involves p53 and p19ARF. K5 E2F1 transgenic mice initiated with DMBA and treated with TPA show an increased number of senescence cells in their epidermis. These experiments demonstrate that E2F1's unique tumor suppressive activity in two-stage skin carcinogenesis can be genetically separated from E2F1-induced apoptosis and suggest that senescence utilizing the p19ARF-p53 pathway plays a role in tumor suppression by E2F1. ^

Induction of ARF tumor suppressor gene expression and cell cycle arrest by transcription factor DMP1

Expression of the DMP1 transcription factor, a cyclin D-binding Myb-like protein, induces growth arrest in mouse embryo fibroblast strains but is devoid of antiproliferative activity in primary diploid fibroblasts that lack the ARF tumor suppressor gene. DMP1 binds to a single canonical recognition site in the ARF promoter to activate gene expression, and in turn, p19ARF synthesis causes p53-dependent cell cycle arrest. Unlike genes such as Myc, adenovirus E1A, and E2F-1, which, when overexpressed, activate the ARF-p53 pathway and trigger apoptosis, DMP1, like ARF itself, does not induce programmed cell death. Therefore, apart from its recently recognized role in protecting cells from potentially oncogenic signals, ARF can be induced in response to antiproliferative stimuli that do not obligatorily lead to apoptosis.

Reprogramming the Cell Cycle for Endoreduplication in Rodent Trophoblast Cells

Differentiation of trophoblast giant cells in the rodent placenta is accompanied by exit from the mitotic cell cycle and onset of endoreduplication. Commitment to giant cell differentiation is under developmental control, involving down-regulation of Id1 and Id2, concomitant with up-regulation of the basic helix-loop-helix factor Hxt and acquisition of increased adhesiveness. Endoreduplication disrupts the alternation of DNA synthesis and mitosis that maintains euploid DNA content during proliferation. To determine how the mammalian endocycle is regulated, we examined the expression of the cyclins and cyclin-dependent kinases during the transition from replication to endoreduplication in the Rcho-1 rat choriocarcinoma cell line. We cultured these cells under conditions that gave relatively synchronous endoreduplication. This allowed us to study the events that occur during the transition from the mitotic cycle to the first endocycle. With giant cell differentiation, the cells switched cyclin D isoform expression from D3 to D1 and altered several checkpoint functions, acquiring a relative insensitivity to DNA-damaging agents and a coincident serum independence. The initiation of S phase during endocycles appeared to involve cycles of synthesis of cyclins E and A, and termination of S was associated with abrupt loss of cyclin A and E. Both cyclins were absent from gap phase cells, suggesting that their degradation may be necessary to allow reinitiation of the endocycle. The arrest of the mitotic cycle at the onset of endoreduplication was associated with a failure to assemble cyclin B/p34cdk1 complexes during the first endocycle. In subsequent endocycles, cyclin B expression was suppressed. Together these data suggest several points at which cell cycle regulation could be targeted to shift cells from a mitotic to an endoreduplicative cycle.

Structural studies of p21Waf1/Cip1/Sdi1 in the free and Cdk2-bound state: conformational disorder mediates binding diversity.

The cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1/Sdi1, important for p53-dependent cell cycle control, mediates G1/S arrest through inhibition of Cdks and possibly through inhibition of DNA replication. Cdk inhibition requires a sequence of approximately 60 amino acids within the p21 NH2 terminus. We show, using proteolytic mapping, circular dichroism spectropolarimetry, and nuclear magnetic resonance spectroscopy, that p21 and NH2-terminal fragments that are active as Cdk inhibitors lack stable secondary or tertiary structure in the free solution state. In sharp contrast to the disordered free state, however, the p21 NH2 terminus adopts an ordered stable conformation when bound to Cdk2, as shown directly by NMR spectroscopy. We have, thus, identified a striking disorder-order transition for p21 upon binding to one of its biological targets, Cdk2. This structural transition has profound implications in light of the ability of p21 to bind and inhibit a diverse family of cyclin-Cdk complexes, including cyclin A-Cdk2, cyclin E-Cdk2, and cyclin D-Cdk4. Our findings suggest that the flexibility, or disorder, of free p21 is associated with binding diversity and offer insights into the role for structural disorder in mediating binding specificity in biological systems. Further, these observations challenge the generally accepted view of proteins that stable secondary and tertiary structure are prerequisites for biological activity and suggest that a broader view of protein structure should be considered in the context of structure-activity relationships.

The brain-specific activator p35 allows Cdk5 to escape inhibition by p27Kip1 in neurons.

Cell cycle withdrawal in postmitotic cells involves cyclin-dependent kinase (Cdk) inhibitors that repress cell cycle Cdk activity. During mouse neurogenesis, cortical postmitotic neurons are shown here to accumulate high levels of the p27 Cdk inhibitor compared with their progenitor neuroblasts. Elevated p27 levels in staged embryo brain extracts correlate with p27 binding to Cdk2, and Cdk inactivation. Yet, Cdk5, which is associated with the noncyclin activator p35 in neurons, remains active in the presence of high p27 levels. Both in vitro and in vivo, p27 and related inhibitors can recognize a cyclin D-Cdk5 complex but not a p35-Cdk5 complex. The results indicate that the choice of activator determines the susceptibility of Cdk5 to p27 and related Cdk inhibitors, and thus its ability to act in postmitotic cells.

Growth suppression by p16ink4 requires functional retinoblastoma protein.

p16ink4 has been implicated as a tumor suppressor that is lost from a variety of human tumors and human cell lines. p16ink4 specifically binds and inhibits the cyclin-dependent kinases 4 and 6. In vitro, these kinases can phosphorylate the product of the retinoblastoma tumor suppressor gene. Thus, p16ink4 could exert its function as tumor suppressor through inhibition of phosphorylation and functional inactivation of the retinoblastoma protein. Here we show that overexpression of p16ink4 in certain cell types will lead to an arrest in the G1 phase of the cell cycle. In addition, we show that p16ink4 can only suppress the growth of human cells that contain functional pRB. Moreover, we have compared the effect of p16ink4 expression on embryo fibroblasts from wild-type and RB homozygous mutant mice. Wild-type embryo fibroblasts are inhibited by p16ink4, whereas the RB nullizygous fibroblasts are not. These data not only show that the presence of pRB is crucial for growth suppression by p16ink4 but also indicate that the pRB is the critical target acted upon by cyclin D-dependent kinases in the G1 phase of the cell cycle.

Inhibition of S/G(2) phase CDK4 reduces mitotic fidelity

Cyclin-dependent kinase 4 (CDK4)/cyclin D has a key role in regulating progression through late G(1) into S phase of the cell cycle. CDK4-cyclin D complexes then persist through the latter phases of the cell cycle, although little is known about their potential roles. We have developed small molecule inhibitors that are highly selective for CDK4 and have used these to define a role for CDK4-cyclin D in G(2) phase. The addition of the CDK4 inhibitor or small interfering RNA knockdown of cyclin D3, the cyclin D partner, delayed progression through G(2) phase and mitosis. The G(2) phase delay was independent of ATM/ATR and p38 MAPK but associated with elevated Wee1. The mitotic delay was because of failure of chromosomes to migrate to the metaphase plate. However, cells eventually exited mitosis, with a resultant increase in cells with multiple or micronuclei. Inhibiting CDK4 delayed the expression of the chromosomal passenger proteins survivin and borealin, although this was unlikely to account for the mitotic phenotype. These data provide evidence for a novel function for CDK4-cyclin D3 activity in S and G(2) phase that is critical for G(2)/M progression and the fidelity of mitosis.

Raf kinase inhibitor protein RKIP enhances signaling by glycogen synthase kinase-3β

Raf kinase inhibitory protein (RKIP) is a physiologic inhibitor of c-RAF kinase and nuclear factor ?B signaling that represses tumor invasion and metastasis. Glycogen synthase kinase-3ß (GSK3ß) suppresses tumor progression by downregulating multiple oncogenic pathways including Wnt signaling and cyclin D1 activation. Here, we show that RKIP binds GSK3 proteins and maintains GSK3ß protein levels and its active form. Depletion of RKIP augments oxidative stress-mediated activation of the p38 mitogen activated protein kinase, which, in turn, inactivates GSK3ß by phosphorylating it at the inhibitory T390 residue. This pathway de-represses GSK3ß inhibition of oncogenic substrates causing stabilization of cyclin D, which induces cell-cycle progression and ß-catenin, SNAIL, and SLUG, which promote epithelial to mesenchymal transition. RKIP levels in human colorectal cancer positively correlate with GSK3ß expression. These findings reveal the RKIP/GSK3 axis as both a potential therapeutic target and a prognosis-based predictor of cancer progression.

De novo methylation of tumor suppressor gene p16/INK4a is a frequent finding in multiple myeloma patients at diagnosis.

The p16 gene competes with cyclin D for binding to CDK4/CDK6 and therefore inhibits CDK4/6 complex kinase activity, resulting in dephosphorylation of pRb and related G1 growth arrest. Inactivation of this gene has been involved in a variety of tumors by different mechanisms: homozygous/hemyzygous deletions, point mutations and methylation of a 5' CpG island into exon E1alpha of the p16 gene. Homozygous deletions have been rarely found in multiple myeloma (MM) and no point mutations have been reported. Two recent studies have reported a high prevalence of methylation in the exon E1alpha of the p16 gene, but included only a small number of cases. We have analyzed the methylation pattern of exon E1alpha of the p16 gene in 101 untreated MM and five primary plasma cell leukemias (PCL). A PCR assay, relying on the inability of some restriction enzymes to digest methylated sequences, was used to analyze the methylation status. Southern blot analysis was used to confirm these results. Forty-one of 101 MM patients (40.5%) as well as four of the five (80%) primary PCL patients had shown methylation of the exon E1alpha. Our study confirms that hypermethylation of the p16 gene is a frequent event in MM. Leukemia (2000) 14, 183-187.

Differential expression of galectin-3, beta-catenin, and cyclin D1 in adenoid cystic carcinoma and polymorphous low-grade adenocarcinoma of salivary glands

Background: Galectin-3 has been implicated in tumor progression of some malignancies as thyroid, prostate, and salivary gland tumors. Recently, it has been suggested that this protein may be an important mediator of the beta-catenin/Wnt pathway. Moreover, nuclear galectin-3 expression has been implicated in cell proliferation, promoting cyclin D1 activation. Thus, the present study aimed to correlate galectin-3 expression with beta-catenin and cyclin D1 expressions in adenoid cystic carcinoma (ACC) and in polymorphous low-grade adenocarcinoma (PLGA). Methods: Fifteen formalin-fixed paraffin-embedded cases of each tumor were retrieved from the files of the Surgical Oral Pathology Service at the University of Sao Paulo and the proteins were analyzed by immunohistochemistry. Results: Adenoid cystic carcinoma showed galectin-3 immunostaining mainly in the nuclei, while PLGA revealed a positive mostly cytoplasmic reaction to galectin-3 in the largest part of tumor cells. Both tumors showed intense cytoplasmic/nuclear staining for beta-catenin in majority of cases. Cyclin D1 immunoreactivity was not detected in 14/15 PLGA and showed specific nuclear staining in 10/15 cases of ACC in more than 5% of the neoplastic cells. Cyclin D1 expression was correlated with cytoplasmic and nuclear galectin-3 expression in ACC (P < 0.05). Conclusions: These results suggest that in ACC galectin-3 may play a role in cellular proliferation through cyclin D1 activation. In addition, nuclear expression of galectin-3 in ACC may be related to a more aggressive behavior of this lesion. Although beta-catenin seems to play a role in carcinogenesis in both lesions, it seems that it does not bind to galectin-3 for cyclin D1 stimulation.

SMYD3 contributes to a more aggressive phenotype of prostate cancer and targets Cyclin D2 through H4K20me3

Prostate cancer (PCa) is one of the most incident cancers worldwide but clinical and pathological parameters have limited ability to discriminate between clinically significant and indolent PCa. Altered expression of histone methyltransferases and histone methylation patterns are involved in prostate carcinogenesis. SMYD3 transcript levels have prognostic value and discriminate among PCa with different clinical aggressiveness, so we decided to investigate its putative oncogenic role on PCa.We silenced SMYD3 and assess its impact through in vitro (cell viability, cell cycle, apoptosis, migration, invasion assays) and in vivo (tumor formation, angiogenesis). We evaluated SET domain's impact in PCa cells' phenotype. Histone marks deposition on SMYD3 putative target genes was assessed by ChIP analysis.Knockdown of SMYD3 attenuated malignant phenotype of LNCaP and PC3 cell lines. Deletions affecting the SET domain showed phenotypic impact similar to SMYD3 silencing, suggesting that tumorigenic effect is mediated through its histone methyltransferase activity. Moreover, CCND2 was identified as a putative target gene for SMYD3 transcriptional regulation, through trimethylation of H4K20.Our results support a proto-oncogenic role for SMYD3 in prostate carcinogenesis, mainly due to its methyltransferase enzymatic activity. Thus, SMYD3 overexpression is a potential biomarker for clinically aggressive disease and an attractive therapeutic target in PCa.