Cell Cycle Regulators P21 Research Articles

Abstract SY01-03: Comparative genomics as a tool for the identification of novel Kras synthetic lethal interactions

Abstract Gene expression profiling has been widely used as a tool to characterize genome-wide changes in expression level in various cancers. Expression profiling is generally used to identify specific genes with altered expression or to identify patterns that distinguish cancer subtypes. More recently, several approaches to use expression data to identify interactions between genes or build cancer-specific networks have been described. We have previously demonstrated that cross-species gene expression analysis can be used as a tool to identify oncogene-specific alterations in gene expression. Cross-species analysis is useful for this because it allows for filtering of noise inherent in human gene expression analysis. The identification of an oncogenic Kras-specific gene expression signature was accomplished using this approach. A central focus of our laboratory has been to use this and other oncogene-specific signatures to identify new critical downstream pathways necessary for oncogene function. Using several computational approaches, we identified several upstream transcriptional regulators of our previously identified oncogenic Kras signature. We hypothesized that some of the transcriptional regulators represent specific dependencies that are required for Kras to function as an oncogene. Thus, inhibition of the transcription factors could uncover novel synthetic lethal interactions specific for cells that express oncogenic Kras. Using an shRNA pooled library, we have confirmed one such synthetic lethal interaction betweeen oncogenic Kras and the Wilms-tumor 1 (Wt1), a gene known to function as a tumor suppressor in some contexts. Loss of Wt1 induces senescence in primary cells expressing oncogenic Kras. Human non-small cell lung cancer cells expressing oncogenic Kras also become senescent when Wt1 is knocked-down using shRNA. Thus, synthetic senescence is induced on Wt1 loss in oncogenic Kras expressing cells. A role for Wt1 in Kras-driven oncogenesis was further confirmed using a mouse model for lung cancer in which a mouse carrying a conditional Kras allele was crossed a mouse carrying an allelel that allows for conditional deletion of Wt1. The biological signficance of this intereation was further demonstrated by using a “Wt1 “high” or “Wt1 low” signature to classify human NSCLC gene expression profiles. This allowed us to determine that human tumor samples that express oncogenic Kras and express high levels of Wt1-regulated genes have a worse prognosis compared to samples expressing oncogenic Kras but having low low level of Wt1-regulated genes. In human NSCLC cell lines, loss of Wt1 leads to significant upregulation of the cell cycle regulator p21. Wt1 appears to regulate p21 levels posttranscriptionally, as p21 mRNA levels did not change. Further studies to elucidate the mechanisms leading to p21 upregulation upon Wt1 loss are underway and preliminary results will be discussed. To take these studies further, we began by generating a more refined Kras-specific signature using FACs-sorted tumor cells from the LSL-KrasG12D mouse model crossed to a fluorescent reporter. We have used this mouse-generated Kras signature for cross-species analysis using a much larger NSCLC dataset than was possible in our previously published studies. We then applied the ARACNE algorithm to identify transcription factors that regulate this Kras-signature. Using this approach, we have identified other transcription factors that are potential regulators of oncogenic Kras. The fact that Wt1 once again was identified as a regulator of oncogenic Kras using this novel method suggests the validity of this approach. Preliminary results testing the functional significance of these transcription factors for Kras-driven oncogenesis will be discussed. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY01-03. doi:10.1158/1538-7445.AM2011-SY01-03

Estrogen reduces cellular aging in human mesenchymal stem cells and chondrocytes

Chondrocyte aging is associated with cartilage degeneration and senescence impairs the regenerative potential of mesenchymal stem cells (MSCs). Estrogen exerts profound effects on human physiology including articular cartilage and MSCs. The present study should analyze the effects of pre- and postmenopausal estrogen concentrations on chondrogenic cells. Physiologic premenopausal concentrations of 17β-estradiol (E(2)) significantly decelerated telomere attrition in MSCs and chondrocytes while postmenopausal E(2) concentration had no significant effects. The estrogen agonist-antagonist tamoxifen did not affect telomere biology, but inhibited the E(2) -stimulated reduction in telomere shortening. E(2) and tamoxifen did not influence cell proliferation, cell morphology, and β-galactosidase staining in chondrogenic cells. E(2) treatment did not affect the telomere-associated proteins TRF1 and TRF2. E(2) had no regulatory effects on the expression rates of the cell cycle regulator p21 and the DNA repair proteins SIRT1 and XRCC5. In spite of reducing telomere shortening in aging MSCs and chondrocytes, estrogen is not able to prevent somatic cells from replicative exhaustion and from finally entering senescence. The fade of telomere shortening under pre- to postmenopausal estrogen concentrations suggests, at least in part, a senescence-dependent cause for the onset of osteoarthritis in women after menopause.

Caffeine-suppressed ATM pathway leads to decreased p53 phosphorylation and increased programmed cell death in gamma-irradiated leukaemic molt-4 cells

Summary Ionising radiation (IR) is one of the main treatment modalities in oncology. However, we still search for substances which can radio-sensitize tumour cells. In this study we used caffeine, a non-specific ataxia-telangiectasia mutated kinase (ATM) inhibitor, and studied its effect on the activation of the proteins involved in cell cycle control and the induction of apoptosis in human T-lymphocyte leukaemic MOLT-4 cells (p53 wt). We evaluated the expression of the tumour-suppressor p53 (itself and phosphorylated on Ser 15 and Ser 392 ), the cell cycle regulator p21, and the anti-apoptotic protein myeloid cell leukemia 1 (Mcl-1). After treatment with 2 mM caffeine, the cells were irradiated by 1 or 3 Gy, lysed and the proteins detected by Western-blotting. Apoptosis was determined by flow-cytometric annexin V/propidium iodine detection. Irradiation by 1 or 3 Gy induced p53 phosphorylation at Ser 15 and Ser 392 after 2 h with maximum after 4 h. Adding caffeine significantly inhibited Ser 15 phosphorylation, which is ATM-dependent but surprisingly also Ser 392 phosphorylation, which is ATM-independent, suggesting that caffeine might have another cellular target (protein kinase). Similarly, caffeine caused a substantial decrease in p21 in combination with both doses of IR and also Mcl-1 was down-regulated. Three days after irradiation, caffeine significantly increased induction of apoptosis. The ATM/p53 pathway was suppressed by caffeine, which led to increased apoptosis accompanied by a p53-independent decrease in Mcl-1. It also caused down-regulation of p21, which possibly contributed to the shortened cell cycle arrest necessary for effective DNA repair and thus impeded radio-resistance. Caffeine promotes the cytotoxic effect of ionising radiation and provides a possible platform for the development of new anti-cancer therapeutics known as radio-sensitizers.

Trefoil factor 1 acts to suppress senescence induced by oncogene activation during the cellular transformation process

Senescence is a cellular stress response characterized by persistent cell growth arrest under various stress conditions, including oncogene activation or tumor suppressor loss, which functions as a critical barrier that must be overcome to allow the progression from a precancerous or preinvasive lesion to a malignant tumor. Trefoil factor 1 (TFF1) is a secreted protein involved in maintaining the gastrointestinal epithelium by serving a tumor-suppressive role; however, TFF1 is overexpressed in several types of cancers. Here we report that TFF1 acts as a promoter of tumorigenesis in the context of prostate and pancreatic cancers by suppressing oncogene-induced senescence (OIS). Expression of TFF1 allows human prostate epithelial cells to escape OIS caused by the activated Ras oncogene or by reduced expression of the tumor suppressor PTEN, in part by the involvement of the EGF receptor-mediated pathway and inhibition of the expression of the cell cycle regulator p21. Without intrinsic promitogenic activity TFF1 may act in both autocrine and paracrine manners to enable cells to undergo the initial transformation and expansion against the restrictive microenvironment during early stage tumorigenesis. Taken together, our findings identify TFF1 as a soluble factor designed to act mainly to antagonize the OIS process to accelerate tumorigenesis.

The adult stem cell marker Musashi‐1 modulates endometrial carcinoma cell cycle progression and apoptosis via Notch‐1 and p21WAF1/CIP1

The RNA-binding protein Musashi-1 has been proposed to maintain stem cell function during development and regenerative processes as a modulator of the Notch-1 signaling pathway. Musashi-1 expression is upregulated in endometrial carcinoma, however, its pathogenetic role in this tumor entity is unknown. Here we investigate the functional impact and mode of action of Musashi-1 on endometrial carcinoma cell behaviour in vitro. Aldehyde dehydrogenase-1 activity and side population (SP) measurement by Hoechst dye exclusion revealed that the Ishikawa endometrial carcinoma cell line contains a pool of putative cancer stem cells. Musashi-1 expression is 20.8-fold upregulated in SP+ compared to SP- and equally distributed between ALDH+ and ALDH- cell pools. siRNA-mediated knockdown of Musashi-1 mRNA expression lead to an altered expression of the signaling receptor Notch-1 and its downstream targets, the transcription factor Hes-1 and the cell cycle regulators p21(WAF1/CIP1) and cyclin B1, as determined by Western blotting and quantitative real-time PCR. Flow cytometric and ELISA analyses revealed that Musashi-1-mediated modulation of these factors exerted an antiproliferative effect on the cell cycle, and increased apoptosis in endometrial carcinoma cells. We conclude that Ishikawa cells contain a subpopulation of cells with stem cell-like properties. Musashi-1 modulates endometrial carcinoma cell cycle progression and apoptosis via the stemness-related factors Notch-1, Hes-1 and p21(WAF1/CIP1) , thus emerging as a novel future target for endometrial carcinoma therapy.

Phosphatidylinositol‐3′‐kinase/AKT signaling is essential in synovial sarcoma

Synovial sarcomas account for 5-10% of all malignant soft tissue tumors. They have been shown to express different membranous growth factor receptors, many of them signaling via intracellular kinase cascades. In our study, the functional role of PI3K/AKT signals in synovial sarcoma is analyzed with regard to tumor biology and therapeutic applicability. Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT, its targets p-(Ser9)-GSK-3β and p-(Ser2448)-mTOR and the cell cycle regulators Cyclin D1 and p27(KIP1) were performed in 36 synovial sarcomas. The PIK3CA gene was screened for mutations. In vitro, four synovial sarcoma cell lines were treated with the PI3K inhibitor LY294002. Phosphorylation of AKT, GSK-3β and mTOR was assessed, and cellular proliferation and apoptosis were analyzed to functionally characterize the effects of PI3K inhibition. Finally, coincubations of LY294002 with cytotoxic drugs were performed. Most tumors showed significant expression levels of p-AKT, p-GSK-3β and p-mTOR, indicating activation of the PI3K/AKT signaling cascade in synovial sarcomas; Cyclin D1 and p27(KIP1) were differentially expressed. Mutations in the PIK3CA gene could be excluded. In vitro, PI3K inhibition diminished synovial sarcoma cell growth accompanied by reduced phosphorylation of AKT, GSK-3β and mTOR. Mechanistically, PI3K pathway inhibition lead to enhanced apoptosis and decreased cellular proliferation linked to reduced Cyclin D1 and increased p27(KIP1) levels. Simultaneous treatment of synovial sarcoma cell lines with LY294002 and cytotoxic drugs resulted in additive effects. In summary, PI3K signaling plays an essential role in growth control of synovial sarcomas and might be successfully targeted in multimodal therapeutic strategies.

MiR-221 and miR-222 expression increased the growth and tumorigenesis of oral carcinoma cells

MicroRNAs are small noncoding RNAs involved in posttranscriptional gene regulation, which play an important role in both physiological functioning and pathological progression. The miR-221/miR-222 microRNA family has been shown to be related to the neoplastic process in a number of different types of cancers; nevertheless, its function in oral squamous cell carcinoma (OSCC) remained uncertain. Paired OSCC and matched noncancerous oral mucosa were examined for miR-221/miR-222 expression using quantitative reverse-transcription PCR. Ectopic expression of miR-221/miR-222 by lentiviral infection was investigated to explore its in vitro and in vivo impact on the oncogenic phenotype and the expression of various target genes. The expression of Cip/Kip cell cycle regulator p27 in tumors was analyzed with immunohistochemistry. The expression levels of miR-221 and miR-222 were highly correlated in OSCC. Increased miR-221/miR-222 expression was found in 40% of OSCC tissues. The ectopic expression of miR-221 or of miR-222 increased growth and anchorage-independent colony formation of OSCC cell lines. It also resulted in an increase in the tumorigenesis of an OSCC cell line in nude mice. Western blot analysis suggested that p27 and p57 might be the targets of miR-221/miR-222. p27 expression was reversely associated with the miR-221 and miR-222 expression level in OSCC tissues. Our findings suggested that increased miR-221/miR-222 expression was associated with the OSCC cell growth.

Molecular predictive factors of outcome of radiotherapy in cervical cancer

Radical radiotherapy with concurrent cisplatin-based chemotherapy is an established treatment for cervical cancer patients with stage FIGO IIB and higher. The tumor control can be achieved in 40-80% of patients, the treatment is associated with the risk of late postiradiation complications in 10 - 15% of cases. Detection of the factors predictive for tumor control and late morbidity is a possible direction how to individualize radiotherapy dose and technique. The aim of our review is to summarize results of studies inquiring various molecular markers predicting tumor response to radiotherapy and a risk of late complications. A lot of candidate molecules were evaluated in histochemical studies: membrane receptors (EGFR, HER-2), cell cycle regulators (p53, p21), proliferative markers (Ki-67), hypoxia and angiogenetic factors (HIF, VEGF), HPV status, and others (COX-2), with promising results in some of them (HPV, HIF-1α, Ku80, ATM polymorphism). Microarray studies identified decades of genes with different expression in radiosensitive/radioresistant cervical tumors and sets of genes are able to comletely separate responding and nonresponding tumors, but these sets differ across studies. Further well designed studies will be necessary to achieve results matured for use in clinical practice.

A Phosphorylation Switch Regulates the Transcriptional Activation of Cell Cycle Regulator p21 by Histone Deacetylase Inhibitors

Histone deacetylase inhibitors induce cell cycle arrest and apoptosis in tumor cells and are, therefore, promising anti-cancer drugs. The cyclin-dependent kinase inhibitor p21 is activated in histone deacetylase (HDAC) inhibitor-treated tumor cells, and its growth-inhibitory function contributes to the anti-tumorigenic effect of HDAC inhibitors. We show here that induction of p21 by trichostatin A involves MAP kinase signaling. Activation of the MAP kinase signaling pathway by growth factors or stress signals results in histone H3 serine 10 phosphorylation at the p21 promoter and is crucial for acetylation of the neighboring lysine 14 and recruitment of activated RNA polymerase II in response to trichostatin A treatment. In non-induced cells, the protein phosphatase PP2A is associated with the p21 gene and counteracts its activation. Induction of p21 is linked to simultaneous acetylation and phosphorylation of histone H3. The dual modification mark H3S10phK14ac at the activated p21 promoter is recognized by the phospho-binding protein 14-3-3ζ, which protects the phosphoacetylation mark from being processed by PP2A. Taken together we have revealed a cross-talk of reversible phosphorylation and acetylation signals that controls the activation of p21 by HDAC inhibitors and identify the phosphatase PP2A as chromatin-associated transcriptional repressor in mammalian cells.

Clioquinol Arrests Cell Cycle at G1 Phase and Triggers Intrinsic Apoptosis In Myeloma and Leukemia Cells by Inhibiting Histone Deacetylases

AbstractAbstract 1836Clioquinol (5-chloro-7-iodo-8-hydroxyquinoline, CQ) is an old and effective antifungal and amoebicidal drug but is restricted or discontinued in some countries because of its suspect causality in inducing subacute myelo-optic neuropathy, however it has been recently revitalized as an anti-cancer drug candidate at both in vitro and in vivo models. Our previous study suggested that CQ induced cell death and displayed anti-leukemia and anti-myeloma activity (Mao × et al, Leukemia, 2009), but its mechanisms are not well known. In this study, we demonstrated that clioquinol-induced cell death is via intrinsic rather than extrinsic apoptotic pathway, clioquinol-induced apoptosis depends on the activation of caspase-9 and -3. Because zinc is essential for the enzymatic activity of histone deacetylases (HDAC) which is currently emerging as a novel target for apoptotis and cancer treatment, and clioquinol is a strong chelator of zinc ion, we questioned whether clioquinol could interfere with HDAC activity by binding to zinc. Thus, we first examined the effects of clioquinol on the most often used hallmarks for HDAC inhibitions, including cyclin D, p21(CIP1), and p27(KIP1) (Nature Reviews Cancer, 2006). DNA microarray analysis indicated that clioquinol and its analogs significantly up-regulated the transcriptional level of p21 > 2–10 folds within 24 hr. The increased expression of p21(CIP1) protein was further confirmed by western blotting assay in various cell lines and primary patient samples. Clioquinol induced p21(CIP1) expression at concentrations as low as 5 μM witin 24 hr. At the same concentration, tumor suppressor and cell cycle regulator p27 (KIP1) was also increased. In addition, clioquinol also down-regulated expression of D-cyclins, including cyclin D2 and D3 in tested cell lines at a concentration consistent with that induced cell apoptosis. All these changes by clioquinol resulted in cell cycle arrest at G0/G1 phase in both leukemia and myeloma cell lines. Because these genes (cyclin D, p21 and p27) are most associated with histone acetylases, we next checked whether clioquinol is effective in inhibiting HDAC activity. Both leukemia and myeloma cell lines and primary patient samples were applied for the analysis of acetylation status of histone 3 (Ac-H3). Using trichostatin A (TSA) as a positive control, we found that clioquinol accumulated Ac-H3 in all tested cell lines and primary patient samples in a concentration- and time-dependent manner, which strongly suggested that clioquinol interfere with HDAC activity. Subsequently, we analyzed the interaction of clioquinol and HDAC. Just like TSA, clioquinol was docked into the active pocket of HDAC, where clioquinol competitively binds to zinc at the active center, which was confirmed by zinc addition. Zinc addition partially abolished the effects of clioquinol on HDAC activity. Thus, our study indicated that clioquinol-induced cell death in both leukemia and myeloma was via an apoptotic pathway by interfering with HDAC activity. Disclosures:No relevant conflicts of interest to declare.

TAp73 Acts via the bHLH Hey2 to Promote Long-Term Maintenance of Neural Precursors

Increasing evidence suggests that deficits in adult stem cell maintenance cause aberrant tissue repair and premature aging [1]. While the mechanisms regulating stem cell longevity are largely unknown, recent studies have implicated p53 and its family member p63. Both proteins regulate organismal aging [2-4] as well as survival and self-renewal of tissue stem cells [5-9]. Intriguingly, haploinsufficiency for a third family member, p73, causes age-related neurodegeneration [10]. While this phenotype is at least partially due to loss of the ΔNp73 isoform, a potent neuronal prosurvival protein [11-16], a recent study showed that mice lacking the other p73 isoform, TAp73, have perturbations in the hippocampal dentate gyrus [17], a major neurogenic site in the adult brain. These findings, and the link between the p53 family, stem cells, and aging, suggest that TAp73 might play a previously unanticipated role in maintenance of neural stem cells. Here, we have tested this hypothesis and show that TAp73 ensures normal adult neurogenesis by promoting the long-term maintenance of neural stem cells. Moreover, we show that TAp73 does this by transcriptionally regulating the bHLH Hey2, which itself promotes neural precursor maintenance by preventing premature differentiation.

Decreased expression of updated NESG1 in nasopharyngeal carcinoma: Its potential role and preliminarily functional mechanism

Human NESG1 (CCDC19) gene was originally isolated in our laboratory from human nasopharynx tissue. However, the biological and clinical significances of this gene remain largely unknown. In this report, two errors in the originally submitted sequence of human NESG1 gene were found, and the open reading frame sequence of NESG1 (Accession number: NM_012337.1) was revised and updated in the NCBI database (Accession number: NM_012337.2). The antibody raised against the revised sequence of NESG1 detected a single band of 66 kD in human nasopharynx tissues. NESG1 transcripts were specifically expressed in the nasopharynx epithelium. Expression of NESG1 transcripts and protein was downregulated or absent in nasopharyngeal carcinoma (NPC) tissues and cell lines in comparison to that in the normal nasopharynx tissues. The levels of NESG1 protein were significantly greater in the low-grade NPC tissues than that in the high-grade NPC tissues. Induced expression of NESG1 in otherwise NESG1-negative 5-8F cells not only significantly decreased cell proliferation, G1-S phase transition, but also markedly inhibited the ability of cell migration and invasion as well as in vivo tumorigenesis. Furthermore, NESG1 also significantly regulated the expression of cell cycle regulator CCNA1 and p21. Our findings first provided evidence that NESG1 may act as a tumor suppressor by inhibiting cell proliferation, invasion and migration of NPC cells.

Upregulation of SOX9 in Lung Adenocarcinoma and Its Involvement in the Regulation of Cell Growth and Tumorigenicity

SOX9 is an important transcription factor required for development and has been implicated in several types of cancer. However, SOX9 has never been linked to lung cancer to date. Here, we show that SOX9 expression is upregulated in lung adenocarcinoma and show how it is associated with cancer cell growth. Data mining with five microarray data sets containing 490 clinical samples, quantitative reverse transcription-PCR validation assay in 57 independent samples, and immunohistochemistry assay with tissue microarrays containing 170 lung tissue cores were used to profile SOX9 mRNA and protein expression. Short interference RNA suppression of SOX9 in cell lines was used to scrutinize functional role(s) of SOX9 and associated molecular mechanisms. SOX9 mRNA and protein were consistently overexpressed in the majority of lung adenocarcinoma. Knockdown of SOX9 in lung adenocarcinoma cell lines resulted in marked decrease of adhesive and anchorage-independent growth in concordance with the upregulation of p21 (CDKN1A) and downregulation of CDK4. In agreement with higher SOX9 expression level in lung adenocarcinoma, the p21 mRNA level was significantly lower in tumors than that in normal tissues, whereas the opposite was true for CDK4, supporting the notion that SOX9 negatively and positively regulated p21 and CDK4, respectively. Finally, whereas SOX9-knockdown cells showed significantly attenuated tumorigenicity in mice, SOX9 transfectants consistently showed markedly stronger tumorigenicity. Our data suggest that SOX9 is a new hallmark of lung adenocarcinoma, in which SOX9 might contribute to gain of tumor growth potential, possibly acting through affecting the expression of cell cycle regulators p21 and CDK4.

Prognostic Significance of the Alterations of the G1-S Checkpoint in Localized Leiomyosarcoma of the Peripheral Soft Tissue

The aim of this study was to investigate the expression of cell cycle regulators p53, p16, cyclin-D1, and retinoblastoma (Rb) gene protein in leiomyosarcoma of the peripheral soft in order to identify expression profiles potentially useful for clinical prognostic purposes. A tissue microarray representing 70 localized leiomyosarcomas of the limbs and limb girdles was created with 3 representative cores from each tumor. Immunohistochemical staining was performed for p53, p16, cyclin-D1, and Rb using standard techniques. Staining was scored as either absent-low (<20% of neoplastic cells) or moderate-diffuse (≥20%). Outcome analysis was performed for local recurrence-free survival (LFS), metastatic disease-free survival (MDFS), and disease-specific survival (DSS). Kaplan-Meier analysis of survival revealed that no single alteration of the factors examined was associated with outcome, but tumors showing concomitant alteration of p16 and p53 were characterized by reduced MDFS and DSS (P=0.01 and P<0.001, respectively). In addition, patients who received adjuvant therapy consisting of radiotherapy alone or radiotherapy and chemotherapy had a better DSS than those receiving surgery alone or surgery and chemotherapy (P=0.05). In multivariate analysis, altered p16/p53 remained the only parameter predictive of MDFS and DSS (P=0.048, hazard ratio [HR]=2.488, 95% confidence interval [95% CI] 1.006-5.116; P=0.043, HR=2.498, 95% CI 1.029-5.909, respectively). Accumulation of cell cycle alterations represents a prognostic indicator in localized soft tissue leiomyosarcoma, and in particular altered p16/p53 expression is associated with an unfavorable prognosis. This may help the clinical management of patients with leiomyosarcomas.

Specific regulation of JNK signalling by the novel rat MKK7γ1 isoform

The c-Jun N-terminal kinases (JNKs) mediate a diversity of physiological and pathophysiological effects. Apart from isoform-specific JNK activation, upstream kinases are supposed to be the relevant regulators, which are involved in the context- and signalosome-depending functions. In the present study we report the cloning and characterization of the novel rat MKK7γ1, a splice variant of MKK7 with an additional exon in the N-terminal region, in the neuronal pheochromocytoma cell line PC12. Transfected MKK7γ1 increased basal JNK activity, in particular phosphorylation of JNK2. Consequently, JNK signalling was changed in mRNA-, protein- and activation-levels of JNK targets, such as transcription factors (c-Jun, p53, c-Myc), cell cycle regulators (p21, CyclinD1) and apoptotic proteins (Fas, Bim, Bcl-2, Bcl-xl). These alterations promote the sensitivity of MKK7γ1-transfected cells towards cell death and repress cell proliferation under normal cell growth conditions. Complexes of JIP-1, MKK7 and JNK2 were the major JNK signalosomes under basal conditions. After stimulation with taxol (5 μM) and tunicamycin (1.4 μg/ml), MKK7γ1- but not MKK7β1-transfection, reduced cell death and even increased cell proliferation. Cellular stress also led to an increased phosphorylation of JNK1 and the almost complete abrogation of complexes of JIP-1, MKK7 and JNK2 in MKK7γ1-transfected PC12 cells. Summarizing, MKK7γ1 affects the function and activity of individual JNK isoforms and the formation of their signalosomes. This study demonstrates for the first time that one splice-variant of MKK7 tightly controls JNK signalling and effectively adapts JNK functions to the cellular context.

Biologic Correlation of 2-[18F]-Fluoro-2-Deoxy-D-Glucose Uptake on Positron Emission Tomography in Thymic Epithelial Tumors

The usefulness of 2-[(18)F]-fluoro-2-deoxy-D-glucose ([(18)F]FDG) positron emission tomography (PET) can help predict the grade of malignancy and staging in thymic epithelial tumors. However, no satisfactory biologic explanation exists for this phenomenon. The aim of this study was to investigate the underlying biologic mechanisms of [(18)F]FDG uptake. Forty-nine patients with thymic epithelial tumors who underwent [(18)F]FDG PET were included in this study. Tumor sections were stained by immunohistochemistry for glucose transporter 1 (GLUT1), glucose transporter 3 (GLUT3), hypoxia-inducible factor-1 alpha (HIF-1alpha), vascular endothelial growth factor (VEGF), microvessels (CD31 and CD34), cell cycle control marker (p53), and apoptosis marker (bcl-2). We also conducted an in vitro study of [(18)F]FDG uptake in a thymic tumor cell line. There was a positive correlation between [(18)F]FDG uptake and GLUT1 (P < .0001), HIF-1alpha (P = .0036), VEGF (P < .0001), microvessel density (MVD; P < .0001), and p53 (P = .0002). GLUT3 and bcl-2 showed no positive correlation with [(18)F]FDG uptake. The expression of Glut1, HIF-1alpha, VEGF, CD31, CD34, and p53 was also significantly associated with the grade of malignancy and poor outcome in thymic epithelial tumors, whereas this relationship was not observed in GLUT3 and bcl-2. Our in vitro study demonstrated that upregulation of GLUT1 and HIF-1alpha was closely associated with [(18)F]FDG uptake into thymic tumor cell. [(18)F]FDG uptake in thymic epithelial tumors is determined by the presence of glucose metabolism (GLUT1), hypoxia (HIF-1alpha), angiogenesis (VEGF and MVD), and cell cycle regulator (p53).

Ionizing Radiation Activates AMP-Activated Kinase (AMPK): A Target for Radiosensitization of Human Cancer Cells

Adenosine monophosphate (AMP)-activated kinase (AMPK) is a molecular energy sensor regulated by the tumor suppressor LKB1. Starvation and growth factors activate AMPK through the DNA damage sensor ataxia-telangiectasia mutated (ATM). We explored the regulation of AMPK by ionizing radiation (IR) and its role as a target for radiosensitization of human cancer cells. Lung, prostate, and breast cancer cells were treated with IR (2-8 Gy) after incubation with either ATM or AMPK inhibitors or the AMPK activator metformin. Then, cells were subjected to either lysis and immunoblotting, immunofluorescence microscopy, clonogenic survival assays, or cell cycle analysis. IR induced a robust phosphorylation and activation of AMPK in all tumor cells, independent of LKB1. IR activated AMPK first in the nucleus, and this extended later into cytoplasm. The ATM inhibitor KU-55933 blocked IR activation of AMPK. AMPK inhibition with Compound C or anti-AMPK alpha subunit small interfering RNA (siRNA) blocked IR induction of the cell cycle regulators p53 and p21(waf/cip) as well as the IR-induced G2/M arrest. Compound C caused resistance to IR, increasing the surviving fraction after 2 Gy, but the anti-diabetic drug metformin enhanced IR activation of AMPK and lowered the surviving fraction after 2 Gy further. We provide evidence that IR activates AMPK in human cancer cells in an LKB1-independent manner, leading to induction of p21(waf/cip) and regulation of the cell cycle and survival. AMPK appears to (1) participate in an ATM-AMPK-p21(waf/cip) pathway, (2) be involved in regulation of the IR-induced G2/M checkpoint, and (3) may be targeted by metformin to enhance IR responses.

Activation of adenosine A2 A receptors restores the altered cell-cycle machinery during impaired wound healing in genetically diabetic mice

Cyclins drive cell-cycle progression by associating with their kinase partners, cyclin-dependent kinases (CDK). We investigated cyclin D1/CDK6, cyclin E/CDK2 complexes, and the cell-cycle negative regulators p15 and p27 in an incisional skin wound model. Wounds were produced on the back of female diabetic mice and their normoglycemic littermates. Animals were treated with polydeoxyribonucleotide (PDRN, 8 mg/kg/i.p.), an agonist of adenosine A2(A) receptors, or its vehicle daily. Granulation tissue proliferation by Ki67 immunostaining, cyclin D/CDK6 and cyclin E/CDK2 complexes, and p21 and p16 proteins (Western blot analysis), and the histologic changes were assessed at different days (3, 6, and 12 days after injury). Numerous Ki67 positive cells were observed at day 3 and day 6 in the granulation tissue of normoglycemic mice. Ki67 positive cells were fewer in diabetic than in normoglycemic mice. PDRN increased Ki67 positive cells in diabetic mice. Normoglycemic mice showed the greatest upregulation of cyclin D1, CDK6, cyclin E, and CDK2 at day 6. Diabetic mice had a markedly lower expression of cyclin D1, CDK6, cyclin E, and CDK2 at day 6. They also showed a greater expression of p15 and p27 at day 6. PDRN administration in diabetic mice increased cyclin D1/CDK6 and cyclin E/CDK2 expression and reduced p15 and p27 inhibitors at day 6 after injury; moreover, it improved the impaired wound healing at day 12. Our results suggest that adenosine A2(A) receptor activation by PDRN might represent a therapeutic strategy to overcome the diabetes-impaired cell-cycle machinery.

Modulation of p53 activity in the pregnant mouse

The pregnancy complications pre-eclampsia and Intrauterine growth restriction are associated with increased trophoblast apoptosis and expression of the cell cycle regulator p53. Previously the authors have demonstrated that activation of...

Immunohistochemical analyses at the late stage of tumor promotion by oxfendazole in a rat hepatocarcinogenesis model

The present study was performed to characterize immunohistochemically the expression levels of molecules related to not only xenobiotic and antioxidant functions but also cell proliferation and apoptosis in neoplastic lesions induced by the benzimidazole anthelmintic, oxfendazole (OX), at the late stage of its tumor promotion in a rat hepatocarcinogenesis model. Male F344 rats were initiated with an intraperitoneal injection of 200mg/kg N-diethylnitrosamine, and 2weeks later they were fed a diet containing 0% (basal diet) or 0.05% OX for 26weeks. All animals were subjected to a two-thirds partial hepatectomy at week 3 and killed at week 28. Histopathologically, OX increased the incidence and multiplicity of altered foci (4.0- and 3.6-fold, respectively) and hepatocellular adenomas (HCAs) (3.0- and 5.5-fold, respectively). OX treatment induced 5.2- and 5.6-fold increases in the number of proliferating cell nuclear antigen (PCNA)-positive cells and single-stranded DNA (ssDNA)-positive cells in HCAs compared with the surrounding tissue, respectively. Staining for the cell cycle regulators P21 and C/EBPα and the AhR-regulated CYP1A1 molecules decreased but increased reactivity of the Nrf2-regulated, detoxifing/antioxidant molecules aldo-keto reductase 7 (AKR7) and glutathione peroxidase 2 (GPX2) were also seen in HCAs compared with the surrounding hepatocytes. These results suggest that dysregulation of cell proliferation and apoptosis and escape from oxidative stress elicited by OX treatment play an important role in OX-induced hepatocarcinogenesis in rats.