Targeting p27Kip1 protein: its relevance in the therapy of human cancer

Constitutive β-Catenin Overexpression Represses Lncrna MIR100HG Transcription via HDAC6-Mediated Histone Modification in Colorectal Cancer

Wnt/β-catenin signaling plays a critical role in colonic carcinogenesis. However, non-coding RNAs (ncRNA) transcriptionally regulated by β-catenin are largely unknown. Herein, we found that lncRNA MIR100HG (lnc-MIR100HG) negatively correlated with target genes of β-catenin from The Cancer Genome Atlas colorectal carcinoma database, which was verified in 48 paired colorectal carcinoma specimens. In addition, constitutive overexpression of β-catenin decreased primary and mature lnc-MIR100HG levels, whereas blockage of β-catenin activity with siRNA or inhibitors significantly increased their expression. DNA pull-down and chromatin immunoprecipitation revealed the binding of β-catenin/TCF4 to the MIR100HG promoter. Moreover, β-catenin-forced expression reduced the enrichment of H3K27Ac, an active transcription marker, on the promoter, whereas β-catenin inhibition reversed this effect. Furthermore, HDAC6 was recruited to the MIR100HG promoter and downregulated H3K27Ac enrichment in a β-catenin-dependent manner. Besides, HDAC6 was upregulated and negatively correlated with lnc-MIR100HG in colorectal carcinoma specimens. Functional studies showed that lnc-MIR100HG overexpression induced cell-cycle G0-G1 arrest and repressed cell proliferation via p57 upregulation in vitro and in vivo. Taken together, we found that ectopic β-catenin transcriptionally repressed lnc-MIR100HG expression through HDAC6-mediated histone modification in colorectal carcinoma. Lnc-MIR100HG regulates the cell cycle through p57.

IMPLICATIONS

It provides a novel downstream mechanism highlighting β-catenin action during colon carcinogenesis and may shed light for further therapeutic approaches.

Synergistic Cytotoxicity between Elephantopus scaber and Tamoxifen on MCF-7-Derived Multicellular Tumor Spheroid

Elephantopus scaber Linn, a traditional herb, exhibited anticancer properties, and it was cytotoxic against the monolayer estrogen receptor-positive breast cancer cell line, MCF-7, in the previous study. In order to determine the potential of E. scaber as a complementary medicine for breast cancer, this study aimed to evaluate the synergism between E. scaber and tamoxifen in cytotoxicity using MCF-7 in the form of 3-dimensional multicellular tumor spheroid (MCTS) cultures. MCTS represents a more reliable model for studying drug penetration as compared to monolayer cells due to its greater resemblance to solid tumor. Combination of E. scaber ethanol extract and tamoxifen, which were used in concentrations lower than their respective IC₅₀ values, had successfully induced apoptosis on MCTS in this study. The combinatorial treatment showed >58% increase of lactate dehydrogenase release in cell media, cell cycle arrest at the S phase, and 1.3 fold increase in depolarization of mitochondrial membrane potential. The treated MCTS also experienced DNA fragmentation; this had been quantified by TUNEL-positive assay, which showed >64% increase in DNA damaged cells. Higher externalization of phospatidylserine and distorted and disintegrated spheroids stained by acridine orange/propidium iodide showed that the cell death was mainly due to apoptosis. Further exploration showed that the combinatorial treatment elevated caspases-8 and 9 activities involving both extrinsic and intrinsic pathways of apoptosis. The treatment also upregulated the expression of proapoptotic gene HSP 105 and downregulated the expression of prosurvival genes such as c-Jun, ICAM1, and VEGF. In conclusion, these results suggested that the coupling of E. scaber to low concentration of tamoxifen showed synergism in cytotoxicity and reducing drug resistance in estrogen receptor-positive breast cancer.

DNAJC5 promotes hepatocellular carcinoma cells proliferation though regulating SKP2 mediated p27 degradation

DNAJC5 (DnaJ heat shock protein family (Hsp40) member C5), also known as cysteine tandem protein (CSPα), is important for maintaining the normal function of nerve tissues, but its oncogenic function remains unknown. Here, we report a unique mechanism underlying the oncogenic function of DNAJC5. DNAJC5 protein expression is highly detectable in human hepatocellular carcinoma (HCC) tissues and is strongly related to a poor prognosis among HCC patients. DNAJC5 overexpression promotes HCC cell proliferation and reduced the ratio of cells in G₁ phase of the cell cycle. Furthermore, DNAJC5 interacts with SKP2 and enhances the degradation of p27 (a cyclin-dependent kinase inhibitor1B) by promoting formation of the SKP2-p27 complex. In contrast, DNAJC5 knockdown rescues the SKP2-mediated decrease in p27 protein levels. These results reveal that the DNAJC5-SKP2-p27 pathway is a novel mechanism for the oncogenic function of DNAJC5 in HCC.

Physical activity and advanced cancer: evidence of exercise-sensitive genes regulating prostate cancer cell proliferation and apoptosis

KEY POINTS

Physical activity is known to protect against cancer. The resistance exercise method whole-body electromyostimulation (WB-EMS) has a significant anti-cancer effect. WB-EMS-conditioned serum from advanced prostate cancer patients decreased human prostate carcinoma cell growth and viability in vitro. Multiplex analysis revealed that genes associated with human prostate cancer cell proliferation and apoptosis are sensitive for exercise. Feasible exercise should be part of multimodal anti-cancer therapies, also for physically weakened patients.

ABSTRACT

Regular physical activity is known to protect against cancer development. In cancer survivors, exercise reduces the risk of cancer recurrence and mortality. However, the link between exercise and decreased cancer risk and improved survival is still not well understood. Serum from exercising healthy individuals inhibits proliferation and activates apoptosis in various cancer cells, suggesting that mechanisms regulating cancer cell growth are affected by exercise. For the first time, we analysed serum from advanced-stage cancer patients with prostate (exercise group n = 8; control group n = 10) or colorectal (exercise n = 6; control n = 6) cancer, after a 12-week whole-body electromyostimulation training (20 min/session, 2×/week; frequency 85 Hz; pulse width 350 µs; 6 s stimulation, 4 s rest), a tolerable, yet effective, resistance exercise for physically weakened patients. We report that serum from these advanced cancer patients inhibits proliferation and enhances apoptosis of human prostate and colon cancer cells in vitro using cell growth and death assays (5-bromo-2'-deoxyuridine incorporation, cell counting, DNA fragmentation). Exercise-mimicking electric pulse stimulation of human primary myotubes showed that electric pulse stimulation-conditioned myotube medium also impairs human cancer cell viability. Gene expression analysis using a multiplex array of cancer-associated genes and subsequent quantitative RT-PCR revealed the presence of exercise-sensitive genes in human prostate cancer cells that potentially participate in the exercise-mediated regulation of malignant cell growth and apoptosis. Our data document the strong efficiency of the anti-oncogenic effects of physical activity and will further support the application of regular therapeutic exercise during cancer disease.

Role of the COP1 protein in cancer development and therapy

COP1, an E3 ubiquitin ligase, has been demonstrated to play a vital role in the regulation of cell proliferation, apoptosis and DNA repair. Accumulated evidence has revealed that COP1 is involved in carcinogenesis via targeting its substrates, including p53, c-Jun, ETS, β-catenin, STAT3, MTA1, p27, 14-3-3σ, and C/EBPα, for ubiquitination and degradation. COP1 can play tumor suppressive and oncogenic roles in human malignancies, urging us to summarize the functions of COP1 in tumorigenesis. In this review, we describe the structure of COP1 and its known substrates. Moreover, we dissect the function of COP1 by physiological (mouse models), pathological (human tumor specimens) and biochemical (ubiquitin substrates) Evidence. Furthermore, we discuss COP1 as a potential therapeutic target for cancer therapy.

Interactions of the super complexes: When mTORC1 meets the proteasome

Homeostatic regulation of energy and metabolic status requires that anabolic and catabolic signaling pathways be precisely regulated and coordinated. Mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is a mega protein complex that promotes energy-consuming anabolic processes of protein and nucleic acid synthesis as well lipogenesis in times of energy and nutrient abundance. However, it is best characterized as the regulator of steps leading to protein synthesis. The ubiquitin-proteasome proteolytic system (UPS) is a major intracellular proteolytic system whose activity is increased during periods of nutrient scarcity and in muscle wasting conditions such as cachexia. Recent studies have examined the impact of mTORC1 on levels and functions of the 26S proteasome, the mega protease complex of the UPS. Here we first briefly review current understanding of the regulation of mTORC1, the UPS, and the 26S proteasome complex. We then review evidence of the effect of each complex on the abundance and functions of the other. Given the fact that drugs that inhibit either complex are either in clinical trials or are approved for treatment of cancer, a muscle wasting condition, we identify studying the effect of combinatory mTORC1-proteasome inhibition on skeletal muscle mass and health as a critical area requiring investigation.

miR‑221‑3p promotes the cell growth of non‑small cell lung cancer by targeting p27

Emerging evidence suggests the critical function of microRNAs in regulating the growth of cancer cells. In the present study, it was demonstrated that miR-221-3p was overexpressed in non-small cell lung cancer (NSCLC) tissues and cell lines compared with that noted in the normal controls. Downregulation of miR-221-3p suppressed the proliferation, colony formation and invasion of NSCLC cells. To further understand the molecular mechanisms underlying the potential oncogenic function of miR-221-3p in NSCLC, the downstream targets of miR-221-3p were predicted using bioinformatic databases. The prediction suggested the cell cycle regulator p27 as one of the targets of miR-221-3p. Molecular experiments showed that miR-221-3p was able to bind with the 3′-untranslated region (UTR) of p27 and decreased the expression of p27 in NSCLC cells. Consistent with the suppressive role of p27 in controlling cell cycle progression, overexpression of miR-221-3p decreased the expression of p27 and promoted cell cycle progression from G1 to S phase. Collectively, our findings identified miR-221-3p as a novel regulator of NSCLC cell growth via modulating the expression of p27.

The function and clinical significance of eIF3 in cancer

Abnormal regulation of gene expression is essential for tumorigenesis. Several studies indicate that regulation of oncogene expression and neoplastic transformation are controlled by subunits of eukaryotic translation initiation factors (eIFs). Eukaryotic translation initiation factor 3 (eIF3) is the largest (800 kDa) and the most complex mammalian initiation factor. It is composed of 13 non-identical polypeptides designated as eIF3a-m and plays a pivotal role in protein synthesis that bridges the 43S pre-initiation complex and eIF4F-bound mRNA. However, the functional roles of individual subunits are not yet very clear. This review presents on several of aberrant expressed eIF3 subunits which are detected in various human cancers and the associated mechanisms have been acknowledged or are still not sure. Finally, identifying novel targets and biomarkers for caner is of great importance in early diagnosis and treatment of cancer. eIF3 may be a novel target molecule in drug development for cancer treatment and prevention.

miR-3074-5p Promotes the Apoptosis but Inhibits the Invasiveness of Human Extravillous Trophoblast-Derived HTR8/SVneo Cells In Vitro

OBJECTIVE

The objective of this study was to observe the effects of the overexpression of miR-3074-5p in human trophoblast cells in vitro.

DESIGN

Experimental in vitro study in HTR8/SVneo cells.

METHODS

HTR8/SVneo cells were transfected with miR-3074-5p mimic. The cell apoptosis and invasion were measured via flow cytometry and transwell assay, respectively. The expression levels of P53, Cyclin Dependent Kinase Inhibitor 1B (P27), BCL-2, BCL2 associated X (BAX), and BCL2 like 14 (BCL-G) in HTR8/SVneo cells were determined by Western blot. The alterations in gene expression profile of HTR8/SVneo cells were evaluated by complementary DNA microarray assay, and the differential expressions of dihydrolipoamide S-succinyltransferase (DLST), growth-associated protein 43 (GAP43), runt-related transcription factor 2 (RUNX2), and C-C type chemokine receptor 3 (CCR3) were validated by Western blot. Biofunctions of these differentially expressed genes were enriched by Gene Ontology analysis.

RESULTS

The overexpression of miR-3074-5p in HTR8/SVneo cells promoted cell apoptosis but inhibited cell invasion, being accompanied by the significantly elevated expressions of P27, BCL-2, and BCL-G. Meanwhile, an increased expression of P27 and P57 was also detected in a small sample size of placental villi of recurrent miscarriage (RM) patients. Totally, 411 genes and 397 genes were screened out, respectively, to be downregulated or upregulated at least by 2-folds in miR-3074-5p overexpressed HTR8/SVneo cells. These differentially expressed genes were involved in several important functions related to pregnancy. Subsequently, the reduced expressions of DLST and GAP43 proteins, as well as the increased expressions of CCR3 and RUNX2 proteins, were validated in miR-3074-5p overexpressed HTR8/SVneo cells.

CONCLUSION

These data suggested a potential contribution of miR-3074-5p in the pathogenesis of RM by disturbing the normal activities of trophoblast cells.

A single nucleotide polymorphism of cyclin-dependent kinase inhibitor 1B (p27Kip1) associated with human vein graft failure affects growth of human venous adventitial cells but not smooth muscle cells

BACKGROUND

Cyclin-dependent kinase inhibitor 1B (p27^Kip1) is a cell-cycle inhibitor whose -838C>A single nucleotide polymorphism (rs36228499; hereafter called p27 SNP) has been associated with the clinical failure of peripheral vein grafts, but the functional effects of this SNP have not been demonstrated.

METHODS

Human saphenous vein adventitial cells and intimal/medial smooth muscle cells (SMCs) were derived from explants obtained at the time of lower extremity bypass operations. We determined the following in adventitial cells and SMCs as a function of the p27 SNP genotype: (1) p27 promoter activity, (2) p27 messenger (m)RNA and protein levels, and (3) growth and collagen gel contraction. Deoxyribonuclease I footprinting was also performed in adventitial cells and SMCs.

RESULTS

p27 promoter activity, deoxyribonuclease I footprinting, p27 mRNA levels, and p27 protein levels demonstrated that the p27 SNP is functional in adventitial cells and SMCs. Both cell types with the graft failure protective AA genotype had more p27 mRNA and protein. As predicted because of higher levels of p27 protein, adventitial cells with the AA genotype grew slower than those of the CC genotype. Unexpectedly, SMCs did not show this genotype-dependent growth response.

CONCLUSIONS

These results support the functionality of the p27 SNP in venous SMCs and adventitial cells, but an effect of the SNP on cell proliferation is limited to only adventitial cells. These data point to a potential role for adventitial cells in human vein graft failure and also suggest that SMCs express factors that interfere with the activity of p27.

MicroRNA-200c is involved in proliferation of gastric cancer by directly repressing p27Kip1

P27^Kip1, also known as Cyclin-dependent kinase inhibitor 1B, is an important check-point protein in the cell cycle. It has been identified that although as a tumor suppressor, P27^Kip1 is expressed in different cancer cell types, which shows the therapeutic potential in tumor genesis. In this study, we examined the upstream regulatory mechanism of P27^Kip1 at the microRNA (miRNA) level in gastric carcinogenesis. We used bioinformatics to predict that microRNA-200c (miR-200c) might be a direct upstream regulator of P27^Kip1. It was also verified in gastric epithelial-derived cell lines that overexpression of miR-200c significantly inhibited the expression levels of P27^Kip1, whereas knockdown of miR-200c promoted P27^Kip1 expression in AGS and BGC-823 cells. Furthermore, we identified the direct binding of miR-200c on the P27^Kip1 3′ -UTR sequence by luciferase assay. MiR-200c could enhance the colony formation of cells by repressing P27^Kip1 expression. In addition, the negative correlation between P27^Kip1 and miR-200c in human gastric cancer tissues and matched normal tissues further supported the tumor-promoting action of miR-200c in vivo. Our finding suggested that miR-200c directly regulates the expression of P27^Kip1 and promotes cell growth in gastric cancer as an oncogene, which may provide new clues to treatment.

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miR-200c is involved in the proliferation of gastric cancer cell lines.

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P27Kip1 is a direct downstream target of miR-200c.

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miR-200c is determined an oncogene in human gastric cancer tissue species.

Activation of AMPK α2 inhibits airway smooth muscle cells proliferation

The aims of the present study were to examine the effect of adenosine monophosphate-activated protein kinase (AMPK) activation on airway smooth muscle cells (ASMCs) proliferation and to address its potential mechanisms. Platelet derived growth factor (PDGF) activated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, and this in turn up-regulated S-phase kinase-associated protein 2 (Skp2) and consequently reduced cyclin dependent kinase inhibitor 1B (p27) leading to ASMCs proliferation. Pre-incubation of cells with metformin, an AMPK activator, blocked PDGF-induced activation of mTOR and its downstream targets changes of Skp2 and p27 without changing Akt phosphorylation and inhibited ASMCs proliferation. Transfection of ASMCs with AMPK α2-specific small interfering RNA (siRNA) reversed the effect of metformin on mTOR phosphorylation, Skp2 and p27 protein expression and cell proliferation. Our study suggests that activation of AMPK, particularly AMPK α2, negatively regulates mTOR activity to suppress ASMCs proliferation and therefore has a potential value in the prevention and treatment of asthma by negatively modulating airway remodeling.

PTHrP Nuclear Localization and Carboxyl Terminus Sequences Modulate Dental and Mandibular Development in Part via the Action of p27

To determine whether the action of the PTHrP nuclear localization sequence and C terminus is mediated through p27 in modulating dental and mandibular development, compound mutant mice, which are homozygous for both p27 deletion and the PTHrP1-84 knock-in mutation (p27(-/-)Pthrp(KI/KI)), were generated. Their teeth and mandibular phenotypes were compared with those of p27(-/-), Pthrp(KI/KI), and wild-type mice. At 2 weeks of age, the mandibular mineral density, alveolar bone volume, osteoblast numbers, and dental volume, dentin sialoprotein-immunopositive areas in the first molar were increased significantly in p27(-/-) mice and decreased dramatically in both Pthrp(KI/KI) and p27(-/-) Pthrp(KI/KI) mice compared with wild-type mice; however, these parameters were partly rescued in p27(-/-) Pthrp(KI/KI) mice compared with Pthrp(KI/KI) mice. These data demonstrate that the deletion of p27 in Pthrp(KI/KI) mice can partially rescue defects in dental and mandibular development. Furthermore, we found that deletion of p27 in Pthrp(KI/KI) mice partially corrected the dental and mandibular phenotype by modulating cell cyclin-regulating molecules and antioxidant enzymes. This study therefore indicates that the p27 pathway may function downstream in the action of PTHrP nuclear localization sequence to regulate dental and mandibular development.

Down-regulation of S100A9 inhibits osteosarcoma cell growth through inactivating MAPK and NF-κB signaling pathways

Background

Osteosarcoma (OS) is well-known for poor prognosis due to its high incidence of proliferation and metastasis. Researches have provided valuable insights into the tumorigenesis of S100A9 in some cancers. We aimed to understand the expression level, functions and mechanisms of S100A9 in human osteosarcoma for the first time.

Methods

The expression of S100A9 protein was detected in 120 human osteosarcoma tissues and 40 normal human bone tissues using tissue microarrays analysis. The knockdown of S100A9 induced by RNA interference (RNAi) method in three osteosarcoma cell lines (U2OS, 143B, MG63) was applied to analyze the effects of S100A9 on cell proliferation, cell cycle distribution, migration, invasion and xenotransplanted tumors. Moreover, MAPK-ERK1/2, MAPK-p38, NF-κB-p65, NF-κB-p50, p21, p27, CDK2 and CDK4 were tested.

Results

The expression of S100A9 was increased in human osteosarcoma issues and was positively correlated with clinical classification and survival rate. Down-regulation of S100A9 inhibited OS cellular proliferation, migration, invasion and cell cycle S phase in vitro and suppressed tumor formation in vivo with the reduction on PCNA and Ki67 proliferation index. Our data also demonstrated that knockdown of S100A9 repressed the protein levels of phospho-ERK1/2, phospho-p50, phospho-p65 except phospho-p38, and prompted up-regulation of p21 and p27 leading to inactivation of cyclin dependent kinase 2(CDK2) and cyclin dependent kinase 4(CDK4).

Conclusions

S100A9 might be a significant role for predicting osteosarcoma prognosis and down-regulation of S100A9 could be used as a potential target for gene therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2294-1) contains supplementary material, which is available to authorized users.

Impact of a Eukaryotic Translation Initiation Factor 3a Polymorphism on Susceptibility to Gastric Cancer

OBJECTIVE

To investigate single nucleotide polymorphisms in the eukaryotic translation initiation factor 3a (eIF3a) gene and the risk for gastric cancer within the Chinese population.

SUBJECTS AND METHODS

A total of 322 patients with gastric cancer were selected as the patient group and 340 non-gastric cancer patients were selected as the control group using the case-control method. Polymerase chain reaction-sequence-specific primer technology was leveraged to genotype the rs77382849 single nucleotide polymorphism in the eIF3a gene. The demographic characteristics of the study population and other exposures to risk factors were collected. Unconditional logistic regression analysis was performed to determine the association between the risk factors and gastric cancer.

RESULTS

A higher frequency of the eIF3a rs77382849 GG homozygote genotype was observed in the gastric cancer patients compared with the controls (63.98 vs. 54.41%, p < 0.05). After adjustment of exposure risks, such as age, gender, smoking, and drinking, the rs77382849 single nucleotide polymorphism was still associated with susceptibility to gastric cancer. When the eIF3a rs77382849 GG homozygote genotype was used as the reference group, the GA genotype (GA vs. GG: OR = 0.545, 95% CI: 0.386-0.769, p = 0.001) and AA genotype (AA vs. GG: OR = 0.245, 95% CI: 0.072-0.836, p = 0.025) were both correlated with a significantly decreased risk for gastric cancer development.

CONCLUSION

An association between eIF3a rs77382849 polymorphism and susceptibility to gastric cancer was observed in these Chinese patients.

Differential somatostatin receptor (SSTR) 1-5 expression and downstream effectors in histologic subtypes of growth hormone pituitary tumors

PURPOSE

The aim of this study was to examine whether differential expression of somatostatin receptors (SSTR) 1-5 and downstream effectors are different in densely (DG) and sparsely (SG) granulated histological growth hormone (GH) pituitary tumor subtypes.

METHODS

The study included 33 acromegalic patients with 23 DG and 10 SG tumors. SSTR1-5 were measured by qPCR and immunoblotting. Signaling candidates downstream of SSTR2 were also assessed.

RESULTS

SSTR2 mRNA and protein levels were significantly higher in DG compared to SG tumors. Downstream of SSTR2, p27(kip1) was decreased (2.6-fold) in SG compared to DG tumors, suggesting a potential mechanism of SSA resistance in SG tumors with intact SSTR2 expression. Re-expression of E-cadherin in GH pituitary cell increased p27(kip1) levels.

CONCLUSIONS

Histological subtyping correlated with SSTR2, E cadherin and p27(kip) protein levels and these may serve as useful biomarkers in GH tumors to predict behavior and response to therapy with SSA.

Histone Deacetylase Inhibitors Increase p27(Kip1) by Affecting Its Ubiquitin-Dependent Degradation through Skp2 Downregulation

Histone deacetylase inhibitors (HDACIs) represent an intriguing class of pharmacologically active compounds. Currently, some HDACIs are FDA approved for cancer therapy and many others are in clinical trials, showing important clinical activities at well tolerated doses. HDACIs also interfere with the aging process and are involved in the control of inflammation and oxidative stress. In vitro, HDACIs induce different cellular responses including growth arrest, differentiation, and apoptosis. Here, we evaluated the effects of HDACIs on p27(Kip1), a key cyclin-dependent kinase inhibitor (CKI). We observed that HDACI-dependent antiproliferative activity is associated with p27(Kip1) accumulation due to a reduced protein degradation. p27(Kip1) removal requires a preliminary ubiquitination step due to the Skp2-SCF E3 ligase complex. We demonstrated that HDACIs increase p27(Kip1) stability through downregulation of Skp2 protein levels. Skp2 decline is only partially due to a reduced Skp2 gene expression. Conversely, the protein decrease is more profound and enduring compared to the changes of Skp2 transcript. This argues for HDACIs effects on Skp2 protein posttranslational modifications and/or on its removal. In summary, we demonstrate that HDACIs increase p27(Kip1) by hampering its nuclear ubiquitination/degradation. The findings might be of relevance in the phenotypic effects of these compounds, including their anticancer and aging-modulating activities.

P27Kip1 serine 10 phosphorylation determines its metabolism and interaction with cyclin-dependent kinases

p27Kip1 is a critical modulator of cell proliferation by controlling assembly, localization and activity of cyclin-dependent kinase (CDK). p27Kip1 also plays important roles in malignant transformation, modulating cell movement and interaction with the extracellular matrix. A critical p27Kip1 feature is the lack of a stable tertiary structure that enhances its "adaptability" to different interactors and explains the heterogeneity of its function. The absence of a well-defined folding underlines the importance of p27Kip1 post-translational modifications that might highly impact the protein functions. Here, we characterize the metabolism and CDK interaction of phosphoserine10-p27Kip1 (pS10- p27Kip1), the major phosphoisoform of p27Kip1. By an experimental strategy based on specific immunoprecipitation and bidimensional electrophoresis, we established that pS10-p27Kip1 is mainly bound to cyclin E/CDK2 rather than to cyclin A/CDK2. pS10- p27Kip1 is more stable than non-modified p27Kip1, since it is not (or scarcely) phosphorylated on T187, the post-translational modification required for p27Kip1 removal in the nucleus. pS10-p27Kip1 does not bind CDK1. The lack of this interaction might represent a mechanism for facilitating CDK1 activation and allowing mitosis completion. In conclusion, we suggest that nuclear p27Kip1 follows 2 almost independent pathways operating at different rates. One pathway involves threonine-187 and tyrosine phosphorylations and drives the protein toward its Skp2-dependent removal. The other involves serine-10 phosphorylation and results in the elongation of p27Kip1 half-life and specific CDK interactions. Thus, pS10-p27Kip1, due to its stability, might be thought as a major responsible for the p27Kip1-dependent arrest of cells in G1/G0 phase.

Inhibition of Notch3 prevents monocrotaline-induced pulmonary arterial hypertension

It has been shown that activation of Notch3 signaling is involved in the development of pulmonary arterial hypertension (PAH) by stimulating pulmonary arteries remodeling, while the molecular mechanisms underlying this are still largely unknown. The aims of this study are to address these issues. Monocrotaline dramatically increased right ventricle systolic pressure to 39.0 ± 2.6 mmHg and right ventricle hypertrophy index to 53.4 ± 5.3% (P < 0.05 versus control) in rats, these were accompanied with significantly increased proliferation and reduced apoptosis of pulmonary vascular cells as well as pulmonary arteries remodeling. Treatment of PAH model with specific Notch inhibitor DAPT significantly reduced right ventricle systolic pressure to 26.6 ± 1.3 mmHg and right ventricle hypertrophy index to 33.5 ± 2.6% (P < 0.05 versus PAH), suppressed proliferation and enhanced apoptosis of pulmonary vascular cells as well as inhibited pulmonary arteries remodeling. Our results further indicated that level of Notch3 protein and NICD3 were increased in MCT-induced model of PAH, this was accompanied with elevation of Skp2 and Hes1 protein level and reduction of P27Kip1. Administration of rats with DAPT-prevented MCT induced these changes. Our results suggest that Notch3 signaling activation stimulated pulmonary vascular cells proliferation by Skp2-and Hes1-mediated P27Kip1 reduction, and Notch3 might be a new target to treat PAH.

δ-Tocotrienol treatment is more effective against hypoxic tumor cells than normoxic cells: potential implications for cancer therapy

Tocotrienols, unsaturated forms of vitamin E, inhibit the proliferation of a variety of cancer cells and suppress angiogenesis. However, the mechanisms underlying those effects on cancer cell growth remain unclear especially under hypoxic conditions. In this study, we demonstrated that δ-tocotrienol (δ-T3) could be used as a novel anticancer agent against human colorectal adenocarcinoma (DLD-1) cells under both normoxic and hypoxic conditions. δ-T3 inhibited the growth of DLD-1 cells in a dose-dependent fashion by inducing cell cycle arrest and apoptosis. This effect was more potent under hypoxic than normoxic conditions. The anticancer effect of δ-T3 was achieved by its up-regulation of cyclin-dependent kinase inhibitors (p21 and p27), the activation of caspases and the suppression of phosphorylation of protein kinase B (Akt) at Thr(308) and Ser(473). In in vivo studies, oral administration of rice bran tocotrienol (RBT3, mainly γ-T3) (10 mg/mouse/day) significantly inhibited tumor growth in nude mice. In tumor analyses, RBT3 activated p21, p27, caspase-3 and caspase-9 and decreased Akt phosphorylation. Furthermore, immunostaining revealed that RBT3 decreased the number of cells positive for CD31/platelet endothelial cell adhesion molecule-1 in microvessels in the tumor. Taken together, these data suggest that tocotrienols are potent antitumor agents capable of inducing apoptosis and inhibiting angiogenesis under both hypoxic and normoxic conditions. Tocotrienols could have significant therapeutic potential in the clinical treatment of tumors.

Brk/Protein tyrosine kinase 6 phosphorylates p27KIP1, regulating the activity of cyclin D-cyclin-dependent kinase 4

Cyclin D and cyclin-dependent kinase 4 (cdk4) are overexpressed in a variety of tumors, but their levels are not accurate indicators of oncogenic activity because an accessory factor such as p27(Kip1) is required to assemble this unstable dimer. Additionally, tyrosine (Y) phosphorylation of p27 (pY88) is required to activate cdk4, acting as an "on/off switch." We identified two SH3 recruitment domains within p27 that modulate pY88, thereby modulating cdk4 activity. Via an SH3-PXXP interaction screen, we identified Brk (breast tumor-related kinase) as a high-affinity p27 kinase. Modulation of Brk in breast cancer cells modulates pY88 and increases resistance to the cdk4 inhibitor PD 0332991. An alternatively spliced form of Brk (Alt Brk) which contains its SH3 domain blocks pY88 and acts as an endogenous cdk4 inhibitor, identifying a potentially targetable regulatory region within p27. Brk is overexpressed in 60% of breast carcinomas, suggesting that this facilitates cell cycle progression by modulating cdk4 through p27 Y phosphorylation. p27 has been considered a tumor suppressor, but our data strengthen the idea that it should also be considered an oncoprotein, responsible for cyclin D-cdk4 activity.

Binding cavities and druggability of intrinsically disordered proteins

To assess the potential of intrinsically disordered proteins (IDPs) as drug design targets, we have analyzed the ligand-binding cavities of two datasets of IDPs (containing 37 and 16 entries, respectively) and compared their properties with those of conventional ordered (folded) proteins. IDPs were predicted to possess more binding cavity than ordered proteins at similar length, supporting the proposed advantage of IDPs economizing genome and protein resources. The cavity number has a wide distribution within each conformation ensemble for IDPs. The geometries of the cavities of IDPs differ from the cavities of ordered proteins, for example, the cavities of IDPs have larger surface areas and volumes, and are more likely to be composed of a single segment. The druggability of the cavities was examined, and the average druggable probability is estimated to be 9% for IDPs, which is almost twice that for ordered proteins (5%). Some IDPs with druggable cavities that are associated with diseases are listed. The optimism versus obstacles for drug design for IDPs is also briefly discussed.

A new tumour suppression mechanism by p27Kip1: EGFR down-regulation mediated by JNK/c-Jun pathway inhibition

p27^Kip1 is a potent inhibitor of cyclin-dependent kinases that drive G₁-to-S cell-cycle transition. Reduced p27^Kip1 expression is prevalent in a wide range of human tumours; however, the exact mechanism(s) of p27^Kip1-mediated tumour suppression remains obscure. In the present study, we identified a close inverse relationship between p27^Kip1 and EGFR (epidermal growth factor receptor) expression: the parental T24 human bladder cancer cells had high p27^Kip1 expression but low EGFR expression and, in striking contrast, the metastatic derivative of T24 (T24T) had low p27^Kip1 expression but high EGFR expression. This relationship was also found in various human cancer tissues, and was not only just correlative but also causal; depletion of p27^Kip1 in MEF (mouse embryonic fibroblast) cells resulted in markedly elevated EGFR expression, a result reproducible with an Egfr promoter-luciferase reporter in both T24 and MEF cells, suggesting transcriptional repression of EGFR by p27^Kip1. Indeed, p27^Kip1 was found to regulate EGFR expression via the JNK (c-Jun N-terminal kinase)/c-Jun transcription factor: p27^Kip1 deficiency activated JNK/c-Jun, whereas inhibition of JNK/c-Jun by dominant-negative mutants dramatically repressed Egfr transcription. Furthermore, the proximal promoter of the Egfr gene was crucial for its transcription, where the recruiting activity of c-Jun was much greater in p27^Kip1−/− cells than in p27^Kip1+/+ cells. Introduction of GFP–p27^Kip1 into T24T cells suppressed JNK/c-Jun activation, EGFR expression and anchorage-independent growth. The results of the present study demonstrate that p27^Kip1 suppresses JNK/c-Jun activation and EGFR expression in MEFs and human bladder cancer cells, and the results obtained are consistent with those from human cancer specimens. The present study provides new insights into p27^Kip1 suppression of cancer cell growth, migration and metastasis.

An inverse relationship between p27^Kip1 and EGFR expression in parental T24 human bladder cancer cells and various human cancer tissues was found. Depletion of p27^Kip1 in cells markedly elevated EGFR expression through transcriptional repression of Egfr by p27^Kip1 via the JNK/c-Jun cascade.

The N-terminal region of p27 inhibits HIF-1α protein translation in ribosomal protein S6-dependent manner by regulating PHLPP-Ras-ERK-p90RSK axis

P27 was identified as a tumor suppressor nearly two decades, being implicated in cell-cycle control, differentiation, senescence, apoptosis and motility. Our present study, for the first time to the best of our knowledge, revealed a potential role of p27 in inhibiting S6-mediated hypoxia-inducible factor-1α (HIF-1α) protein translation, which contributed to the protection from environmental carcinogen (sodium arsenite)-induced cell transformation. Our findings showed that depletion of p27 expression by knockout and knockdown approaches efficiently enhanced S6 phosphorylation in arsenite response via overactivating Ras/Raf/MEK/ERK pathway, which consequently resulted in the stimulation of p90RSK (90 kDa ribosomal S6 kinase), a direct kinase for S6 phosphorylation. Although PI3K/AKT pathway was also involved in S6 activation, blocking AKT and p70S6K activation did not attenuate arsenite-induced S6 activation in p27−/− cells, suggesting p27 specifically targeted Ras/ERK pathway rather than PI3K/AKT pathway for inhibition of S6 activation in response to arsenite exposure. Further functional studies found that p27 had a negative role in cell transformation induced by chronic low-dose arsentie exposure. Mechanistic investigations showed that HIF-1α translation was upregulated in p27-deficient cells in an S6 phosphorylation-dependent manner and functioned as a driving force in arsenite-induced cell transformation. Knockdown of HIF-1α efficiently reversed arsenite-induced cell transformation in p27-depleted cells. Taken together, our findings provided strong evidence showing that by targeting Ras/ERK pathway, p27 provided a negative control over HIF-1α protein synthesis in an S6-dependent manner, and abrogated arsenite-induced cell transformation via downregulation of HIF-1α translation.

Reduced expression of the retinoblastoma protein shows that the related signaling pathway is essential for mediating the antineoplastic activity of erufosine

Erufosine is a new antineoplastic agent of the group of alkylphosphocholines, which interferes with signal transduction and induces apoptosis in various leukemic and tumor cell lines. The present study was designed to examine for the first time the mechanism of resistance to erufosine in malignant cells with permanently reduced expression of the retinoblastoma (Rb) protein. Bearing in mind the high number of malignancies with reduced level of this tumor-suppressor, this investigation was deemed important for using erufosine, alone or in combination, in patients with compromised RB1 gene expression. For this purpose, clones of the leukemic T-cell line SKW-3 were used, which had been engineered to constantly express differently low Rb levels. The alkylphosphocholine induced apoptosis, stimulated the expression of the cyclin dependent kinase inhibitor p27^Kip1 and inhibited the synthesis of cyclin D3, thereby causing a G₂ phase cell cycle arrest and death of cells with wild type Rb expression. In contrast, Rb-deficiency impeded the changes induced by eru-fosine in the expression of these proteins and abrogated the induction of G₂ arrest, which was correlated with reduced antiproliferative and anticlonogenic activities of the compound. In conclusion, analysis of our results showed for the first time that the Rb signaling pathway is essential for mediating the antineoplastic activity of erufosine and its efficacy in patients with malignant diseases may be predicted by determining the Rb status.

p27 protein protects metabolically stressed cardiomyocytes from apoptosis by promoting autophagy

p27(Kip1) (p27), a key regulator of cell division, has been implicated in autophagy of cancer cells. However, its role in autophagy, the evolutionarily conserved catabolic process that enables cells to remove unwanted proteins and damaged organelles, had not been examined in the heart. Here we report that ectopic delivery of a p27 fusion protein (TAT-p27) was sufficient to induce autophagy in neonatal rat ventricular cardiomyocytes in vitro, under basal conditions and after glucose deprivation. Conversely, lentivirus-delivered shRNA against p27 successfully reduced p27 levels and suppressed basal and glucose-deprived levels of autophagy in cardiomyocytes in vitro. Glucose deprivation mimics myocardial ischemia and induces apoptosis in cardiomyocytes. During glucose deprivation, TAT-p27 inhibited apoptosis, whereas down-regulation of p27 decreased survival of cardiomyocytes. However, inhibition of autophagy by pharmacological (3-methyladenine, chloroquine, or bafilomycin A1) or genetic approaches (siRNA-mediated knockdown of Atg5) sensitized cardiomyocytes to glucose deprivation-induced apoptosis, even in the presence of TAT-p27. TAT-p27 was also able to provoke greater levels of autophagy in resting and fasting cardiomyocytes in vivo. Further, TAT-p27 enhanced autophagy and repressed cardiomyocytes apoptosis, improved cardiac function, and reduced infarct size following myocardial infarction. Again, these effects were lost when cardiac autophagy in vivo was blocked by chloroquine. Taken together, these data show that p27 positively regulates cardiac autophagy in vitro and in vivo, at rest and after metabolic stress, and that TAT-p27 inhibits apoptosis by promoting autophagy in glucose-deprived cardiomyocytes in vitro and in post-myocardial infarction hearts in vivo.

The prognostic value of altered eIF3a and its association with p27 in non-small cell lung cancers

BACKGROUND

Over-expressed eukaryotic initiation factor 3a (eIF3a) in non-small cell lung cancer (NSCLC) contributed to cisplatin sensitivity. However, the role of eIF3a in oncogenesis was still controversial. This study was designed to investigate the prognostic impact of eIF3a and p27 in radically resected NSCLC patients.

METHODS

The expression levels of subcellular eIF3a and p27 were evaluated immunohistochemically in 537 radically resected NSCLC samples, and another cohort of 210 stage II NSCLC patients. Disease specific survival (DSS) and disease free survival (DFS) were analyzed by Kaplan-Meier method and Cox regression model.

RESULTS

The subcellular expression of eIF3a was strongly correlated with status of p27 (Spearman rank coefficient correlation for cytoplasmic eIF3a and p27=0.653, for nuclear staining=0.716). Moreover, survival analysis revealed favorable prognostic impact of nuclear eIF3a, p27, and the combination high nuclear staining on NSCLC (Hazards Ratio=0.360, 95%CI=0.109-0.782, P=0.028). In addition, interaction research between biomarkers and chemotherapy status disclosed cisplatin-based regimen trend to prolong DSS of stage II NSCLC patients with high eIF3a-C (P=0.036)and low p27-N (P=0.031).

CONCLUSIONS

Our findings suggested altered eIF3a expression closely correlated with p27 status, and the association was of prognostic value for resected NSCLC. Altered expression of eIF3a and p27 predicted prognosis of NSCLC independently.

IKK-β/NF-κB p65 mediates p27(Kip1) protein degradation in arsenite response

p27(Kip1) is a potent inhibitor of the cyclin-dependent kinases that drive G1 to S phase transition. Since deregulation of p27(Kip1) is found in many malignancies and is associated with the poor prognosis, elucidation of the molecular bases for regulation of p27(Kip1) expression is of great significance, not only in providing insight into the understanding of biological p27(Kip1), but also in the development of new cancer therapeutic tactics. We here explored the inhibitory regulation of IKKβ on p27(Kip1) expression following arsenite exposure. We found that although the basal level of p27(Kip1) expression in the IKKβ(-/-) cells is much lower than that in the IKKβ(+/+) cells, the deletion of IKKβ in the MEFs led to a marked increase in p27(Kip1) protein induction due to arsenite exposure in comparison to that in the IKKβ(+/+) cells. The IKKβ regulatory effect on p27(Kip1) expression was also verified in the IKKβ(-/-) and IKKβ(-/-) cells with IKKβ reconstitutional expression, IKKβ(-/-) (IKKβ). Further studies indicated that IKKβ-mediated p27(Kip1) downregulation occurred at protein degradation level via p65-dependent and p50-independent manner. Moreover, the results obtained from the comparison of arsenite-induced GSK3β activation among transfectants of WT, IKKβ(-/-) and IKKβ(-/-) (IKKβ), and the utilization of GSKβ shRNA, demonstrated that IKKβ regulation of p27 protein degradation was mediated by GSK3β following arsenite exposure.

Loss of p27 upregulates MnSOD in a STAT3-dependent manner, disrupts intracellular redox activity and enhances cell migration

Cell migration is a dynamic process that is central to a variety of physiological functions as well as disease pathogenesis. The modulation of cell migration by p27 (officially known as CDKN1B) has been reported, but the exact mechanism(s) whereby p27 interacts with downstream effectors that control cell migration have not been elucidated. By systematically comparing p27(+/+) mouse embryonic fibroblasts (MEFs) with genetically ablated p27(-/-) MEFs using wound-healing, transwell and time-lapse microscopic analyses, we provide direct evidence that p27 inhibits both directional and random cell migration. Identical results were obtained with normal and cancer epithelial cells using complementary knockdown and overexpression approaches. Additional studies revealed that overexpression of manganese superoxide dismutase (MnSOD, officially known as SOD2) and reduced intracellular oxidation played a key role in increased cell migration in p27-deficient cells. Furthermore, we identified signal transducer and activator of transcription 3 (STAT3) as the transcription factor responsible for p27-regulated MnSOD expression, which was further mediated by ERK- and ATF1-dependent transactivation of the cAMP response element (CRE) within the Stat3 promoter. Collectively, our data strongly indicate that p27 plays a crucial negative role in cell migration by inhibiting MnSOD expression in a STAT3-dependent manner.

Highly effective combination of LSD1 (KDM1A) antagonist and pan-histone deacetylase inhibitor against human AML cells

The histone demethylase LSD1 (KDM1A) demethylates mono- and di-methylated (Me2) lysine (K) 4 on histone H3. High LSD1 expression blocks differentiation and confers a poor prognosis in AML. Here, treatment with the novel LSD1 antagonist SP2509 attenuated the binding of LSD1 with the co-repressor CoREST, increased the permissive H3K4Me3 mark on the target gene promoters, and increased the levels of p21, p27 and C/EBPα in cultured AML cells. Additionally, SP2509 treatment or LSD1 shRNA inhibited the colony growth of AML cells. SP2509 also induced morphologic features of differentiation in the cultured and primary AML blasts. SP2509 induced more apoptosis of AML cells expressing mutant NPM1 than MLL fusion oncoproteins. Treatment with SP2509 alone significantly improved the survival of immune-depleted mice following tail-vein infusion and engraftment of cultured or primary human AML cells. Co-treatment with pan-HDAC inhibitor (HDI) panobinostat (PS) and SP2509 was synergistically lethal against cultured and primary AML blasts. Compared to each agent alone, co-treatment with SP2509 and PS significantly improved the survival of the mice engrafted with the human AML cells, without exhibiting any toxicity. Collectively, these findings show that the combination of LSD1 antagonist and pan-HDI is a promising therapy warranting further testing against AML.

Differential role of the estrogen receptors ESR1 and ESR2 on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats

The aim of the present study was to investigate the role of each estrogen receptors on the regulation of proteins involved with proliferation and differentiation of Sertoli cells from 15-day-old rats. Activation of ESR1 by 17β-estradiol (E2) and ESR1-selective agonist PPT increased CCND1 expression, and this effect was dependent on NF-kB activation. E2 and the ESR2-selective agonist DPN, but not PPT, increased, in a PI3K and CREB-dependent manner, the expression of CDKN1B and the transcription factors GATA-1 and DMRT1. Analyzing the expression of ESR1 and ESR2 in different stages of development of Sertoli cells, we observed that the ESR1/ESR2 ratio decreased with age, and this ratio seems to be important to determine the end of cell proliferation and the start of cell differentiation. In Sertoli cells from 15-day-old rats, the ESR1/ESR2 ratio favors the effect of ESR1 and the activation of this receptor increased [Methyl-(3)H]thymidine incorporation. We propose that in Sertoli cells from 15-day-old rats E2 modulates Sertoli cell proliferation through ESR1/NF-kB-mediated increase of CCND1, and cell cycle exit and differentiation through ESR2/CREB-mediated increase of CDKN1B, GATA-1 and DMRT1. The present study reinforces the important role of estrogen for normal testis development.

MicroRNA-196a promotes cervical cancer proliferation through the regulation of FOXO1 and p27Kip1

Background:

The phosphoinositide 3-kinase (PI3K)/Akt signalling pathway appears to be a key regulator in cervical carcinogenesis. However, the downstream regulatory mechanism of PI3K/Akt signalling remains largely unknown.

Methods:

The expression of miR-196a in cervical cancer cell lines and cervical cancer tissues was examined using real-time PCR. The effects of miR-196a on PI3K/Akt signalling and cellular proliferation were evaluated by bromodeoxyuridine labelling, 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazoliumbromide, colony formation assays and luciferase assays.

Results:

The expression level of miR-196a was markedly increased in cervical cancer tissues and cell lines compared with normal cervical tissue and normal cervical squamous cells. Upregulation of miR-196a was correlated with advanced tumour stage and poor overall and recurrence-free survival in cervical cancer patients. Upregulation of miR-196a enhanced G1/S-phase transition and the proliferative ability of cervical cancer cells, whereas suppression of miR-196a had the opposite effect. Using bioinformatics and biological approaches, we showed that FOXO1 and p27^Kip1, two key effectors of PI3K/Akt signalling, were direct targets of miR-196a.

Conclusions:

Our findings suggest that miR-196a has an important role in promoting human cervical cancer cell proliferation and may represent a novel therapeutic target of microRNA-mediated suppression of cell proliferation in cervical cancer.

Calmodulin as a potential target by which berberine induces cell cycle arrest in human hepatoma Bel7402 cells

Berberine is an isoquinoline alkaloid that has drawn extensive attention because it possesses various biological activities. Several mechanisms have been proposed to interpret the anticancer activity of berberine. However, these explanations are mostly based on its downstream-regulated genes or proteins; information on the direct target proteins that mediate the antiproliferative action of berberine remains unclear. In this study, a computational pipeline based on a ligand-protein inverse docking program and mining of the 'Connectivity MAP' data was adopted to explore the potential target proteins for berberine. The results showed that four proteins, that is calmodulin, cytochrome P450 3A4, sex hormone-binding globulin, and carbonic anhydrase II, were suggested to be the potential targets of berberine. The anticalmodulin property of berberine was demonstrated with an in vitro phosphodiesterase activity assay. Flow cytometric analysis found that G1 cell cycle arrest induced by berberine in Bel7402 cells was enhanced by cotreatment with calmodulin inhibitors. Western blotting results indicated that berberine treatment decreased phosphorylation of calmodulin kinase II and blocked subsequent MEK1 activation as well as p27 protein degradation. These results suggested that calmodulin might play crucial roles in berberine-induced cell cycle arrest in cancer cells.

Napsin A is possibly useful marker to predict the tumorigenic potential of lung bronchiolo-alveolar hyperplasia in F344 rats

There are 2 types of bronchiolo-alveolar hyperplasia found in rat lungs. One is 'inflammatory hyperplasia' with a potential to recover in future with removal of the stimulating insult and the other is 'latent tumorigenic hyperplasia' as an independent preneoplastic lesion for adenocarcinoma. In the present experiment, we focused on rat lung bronchiolo-alveolar hyperplasia induced by 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which decreases with time after induction and reverts to normal, or by N-bis(2-hydroxypropyl)nitrosamine (DHPN), with tumorigenic potential to progress to adenoma and adenocarcinoma. Though NNK is a typical carcinogen inducing lung adenocarcinoma in female A/J mice, the tumorigenic potential by NNK in rats is weak. Differences between hyperplasias induced by DHPN and by NNK were here examined immunohistochemically. Formalin fixed paraffin embedded lung samples with hyperplastic and inflammatory lesions were obtained from rats exposed to DHPN or NNK and from lung inflammation models induced with fine particles like CuO, NiO and quartz. The 19 markers were examined immunohistochemically. Napsin A, in the inflammatory lesions and hyperplasia induced by NNK, was positive for macrophages and secretions in the alveoli spaces but less so in the walls of the alveoli. In the proliferative lesions including hyperplasia induced by DHPN, strong positive staining for napsin A was observed in the walls of the alveoli. Thus high expression was suggested to be possibly useful for detecting tumorigenic potential of rat lung hyperplasia.

MAPK kinase 3 is a tumor suppressor with reduced copy number in breast cancer

Cancers are initiated as a result of changes that occur in the genome. Identification of gains and losses in the structure and expression of tumor-suppressor genes and oncogenes lies at the root of the understanding of cancer cell biology. Here, we show that the mitogen-activated protein kinase (MAPK) MKK3 suppresses the growth of breast cancer, in which it varies in copy number. A pervasive loss of MKK3 gene copy number in patients with breast cancer is associated with an impairment of MKK3 expression and protein level in malignant tissues. To assess the functional role of MKK3 in breast cancer, we showed in an animal model that MKK3 activity is required for suppression of tumor growth. Active MKK3 enhanced expression of the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27(Kip1), leading to increased cell-cycle arrest in G1 phase of the cell cycle. Our results reveal the functional significance of MKK3 as a tumor suppressor and improve understanding of the dynamic role of the MAPK pathway in tumor progression.

Inorganic Phosphate as a Novel Signaling Molecule with Antiproliferative Action in MDA-MB-231 Breast Cancer Cells

Inorganic phosphate (P_i) is an essential nutrient for living organisms. It plays a key role in diverse physiological functions, including osteoblast differentiation and skeletal mineralization. Relevantly, P_i is emerging as an important signaling molecule capable of modulating multiple cellular functions by altering signal transduction pathways, gene expression, and protein abundance in many cell types. To our knowledge, the consequences of elevated P_i on behavior of breast cancer cells have been poorly addressed. In this study we investigate the effects of P_i on proliferation of MDA-MB-231 breast cancer cells. We report that P_i inhibits proliferation of MDA-MB-231 cells by slowing cell cycle progression, without apoptosis occurrence. We found that P_i causes cells to accumulate in G1 phase in a time-dependent manner. Accordingly, G1 accumulation was associated with a decrease of cyclin A and cyclin E and an increase of cell cycle inhibitors p21 and p27 protein levels, respectively. Moreover, the P_i-induced antiproliferative effect was dynamically accompanied by profound changes in ERK1/2 and STAT3 protein and phosphorylation levels in response to P_i. Altogether, our data represent the first evidence of P_i acting as a novel signaling molecule in MDA-MB-231 breast cancer cells, capable of eliciting a strong antiproliferative action and suggest that targeting P_i levels at local sites might represent the rationale for developing novel strategies for therapeutic intervention in triple-negative breast cancer.

MicroRNA profiling in human neutrophils during bone marrow granulopoiesis and in vivo exudation

The purpose of this study was to describe the microRNA (miRNA) expression profiles of neutrophils and their precursors from the initiation of granulopoiesis in the bone marrow to extravasation and accumulation in skin windows. We analyzed three different cell populations from human bone marrow, polymorphonuclear neutrophil (PMNs) from peripheral blood, and extravasated PMNs from skin windows using the Affymetrix 2.0 platform. Our data reveal 135 miRNAs differentially regulated during bone marrow granulopoiesis. The majority is differentially regulated between the myeloblast/promyelocyte (MB/PM) and myelocyte/metamyelocyte (MC/MM) stages of development. These 135 miRNAs were divided into six clusters according to the pattern of their expression. Several miRNAs demonstrate a pronounced increase or reduction at the transition between MB/PM and MC/MM, which is associated with cell cycle arrest and the initiation of terminal differentiation. Seven miRNAs are differentially up-regulated between peripheral blood PMNs and extravasated PMNs and only one of these (miR-132) is also differentially regulated during granulopoiesis. The study indicates that several different miRNAs participate in the regulation of normal granulopoiesis and that miRNAs might also regulate activities of extravasated neutrophils. The data present the miRNA profiles during the development and activation of the neutrophil granulocyte in healthy humans and thus serves as a reference for further research of normal and malignant granulocytic development.

DFMO/eflornithine inhibits migration and invasion downstream of MYCN and involves p27Kip1 activity in neuroblastoma

Neuroblastoma (NB) is the most common extracranial pediatric tumor. NB patients over 18 months of age at the time of diagnosis are often in the later stages of the disease, present with widespread dissemination, and often possess MYCN tumor gene amplification. MYCN is a transcription factor that regulates the expression of a number of genes including ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Inhibiting ODC in NB cells produces many deleterious effects including G₁ cell cycle arrest, inhibition of cell proliferation, and decreased tumor growth, making ODC a promising target for drug interference. DFMO treatment leads to the accumulation of the cyclin-dependent kinase inhibitor p27^Kip1 protein and causes p27^Kip1/Rb-coupled G₁ cell cycle arrest in MYCN-amplified NB tumor cells through a process that involves p27^Kip1 phosphorylation at residues Ser10 and Thr198. While p27^Kip1 is well known for its role as a cyclin-dependent kinase inhibitor, recent studies have revealed a novel function of p27^Kip1 as a regulator of cell migration and invasion. In the present study we found that p27^Kip1 regulates the migration and invasion in NB and that these events are dependent on the state of phosphorylation of p27^Kip1. DFMO treatments induced MYCN protein downregulation and phosphorylation of Akt/PKB (Ser473) and GSK3-β (Ser9), and polyamine supplementation alleviated the DFMO-induced effects. Importantly, we provide strong evidence that p27^Kip1 mRNA correlates with clinical features and the survival probability of NB patients.

Androgen receptor may be responsible for gender disparity in gastric cancer

Men are at a higher risk of developing gastric cancer than women. However, the exact mechanisms responsible for the gender differences remain unclear. Recently, a number of epidemiological and genotyping studies have attributed the gender disparity in male-predominant cancers to the disruption of androgen receptor (AR) homeostasis. Moreover, previous data indicated that AR expression is an independent unfavorable prognostic factor in gastric cancer, suggesting that AR may play an important role in gastric carcinogenesis. In addition, mounting evidence suggests that AR is involved in many signaling pathways associated with gastric carcinogenesis. On the basis of the aforementioned evidence, we postulate that AR exhibits oncogenic properties in gastric cancer via several possible mechanisms, which may partly explain the higher prevalence of gastric cancer among males.

Prodigiosin down-regulates SKP2 to induce p27(KIP1) stabilization and antiproliferation in human lung adenocarcinoma cells

BACKGROUND AND PURPOSE

High levels of SKP2 are a poor prognostic factor in multiple human cancers and mostly correlate with low p27(KIP1) levels. Prodigiosin is a bacterial tripyrrole pigment with strong pro-apoptotic activity. Induction of cell cycle blockade underlies one of its anticancer actions but the mechanisms involved are unclear. The aim of this study was to explore the role of the SKP2-p27(KIP1) axis in prodigiosin's cytostatic effect on human lung adenocarcinoma cells.

EXPERIMENTAL APPROACH

Prodigiosin's effects on cell cycle progression and long-term cell proliferation of human lung adenocarcinoma cells were characterized by flow cytometry and colony formation assay, respectively. Real-time RT-PCR and promoter activity analyses were performed for assessing transcriptional control, while cycloheximide chase analysis evaluated protein stability. Immunoblotting was employed for mechanistic study.

KEY RESULTS

Prodigiosin increased p27(KIP1) expression mainly by stabilizing p27(KIP1) through transcriptional repression of SKP2. Importantly, SKP2 overexpression or p27(KIP1) depletion restored the colony forming capacity of prodigiosin-treated cells. Furthermore, prodigiosin induced PKB dephosphorylation, leading to PKB inhibition as revealed by decreased serine 9 phosphorylation of GSK-3β. Constitutive PKB activation reduced prodigiosin-induced SKP2 repression. Prodigiosin also down-regulated E2F1 (mediates PI3K/PKB-induced SKP2 transcription), but E2F1 overexpression failed to restore SKP2 expression in prodigiosin-treated cells.

CONCLUSIONS AND IMPLICATIONS

Transcriptional repression of SKP2 and the consequent accumulation of p27(KIP1) are essential for prodigiosin's antiproliferative action. Mechanistically, prodigiosin induces PKB inhibition to down-regulate SKP2 in a GSK-3β- and E2F1-independent manner. Our findings further implicate the potential for developing prodigiosin as a novel class of SKP2-targeting anticancer agent.

Reversal by RARα agonist Am580 of c-Myc-induced imbalance in RARα/RARγ expression during MMTV-Myc tumorigenesis

INTRODUCTION

Retinoic acid signaling plays key roles in embryonic development and in maintaining the differentiated status of adult tissues. Recently, the nuclear retinoic acid receptor (RAR) isotypes α, β and γ were found to play specific functions in the expansion and differentiation of the stem compartments of various tissues. For instance, RARγ appears to be involved in stem cell compartment expansion, while RARα and RARβ are implicated in the subsequent cell differentiation. We found that over-expressing c-Myc in normal mouse mammary epithelium and in a c-Myc-driven transgenic model of mammary cancer, disrupts the balance between RARγ and RARα/β in favor of RARγ.

METHODS

The effects of c-Myc on RAR isotype expression were evaluated in normal mouse mammary epithelium, mammary tumor cells obtained from the MMTV-Myc transgenic mouse model as well as human normal immortalized breast epithelial and breast cancer cell lines. The in vivo effect of the RARα-selective agonist 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)carboxamido]benzoic acid (Am580) was examined in the MMTV-Myc mouse model of mammary tumorigenesis.

RESULTS

Modulation of the RARα/β to RARγ expression in mammary glands of normal mice, oncomice, and human mammary cell lines through the alteration of RAR-target gene expression affected cell proliferation, survival and tumor growth. Treatment of MMTV-Myc mice with the RARα-selective agonist Am580 led to significant inhibition of mammary tumor growth (~90%, P<0.001), lung metastasis (P<0.01) and extended tumor latency in 63% of mice. Immunocytochemical analysis showed that in these mice, RARα responsive genes such as Cyp26A1, E-cadherin, cellular retinol-binding protein 1 (CRBP1) and p27, were up-regulated. In contrast, the mammary gland tumors of mice that responded poorly to Am580 treatment (37%) expressed significantly higher levels of RARγ. In vitro experiments indicated that the rise in RARγ was functionally linked to promotion of tumor growth and inhibition of differentiation. Thus, activation of the RARα pathway is linked to tumor growth inhibition, differentiation and cell death.

CONCLUSIONS

The functional consequence of the interplay between c-Myc oncogene expression and the RARγ to RARα/β balance suggests that prevalence of RARγ over-RARα/β expression levels in breast cancer accompanied by c-Myc amplification or over-expression in breast cancer should be predictive of response to treatment with RARα-isotype-specific agonists and warrant monitoring during clinical trials.

Primary cilia and coordination of receptor tyrosine kinase (RTK) signalling

Primary cilia are microtubule-based sensory organelles that coordinate signalling pathways in cell-cycle control, migration, differentiation and other cellular processes critical during development and for tissue homeostasis. Accordingly, defects in assembly or function of primary cilia lead to a plethora of developmental disorders and pathological conditions now known as ciliopathies. In this review, we summarize the current status of the role of primary cilia in coordinating receptor tyrosine kinase (RTK) signalling pathways. Further, we present potential mechanisms of signalling crosstalk and networking in the primary cilium and discuss how defects in ciliary RTK signalling are linked to human diseases and disorders.

High cytoplasmic expression of p27(Kip1) is associated with a worse cancer-specific survival in clear cell renal cell carcinoma

What's known on the subject? and What does the study add? The loss of p27(Kip1) correlates with poor prognosis in various human cancers, and was postulated as a biomarker in RCC. Up to now p27(Kip1) analysis in RCC was focused on its nuclear localization. We confirmed higher p27(Kip1) expression in the nucleus and cytoplasm of RCC and correlated high cytoplasmic p27(Kip1) with an unfavourable clinic and a reduced survival.

OBJECTIVES

To analyse the cytoplasmic and nuclear differences of p27(Kip1) expression and localization in benign and clear cell renal cell carcinoma (ccRCC) with regard to overall survival (OS) and cancer-specific survival (CSS). p27(Kip1) is considered to contribute to the progression of ccRCC and is targeted by next generation dual-therapies.

PATIENTS AND METHODS

In 140 patients, ccRCC and corresponding benign kidney tissue were analyzed for nuclear and cytoplasmic staining of p27(Kip1) by immunohistochemistry using a tissue microarray technique. Staining intensity and percentage of positive stained cells are given as expression scores. p27(Kip1) expression was categorized as high if ccRCC tissue stained stronger than the respective level of the corresponding benign tissue and categorized as low if ccRCC tissue stained less than or equal to the corresponding benign tissue. Differences in OS and CSS were analyzed by log-rank analysis and expression levels were correlated with tumour and patient characteristics using Fisher's exact test.

RESULTS

Cytoplasmatic (mean [sd]: 13.8% [1.2%] vs 10.7% [1.7%]; P= 0.04) and nuclear (mean [sd]: 75.6% [2.7%] vs 13.6% [2.1%]; P < 0.001) staining of p27(Kip1) were significantly stronger in ccRCC tissues compared to benign tissue. High cytoplasmic p27(Kip1) expression was significantly associated with a higher T and N stage, Fuhrman grade and the presence of metastatic disease (P < 0.001). The median follow-up time was 38.2 months. There was no difference in OS between the low and high expression groups, although CSS was significantly lower in patients with high cytoplasmic p27(Kip1) (P < 0.001) and CSS heavily tended to be lower in the nuclear low expression group (P= 0.069).

CONCLUSIONS

High cytoplasmic p27(Kip1) levels in renal cancer tissues are associated with advanced disease and reduced cancer specific survival, whereas low nuclear expression levels appear to be beneficial. The present study corroborates the consideration of cytoplasmic p27(Kip1) for future diagnostic and targeted therapeutic approaches in RCC establishing a potential protective shift of p27(Kip1) from the cytoplasm to the nucleus.

Mouse models of follicular and papillary thyroid cancer progression

A significant number of well-differentiated thyroid cancers progress or recur, becoming resistant to current therapeutic options. Mouse models recapitulating the genetic and histological features of advanced thyroid cancer have been an invaluable tool to dissect the mechanisms involved in the progression from indolent, well differentiated tumors to aggressive, poorly differentiated carcinomas, and to identify novel therapeutic targets. In this review, we focus on the lessons learned from models of epithelial cell-derived thyroid cancer showing progression from hyperplastic lesions to locally invasive and metastatic carcinomas.