Reduction of 14-3-3 proteins correlates with increased sensitivity to killing of human lung cancer cells by ionizing radiation

Targeting 14-3-3ε-CDC25A interactions to trigger apoptotic cell death in skin cancer

Non-melanoma skin cancer is the most common form of cancer worldwide. We previously documented an anti-apoptotic role for CDC25A in cutaneous squamous cell carcinoma (SCC), an activity dependent on its association with 14-3-3 proteins. We hypothesized that targeting CDC25A-14-3-3ε interactions may be an effective strategy for inducing skin cancer cell apoptosis. Co-immunoprecipitation revealed that CDC25A associated with 14-3-3ε, 14-3-3γ and 14-3-3ζ in SCC cells but not normal keratinocytes. 14-3-3ε and CDC25A activated Akt/BAD/Survivin pro-survival signaling. To target the interaction of 14-3-3ε with CDC25A for cancer therapy, we developed two novel phospho-peptides, pS and pT, corresponding to each of the 14-3-3 binding sites of CDC25A, to specifically interfere with 14-3-3ε binding to CDC25A. Peptides pT (IC₅₀ = 22.1 μM), and pS (IC₅₀ = 29 μM) induced SCC cell death and blocked 14-3-3ε binding to CDC25A. pS or pT treatment of SCC xenografts increased apoptotic cell death and decreased pro-survival P-Akt (S473) and Survivin, demonstrating the effectiveness of the peptides in vivo. These findings lay a framework for the further development of peptides to target 14-3-3ε-CDC25A interactions for skin cancer treatment.

Differential Subcellular Distribution and Translocation of Seven 14-3-3 Isoforms in Response to EGF and During the Cell Cycle

Multiple isoforms of 14-3-3 proteins exist in different organisms. In mammalian cells, 14-3-3 protein has seven isoforms (α/β, ε, η, γ, σ, θ/τ, and δ/ζ), with α and δ representing the phosphorylated versions of β and ζ, respectively. While the existence of multiple isoforms may represent one more level of regulation in 14-3-3 signaling, our knowledge regarding the isoform-specific functions of 14-3-3 proteins is very limited. Determination of the subcellular localization of the different 14-3-3 isoforms could give us important clues of their specific functions. In this study, by using indirect immunofluorescence, subcellular fractionation, and immunoblotting, we studied the subcellular localization of the total 14-3-3 protein and each of the seven 14-3-3 isoforms; their redistribution throughout the cell cycle; and their translocation in response to EGF in Cos-7 cells. We showed that 14-3-3 proteins are broadly distributed throughout the cell and associated with many subcellular structures/organelles, including the plasma membrane (PM), mitochondria, ER, nucleus, microtubules, and actin fibers. This broad distribution underlines the multiple functions identified for 14-3-3 proteins. The different isoforms of 14-3-3 proteins have distinctive subcellular localizations, which suggest their distinctive cellular functions. Most notably, 14-3-3ƞ is almost exclusively localized to the mitochondria, 14-3-3γ is only localized to the nucleus, and 14-3-3σ strongly and specifically associated with the centrosome during mitosis. We also examined the subcellular localization of the seven 14-3-3 isoforms in other cells, including HEK-293, MDA-MB-231, and MCF-7 cells, which largely confirmed our findings with Cos-7 cells.

[14-3-3ζ protein mediates gemcitabine resistance in NK/T-cell lymphoma]

Objective: To explore the molecular mechanisms of 14-3-3ζ in gemcitabine resistance in extranodal NK/T-cell lymphoma, nasal type (ENKTL) . Methods: The effects of cell proliferation and invasion were detected by cell counting kit-8 (CCK-8) assay and transwell assay. YTS cells were exposed to gradually increased concentrations of gemcitabine to establish gemcitabine-resistant YTS cells (YTS-gem) in vitro. 14-3-3ζ specific siRNA lentiviral vector was transfected into YTS and YTS-gem cells to downregulate 14-3-3ζ expression, and stable transfected cell clones were screened. The protein expression was determined by Western blot. Results: ①14-3-3ζ expression was significantly up-regulated in gemcitabine resistant YTS-gem cells, comparing with that of YTS cells (P<0.05) . ②The results of CCK-8 and transwell assay showed that downregulation of 14-3-3ζ significantly reduced the cell proliferation and invasion abilities (P<0.05) . ③Downregulation of 14-3-3ζ could restore gemcitabine sensitivity in gemcitabine resistant YTS-gem cells (P<0.05) . ④Western blotting results showed that knockdown of 14-3-3ζ significantly upregulated pro-apoptotic Bax, and downregulated anti-apoptotic Bcl-2, Caspase-3, cleaved caspase-3, Cyclin D1 in gemcitabine-resistant YTS-gem cells (P<0.05) . There was no significant difference in p53 ang P-gp expression levels. Conclusions: 14-3-3ζ was upregulated in gemcitabine resistant YTS cells. Overexpression of 14-3-3ζ promoted cell proliferation and enhanced cell migration. 14-3-3ζ contributed to gemcitabine resistance to ENKTL through anti-apoptosis.

CDK16 overexpressed in non-small cell lung cancer and regulates cancer cell growth and apoptosis via a p27-dependent mechanism

Cyclin-dependent kinase 16 (CDK16, PCTAIRE1) expression is upregulated in a wide variety of human malignancies. However, the function(s) of CDK16 in non-small cell lung cancer (NSCLC) remain unknown. Therefore, here we investigated the role of CDK16 in NSCLC. From 43 NSCLC tumors and matching healthy control lung tissues, immunohistochemistry revealed significantly greater CDK16 and phospho-p27^Ser10 staining levels in NSCLC samples relative to healthy controls. The NSCLC cell line EKVX was transfected with a control siRNA, a CDK16-siRNA, or CDK16-siRNA + p27-siRNA. We found significantly decreased proliferation levels and significantly increased apoptosis levels in CDK16-silenced NSCLC cells. However, these effects were abrogated in cells treated with both the CDK16-siRNA and the p27-siRNA. In CDK16-silenced NSCLC cells, we found upregulated p27 and downregulated phospho-p27^Ser10 protein expression but downregulated ubiquitinated p27 and ubiquitinated phospho-p27^Ser10 protein expression. Cycloheximide-treated CDK16-silenced NSCLC cells displayed a much milder reduction in p27 protein expression over time relative to untreated CDK16-silenced NSCLC cells. In summary, CDK16 is significantly upregulated in human NSCLC tumor tissue and plays an oncogenic role in NSCLC cells via promoting cell proliferation and inhibiting apoptosis in a p27-dependent manner. Moreover, CDK16 negatively regulates expression of the p27 via ubiquination and protein degradation.

Clinical Significance of 14-3-3 Zeta in Human Esophageal Cancer

We recently found 14-3-3 zeta to be overexpressed in esophageal squamous cell carcinomas (ESCCs) by differential display. In the present study we determined the clinical significance of 14-3-3 zeta in esophageal tumorigenesis. Immunohistochemical analysis was carried out in 61 ESCCs, 33 dysplasia samples, 14 hyperplasia samples and 7 matched histologically normal esophageal tissues and correlated with clinicopathological parameters. Cytoplasmic expression of 14-3-3 zeta protein was observed in 95% of ESCCs; 63% of tumors also showed nuclear localization. All hyperplastic and dysplastic tissues distant from ESCCs as well as dysplastic endoscopic biopsies showed cytoplasmic immunopositivity for 14-3-3 zeta, while nuclear localization was observed in 58% of dysplasia and 36% of hyperplasia samples. Matched distant histologically normal epithelia either showed basal cytoplasmic expression of 14-3-3 zeta or no detectable nuclear expression of the protein. Interestingly, immunopositivity observed in normal esophageal tissues and early hyperplasia was confined to cytoplasm only, though significant nuclear expression was detected in dysplasia and ESCC. Immunoblotting and RT-PCR analyses further confirmed 14-3-3 zeta expression in dysplasia and ESCC. To our knowledge, this is the first report demonstrating overexpression of 14-3-3 zeta in esophageal hyperplasia, dysplasia and squamous cell carcinoma, suggesting that alteration in its expression occurs in early stages and is associated with esophageal tumorigenesis.

Expression analysis on 14-3-3 proteins in regenerative liver following partial hepatectomy

14-3-3 proteins play a vital part in the regulation of cell cycle and apoptosis as signaling integration points. During liver regeneration, the quiescent hepatocytes go through hypertrophy and proliferation to restore liver weight. Therefore, we speculated that 14-3-3 proteins regulate the progression of liver regeneration. In this study, we analyzed the expression patterns of 14-3-3 proteins during liver regeneration of rat to provide an insight into the regenerative mechanism using western blotting. Only four isoforms (γ, ε, σ and τ/θ) of the 14-3-3 proteins were expressed in regenerative liver after partial hepatectomy (PH). The dual effects, the significant down-regulation of 14-3-3ε and the significant up-regulation of 14-3-3τ/θ at 2 h after PH, might play particularly important roles in S-phase entry. The significant peaks of 14-3-3σ at 30 h and of ε and τ/θ at 24 h might be closely related not only to the G₂/M transition but also to the size of hepatocytes. Possibly, the peak of 14-3-3ε expression seen at 168 h plays critical roles in the termination of liver regeneration by inhibiting cellular proliferation.

Interaction between Rho GTPases and 14-3-3 Proteins

The Rho GTPase family accounts for as many as 20 members. Among them, the archetypes RhoA, Rac1, and Cdc42 have been the most well-characterized. Like all members of the small GTPases superfamily, Rho proteins act as molecular switches to control cellular processes by cycling between active, GTP-bound and inactive, GDP-bound states. The 14-3-3 family proteins comprise seven isoforms. They exist as dimers (homo- or hetero-dimer) in cells. They function by binding to Ser/Thr phosphorylated intracellular proteins, which alters the conformation, activity, and subcellular localization of their binding partners. Both 14-3-3 proteins and Rho GTPases regulate cell cytoskeleton remodeling and cell migration, which suggests a possible interaction between the signaling pathways regulated by these two groups of proteins. Indeed, more and more emerging evidence indicates the mutual regulation of these two signaling pathways. There have been many documented reviews of 14-3-3 protein and Rac1 separately, but there is no review regarding the interaction and mutual regulation of these two groups of proteins. Thus, in this article we thoroughly review all the reported interactions between the signaling pathways regulated by 14-3-3 proteins and Rho GTPases (mostly Rac1).

The functional significance of 14-3-3 proteins in cancer: focus on lung cancer

The 14-3-3 family proteins are phosphoserine/phosphothreonine binding proteins constituting a conserved class of proteins which are detected in all eukaryotic cells. In mammalians, 14-3-3 proteins have seven distinct isoforms (β, γ, ε, η, ζ, σ and τ/θ) which are involved in various cellular processes including signal transduction, cell cycle, cell proliferation, apoptosis, differentiation and survival. 14-3-3 proteins do not have a distinct catalytic activity and often regulate the activity, stability, subcellular localization and interactions of other proteins. The 14-3-3 family proteins function through interacting with their client proteins or facilitating the interaction of other proteins likely as adaptor proteins. The versatile functions of these proteins in the regulation of cell growth, cell division, cell death and cell migration make them candidate proteins for which an important role in cancer development could be envisioned. Indeed, analysis of cancer cell lines and tumor-derived tissues have indicated the differential abundance or post-translational modification of some 14-3-3 isoforms. In this review, we aimed to show how deregulation of 14-3-3 proteins contributes to initiation, establishment and progression of cancers with a particular emphasis on lung cancer. The role of these proteins in cancer-relevant processes including cell cycle, cell migration, cell-cell communication and programmed cell death will be discussed in detail.

Cytotoxicity and Genotoxicity Assessment of Sandalwood Essential Oil in Human Breast Cell Lines MCF-7 and MCF-10A

Sandalwood essential oil (SEO) is extracted from Santalum trees. Although α-santalol, a main constituent of SEO, has been studied as a chemopreventive agent, the genotoxic activity of the whole oil in human breast cell lines is still unknown. The main objective of this study was to assess the cytotoxic and genotoxic effects of SEO in breast adenocarcinoma (MCF-7) and nontumorigenic breast epithelial (MCF-10A) cells. Proteins associated with SEO genotoxicity were identified using a proteomics approach. Commercially available, high-purity, GC/MS characterized SEO was used to perform the experiments. The main constituents reported in the oil were (Z)-α-santalol (25.34%), (Z)-nuciferol (18.34%), (E)-β-santalol (10.97%), and (E)-nuciferol (10.46%). Upon exposure to SEO (2-8 μg/mL) for 24 hours, cell proliferation was determined by the MTT assay. Alkaline and neutral comet assays were used to assess genotoxicity. SEO exposure induced single- and double-strand breaks selectively in the DNA of MCF-7 cells. Quantitative LC/MS-based proteomics allowed identification of candidate proteins involved in this response: Ku70 (p = 1.37E - 2), Ku80 (p = 5.8E - 3), EPHX1 (p = 3.3E - 3), and 14-3-3ζ (p = 4.0E - 4). These results provide the first evidence that SEO is genotoxic and capable of inducing DNA single- and double-strand breaks in MCF-7 cells.

Identification of 14-3-3zeta associated protein networks in oral cancer

Advancements in genomics, proteomics, and bioinformatics have improved our understanding of gene/protein networks involved in intra- and intercellular communication and tumor-host interactions. Using proteomics integrated with bioinformatics, previously we reported overexpression of 14-3-3ζ in premalignant oral lesions and oral squamous cell carcinoma tissues in comparison with normal oral epithelium. 14-3-3ζ emerged as a novel molecular target for therapeutics and a potential prognostic marker in oral squamous cell carcinoma patients. However, the role of 14-3-3ζ in development and progression of oral cancer is not known yet. This study aimed to identify the 14-3-3ζ associated protein networks in oral cancer cell lines using IP-MS/MS and bioinformatics. A total of 287 binding partners of 14-3-3ζ were identified in metastatic (MDA1986) and nonmetastatic (SCC4) oral cancer cell lines including other 14-3-3 isoforms (2%), proteins involved in apoptosis (2%), cytoskeleton (9%), metabolism (16%), and maintenance of redox potential (2%). Our bioinformatics analysis revealed involvement of 14-3-3ζ in protein networks regulating cell cycle, proliferation, apoptosis, cellular trafficking, and endocytosis in oral cancer. In conclusion, our data revealed several novel protein interaction networks involving 14-3-3ζ in oral cancer progression and metastasis.

14-3-3ζ reduces DNA damage by interacting with and stabilizing proliferating cell nuclear antigen

Proliferating cell nuclear antigen (PCNA) is a processivity factor of DNA replication which plays critical roles in the regulation of DNA replication and repair. In this study, we show that PCNA interacts directly in vitro and in cells with 14-3-3ζ, an adaptor protein that regulates cell growth and response to DNA damage in eukaryotes. The interaction is mediated by at least two PCNA-binding sites on 14-3-3ζ, one of which is a novel non-canonical PIP (PCNA interacting protein) box. We find that DNA damages induced by UVC irradiation and MMS (methyl methanesulfonate) can enhance both the interaction of these two proteins and their co-localization with chromatin. Functional analyses suggest that 14-3-3ζ stabilizes PCNA possibly by regulating its ubiquitination, which impacts on DNA damage repair and cell viability.

High LET (56)Fe ion irradiation induces tissue-specific changes in DNA methylation in the mouse

DNA methylation is an epigenetic mechanism that drives phenotype and that can be altered by environmental exposures including radiation. The majority of human radiation exposures occur in a relatively low dose range; however, the biological response to low dose radiation is poorly understood. Based on previous observations, we hypothesized that in vivo changes in DNA methylation would be observed in mice following exposure to doses of high linear energy transfer (LET) (56) Fe ion radiation between 10 and 100 cGy. We evaluated the DNA methylation status of genes for which expression can be regulated by methylation and that play significant roles in radiation responses or carcinogenic processes including apoptosis, metastasis, cell cycle regulation, and DNA repair (DAPK1, EVL, 14.3.3, p16, MGMT, and IGFBP3). We also evaluated DNA methylation of repeat elements in the genome that are typically highly methylated. No changes in liver DNA methylation were observed. Although no change in DNA methylation was observed for the repeat elements in the lungs of these same mice, significant changes were observed for the genes of interest as a direct effect and a delayed effect of irradiation 1, 7, 30, and 120 days post exposure. At delayed times, differences in methylation profiles among genes were observed. DNA methylation profiles also significantly differed based on dose, with the lowest dose frequently affecting the largest change. The results of this study are the first to demonstrate in vivo high LET radiation-induced changes in DNA methylation that are tissue and locus specific, and dose and time dependent.

Cell cycle regulators guide mitochondrial activity in radiation-induced adaptive response

SIGNIFICANCE

There are accruing concerns on potential genotoxic agents present in the environment including low-dose ionizing radiation (LDIR) that naturally exists on earth's surface and atmosphere and is frequently used in medical diagnosis and nuclear industry. Although its long-term health risk is being evaluated and remains controversial, LDIR is shown to induce temporary but significant adaptive responses in mammalian cells and animals. The mechanisms guiding the mitochondrial function in LDIR-induced adaptive response represent a unique communication between DNA damage and cellular metabolism. Elucidation of the LDIR-regulated mitochondrial activity may reveal new mechanisms adjusting cellular function to cope with hazardous environmental stress.

RECENT ADVANCES

Key cell cycle regulators, including Cyclin D1/CDK4 and Cyclin B1/cyclin-dependent kinase 1 (CDK1) complexes, are actively involved in the regulation of mitochondrial functions via phosphorylation of their mitochondrial targets. Accumulating new evidence supports a concept that the Cyclin B1/CDK1 complex acts as a mediator in the cross talk between radiation-induced DNA damage and mitochondrial functions to coordinate cellular responses to low-level genotoxic stresses.

CRITICAL ISSUES

The LDIR-mediated mitochondrial activity via Cyclin B1/CDK1 regulation is an irreplaceable network that is able to harmonize vital cellular functions with adjusted mitochondrial metabolism to enhance cellular homeostasis.

FUTURE DIRECTIONS

Further investigation of the coordinative mechanism that regulates mitochondrial activities in sublethal stress conditions, including LDIR, will reveal new insights of how cells cope with genotoxic injury and will be vital for future targeted therapeutic interventions that reduce environmental injury and cancer risk.

Knockdown of 14-3-3ζ enhances radiosensitivity and radio-induced apoptosis in CD133(+) liver cancer stem cells

14-3-3ζ is related to many cancer survival cellular processes. In a previous study, we showed that silencing 14-3-3ζ decreases the resistance of hepatocellular carcinoma (HCC) to chemotherapy. In this study, we investigated whether silencing 14-3-3ζ affects the radioresistance of cancer stem-like cells (CSCs) in HCC. Knockdown of 14-3-3ζ decreased cell viability and the number of spheres by reducing radioresistance in CSCs after γ-irradiation (IR). Furthermore, the levels of pro-apoptotic proteins were upregulated in CSCs via silencing 14-3-3ζ after IR. These results suggest that 14-3-3ζ knockdown enhances radio-induced apoptosis by reducing radioresistance in liver CSCs.

DNA-PK target identification reveals novel links between DNA repair signaling and cytoskeletal regulation

The DNA-dependent protein kinase (DNA-PK) may function as a key signaling kinase in various cellular pathways other than DNA repair. Using a two-dimensional gel electrophoresis approach and stable DNA double-strand break-mimicking molecules (Dbait32Hc) to activate DNA-PK in the nucleus and cytoplasm, we identified 26 proteins that were highly phosphorylated following DNA-PK activation. Most of these proteins are involved in protein stability and degradation, cell signaling and the cytoskeleton. We investigated the relationship between DNA-PK and the cytoskeleton and found that the intermediate filament (IF) vimentin was a target of DNA-PK in vitro and in cells. Vimentin was phosphorylated at Ser459, by DNA-PK, in cells transfected with Dbait32Hc. We produced specific antibodies and showed that Ser459-P-vimentin was mostly located at cell protrusions. In migratory cells, the vimentin phosphorylation induced by Dbait32Hc was associated with a lower cellular adhesion and migration capacity. Thus, this approach led to the identification of downstream cytoplasmic targets of DNA-PK and revealed a connection between DNA damage signaling and the cytoskeleton.

Proteomic analysis of differentially expressed proteins in vitamin C-treated AGS cells

BACKGROUND

Vitamin C (ascorbic acid) is an essential nutrient of most living tissues that readily acts as a strong reducing agent, which is abundant in fruits and vegetables. Although, it inhibits cell growth in many human cancer cells in vitro, treatment in cancer is still controversial. Hence, the purpose of this study was to investigate the molecular mechanism of the inhibitory effect of vitamin C on AGS cell growth, and protein profiles in AGS cells after exposure to vitamin C treatment, by using proteomic tools.

RESULTS

Vitamin C showed a cytotoxic effect on AGS cells (IC50 300 μg/mL) and, 20 differentially expressed proteins (spot intensities which show ≥2 fold change and statistically significant, p<0.05 between the control and vitamin-C treated group) were successfully identified by assisted laser desorption/ ionization-time of flight/mass spectrometry (MALDI-TOF/MS). Of the 20 proteins, six were up-regulated and fourteen were down-regulated. Specifically, 14-3-3σ, 14-3-3ϵ, 14-3-3δ, tropomyosin alpha-3 chain and tropomyosin alpha-4 chain were down-regulated and peroxiredoxin-4 and thioredoxin domain-containing proteins 5 were up-regulated. The identified proteins are mainly involved in cell mobility, antioxidant and detoxification, signal transduction and protein metabolism. Further, the expressions of 14-3-3 isoforms were verified with immuno-blotting analysis.

CONCLUSIONS

Our proteome results suggest that the apoptosis related proteins were involved in promoting and regulating cell death of AGS cells, and might be helpful to understand the molecular mechanism of vitamin C on AGS cell growth inhibition.

Glypican 1 stimulates S phase entry and DNA replication in human glioma cells and normal astrocytes

Malignant gliomas are highly lethal neoplasms with limited treatment options. We previously found that the heparan sulfate proteoglycan glypican 1 (GPC1) is universally and highly expressed in human gliomas. In this study, we investigated the biological activity of GPC1 expression in both human glioma cells and normal astrocytes in vitro. Expression of GPC1 inactivates the G1/S checkpoint and strongly stimulates DNA replication. Constitutive expression of GPC1 causes DNA rereplication and DNA damage, suggesting a mutagenic activity for GPC1. GPC1 expression leads to a significant downregulation of the tumor suppressors pRb, Cip/Kip cyclin-dependent kinase inhibitors (CKIs), and CDH1, and upregulation of the pro-oncogenic proteins cyclin E, cyclin-dependent kinase 2 (CDK2), Skp2, and Cdt1. These GPC1-induced changes are accompanied by a significant reduction in all types of D cyclins, which is independent of serum supplementation. It is likely that GPC1 stimulates the so-called Skp2 autoinduction loop, independent of cyclin D-CDK4/6. Knockdown of Skp2, CDK2, or cyclin E, three key elements within the network modulated by GPC1, results in a reduction of the S phase and aneuploid fractions, implying a functional role for these regulators in GPC1-induced S phase entry and DNA rereplication. In addition, a significant activation of both the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways by GPC1 is seen in normal human astrocytes even in the presence of growth factor supplement. Both pathways are constitutively activated in human gliomas. The surprising magnitude and the mitogenic and mutagenic nature of the effect exerted by GPC1 on the cell cycle imply that GPC1 may play an important role in both glioma tumorigenesis and growth.

A time-resolved fluorescence resonance energy transfer assay for high-throughput screening of 14-3-3 protein-protein interaction inhibitors

Protein-protein interaction networks mediate diverse biological processes by regulating various signaling hubs and clusters. 14-3-3 proteins, a family of phosphoserine/threonine-binding molecules, serve as major interaction hubs in eukaryotic cells and have emerged as promising therapeutic targets for various human diseases. In order to identify chemical probes for mechanistic studies and for potential therapeutic development, we have developed highly sensitive bioassays to monitor the interaction of 14-3-3 with a client protein. In this study, we describe a homogenous time-resolved fluorescence resonance energy transfer (TR-FRET) assay to detect the interaction of 14-3-3 with Bad, a proapoptotic member of the Bcl-2 family. Through a series of titration studies in which europium-labeled 14-3-3 serves as an FRET donor and a Dy647-labeled phosphorylated Bad, the peptide acts as an FRET acceptor, we have achieved a robust TR-FRET assay that is suitable for high-throughput screening (HTS) with an excellent signal-to-background ratio of >20 and Z' values >0.7. This assay was further miniaturized to a 1,536-well format for ultra-HTS (uHTS), and exhibited a similar robust performance. The utility and performance of the assay for uHTS were validated by (i) known inhibitors, including peptide R18 and small molecule FOBISIN101, and (ii) screening of a 51,200 compound library. This simple and robust assay is generally applicable to detect the interaction of 14-3-3 with other client proteins. It provides a sensitive and easy-to-use tool to facilitate the discovery of 14-3-3 protein inhibitors as well as to study 14-3-3-mediated protein-protein interactions.

Pharmacoproteomic investigation into antidepressant response in two mouse inbred strains

In this study, we present a pharmacoproteomic investigation of response to antidepressants two inbred strains. Our aim was to uncover molecular mechanisms underlying antidepressant action and identify new biomarkers to determine therapeutic response to two antidepressants with proven efficacy in the treatment of depression but divergent mechanisms of action. Mice were treated with the pro-noradrenergic drug nortriptyline, the pro-serotonergic drug escitalopram or saline. Quantitative proteomic analyses were undertaken on hippocampal tissue from a study design that used two inbred mouse strains, two depressogenic protocols and a control condition, (maternal separation, chronic mild stress, control), two antidepressant drugs and two dosing protocols. The proteomic analysis was aimed at the identification of specific drug-response markers. Complementary approaches, 2DE and isobaric tandem mass tagging (TMT), were applied to the selected experimental groups. To investigate the relationship between proteomic profiles, depressogenic protocols and drug response, 2DE and TMT data sets were analysed using multivariate methods. The results highlighted significant strain- and stress-related differences across both 2DE and TMT data sets and identified the three gene products involved in serotonergic (PXBD5, YHWAB, SLC25A4) and one in noradrenergic antidepressant action (PXBD6).

14-3-3 Proteins are Regulators of Autophagy

14-3-3 proteins are implicated in the regulation of proteins involved in a variety of signaling pathways. 14-3-3-dependent protein regulation occurs through phosphorylation-dependent binding that results, in many cases, in the release of survival signals in cells. Autophagy is a cell digestion process that contributes to overcoming nutrient deprivation and is initiated under stress conditions. However, whether autophagy is a cell survival or cell death mechanism remains under discussion and may depend on context. Nevertheless, autophagy is a cellular process that determines cell fate and is tightly regulated by different signaling pathways, some of which, for example MAPK, PI3K and mTOR, are tightly regulated by 14-3-3 proteins. It is therefore important to understand the role of 14-3-3 protein in modulating the autophagic process. Within this context, direct binding of 14-3-3 to mTOR regulatory proteins, such as TSC2 and PRAS40, connects 14-3-3 with autophagy regulatory processes. In addition, 14-3-3 binding to human vacuolar protein sorting 34 (hVps34), a class III phosphatidylinositol-3-kinase (PI3KC3), indicates the involvement of 14-3-3 proteins in regulating autophagosome formation. hVps34 is involved in vesicle trafficking processes such as autophagy, and its activation is needed for initiation of autophagy. Chromatography and overlay techniques suggest that hVps34 directly interacts with 14-3-3 proteins under physiological conditions, thereby maintaining hVps34 in an inactive state. In contrast, nutrient starvation promotes dissociation of the 14-3-3–hVps34 complex, thereby enhancing hVps34 lipid kinase activity. Thus, 14-3-3 proteins are regulators of autophagy through regulating key components of the autophagic machinery. This review summarizes the role of 14-3-3 protein in the control of target proteins involved in regulating the master switches of autophagy.

5-aza-2'-Deoxycytidine enhances the radiosensitivity of breast cancer cells

PURPOSE

To investigate the effect of the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (DAC), on radiosensitivity in breast cancer cells.

MATERIALS AND METHODS

Two breast cancer cell lines, MDA-MB-231 and MDA-MB-435, were evaluated. The methylation status and the mRNA expression of three genes (ER, PR, and HIC-1) that were frequently hypermethylated in these cell lines were determined as a function of DAC exposure. 3-(4,5)-dimethylthiahiazo-(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) absorbance and a colony-forming assay were used to estimate cell viability and radiosensitivity. Using cell-cycle analysis, γ-histone H2A (γ-H2AX) formation assays and methylation-specific polymerase chain reaction (MSP) analysis of three genes correlated with radiosensitivity (BRCA1, 14-3-3σ, and E-cadherin), the mechanism of DAC enhancement of radiosensitivity was explored.

RESULTS

DAC induced the demethylation and reactivation of silent genes in both cell lines. The combination of DAC and irradiation induced growth suppression in vitro. DAC, 5 μM, enhanced sensitivity to ionizing radiation. DAC followed by irradiation correlated with G2/M arrest and the retardation of repair of radiation-induced double strand breaks. DAC reversed the methylation status of genes connected with radiosensitization. The different radiosensitization effects observed with different breast cancers cells may correlate with the primary methylation status of radiosensitizing genes.

CONCLUSIONS

Treatment strategies that include DAC present promising options for sensitizing breast cancer cells to irradiation.

14-3-3ζ positive expression is associated with a poor prognosis in patients with glioblastoma

BACKGROUND

When identifying clinical markers predicting clinical outcome, disease recurrence and resistance to therapies often determine the diagnosis and therapy of some cancer types.

OBJECTIVE

To investigate whether 14-3-3zeta positive expression is an indicator of prognosis in patients with glioblastoma.

METHODS

Forty-seven patients treated with surgery, radiotherapy, and adjuvant chemotherapy between 2005 and 2007 were divided into 2 groups according to 14-3-3zeta expression in an immunohistochemical study: the 14-3-3zeta negative group (n = 12 patients) and the 14-3-3zeta positive group (n = 35 patients). The clinicopathologic features and survival data for patients in the 14-3-3zeta positive group were compared with data from the patients in the 14-3-3zeta negative group. Kaplan-Meier survival analysis and univariate and multivariate analyses were performed to determine the prognostic factors that influenced patient survival.

RESULTS

14-3-3zeta positive expression was observed in approximately 74.5% of patients with glioblastoma. Patients in the 14-3-3zeta positive group had lower overall survival rates and median survival time than those in the 14-3-3zeta negative group (overall 2-year actuarial survival rates, 8.6% for the 14-3-3zeta positive group vs 16.7% for the 14-3-3zeta negative group; overall 2-year median survival time, 12.9 months for the 14-3-3zeta positive group vs 17.9 months for the 14-3-3zeta negative group, P = .019). 14-3-3zeta positive expression in tumor cells also was correlated with a shorter interval to tumor recurrence (median interval to recurrence, 5.9 months in the 14-3-3zeta positive group vs 8.3 months in the 14-3-3zeta negative group, P = .002). Univariate and multivariate analyses showed that 14-3-3zeta positive expression was an independent prognostic factor.

CONCLUSION

14-3-3zeta positive expression can be used as a potential molecular risk factor in patients with glioblastoma.

Transcriptome and gene expression profile of ovarian follicle tissue of the triatomine bug Rhodnius prolixus

Insect oocytes grow in close association with the ovarian follicular epithelium (OFE), which escorts the oocyte during oogenesis and is responsible for synthesis and secretion of the eggshell. We describe a transcriptome of OFE of the triatomine bug Rhodnius prolixus, a vector of Chagas disease, to increase our knowledge of the role of FE in egg development. Random clones were sequenced from a cDNA library of different stages of follicle development. The transcriptome showed high commitment to transcription, protein synthesis, and secretion. The most abundant cDNA was a secreted (S) small, proline-rich protein with maximal expression in the vitellogenic follicle, suggesting a role in oocyte maturation. We also found Rp45, a chorion protein already described, and a putative chitin-associated cuticle protein that was an eggshell component candidate. Six transcripts coding for proteins related to the unfolded-protein response (UPR) by were chosen and their expression analyzed. Surprisingly, transcripts related to UPR showed higher expression during early stages of development and downregulation during late stages, when transcripts coding for S proteins participating in chorion formation were highly expressed. Several transcripts with potential roles in oogenesis and embryo development are also discussed. We propose that intense protein synthesis at the FE results in reticulum stress (RS) and that lowering expression of a set of genes related to cell survival should lead to degeneration of follicular cells at oocyte maturation. This paradoxical suppression of UPR suggests that ovarian follicles may represent an interesting model for studying control of RS and cell survival in professional S cell types.

The prognostic value of 14-3-3 isoforms in vulvar squamous cell carcinoma cases: 14-3-3β and ε are independent prognostic factors for these tumors

Background

The 14-3-3 family is comprised of highly conserved proteins that are functionally important in the maintenance of homeostasis. Their involvement with the cell cycle, their association with proto-oncogenes and oncogenes, and their abnormal expression in various tumors has linked this family of proteins to the etiology of human cancer. Mounting evidence now indicates that 14-3-3σ is a cancer suppressor gene but the roles of the other 14-3-3 isoforms and their interactions in tumorigenesis have not yet been elucidated. In our current study, we examined the expression of 14-3-3β, γ, ε, ζ, η and τ in a large series of vulvar squamous cell carcinomas to evaluate any clinical significance.

Methods

Tumor biopsies from 298 vulvar carcinomas were examined by immunohistochemistry for the expression of 14-3-3β, γ, ε, ζ, η and τ. Statistical analyses were employed to validate any associations between the expression of any 14-3-3 isoform and clinicopathologic variables for this disease.

Results

High cytoplasmic levels of 14-3-3β, γ, ζ, ε and η were observed in 79%, 58%, 50%, 86% and 54% of the vulvar carcinomas analyzed, respectively, whereas a low nuclear expression of 14-3-3τ was present in 80% of these cases. The elevated cytoplasmic expression of 14-3-3β, γ, ε, ζ and η was further found to be associated with advanced disease and aggressive features of these cancers. The overexpression of cytoplasmic 14-3-3β and ε significantly correlated with a poor disease-specific survival by univariate analysis (P = 0.007 and P = 0.04, respectively). The independent prognostic significance of these factors was confirmed by multivariate analysis (P = 0.007 and P = 0.009, respectively).

Conclusions

We reveal for the first time that the 14-3-3β, γ, ε, ζ, η and τ isoforms may be involved in the progression of vulvar carcinomas. Furthermore, our analyses show that high cytoplasmic levels of 14-3-3β and ε independently correlate with poor disease-specific survival.

14-3-3ζ as a prognostic marker and therapeutic target for cancer

IMPORTANCE OF THE FIELD

The ubiquitously expressed 14-3-3ζ protein is involved in numerous important cellular pathways involved in cancer. Recent research suggests 14-3-3ζ may play a central role regulating multiple pathways responsible for cancer initiation and progression. This review will provide an overview of 14-3-3 proteins and address the role of 14-3-3ζ overexpression in cancer.

AREAS COVERED IN THIS REVIEW

The review covers the basic role of 14-3-3 in regulation of multiple pathways with a focus on 14-3-3ζ as a clinically relevant biomarker for cancer recurrence.

WHAT THE READER WILL GAIN

14-3-3ζ overexpression has been found in multiple cancers; however, the clinical implications were unclear. Recently, 14-3-3ζ has been identified as a biomarker for poor prognosis and chemoresistance in multiple tumor types, indicating a potential clinical application for using 14-3-3ζ in selecting treatment options and predicting cancer patients' outcome.

TAKE HOME MESSAGE

14-3-3ζ is a potential prognostic marker of cancer recurrence and predictive marker for therapeutic resistance. The overexpression of 14-3-3ζ in multiple cancers suggests that it may be a common target to intervene tumor progression; therefore, more efforts are needed for the development of 14-3-3 inhibitors.

MTBP plays a crucial role in mitotic progression and chromosome segregation

Murine double minute 2 (MDM2) binding protein (MTBP) has been implicated in tumor cell proliferation, but the underlying mechanisms remain unclear. The results of MTBP expression analysis during cell cycle progression demonstrated that MTBP protein was rapidly degraded during mitosis. Immunofluorescence studies revealed that a portion of MTBP was localized at the kinetochores during prometaphase. MTBP overexpression delayed mitotic progression from nuclear envelope breakdown (NEB) to anaphase onset and induced abnormal chromosome segregation such as lagging chromosomes, chromosome bridges, and multipolar chromosome segregation. Conversely, MTBP downmodulation caused an abbreviated metaphase and insufficient mitotic arrest, resulting in abnormal chromosome segregation, aneuploidy, decreased cell proliferation, senescence, and cell death, similar to that of Mad2 (mitotic arrest-deficient 2) downmodulation. Furthermore, MTBP downmodulation inhibited the accumulation of Mad1 and Mad2, but not BubR1 (budding uninhibited by benzimidazoles related 1), on the kinetochores, whereas MTBP overexpression inhibited the release of Mad2 from the metaphase kinetochores. These results may imply that MTBP has an important role in recruiting and/or retaining the Mad1/Mad2 complex at the kinetochores during prometaphase, but its degradation is required for silencing the mitotic checkpoint. Together, this study indicates that MTBP has a crucial role in proper mitotic progression and faithful chromosome segregation, providing new insights into regulation of the mitotic checkpoint.

A proteomic approach to study parathyroid glands

Parathyroid tumours are heterogeneous and in some cases the diagnosis may be difficult using histological features. In this study we used a two-dimensional electrophoresis (2D)/mass spectrometry (MS)-based approach to examine the global changes of parathyroid adenoma tissues protein profile compared to the parathyroid normal tissues. Validation of protein expression was performed by immunoblotting using specific antibodies. Ingenuity software was used to identify the biological processes to which these proteins belong and to construct a potential network. A total of 30 proteins were found to be differentially expressed, of which 22 resulted in being over-expressed. Proteins identified by 2D/MS/MS proteomics were classified into functional categories and a major change (≥ 2-fold) in terms of expression was found in proteins involved in response to biotic stimuli, cell organization and signal transduction. After Ingenuity analysis, 14-3-3 ζ/δ appears to be a key protein in the network of parathyroid adenoma, where it is linked to other proteins such as annexin A2, B box and SPRY domain-containing protein (BSPRY), p53 and epidermal growth factor receptor (EGFR). Our results suggest that the proteomic approach was able to differentiate the protein profiles of normal parathyroid and parathyroid adenoma and identify a panel of proteins which are differentially expressed. The functional role of these proteins in the network of intracellular pathways is discussed.

DIGE-based protein expression analysis of B[a]P-exposed hepatoma cells reveals a complex stress response including alterations in oxidative stress, cell cycle control, and cytoskeleton motility at toxic and subacute concentrations

Although the effects of high concentrations of the carcinogen benzo[a]pyrene (B[a]P) have been studied extensively, little is known about its effects at subacute toxic concentrations, which are typical for environmental pollutants. We exposed murine Hepa1c1c7 cells to a toxic concentration (5 μM) and a subacute concentration (50 nM) of B[a]P over a period of 2-24 h to differentiate between acute and pseudochronic effects and conducted a time-course analysis of B[a]P-influenced protein expression by DIGE. In total, a set of 120 spots were found to be significantly altered due to B[a]P exposure of which 112 were subsequently identified by mass spectrometry. Clustering and principal component analysis were conducted to identify sets of proteins responding in a concerted manner to the exposure. Our results indicate an immediate response to the contaminant at the protein level and demonstrate that B[a]P exposure alters the cellular response by disturbing proteins involved in oxidative stress, cell cycle regulation, apoptosis, and cytoskeleton organization. Furthermore, network analysis of protein-protein interactions revealed a complex network of interacting, B[a]P-regulated proteins mostly belonging to the cytoskeleton organization and several signal transduction pathways.

Role of 14-3-3 proteins in tumorigenesis and tumor progression

14-3-3 proteins are a family of acidic proteins that are predominantly localized in the cytoplasm. They have been known to play a role in tumorigenesis and tumor progression by regulating tumor cell growth, survival, proliferation, migration, and apoptosis. Of all 14-3-3 proteins, 14-3-3σ has tumor-suppressor activity, while other members have tumor-promoting activity. In this paper, we briefly review the role of 14-3-3 proteins in tumor pathogenesis.

Small interfering RNA targeting 14-3-3ζ increases efficacy of chemotherapeutic agents in head and neck cancer cells

Patients diagnosed in advanced stages of head and neck squamous cell carcinoma often show limited response to chemotherapeutic agents. Recently, we reported the overexpression of 14-3-3ζ protein in head and neck premalignant and cancer tissues using liquid chromatography-tandem mass spectrometry with isotopic labeling and revealed its significance as a prognostic marker using immunohistochemical analysis. In this study, we determined the potential of 14-3-3ζ as a therapeutic target for head and neck cancer. Small interfering RNA (siRNA) targeting 14-3-3ζ was used to downregulate its expression in head and neck cancer cells in culture. Cell cycle analysis showed that head and neck cancer cells transfected with siRNA targeting 14-3-3ζ showed G(2)-M arrest. These siRNA transfectants also showed increased cell death on treatment with any one of the following chemotherapeutic agents: cisplatin, 5-fluorouracil, paclitaxel, or doxorubicin in comparison with the no transfection controls. Flow cytometric analysis using propidium iodide staining showed increased sub-G(0) fraction in siRNA-transfected cells treated with any of these chemotherapeutic agents, suggesting cell death; in addition, Annexin V staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay revealed increased apoptosis. Taken together, our results strongly showed that downregulation of 14-3-3ζ expression may serve to improve the sensitivity of head and neck cancer cells to chemotherapeutic agents.

iTRAQ quantitative analysis of multidrug resistance mechanisms in human gastric cancer cells

Multidrug resistance (MDR) is a major obstacle towards a successful treatment of gastric cancer. However, the mechanisms of MDR are intricate and have not been fully understood. To elucidate the molecular mechanisms of MDR in gastric cancer, we employed the proteomic approach of isobaric tags for relative and absolute quantification (iTRAQ), followed by LC-MS/MS, using the vincristine-resistant SGC7901/VCR cell line and its parental SGC7901 cell line as a model. In total, 820 unique proteins were identified and 91 proteins showed to be differentially expressed in SGC7901/VCR compared with SGC7901. Several differentially expressed proteins were further validated by western blot analysis. Furthermore, the association of MVP, one of the highly expressed proteins in SGC7901/VCR, with MDR was verified. Our study is the first application of iTRAQ technology for MDR mechanisms analysis in gastric cancer, and many of the differentially expressed proteins identified have not been linked to MDR in gastric cancer before, which showed the value of this technology in identifying differentially expressed proteins in cancer.

Proteomic identification of molecular targets of gambogic acid: role of stathmin in hepatocellular carcinoma

Gamboge has been developed as an injectable drug for cancer treatment in China. In this study, the inhibition ratio and their IC(50) values of two derivatives from Gamboge in hepatocellular carcinoma (HCC) were determined. Proteomic approach was employed to reveal the target proteins of these two derivatives, gambogic acid (GA), and gambogenic acid (GEA). HCC cells were cultured under varied conditions with the addition of either GA or GEA. Twenty differentially expressed proteins were identified and the four most distinctly expressed proteins were further validated by Western blotting. GA and GEA revealed inhibitory effects on HCC cell proliferation. The expression of cyclin-dependent kinase 4 inhibitor A and guanine nucleotide-binding protein beta subunit 1 were upregulated by both xanthones, whilst the expression of 14-3-3 protein sigma and stathmin 1 (STMN1) were downregulated. Furthermore, overexpression of STMN1 in HCC cells decreased their sensitivity, whilst small interfering RNAs targeting STMN1 enhanced their sensitivity to GA and GEA. In conclusion, our study suggested for the first time that STMN1 might be a major target for GA and GEA in combating HCC. Further investigation may lead to a new generation of anticancer drugs exerting synergistic effect with conventional therapy, thus to promote treatment efficacy.

Copy number gain and oncogenic activity of YWHAZ/14-3-3zeta in head and neck squamous cell carcinoma

Gene amplification, a common mechanism for oncogene activation in cancers, has been used in the discovery of novel oncogenes. Low-level copy number gains are frequently observed in head and neck squamous cell carcinomas (HNSCCs) where numerous amplification events and potential oncogenes have already been reported. Recently, we applied restriction landmark genome scanning to study gene amplifications in HNSCC and located novel and uncharacterized regions in primary tumor samples. Gain on chromosome 8q22.3, the location of YWHAZ (14-3-3zeta), is found in 30-40% HNSCC cases. Data obtained from fluorescence in situ hybridization and immunohistochemistry on HNSCC tissue microarrays confirmed frequent low-level YWHAZ copy number gain and protein overexpression. YWHAZ mRNA was frequently upregulated in patients' tumor tissues. Furthermore, YWHAZ RNAi significantly suppressed the growth rate of HNSCC cell lines, and overexpression of YWHAZ in HaCaT immortalized human skin keratinocytes promotes overgrowth, as well as morphological changes. Reduced YWHAZ levels increased the G1/G0-phase proportion, decreased the S-phase proportion and the rate of DNA synthesis. Based on this evidence, we suggest that YWHAZ is a candidate proto-oncogene and deserves further investigation into its role in HNSCC carcinogenesis.

14-3-3zeta mediates resistance of diffuse large B cell lymphoma to an anthracycline-based chemotherapeutic regimen

Patients presenting with diffuse large B cell lymphoma (DLBCL) are treated with a standard anthracycline-based chemotherapeutic mixture consisting of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP). Half of DLBCL patients will develop chemo-refractory tumors due to the emergence of CHOP-resistant DLBCL cells. We isolated DLBCL cells that were resistant to CHOP as a model system to investigate the molecular basis of CHOP resistance. Resistant cells emerged from CHOP-sensitive DLBCL populations after repeated cycles of on-off exposure to stepwise increased dosages of CHOP. A proteomic analysis of CHOP-sensitive and -resistant DLBCL cells identified the zeta isoform of the 14-3-3 family as a differentially expressed protein. CHOP-sensitive cells showed reduced expression of 14-3-3zeta protein in the presence of high-dose CHOP relative to control cells. In contrast, CHOP-resistant cells expressed markedly higher levels of 14-3-3zeta regardless the presence of high-dose CHOP. Because 14-3-3zeta is known to exert anti-apoptotic influences and chemoresistance in lung, colon, and prostate carcinoma, we hypothesized that 14-3-3zeta promotes survival of DLBCL cells in CHOP. In support of our hypothesis, knockdown of 14-3-3zeta by small interfering RNA restored the sensitivity of resistant DLBCL to CHOP-induce apoptosis. In addition, 14-3-3zeta expression was highly up-regulated in a resected DLBCL lymph node relative to a normal lymph node by Western blot analysis. Furthermore, more than half of 35 DLBCL tissues showed elevated 14-3-3zeta expression relative to normal lymph tissue by immunohistochemical analysis. Our study implicates 14-3-3zeta in the pathogenesis of DLBCL and suggests a promising combination strategy with a 14-3-3 inhibitor for the treatment of refractory DLBCL.

MP470, a novel receptor tyrosine kinase inhibitor, in combination with Erlotinib inhibits the HER family/PI3K/Akt pathway and tumor growth in prostate cancer

BACKGROUND

Prostate cancer is a common disease in men and at present there is no effective therapy available due to its recurrence despite androgen deprivation therapy. The epidermal growth factor receptor family (EGFR/HER1, HER2/neu and HER3)/PI3K/Akt signaling axis has been implicated in prostate cancer development and progression. However, Erlotinib, an EGFR tyrosine kinase inhibitor, has less effect on proliferation and apoptosis in prostate cancer cell lines. In this study, we evaluate whether MP470, a novel receptor tyrosine kinase inhibitor alone or in combination with Erlotinib has inhibitory effect on prostate cancer in vitro and in vivo.

METHODS

The efficacy of MP470 or MP470 plus Erlotinib was evaluated in vitro using three prostate cancer cell lines by MTS and apoptosis assays. The molecular mechanism study was carried out by phosphorylation antibody array, immunoblotting and immunohistochemistry. A LNCaP mouse xenograft model was also used to determine the tumor growth inhibition by MP470, Erlotinib or the combination treatments.

RESULTS

MP470 exhibits low microM IC50 in prostate cancer cell lines. Additive effects on both cytotoxicity and induction of apoptosis were observed when LNCaP were treated with MP470 in combination with Erlotinib. This combination treatment completely inhibited phosphorylation of the HER family members (HER1, 2, 3), binding of PI3K regulatory unit p85 to HER3 and downstream Akt activity even after androgen depletion. Furthermore, in a LNCaP mouse xenograft model, the MP470-Erlotinib combination produced 30-65% dose-dependent tumor growth inhibition (TGI).

CONCLUSION

We propose that MP470-Erlotinib targets the HER family/PI3K/Akt pathway and may represent a novel therapeutic strategy for prostate cancer.

Shear stress induced reorganization of the keratin intermediate filament network requires phosphorylation by protein kinase C zeta

Keratin intermediate filaments (KIFs) form a fibrous polymer network that helps epithelial cells withstand external mechanical forces. Recently, we established a correlation between the structure of the KIF network and its local mechanical properties in alveolar epithelial cells. Shear stress applied across the cell surface resulted in the structural remodeling of KIF and a substantial increase in the elastic modulus of the network. This study examines the mechanosignaling that regulates the structural remodeling of the KIF network. We report that the shear stress-mediated remodeling of the KIF network is facilitated by a twofold increase in the dynamic exchange rate of KIF subunits, which is regulated in a PKC zeta and 14-3-3-dependent manner. PKC zeta phosphorylates K18pSer33, and this is required for the structural reorganization because the KIF network in A549 cells transfected with a dominant negative PKC zeta, or expressing the K18Ser33Ala mutation, is unchanged. Blocking the shear stress-mediated reorganization results in reduced cellular viability and increased apoptotic levels. These data suggest that shear stress mediates the phosphorylation of K18pSer33, which is required for the reorganization of the KIF network, resulting in changes in mechanical properties of the cell that help maintain the integrity of alveolar epithelial cells.

Differential tissue-specific protein markers of vaginal carcinoma

The objective was to identify proteins differentially expressed in vaginal cancer to elucidate relevant cancer-related proteins. A total of 16 fresh-frozen tissue biopsies, consisting of 5 biopsies from normal vaginal epithelium, 6 from primary vaginal carcinomas and 5 from primary cervical carcinomas, were analysed using two-dimensional gel electrophoresis (2-DE) and MALDI-TOF mass spectrometry. Of the 43 proteins identified with significant alterations in protein expression between non-tumourous and tumourous tissue, 26 were upregulated and 17 were downregulated. Some were similarly altered in vaginal and cervical carcinoma, including cytoskeletal proteins, tumour suppressor proteins, oncoproteins implicated in apoptosis and proteins in the ubiquitin–proteasome pathway. Three proteins were uniquely altered in vaginal carcinoma (DDX48, erbB3-binding protein and biliverdin reductase) and five in cervical carcinoma (peroxiredoxin 2, annexin A2, sarcomeric tropomyosin kappa, human ribonuclease inhibitor and prolyl-4-hydrolase beta). The identified proteins imply involvement of multiple different cellular pathways in the carcinogenesis of vaginal carcinoma. Similar protein alterations were found between vaginal and cervical carcinoma suggesting common tumourigenesis. However, the expression level of some of these proteins markedly differs among the three tissue specimens indicating that they might be useful molecular markers.

14-3-3zeta overexpression defines high risk for breast cancer recurrence and promotes cancer cell survival

The ubiquitously expressed 14-3-3 proteins are involved in numerous important cellular functions. The loss of 14-3-3sigma is a common event in breast cancer; however, the role of other 14-3-3s in breast cancer is unclear. Recently, we found that 14-3-3zeta overexpression occurs in early stage breast diseases and contributes to transformation of human mammary epithelial cells. Here, we show that 14-3-3zeta overexpression also persisted in invasive ductal carcinoma and contributed to the further progression of breast cancer. To examine the clinical effect of 14-3-3zeta overexpression in advanced stage breast cancer, we performed immunohistochemical analysis of 14-3-3zeta expression in primary breast carcinomas. 14-3-3zeta overexpression occurred in 42% of breast tumors and was determined to be an independent prognostic factor for reduced disease-free survival. 14-3-3zeta overexpression combined with ErbB2 overexpression and positive lymph node status identified a subgroup of patients at high risk for developing distant metastasis. To investigate whether 14-3-3zeta overexpression causally promotes breast cancer progression, we overexpressed 14-3-3zeta by stable transfection or reduced 14-3-3zeta expression by siRNA in cancer cell lines. Increased 14-3-3zeta expression enhanced anchorage-independent growth and inhibited stress-induced apoptosis, whereas down-regulation of 14-3-3zeta reduced anchorage-independent growth and sensitized cells to stress-induced apoptosis via the mitochondrial apoptotic pathway. Transient blockade of 14-3-3zeta expression by siRNA in cancer cells effectively reduced the onset and growth of tumor xenografts in vivo. Therefore, 14-3-3zeta overexpression is a novel molecular marker for disease recurrence in breast cancer patients and may serve as an effective therapeutic target in patients whose tumors overexpress 14-3-3zeta.

A novel resveratrol derivative, HS1793, overcomes the resistance conferred by Bcl-2 in human leukemic U937 cells

The chemopreventive and chemotherapeutic properties associated with resveratrol offer promise for the design of new chemotherapeutic agents. However, resveratrol is not a potent cytotoxic compound when compared with other chemotherapeutic drugs. Thus, several studies were undertaken to obtain synthetic analogues of resveratrol with potent activity. The present study was undertaken to examine whether four resveratrol analogues (HS-1784, -1792, -1791 and -1793) that we had designed and synthesized show antitumor activity. Here, we observed that all of these resveratrol analogues displayed stronger antitumor effects than resveratrol in most cancer cells tested. We further examined whether HS-1793, showing potent antitumor effects in most cancer cells tested, overcomes the resistance conferred by Bcl-2, since overcoming the resistance conferred by Bcl-2 represents an attractive therapeutic strategy against cancer. Our viability assay showed that HS-1793 overcomes the resistance conferred by Bcl-2 in human leukemic U937 cells. Various apoptosis assessment assays demonstrated that HS-1793 overcomes the resistance conferred by Bcl-2 in human leukemic U937 cells by inducing apoptosis. Noticeably, we elucidated the marked downregulation of 14-3-3 protein by HS-1793, indicating that HS-1793 overcomes the resistance conferred by Bcl-2 in U937 cells via 14-3-3. We also observed that HS-1793 exerts its antitumor activity via Bad. However, overall data obtained from methylation specific PCR, RT-PCR and real-time PCR suggest that HS-1793 plays a role in the downregulation of 14-3-3 at a post-transcriptional level. Further understanding exactly how HS-1793 overcomes the resistance conferred by Bcl-2 via 14-3-3 may guide the development of future anticancer agents.

Cyclin D1 in low-dose radiation-induced adaptive resistance

Cyclin D1 is involved in cell-cycle arrest in DNA-damage response. This study tested the hypothesis that cyclin D1 regulates mitochondrial apoptosis. Cyclin D1 was induced by low-dose ionizing radiation (LDIR; 10-cGy X-ray) in human keratinocytes with an adaptive radioresistance that can be inhibited by short interfering RNA (siRNA)-mediated cyclin D1 inhibition. Cyclin D1 was found to form complex with chaperon 14-3-3zeta in unstressed cells and mutation of 14-3-3zeta Ser-58 to Asp (S58D) significantly impaired 14-3-3zeta binding to cyclin D1. The formation of cyclin D1/14-3-3zeta complex was differently regulated by exposure to low (10-cGy X-ray) versus high (5-Gy gamma-ray) doses of radiation. Unlike exposure to 5-Gy that predominantly enhanced cyclin D1 nuclear accumulation, LDIR induced the dissociation of the cyclin D1/14-3-3zeta complex without nuclear translocation, indicating that cytosolic accumulation of cyclin D1 was required for LDIR-induced adaptive response. Further studies revealed a direct interaction of cyclin D1 with proapoptotic Bax and an improved mitochondrial membrane potential (Deltapsi(m)) in LDIR-treated cells. Consistently, blocking cyclin D1/Bax formation by cyclin D1 siRNA reversed Deltapsi(m) and inhibited the LDIR-associated antiapoptotic response. These results demonstrate the evidence that cytosolic cyclin D1 is able to regulate apoptosis by interaction with Bax in LDIR-induced adaptive resistance.

Prognostic significance of 14-3-3sigma expression in oral squamous cell carcinoma (OSCC)

14-3-3sigma an intracellular phosphoserine binding protein regulates different cellular signalling processes and is involved in cancer development. In this study, we examined the expression of 14-3-3sigma and evaluated its clinical significance in OSCC. Tumour tissue from 95 OSCC patients was analysed for 14-3-3sigma and p53 expression, respectively. The correlation of these proteins with survival and clinical parameters was assessed. 14-3-3sigma high expression was observed in 44.2% of OSCC patients. A significant role of 14-3-3sigma expression on survival was shown by Kaplan-Meier analysis. Median survival time was 4.1years for patients with 14-3-3sigma low tumours, compared with 1.36years for 14-3-3sigma high tumours (P=.0021). Subset analysis in patients receiving adjuvant chemotherapy showed that the overall survival was significantly decreased in 14-3-3sigma high tumours than in 14-3-3sigma low tumours (P=.02). p53 expression was not significant in univariate analyses. In multivariate regression analysis, 14-3-3sigma expression emerged as a significant independent parameter (P=.003). These results provide evidence that 14-3-3sigma expression is involved in OSCC and, in contrast to p53 expression represents a new prognostic marker for OSCC and therapy response. Pending validation targeting 14-3-3sigma might also be a new opportunity to improve therapy.

Glypican-1 regulates anaphase promoting complex/cyclosome substrates and cell cycle progression in endothelial cells

Glypican-1 (GPC1), a member of the mammalian glypican family of heparan sulfate proteoglycans, is highly expressed in glioma blood vessel endothelial cells (ECs). In this study, we investigated the role of GPC1 in EC replication by manipulating GPC1 expression in cultured mouse brain ECs. Moderate GPC1 overexpression stimulates EC growth, but proliferation is significantly suppressed when GPC1 expression is either knocked down or the molecule is highly overexpressed. Flow cytometric and biochemical analyses show that high or low expression of GPC1 causes cell cycle arrest at mitosis or the G2 phase of the cell cycle, accompanied by endoreduplication and consequently polyploidization. We further show that GPC1 inhibits the anaphase-promoting complex/cyclosome (APC/C)-mediated degradation of mitotic cyclins and securin. High levels of GPC1 induce metaphase arrest and centrosome overproduction, alterations that are mimicked by overexpression of cyclin B1 and cyclin A, respectively. These observations suggest that GPC1 regulates EC cell cycle progression at least partially by modulating APC/C-mediated degradation of mitotic cyclins and securin.

14-3-3 zeta down-regulates p53 in mammary epithelial cells and confers luminal filling

Recent progress in diagnostic tools allows many breast cancers to be detected at an early preinvasive stage. Thus, a better understanding of the molecular basis of early breast cancer progression is essential. Previously, we discovered that 14-3-3 zeta is overexpressed in >40% of advanced breast cancers, and this overexpression predicts poor patient survival. Here, we examined at what stage of breast disease 14-3-3 zeta overexpression occurs, and we found that increased expression of 14-3-3 zeta begins at atypical ductal hyperplasia, an early stage of breast disease. To determine whether 14-3-3 zeta overexpression is a decisive early event in breast cancer, we overexpressed 14-3-3 zeta in MCF10A cells and examined its effect in a three-dimensional culture model. We discovered that 14-3-3 zeta overexpression severely disrupted the acini architecture resulting in luminal filling. Proper lumen formation is a result of anoikis, apoptosis due to detachment from the basement membrane. We found that 14-3-3 zeta overexpression conferred resistance to anoikis. Additionally, 14-3-3 zeta overexpression in MCF10A cells and in mammary epithelial cells (MEC) from 14-3-3 zeta transgenic mice reduced expression of p53, which is known to mediate anoikis. Mechanistically, 14-3-3 zeta induced hyperactivation of the phosphoinositide 3-kinase/Akt pathway which led to phosphorylation and translocation of the MDM2 E3 ligase resulting in increased p53 degradation. Ectopic expression of p53 restored luminal apoptosis in 14-3-3 zeta-overexpressing MCF10A acini in three-dimensional cultures. These data suggest that 14-3-3 zeta overexpression is a critical event in early breast disease, and down-regulation of p53 is one of the mechanisms by which 14-3-3 zeta alters MEC acini structure and increases the risk of breast cancer.

Discovery and verification of head-and-neck cancer biomarkers by differential protein expression analysis using iTRAQ labeling, multidimensional liquid chromatography, and tandem mass spectrometry

Multidimensional LC-MS/MS has been used for the analysis of biological samples labeled with isobaric mass tags for relative and absolute quantitation (iTRAQ) to identify proteins that are differentially expressed in human head-and-neck squamous cell carcinomas (HNSCCs) in relation to non-cancerous head-and-neck tissues (controls) for cancer biomarker discovery. Fifteen individual samples (cancer and non-cancerous tissues) were compared against a pooled non-cancerous control (prepared by pooling equal amounts of proteins from six non-cancerous tissues) in five sets by on-line and off-line separation. We identified 811 non-redundant proteins in HNSCCs, including structural proteins, signaling components, enzymes, receptors, transcription factors, and chaperones. A panel of proteins showing consistent differential expression in HNSCC relative to the non-cancerous controls was discovered. Some of the proteins include stratifin (14-3-3sigma); YWHAZ (14-3-3zeta); three calcium-binding proteins of the S100 family, S100-A2, S100-A7 (psoriasin), and S100-A11 (calgizarrin); prothymosin alpha (PTHA); L-lactate dehydrogenase A chain; glutathione S-transferase Pi; APC-binding protein EB1; and fascin. Peroxiredoxin2, carbonic anhydrase I, flavin reductase, histone H3, and polybromo-1D (BAF180) were underexpressed in HNSCCs. A panel of the three best performing biomarkers, YWHAZ, stratifin, and S100-A7, achieved a sensitivity of 0.92 and a specificity of 0.91 in discriminating cancerous from non-cancerous head-and-neck tissues. Verification of differential expression of YWHAZ, stratifin, and S100-A7 proteins in clinical samples of HNSCCs and paired and non-paired non-cancerous tissues by immunohistochemistry, immunoblotting, and RT-PCR confirmed their overexpression in head-and-neck cancer. Verification of YWHAZ, stratifin, and S100-A7 in an independent set of HNSCCs achieved a sensitivity of 0.92 and a specificity of 0.87 in discriminating cancerous from non-cancerous head-and-neck tissues, thereby confirming their overexpressions and utility as credible cancer biomarkers.

Human 14-3-3 gamma protein results in abnormal cell proliferation in the developing eye of Drosophila melanogaster

Background

14-3-3 proteins are a family of adaptor proteins that participate in a wide variety of cellular processes. Recent evidence indicates that the expression levels of these proteins are elevated in some human tumors providing circumstantial evidence for their involvement in human cancers. However, the mechanism through which these proteins act in tumorigenesis is uncertain.

Results

To determine whether elevated levels of 14-3-3 proteins may perturb cell growth we overexpressed human 14-3-3 gamma (h14-3-3 gamma) in Drosophila larvae using the heat shock promoter or the GMR-Gal4 driver and then examined the effect that this had on cell proliferation in the eye imaginal discs of third instar larvae. We found that induction of h14-3-3 gamma resulted in the abnormal appearance of replicating cells in the differentiating proneural photoreceptor cells of eye imaginal discs where h14-3-3 gamma was driven by the heat shock promoter. Similarly, we found that driving h14-3-3 gamma expression specifically in developing eye discs with the GMR-Gal4 driver resulted in increased numbers of replicative cells following the morphogenetic furrow. Interestingly, we found that the effects of overexpressing h1433 gamma on eye development were increased in a genetic background where String (cdc25) function was compromised.

Conclusion

Taken together our results indicate that h14-3-3 gamma can promote abnormal cell proliferation and may act through Cdc25. This has important implications for 14-3-3 gamma as an oncogene as it suggests that elevated levels of 14-3-3 may confer a growth advantage to cells that overexpress it.