Down-regulation of the stathmin/Op18 and FKBP25 genes following p53 induction

STNM1 in human cancers: role, function and potential therapy sensitizer

STMN1 belongs to the stathmin gene family, it encodes a cytoplasmic phosphorylated protein, stathmin1, which is commonly observed in vertebrate cells. STMN1 is a structural microtubule-associated protein (MAP) that binds to microtubule protein dimers rather than microtubules, with each STMN1 binding two microtubule protein dimers and preventing their aggregation, leading to microtubule instability. STMN1 expression is elevated in a number of malignancies, and inhibition of its expression can interfere with tumor cell division. Its expression can change the division of tumor cells, thereby arresting cell growth in the G2/M phase. Moreover, STMN1 expression affects tumor cell sensitivity to anti-microtubule drug analogs, including vincristine and paclitaxel. The research on MAPs is limited, and new insights on the mechanism of STMN1 in different cancers are emerging. The effective application of STMN1 in cancer prognosis and treatment requires further understanding of this protein. Here, we summarize the general characteristics of STMN1 and outline how STMN1 plays a role in cancer development, targeting multiple signaling networks and acting as a downstream target for multiple microRNAs, circRNAs, and lincRNAs. We also summarize recent findings on the function role of STMN1 in tumor resistance and as a therapeutic target for cancer.

Regulation of miRNAs Expression by Mutant p53 Gain of Function in Cancer

The p53 roles have been largely described; among them, cell proliferation and apoptosis control are some of the best studied and understood. Interestingly, the mutations on the six hotspot sites within the region that encodes the DNA-binding domain of p53 give rise to other very different variants. The particular behavior of these variants led to consider p53 mutants as separate oncogene entities; that is, they do not retain wild type functions but acquire new ones, namely Gain-of-function p53 mutants. Furthermore, recent studies have revealed how p53 mutants regulate gene expression and exert oncogenic effects by unbalancing specific microRNAs (miRNAs) levels that provoke epithelial-mesenchymal transition, chemoresistance, and cell survival, among others. In this review, we discuss recent evidence of the crosstalk between miRNAs and mutants of p53, as well as the consequent cellular processes dysregulated.

Synthetic lethality of RB1 and aurora A is driven by stathmin-mediated disruption of microtubule dynamics

RB1 mutational inactivation is a cancer driver in various types of cancer including lung cancer, making it an important target for therapeutic exploitation. We performed chemical and genetic vulnerability screens in RB1-isogenic lung cancer pair and herein report that aurora kinase A (AURKA) inhibition is synthetic lethal in RB1-deficient lung cancer. Mechanistically, RB1^−/− cells show unbalanced microtubule dynamics through E2F-mediated upregulation of the microtubule destabilizer stathmin and are hypersensitive to agents targeting microtubule stability. Inhibition of AURKA activity activates stathmin function via reduced phosphorylation and facilitates microtubule destabilization in RB1^−/− cells, heavily impacting the bipolar spindle formation and inducing mitotic cell death selectively in RB1^−/− cells. This study shows that stathmin-mediated disruption of microtubule dynamics is critical to induce synthetic lethality in RB1-deficient cancer and suggests that upstream factors regulating microtubule dynamics, such as AURKA, can be potential therapeutic targets in RB1-deficient cancer.

Retinoblastoma susceptibility gene (RB1) is frequently mutated in lung cancers. Here the authors perform chemical and genetic vulnerability screens and identify aurora A kinase (AURKA) as a synthetic lethal candidate for RB1-deficient lung cancer cells and that AURKA inhibition sensitizes these cells to mitotic cell death.

Screening and Identification of Molecular Targets Involved in Preventing Gastric Precancerous Lesions in Chronic Atrophic Gastritis by Qilianshupi Decoction

Chronic atrophic gastritis (CAG) is a common and possibly precancerous digestive tract disease. Development of drugs with effect of preventing precancerous lesions draws the eyes of global researchers. Qilianshupi decoction (QLSP) is a Traditional Chinese Medicine (TCM) that is commonly used to treat CAG, but few studies have explored the mechanism of QLSP on treating CAG. This study investigated the molecular targets of the component herbs of QLSP in preventing precancerous lesions based on network pharmacology. Network pharmacology analysis revealed that the 6 herbs regulated multiple CAG-related genes, among which the most important were cancer-related pathway (apoptosis, p53, and VEGF) and epithelial cell signaling in Helicobacter pylori infection. Further animal experiments showed that the expression of survivin and p53 in precancerous lesions of CAG rats was significantly increased which was suppressed by QLSP. Moreover, telomerase activity was inhibited in precancerous lesions of CAG rats, and telomere length of gastric mucosa was increased, which was reversed by QLSP. Our results suggest that the components of QLSP prevents gastric precancerous lesions through decreasing the expression of survivin and p53 and regulating telomerase activity and telomere length in CAG.

The human T-cell leukemia virus type-1 tax oncoprotein dissociates NF-κB p65RelA-Stathmin complexes and causes catastrophic mitotic spindle damage and genomic instability

Genomic instability is a hallmark of many cancers; however, the molecular etiology of chromosomal dysregulation is not well understood. The human T-cell leukemia virus type-1 (HTLV-1) oncoprotein Tax activates NF-κB-signaling and induces DNA-damage and aberrant chromosomal segregation through diverse mechanisms which contribute to viral carcinogenesis. Intriguingly, Stathmin/oncoprotein-18 (Op-18) depolymerizes tubulin and interacts with the p65^RelA subunit and functions as a cofactor for NF-κB-dependent transactivation. We thus hypothesized that the dissociation of p65^RelA-Stathmin/Op-18 complexes by Tax could lead to the catastrophic destabilization of microtubule (MT) spindle fibers during mitosis and provide a novel mechanistic link between NF-κB-signaling and genomic instability. Here we report that the inhibition of Stathmin expression by the retroviral latency protein, p30^II, or knockdown with siRNA-stathmin, dampens Tax-mediated NF-κB transactivation and counters Tax-induced genomic instability and cytotoxicity. The Tax-G148V mutant, defective for NF-κB activation, exhibited reduced p65^RelA-Stathmin binding and diminished genomic instability and cytotoxicity. Dominant-negative inhibitors of NF-κB also prevented Tax-induced multinucleation and apoptosis. Moreover, cell clones containing the infectious HTLV-1 ACH. p30^II mutant provirus, impaired for p30^II production, exhibited increased multinucleation and the accumulation of cytoplasmic tubulin aggregates following nocodozole-treatment. These findings allude to a mechanism whereby NF-κB-signaling regulates tubulin dynamics and mitotic instability through the modulation of p65^RelA-Stathmin/Op-18 interactions, and support the notion that p30^II enhances the survival of Tax-expressing HTLV-1-transformed cells.

Taking the Tube: From Normal Fallopian Tube Epithelium to Ovarian High-grade Serous Carcinoma

Detailed pathologic studies over the past decade suggest a distal fallopian tube origin for the majority of "ovarian" high-grade serous carcinomas (HGSC). This review will summarize molecular alterations observed in tubal precursors for HGSC, namely p53 signatures and serous tubal intraepithelial carcinomas, and in nonmalignant fallopian tube epithelial cells obtained from women at increased genetic risk for HGSC. Recent experiments investigating the impact of follicular fluid exposure and retrograde menstruation on tumor development in the fallopian tube will also be discussed. These data will be reconciled with traditional ovarian cancer risk factors related to reproductive history.

The prolyl isomerase FKBP25 regulates microtubule polymerization impacting cell cycle progression and genomic stability

FK506 binding proteins (FKBPs) catalyze the interconversion of cis-trans proline conformers in proteins. Importantly, FK506 drugs have anti-cancer and neuroprotective properties, but the effectors and mechanisms underpinning these properties are not well understood because the cellular function(s) of most FKBP proteins are unclear. FKBP25 is a nuclear prolyl isomerase that interacts directly with nucleic acids and is associated with several DNA/RNA binding proteins. Here, we show the catalytic FKBP domain binds microtubules (MTs) directly to promote their polymerization and stabilize the MT network. Furthermore, FKBP25 associates with the mitotic spindle and regulates entry into mitosis. This interaction is important for mitotic spindle dynamics, as we observe increased chromosome instability in FKBP25 knockdown cells. Finally, we provide evidence that FKBP25 association with chromatin is cell-cycle regulated by Protein Kinase C phosphorylation. This disrupts FKBP25-DNA contacts during mitosis while maintaining its interaction with the spindle apparatus. Collectively, these data support a model where FKBP25 association with chromatin and MTs is carefully choreographed to ensure faithful genome duplication. Additionally, they highlight that FKBP25 is a MT-associated FK506 receptor and potential therapeutic target in MT-associated diseases.

The basic tilted helix bundle domain of the prolyl isomerase FKBP25 is a novel double-stranded RNA binding module

Prolyl isomerases are defined by a catalytic domain that facilitates the cis–trans interconversion of proline residues. In most cases, additional domains in these enzymes add important biological function, including recruitment to a set of protein substrates. Here, we report that the N-terminal basic tilted helix bundle (BTHB) domain of the human prolyl isomerase FKBP25 confers specific binding to double-stranded RNA (dsRNA). This binding is selective over DNA as well as single-stranded oligonucleotides. We find that FKBP25 RNA-association is required for its nucleolar localization and for the vast majority of its protein interactions, including those with 60S pre-ribosome and early ribosome biogenesis factors. An independent mobility of the BTHB and FKBP catalytic domains supports a model by which the N-terminus of FKBP25 is anchored to regions of dsRNA, whereas the FKBP domain is free to interact with neighboring proteins. Apart from the identification of the BTHB as a new dsRNA-binding module, this domain adds to the growing list of auxiliary functions used by prolyl isomerases to define their primary cellular targets.

Nam Dia long, a Vietnamese folk formula, induces apoptosis in MCF-7 cells through various mechanisms of action

Background

The holistic approach of traditional medicine renders the identification of its mechanisms of action difficult. Microarray technology provides an efficient way to analyze the complex genome-wide gene expression of cells treated with mixtures of medicinal ingredients. We performed transcriptional profiling of MCF-7 cells treated with Nam Dia Long (NDL), a Vietnamese traditional formula, to explore the mechanism of action underlying the apoptosis inducing effect of this formula reported in a previous study.

Methods

MCF-7 cells were treated with aqueous extracts of NDL at the IC₅₀ concentration for 24, 36 and 48 h. Total RNAs at 24 h and 48 h were subsequently extracted, reverse transcribed and submitted to microarray expression profiling using the Human HT-12 v4.0 Expression Bead Chip (Illumina). Functional analyses were performed using the Database for Annotation, Visualization and Integrated Discovery and the Ingenuity Pathways Analysis. The expression level from selected genes at the three time points were assessed by quantitative real-time RT-PCR and Western blot.

Results

Fifty-four and 601 genes were differentially expressed at 24 and 48 h of NDL treatment, respectively. Genes with altered expression at 24 h were mostly involved in cell responses to xenobiotic stress whereas genes differentially expressed at 48 h were related to endoplasmic reticulum stress, DNA damage and cell cycle control. Apoptosis of NDL treated MCF-7 cells resulted from a combination of different mechanisms including the intrinsic and extrinsic pathways, cell cycle arrest- and oxidative stress-related cell death.

Conclusion

NDL elicited a two-stage response in MCF-7 treated cells with apoptosis as the ultimate result. The various mechanisms inducing apoptosis reflected the complexity of the formula composition.

Electronic supplementary material

The online version of this article (10.1186/s12906-017-2027-2) contains supplementary material, which is available to authorized users.

Peptidylprolyl Isomerases as In Vivo Carriers for Drugs That Target Various Intracellular Entities

Analyses of sequences and structures of the cyclosporine A (CsA)-binding proteins (cyclophilins) and the immunosuppressive macrolide FK506-binding proteins (FKBPs) have revealed that they exhibit peculiar spatial distributions of charges, their overall hydrophobicity indexes vary within a considerable level whereas their points isoelectric (pIs) are contained from 4 to 11. These two families of peptidylprolyl cis/trans isomerases (PPIases) have several distinct functional attributes such as: (1) high affinity binding to some pharmacologically-useful hydrophobic macrocyclic drugs; (2) diversified binding epitopes to proteins that may induce transient manifolds with altered flexibility and functional fitness; and (3) electrostatic interactions between positively charged segments of PPIases and negatively charged intracellular entities that support their spatial integration. These three attributes enhance binding of PPIase/pharmacophore complexes to diverse intracellular entities, some of which perturb signalization pathways causing immunosuppression and other system-altering phenomena in humans.

Structural basis of nucleic acid recognition by FK506-binding protein 25 (FKBP25), a nuclear immunophilin

The nuclear immunophilin FKBP25 interacts with chromatin-related proteins and transcription factors and is suggested to interact with nucleic acids. Currently the structural basis of nucleic acid binding by FKBP25 is unknown. Here we determined the nuclear magnetic resonance (NMR) solution structure of full-length human FKBP25 and studied its interaction with DNA. The FKBP25 structure revealed that the N-terminal helix-loop-helix (HLH) domain and C-terminal FK506-binding domain (FKBD) interact with each other and that both of the domains are involved in DNA binding. The HLH domain forms major-groove interactions and the basic FKBD loop cooperates to form interactions with an adjacent minor-groove of DNA. The FKBP25–DNA complex model, supported by NMR and mutational studies, provides structural and mechanistic insights into the nuclear immunophilin-mediated nucleic acid recognition.

The p53 inhibitor, pifithrin-α, disrupts microtubule organization, arrests growth, and induces polyploidy in the rainbow trout gill cell line, RTgill-W1

Pifithrin-α (PFT-α) blocks p53-dependent transcription and is an example of the many drugs being developed to target the p53 pathway in humans that could be released into the environment with potential impacts on aquatic animals if they were to become successful pharmaceuticals. In order to understand how p53 drugs might act on fish, the effects of PFT-α on rainbow trout gill epithelial cell line, RTgill-W1, were studied. PFT-α was not cytotoxic to RTgill-W1 in cultures with or without fetal bovine serum (FBS), but at 5.25μg/ml, PFT-α completely arrested proliferation. When FBS was present, PFT-α increased the number of polyploid cells over 12days. Those results suggest that like in mammals, p53 appears to regulate ploidy in fish. However, several effects were seen that have not been observed with mammalian cells. PFT-α caused a transient rise in the mitotic index and a disruption in cytoskeletal microtubules. These results suggest that in fish cells PFT-α affects microtubules either directly through an off-target action on tubulin or indirectly through an on-target action on p53-regulated transcription.

FKBP25 and FKBP38 regulate non-capacitative calcium entry through TRPC6

Non-capacitative calcium entry (NCCE) contributes to cell activation in response to the occupation of G protein-coupled membrane receptors. Thrombin administration to platelets evokes the synthesis of diacylglycerol downstream of PAR receptor activation. Diacylglycerol evokes NCCE through activating TRPC3 and TRPC6 in human platelets. Although it is known that immunophilins interact with TRPCs, the role of immunophilins in the regulation of NCCE remains unknown. Platelet incubation with FK506, an immunophilin antagonist, reduced OAG-evoked NCCE in a concentration-dependent manner, an effect that was independent on the inactivation of calcineurin (CaN). FK506 was unable to reduce NCCE evoked by OAG in platelets from TRPC6-/- mice. In HEK-293 cells overexpressing TRPC6, currents through TRPC6 were altered in the presence of FK506. We have found interaction between FKBP38 and other FKBPs, like FKBP25, FKBP12, and FKBP52 that were not affected by FK506, as well as with calmodulin (CaM). FK506 modified the pattern of association between FKBP25 and TRPCs as well as impaired OAG-evoked TRPC3 and TRPC6 coupling in both human and mouse platelets. By performing biotinylation experiments we have elucidated that FKBP25 and FKBP38 might be found at different cellular location, the plasma membrane and the already described intracellular locations. Finally, FKBP25 and FKBP38 silencing significantly inhibits OAG-evoked NCCE in MEG-01 and HEK293 cells, while overexpression of FKBP38 does not modify NCCE in HEK293 cells. All together, these findings provide strong evidence for a role of immunophilins, including FKBP25 and FKBP38, in NCCE mediated by TRPC6.

FUSE Binding Protein 1 Facilitates Persistent Hepatitis C Virus Replication in Hepatoma Cells by Regulating Tumor Suppressor p53

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis C (CHC), liver cirrhosis, and hepatocellular carcinoma (HCC). Immunohistochemistry of archived HCC tumors showed abundant FBP1 expression in HCC tumors with the CHC background. Oncomine data analysis of normal versus HCC tumors with the CHC background indicated a 4-fold increase in FBP1 expression with a concomitant 2.5-fold decrease in the expression of p53. We found that FBP1 promotes HCV replication by inhibiting p53 and regulating BCCIP and TCTP, which are positive and negative regulators of p53, respectively. The severe inhibition of HCV replication in FBP1-knockdown Huh7.5 cells was restored to a normal level by downregulation of either p53 or BCCIP. Although p53 in Huh7.5 cells is transcriptionally inactive as a result of Y220C mutation, we found that the activation and DNA binding ability of Y220C p53 were strongly suppressed by FBP1 but significantly activated upon knockdown of FBP1. Transient expression of FBP1 in FBP1 knockdown cells fully restored the control phenotype in which the DNA binding ability of p53 was strongly suppressed. Using electrophoretic mobility shift assay (EMSA) and isothermal titration calorimetry (ITC), we found no significant difference in in vitro target DNA binding affinity of recombinant wild-type p53 and its Y220C mutant p53. However, in the presence of recombinant FBP1, the DNA binding ability of p53 is strongly inhibited. We confirmed that FBP1 downregulates BCCIP, p21, and p53 and upregulates TCTP under radiation-induced stress. Since FBP1 is overexpressed in most HCC tumors with an HCV background, it may have a role in promoting persistent virus infection and tumorigenesis.

IMPORTANCE

It is our novel finding that FUSE binding protein 1 (FBP1) strongly inhibits the function of tumor suppressor p53 and is an essential host cell factor required for HCV replication. Oncomine data analysis of a large number of samples has revealed that overexpression of FBP1 in most HCC tumors with chronic hepatitis C is significantly linked with the decreased expression level of p53. The most significant finding is that FBP1 not only physically interacts with p53 and interferes with its binding to the target DNA but also functions as a negative regulator of p53 under cellular stress. FBP1 is barely detectable in normal differentiated cells; its overexpression in HCC tumors with the CHC background suggests that FBP1 has an important role in promoting HCV infection and HCC tumors by suppressing p53.

Loss of miR-223 and JNK Signaling Contribute to Elevated Stathmin in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is often fatal, and studies have revealed that aberrant miRNAs contribute to MPM development and aggressiveness. Here, a screen of miRNAs identified reduced levels of miR-223 in MPM patient specimens. Interestingly, miR-223 targets Stathmin (STMN1), a microtubule regulator that has been associated with MPM. However, whether miR-223 regulates STMN1 in MPM and the functions of miR-223 and STMN1 in this disease are yet to be determined. STMN1 is also regulated by c-Jun N-terminal kinase (JNK) signaling, but whether this occurs in MPM and whether miR-223 plays a role are unknown. The relationship between STMN1, miR-223, and JNK was assessed using MPM cell lines, cells from pleural effusions, and MPM tissue. Evidence indicates that miR-223 is decreased in all MPM tissue compared with normal/healthy tissue. Conversely, STMN1 expression was higher in MPM cell lines when compared with primary mesothelial cell controls. Following overexpression of miR-223 in MPM cell lines, STMN1 levels were reduced, cell motility was inhibited, and tubulin acetylation induced. Knockdown of STMN1 using siRNAs led to inhibition of MPM cell proliferation and motility. Finally, miR-223 levels increased while STMN1 was reduced following the re-expression of the JNK isoforms in JNK-null murine embryonic fibroblasts, and STMN1 was reduced in MPM cell lines following the activation of JNK signaling.

IMPLICATIONS

miR-223 regulates STMN1 in MPM, and both are in turn regulated by the JNK signaling pathway. As such, miR-223 and STMN1 play an important role in regulating MPM cell motility and may be therapeutic targets.

The emerging role of peptidyl-prolyl isomerase chaperones in tau oligomerization, amyloid processing, and Alzheimer's disease

Peptidyl-prolyl cis/trans isomerases (PPIases), a unique family of molecular chaperones, regulate protein folding at proline residues. These residues are abundant within intrinsically disordered proteins, like the microtubule-associated protein tau. Tau has been shown to become hyperphosphorylated and accumulate as one of the two main pathological hallmarks in Alzheimer's disease, the other being amyloid beta (Ab). PPIases, including Pin1, FK506-binding protein (FKBP) 52, FKBP51, and FKBP12, have been shown to interact with and regulate tau biology. This interaction is particularly important given the numerous proline-directed phosphorylation sites found on tau and the role phosphorylation has been found to play in pathogenesis. This regulation then affects downstream aggregation and oligomerization of tau. However, many PPIases have yet to be explored for their effects on tau biology, despite the high likelihood of interaction based on proline content. Moreover, Pin1, FKBP12, FKBP52, cyclophilin (Cyp) A, CypB, and CypD have been shown to also regulate Ab production or the toxicity associated with Ab pathology. Therefore, PPIases directly and indirectly regulate pathogenic protein multimerization in Alzheimer's disease and represent a family rich in targets for modulating the accumulation and toxicity.

Interaction of p53 with prolyl isomerases: Healthy and unhealthy relationships

BACKGROUND

The p53 protein family, comprising p53, p63 and p73, is primarily involved in preserving genome integrity and preventing tumor onset, and also affects a range of physiological processes. Signal-dependent modifications of its members and of other pathway components provide cells with a sophisticated code to transduce a variety of stress signaling into appropriate responses. TP53 mutations are highly frequent in cancer and lead to the expression of mutant p53 proteins that are endowed with oncogenic activities and sensitive to stress signaling.

SCOPE OF REVIEW

p53 family proteins have unique structural and functional plasticity, and here we discuss the relevance of prolyl-isomerization to actively shape these features.

MAJOR CONCLUSIONS

The anti-proliferative functions of the p53 family are carefully activated upon severe stress and this involves the interaction with prolyl-isomerases. In particular, stress-induced stabilization of p53, activation of its transcriptional control over arrest- and cell death-related target genes and of its mitochondrial apoptotic function, as well as certain p63 and p73 functions, all require phosphorylation of specific S/T-P motifs and their subsequent isomerization by the prolyl-isomerase Pin1. While these functions of p53 counteract tumorigenesis, under some circumstances their activation by prolyl-isomerases may have negative repercussions (e.g. tissue damage induced by anticancer therapies and ischemia-reperfusion, neurodegeneration). Moreover, elevated Pin1 levels in tumor cells may transduce deregulated phosphorylation signaling into activation of mutant p53 oncogenic functions.

GENERAL SIGNIFICANCE

The complex repertoire of biological outcomes induced by p53 finds mechanistic explanations, at least in part, in the association between prolyl-isomerases and the p53 pathway. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.

Pleiotropic roles in cancer biology for multifaceted proteins FKBPs

BACKGROUND

FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.

SCOPE OF THE REVIEW

The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.

MAJOR CONCLUSIONS

Some family members appear to promote disease while others are protective against tumorigenesis.

GENERAL SIGNIFICANCE

FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.

Unbiased proteomic and transcript analyses reveal that stathmin-1 silencing inhibits colorectal cancer metastasis and sensitizes to 5-fluorouracil treatment

Colorectal cancer metastasis is a major cause of mortality worldwide, which may only be controlled with novel methods limiting tumor dissemination and chemoresistance. High stathmin-1 (STMN1) expression was previously established as a hallmark of colorectal cancer progression and predictor of poor survival; however, the mechanism of action is less clear. This work demonstrates that STMN1 silencing arrests tumor-disseminative cascades by inhibiting multiple metastatic drivers, and repressing oncogenic and mesenchymal transcription. Using a sensitive iTRAQ labeling proteomic approach that quantified differential abundance of 4562 proteins, targeting STMN1 expression was shown to reinstate the default cellular program of metastatic inhibition, and promote cellular adhesion via amplification of hemidesmosomal junctions and intermediate filament tethering. Silencing STMN1 also significantly improved chemoresponse to the classical colorectal cancer therapeutic agent, 5FU, via a novel caspase-6 (CASP6)-dependent mechanism. Interestingly, the prometastatic function of STMN1 was independent of p53 but required phosphorylations at S25 or S38; abrogating phosphorylative events may constitute an alternative route to achieving metastatic inhibition. These findings establish STMN1 as a potential target in antimetastatic therapy, and demonstrate the power of an approach coupling proteomics and transcript analyses in the global assessment of treatment benefits and potential side-effects.

IMPLICATIONS

Stathmin-1 is a potential candidate in colorectal cancer therapy that targets simultaneously the twin problems of metastatic spread and chemoresistance.

The role of polo-like kinase 1 in carcinogenesis: cause or consequence?

Polo-like kinase 1 (Plk1) is a well-established mitotic regulator with a diverse range of biologic functions continually being identified throughout the cell cycle. Preclinical evidence suggests that the molecular targeting of Plk1 could be an effective therapeutic strategy in a wide range of cancers; however, that success has yet to be translated to the clinical level. The lack of clinical success has raised the question of whether there is a true oncogenic addiction to Plk1 or if its overexpression in tumors is solely an artifact of increased cellular proliferation. In this review, we address the role of Plk1 in carcinogenesis by discussing the cell cycle and DNA damage response with respect to their associations with classic oncogenic and tumor suppressor pathways that contribute to the transcriptional regulation of Plk1. A thorough examination of the available literature suggests that Plk1 activity can be dysregulated through key transformative pathways, including both p53 and pRb. On the basis of the available literature, it may be somewhat premature to draw a definitive conclusion on the role of Plk1 in carcinogenesis. However, evidence supports the notion that oncogene dependence on Plk1 is not a late occurrence in carcinogenesis and it is likely that Plk1 plays an active role in carcinogenic transformation.

Cell cycle inhibition therapy that targets stathmin in in vitro and in vivo models of breast cancer

Stathmin is the founding member of a family of microtubule-destabilizing proteins that have a critical role in the regulation of mitosis. Stathmin is expressed at high levels in breast cancer and its overexpression is linked to disease progression. Although there is a large body of evidence to support a role for stathmin in breast cancer progression, the validity of stathmin as a viable therapeutic target for breast cancer has not been investigated. Here, we used a bicistronic adenoviral vector that co-expresses green fluorescent protein and a ribozyme that targets stathmin messenger RNA in preclinical breast cancer models with different estrogen receptor (ER) status. We examined the effects of anti-stathmin ribozyme on the malignant phenotype of breast cancer cells in vitro and in xenograft models in vivo both as a single agent and in combination with chemotherapeutic agents. Adenovirus-mediated gene transfer of anti-stathmin ribozyme resulted in a dose-dependent inhibition of proliferation and clonogenicity associated with a G2/M arrest and increase in apoptosis in both ER-positive and ER-negative breast cancer cell lines. This inhibition was markedly enhanced when stathmin-inhibited breast cancer cells were exposed to low concentrations of taxol, which resulted in virtually complete loss of the malignant phenotype. Interestingly, breast cancer xenografts treated with low doses of anti-stathmin therapy and taxol showed regression in a majority of tumors, while some tumors stopped growing completely. In contrast, combination of anti-stathmin ribozyme and adriamycin resulted in only a modest inhibition of growth in vitro and in breast cancer xenografts in vivo. Although inhibition of tumor growth was observed in both the combination treatment groups compared with groups treated with single agent alone, combination of anti-stathmin therapy and taxol had a more profound inhibition of tumorigenicity, as both agents target the microtubule pathway. Clinically, these findings are highly relevant because taxol is one of the most active chemotherapeutic agents in breast cancer. These studies provide the proof-of-principle that stathmin provides an attractive molecular target, which could serve as a primary focus of novel approaches to breast cancer.

Gain-of-function mutant p53 downregulates miR-223 contributing to chemoresistance of cultured tumor cells

Mutant p53 proteins are expressed at high frequency in human tumors and are associated with poor clinical prognosis and resistance to chemotherapeutic treatments. Here we show that mutant p53 proteins downregulate micro-RNA (miR)-223 expression in breast and colon cancer cell lines. Mutant p53 binds the miR-223 promoter and reduces its transcriptional activity. This requires the transcriptional repressor ZEB-1. We found that miR-223 exogenous expression sensitizes breast and colon cancer cell lines expressing mutant p53 to treatment with DNA-damaging drugs. Among the putative miR-223 targets, we focused on stathmin-1 (STMN-1), an oncoprotein known to confer resistance to chemotherapeutic drugs associated with poor clinical prognosis. Mutant p53 silencing or miR-223 exogenous expression lowers the levels of STMN-1 and knockdown of STMN-1 by small interfering RNA increases cell death of mutant p53-expressing cell lines. On the basis of these findings, we propose that one of the pathways affected by mutant p53 to increase cellular resistance to chemotherapeutic agents involves miR-223 downregulation and the consequent upregulation of STMN-1.

Stathmin is dispensable for tumor onset in mice

The microtubule-destabilizing protein stathmin is highly expressed in several types of tumor, thus deserving the name of oncoprotein 18. High levels of stathmin expression and/or activity favor the metastatic spreading and mark the most aggressive tumors, thus representing a realistic marker of poor prognosis. Stathmin is a downstream target of many signaling pathways, including Ras-MAPK, PI3K and p53, involved in both tumor onset and progression. We thus hypothesized that stathmin could also play a role during the early stages of tumorigenesis, an issue completely unexplored. In order to establish whether stathmin expression is necessary for tumor initiation, we challenged wild type (WT), stathmin heterozygous and stathmin knock-out (KO) mice with different carcinogens. Using well-defined mouse models of carcinogenesis of skin, bladder and muscle by the means of 7,12-dimethylbenz[α]antracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA), N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) and 3-methylcholanthrylene (3MC) treatments, respectively, we demonstrated that knock-out of stathmin has no impact on the onset of cancer in mice. No significant difference was noticed either when the Ras oncogene was mutated (skin carcinogenesis model) or when the p53 pathway was inactivated (bladder carcinomas and fibrosarcomas). Finally, we concomitantly impinged on p53 and Ras pathways, by generating WT and stathmin KO mouse embryo fibroblasts transformed with papilloma virus large T antigen (LgTAg) plus the K-Ras^G12V oncogene. In vivo growth of xenografts from these transformed fibroblasts did not highlight any significant difference depending on the presence or absence of stathmin. Overall, our work demonstrates that stathmin expression is dispensable for tumor onset, at least in mice, thus making stathmin a virtually exclusive marker of aggressive disease and a promising therapeutic target for advanced cancers.

Suspected leukemia oncoproteins CREB1 and LYL1 regulate Op18/STMN1 expression

Stathmin (STMN1) is a microtubule destabilizing protein with a key role in cell cycle progression and cell migration that is up-regulated in several cancers and may contribute to the malignant phenotype. However, the factors that regulate its expression are not well understood. Loss as well as gain-of-function p53 mutations up-regulate STMN1 and in acute myelogenous leukemia where p53 is predominantly wild-type, STMN1 is also over-expressed. Here we show regulatory control of STMN1 expression by the leucine zipper transcription factor (TF) CREB1 and the basic helix-loop-helix TF LYL1. By ChIP-chip experiments we demonstrate in vivo the presence of LYL1 and CREB1 in close proximity on the STMN1 promoter and using promoter assays we reveal co-regulation of STMN1 by CREB1 and LYL1. By contrast, TAL1, another suspected oncoprotein in leukemia and close relative of LYL1, exerts no regulatory effect on the STMN1 promoter. NLI, LMO2 and GATA2 are previously described co-activators of Tal1/Lyl1-E47 transcriptional complexes and potentiate Lyl1 activation of the STMN1 promoter while having no effect on TAL1 transactivation. Promoter mutations that abrogate CREB1 proximal binding or mutations of the DNA-binding domain of CREB1 abolish LYL1 transcriptional activation. These results show that CRE and Ebox sites function as coordinated units and support previous evidence of joint CREB1-and LYL1 transcription events activating an aberrant subset of promoters in leukemia. CREB1 or LYL1 shRNA knock-down down-regulate STMN1 expression. Because down-regulation of STMN1 has been shown to have anti-proliferative effects, while CREB1 and LYL1 are suspected oncoproteins, interference with CREB1-LYL1 interactions may complement standard chemotherapy and yield additional beneficial effects.

The E2F transcription factor 1 transactives stathmin 1 in hepatocellular carcinoma

BACKGROUND

Through data mining the Stanford Microarray Database, the stathmin 1 (STMN1) transcript was found to be frequently upregulated in the hepatocellular carcinoma (HCC) with low alpha-fetoprotein level. The molecular mechanism of STMN1 upregulation in HCCs remained unclear.

METHODS

Quantitative RT-PCR, immunoblotting, immunohistochemistry, and transfection of expression or small hairpin RNA interference plasmids, chromatin immunoprecipitation (ChIP), and quantitative ChIP assays were performed in HCC specimens or 2 distinct HCC-derived cell lines. Dual luciferase assay and site-directed mutagenesis were applied to analyze the activities of STMN1 proximal promoter region.

RESULTS

STMN1 mRNA and proteins were significantly associated with several clinicopathological features. High STMN1 or E2F1 immunoexpression was predictive of poor overall survival (OS) rate (P < .01). In HCC-derived cell lines, E2F1 was elevated before STMN1 mRNA during the cell cycle. Exogenous expression of E2F1 or both transcription factor DP-1 (TFDP1) and E2F1 genes induced E2F1 and STMN1 mRNA (P < .01). Knockdown of the E2F1 gene suppressed E2F1 and STMN1 mRNA and E2F1 and STMN1 protein levels (P < .05). The promoter activity of STMN1 gene increased with overexpression of both E2F1 and TFDP1 genes (P < .05); however, it decreased when mutations were introduced in the E2F1-binding sites (P < .05).

CONCLUSIONS

Upregulation of E2F1 and STMN1 proteins associate with worse outcomes in patients with HCC. E2F1 significantly correlates with STMN1 protein level in HCC lesions and in vitro transactivation assays, suggesting that STMN1 gene is transactivated by the E2F1 protein.

Stathmin 1: a protein with many tasks. New biomarker and potential target in cancer

Stathmin 1 (STMN1) is a critical protein involved in microtubule polymerization and is necessary for survival of cancer cells. This editorial describes the role of targeted therapeutics which disrupt STMN1 modulation and such effect on cancer survival.

Improved risk assessment of endometrial cancer by combined analysis of MSI, PI3K-AKT, Wnt/β-catenin and P53 pathway activation

OBJECTIVE

To investigate if analysis of genetic alterations in the main pathways involved in endometrioid type carcinogenesis (PI3K-AKT, Wnt/β-catenin, P53-activation and MSI) improves the current risk assessment based on clinicopathological factors.

METHODS

Formalin fixed paraffin embedded (FFPE) primary tumor samples of 65 patients with FIGO-stage I endometrioid type endometrial cancer (EEC) were selected from the randomized PORTEC-2 trial. Tumors were stained by immunohistochemistry for P53, PTEN and β-catenin. Tumor DNA was isolated for sequence analysis of TP53 (exons 4 to 8), hotspot mutation analysis of KRAS (exon 1) and PI3K (exon 9 and 20) and microsatellite-instability (MSI) analysis including MLH1 promotor-methylation status. Univariate and multivariate analyses for disease-free survival (DFS) using Cox regression models were performed.

RESULTS

P53 status (HR 6.7, 95%CI 1.75-26.0, p=0.006) and MSI were the strongest single genetic prognostic factors for decreased DFS, while high PI3K-AKT pathway activation showed a trend and β-catenin was not prognostic. The combination of multiple activated pathways was the most powerful prognostic factor for decreased DFS (HR 5.0; 95%CI 1.59-15.6 p=0.006). Multiple pathway activation, found in 8% of patients, was strongly associated with aggressive clinical course. In contrast, 40% of patients had no alterations in the investigated pathways and had a very low risk of disease progression.

CONCLUSIONS

Activation of multiple oncogenic pathways in EEC was the most powerful prognostic factor for decreased DFS, resulting in an individual risk assessment superior to the current approach based on clinicopathological factors.

LRRC4 inhibits the proliferation of human glioma cells by modulating the expression of STMN1 and microtubule polymerization

LRRC4 is a tumor suppressor of glioma, and it is epigenetically inactivated commonly in glioma. Our previous study has shown that induction of LRRC4 expression inhibits the proliferation of glioma cells. However, little is known about the mechanisms underlying the action of LRRC4 in glioma cells. We employed two-dimensional fluorescence differential gel electrophoresis (2-D DIGE) and MALDI -TOF/TOF-MS/MS to identify 11 differentially expressed proteins, including the significantly down-regulated STMN1 expression in the LRRC4-expressing U251 glioma cells. The levels of STMN1 expression appeared to be positively associated with the pathogenic degrees of human glioma. Furthermore, induction of LRRC4 over-expression inhibited the STMN1 expression and U251 cell proliferation in vitro, and the glioma growth in vivo. In addition, induction of LRRC4 or knockdown of STMN1 expression induced cell cycle arrest in U251 cells, which was associated with modulating the p21, cyclin D1, and cyclin B expression, and the ERK phosphorylation, and inhibiting the CDK5 and cdc2 kinase activities, but increasing the microtubulin polymerization in U251 cells. LRRC4, at least partially by down-regulating the STMN1expression, acts as a major glioma suppressor, induces cell cycle arrest and modulates the dynamic process of microtubulin, leading to the inhibition of glioma cell proliferation and growth. Potentially, modulation of LRRC4 or STMN1 expression may be useful for design of new therapies for the intervention of glioma.

The microtubule cytoskeleton is required for a G2 cell cycle delay in cancer cells lacking stathmin and p53

In several cancer cell lines, depleting the microtubule (MT)-destabilizing protein stathmin/oncoprotein18 leads to a G2 cell cycle delay and apoptosis. These phenotypes are observed only in synergy with low levels of p53, but the pathway(s) activated by stathmin depletion to delay the cell cycle are unknown. We found that stathmin depletion caused greater MT stability in synergy with loss of p53, measured by the levels of acetylated α-tubulin and the rate of centrosomal MT nucleation. Nocodazole or vinblastine-induced MT depolymerization abrogated the stathmin-depletion induced G2 delay, measured by the percentage of cells staining positive for several markers (TPX2, CDK1 with inhibitory phosphorylation), indicating that MTs are required to lengthen G2. Live cell imaging showed that stathmin depletion increased time in G2 without an impact on the duration of mitosis, indicating that the longer interphase duration is not simply a consequence of a previous slowed mitosis. In contrast, stabilization of MTs with paclitaxel (8 nM) slowed mitosis without lengthening the duration of interphase, demonstrating that increased MT stability alone is not sufficient to delay cells in G2.

Stathmin1 plays oncogenic role and is a target of microRNA-223 in gastric cancer

Stathmin1 (STMN1) is a candidate oncoprotein and prognosis marker in several kinds of cancers. This study was aimed to analyze its expression and biological functions in gastric cancer. The expression of STMN1 was evaluated by qRT-PCR, western blot and immunohistochemistry. The biological function of STMN1 was determined by MTT proliferation assays, monolayer colony formation and cell invasion assays using small interference RNA technique in gastric cancer cell lines. We also explored the regulation of STMN1 expression by microRNA-223. STMN1 was upregulated in gastric cancer cell lines and primary gastric adenocarcinomas. STMN1-positive tumors were more likely to be found in old age group and associated with p53 nuclear expression. In diffuse type gastric adenocarcinomas, STMN1 expression was correlated with age (p = 0.043), T stage (p = 0.004) and lymph node metastasis (p = 0.046). Expression of STMN1 in diffuse type gastric adenocarcinoma was associated with poor disease specific survival by univariate analysis (p = 0.01). STMN1 knockdown in AGS and MKN7 cell lines suppressed proliferation (p<0.001), reduced monolayer colony formation (p<0.001), inhibited cell invasion and migration ability (p<0.001) and induced G1 phase arrest. siSTMN1 could also suppress cell growth in vivo (p<0. 01). We finally confirmed that STMN1 is a putative downstream target of miR-223 in gastric cancer. Our findings supported an oncogenic role of STMN1 in gastric cancer. STMN1 might serve as a prognostic marker and a potential therapeutic target for gastric cancer.

Alteration of G1/S transition regulators influences recurrences in head and neck squamous carcinomas

Head-Neck Squamous Cell Carcinoma (HN-SCC) is a clinically challenging disease associated with a high mortality rate. The chemo-radiotherapy treatments that aim to preserve the organ represent the current gold standard therapy for advanced laryngeal disease, reserving surgery only for non-responsive or relapsed cases. Despite these aggressive approaches, local persistent or recurrent disease remains the primary cause of treatment failure but we still do not have known factors and/or markers able to predict the outcome of the disease and in particular the risk of local relapse. Here we address this point on a series of 54 cases of HN-SCC for whom the presence of local relapse was known. Using immunohistochemistry (IHC) analysis to evaluate protein expression and localization in the recurrence free and recurrence positive samples, we studied the expression of key cell cycle regulators including p53, p16, p27, pRB, Cyclin D1, Cyclin D3, and Stathmin. Overall by analyzing seven different cell cycle regulators we can hypothesize that the alteration of G1/S regulation represents a fundamental event in the onset/progression of HN-SCC cancers and that the associate use of Cyclin D1/p16 expression should be considered as a possible biomarker toward the identification of those patients that will probably develop a recurrent disease and thus should benefit of a more aggressive treatment.

Stathmin: a protein with many tasks. New biomarker and potential target in cancer

INTRODUCTION

Stathmin is a microtubule-destabilizing phosphoprotein, firstly identified as the downstream target of many signal transduction pathways. Several studies then indicated that stathmin is overexpressed in many types of human malignancies, thus deserving the name of Oncoprotein 18 (Op18). At molecular level, stathmin depolymerizes microtubules by either sequestering free tubulin dimers or directly inducing microtubule-catastrophe. A crucial role for stathmin in the control of mitosis has been proposed, since both its overexpression and its downregulation induce failure in the correct completion of cell division. Accordingly, stathmin is an important target of the main regulator of M phase, cyclin-dependent kinase 1.

AREAS COVERED

Recent evidences support a role for stathmin in the regulation of cell growth and motility, both in vitro and in vivo, and indicate its involvement in advanced, invasive and metastatic cancer more than in primary tumors.

EXPERT OPINION

Many studies suggest that high stathmin expression levels in cancer negatively influence the response to microtubule-targeting drugs. These notions together with the fact that stathmin is expressed at very low levels in most adult tissues strongly support the use of stathmin as marker of prognosis and as target for novel anti-tumoral and anti-metastatic therapies.

Identification of candidate substrates for poly(ADP-ribose) polymerase-2 (PARP2) in the absence of DNA damage using high-density protein microarrays

Poly(ADP-ribose) polymerase-2 (PARP2) belongs to the ADP-ribosyltransferase family of enzymes that catalyze the addition of ADP-ribose units to acceptor proteins, thus affecting many diverse cellular processes. In particular, PARP2 shares with PARP1 and, as recently highlighted, PARP3 the sole property of being catalytically activated by DNA-strand breaks, implying key downstream functions in the cellular response to DNA damage for both enzymes. However, evidence from several studies suggests unique functions for PARP2 in additional processes, possibly mediated through its basal, DNA-damage unstimulated ADP-ribosylating activity. Here, we describe the development and application of a protein microarray-based approach tailored to identify proteins that are ADP-ribosylated by PARP2 in the absence of DNA damage mimetics and might thus represent useful entry points to the exploration of novel PARP2 functions. Several candidate substrates for PARP2 were identified and global hit enrichment analysis showed a clear enrichment in translation initiation and RNA helicase molecular functions. In addition, the top scoring candidates FK506-binding protein 3 and SH3 and cysteine-rich domain-containing protein 1 were selected and confirmed in a complementary assay format as substrates for unstimulated PARP2.

p53 directly suppresses BNIP3 expression to protect against hypoxia-induced cell death

Hypoxia stabilizes the tumour suppressor p53, allowing it to function primarily as a transrepressor; however, the function of p53 during hypoxia remains unclear. In this study, we showed that p53 suppressed BNIP3 expression by directly binding to the p53-response element motif and recruiting corepressor mSin3a to the BNIP3 promoter. The DNA-binding site of p53 must remain intact for the protein to suppress the BNIP3 promoter. In addition, taking advantage of zebrafish as an in vivo model, we confirmed that zebrafish nip3a, a homologous gene of mammalian BNIP3, was indeed induced by hypoxia and p53 mutation/knockdown enhanced nip3a expression under hypoxia resulted in cell death enhancement in p53 mutant embryos. Furthermore, p53 protected against hypoxia-induced cell death mediated by p53 suppression of BNIP3 as illustrated by p53 knockdown/loss assays in both human cell lines and zebrafish model, which is in contrast to the traditional pro-apoptotic role of p53. Our results suggest a novel function of p53 in hypoxia-induced cell death, leading to the development of new treatments for ischaemic heart disease and cerebral stroke.

Stathmin 1, a marker of PI3K pathway activation and regulator of microtubule dynamics, is expressed in early pelvic serous carcinomas

BACKGROUND

Most high-grade pelvic serous carcinomas (HGPSCs) arise from fallopian tube epithelium (FTE). To date, few markers have been shown to characterize FTE transformation. Stathmin 1 (STMN1) is a candidate oncogene whose activity is influenced by p53, p27Kip1 (p27), and PI3K/Akt pathway activation. As a microtubule destabilizing protein, STMN1 regulates cytoskeletal dynamics, cell cycle progression, mitosis, and cell migration. This study examines the expression of STMN1 and its negative regulator p27 along the morphologic continuum from normal FTE to invasive carcinoma.

METHODS

STMN1 and p27 expression were examined by immunohistochemistry (IHC) in benign (n=12) and malignant (n=13) fallopian tubes containing normal epithelium, morphologically benign putative precursor lesions ("p53 signatures"), potential transitional precursor lesions ("proliferative p53 signatures"), tubal intraepithelial carcinoma (TIC), and/or invasive serous carcinoma. STMN1 expression was further assessed in 131 late-stage HGPSCs diagnosed as primary ovarian and in 6 ovarian cancer cell lines by IHC and Western blot, respectively.

RESULTS

STMN1 expression was absent in benign FTE and infrequently detected in p53 signatures. However, it was weakly expressed in proliferative p53 signatures and robustly induced upon progression to TIC and invasive carcinoma, typically accompanied by decreased p27 levels. STMN1 was expressed in >80% of high-grade serous ovarian carcinomas and cell lines.

CONCLUSIONS

STMN1 is a novel marker of early serous carcinoma that may play a role in FTE tumor initiation. Our data are consistent with a model by which STMN1 overexpression, resulting from loss of p27-mediated regulation, may potentiate aberrant cell proliferation, migration, and/or loss of polarity during early tumorigenesis.

To repress or not to repress: this is the guardian's question

p53 is possibly the most central tumor suppressor gene of our cells, integrating stress signals to activate a transcriptional program responsible for maintaining cellular homeostasis. Many of the downstream effects of p53 are a consequence of its activity as a transcription factor, resulting in the induction of multiple target genes. In addition to gene activation, however, gene repression is an essential part of the p53 cellular response. Despite extensive research efforts towards the elucidation of p53 functions, the molecular mechanisms and biological consequences of gene repression by p53 have not been studied extensively. We review our current knowledge of the mechanisms and biological consequences of p53 repression, with special attention to recently discovered mechanisms of repression that involve non-coding RNA molecules, an emerging aspect of regulation in the p53 cellular network.

One function--multiple mechanisms: the manifold activities of p53 as a transcriptional repressor

Maintenance of genome integrity is a dynamic process involving complex regulation systems. Defects in one or more of these pathways could result in cancer. The most important tumor-suppressor is the transcription factor p53, and its functional inactivation is frequently observed in many tumor types. The tumor suppressive function of p53 is mainly attributed to its ability to regulate numerous target genes at the transcriptional level. While the mechanism of transcriptional induction by p53 is well characterized, p53-dependent repression is not understood in detail. Here, we review the manifold mechanisms of p53 as a transcriptional repressor. We classify two different categories of repressed genes based on the underlying mechanism, and novel mechanisms which involve regulation through noncoding RNAs are discussed. The complete elucidation of p53 functions is important for our understanding of its tumor-suppressor activity and, therefore, represents the key for the development of novel therapeutic approaches.

p53 impairs endothelial function by transcriptionally repressing Kruppel-Like Factor 2

OBJECTIVE

To evaluate if p53 decreases Kruppel-Like Factor 2 (KLF2) expression and determine whether p53-mediated suppression of KLF2 plays a role in p53-induced endothelial dysfunction.

METHODS AND RESULTS

Endothelial KLF2 mediates endothelium-dependent vascular homeostasis by differentially regulating endothelial genes, leading to an anti-inflammatory and antithrombotic endothelial surface with normal vasodilatory function. In contrast, the tumor suppressor p53 leads to inflammatory gene expression and impairs endothelium-dependent vasodilatation, thus promoting endothelial dysfunction. The effect of p53 on KLF2 expression was determined. p53 inhibited KLF2 transcription in a histone deacetylase-dependent and a histone acetyltransferase-independent fashion. KLF2 expression was suppressed by p53 via a conserved p53-binding repressor sequence in its promoter. p53 bound to, and stimulated, deacetylation of Histone H3 at the KLF2 promoter. The effect of p53 on endothelial KLF2 target genes was examined. Downregulation of p53 increased expression of endothelial NO synthase and thrombomodulin and inhibited expression of plasminogen activator inhibitor 1. Conversely, overexpression of p53 suppressed endothelial NO synthase and thrombomodulin expression and stimulated plasminogen activator inhibitor 1 and endothelin-1 expression. Knockdown of KLF2 abolished the p53-induced decrease in thrombomodulin and increase in endothelin-1. Both, overexpression of p53 and knockdown of KLF2 in endothelial cells increased blood coagulation on an endothelial cell monolayer. The p53-induced increase in coagulation was rescued by forced expression of KLF2. p53 also impaired endothelium-dependent vasodilatation and decreased bioavailable vascular NO, both of which were rescued by forced KLF2 expression.

CONCLUSIONS

These findings illustrate a novel p53-dependent mechanism for the regulation of endothelial KLF2 expression. In addition, they show that downregulation of KLF2, in part, mediates a p53-stimulated dysfunctional endothelium.

Expression profiling of tubulin isotypes and microtubule-interacting proteins using real-time polymerase chain reaction

Real-time polymerase chain reaction (PCR) has been used for quantification of intracellular mRNA levels in cell culture and tissue samples. It is an important tool for studying antimitotic drug effects on tubulin isotype and microtubule-interacting protein levels and for measuring differences in normal and tumor tissue samples that could have predictive or prognostic applications. Both quantitative and comparative methods are valuable approaches; however, the selection of either approach requires an understanding of their benefits and challenges. In this chapter, we provide detailed protocols for real-time PCR experiments, discuss issues to consider in selecting real-time PCR methodologies, and give examples utilizing either quantitative or comparative approaches.

Identification and comparative analysis of the peptidyl-prolyl cis/trans isomerase repertoires of H. sapiens, D. melanogaster, C. elegans, S. cerevisiae and Sz. pombe

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins comprises three member families that are found throughout nature and are present in all the major compartments of the cell. Their numbers appear to be linked to the number of genes in their respective genomes, although we have found the human repertoire to be smaller than expected due to a reduced cyclophilin repertoire. We show here that whilst the members of the cyclophilin family (which are predominantly found in the nucleus and cytoplasm) and the parvulin family (which are predominantly nuclear) are largely conserved between different repertoires, the FKBPs (which are predominantly found in the cytoplasm and endoplasmic reticulum) are not. It therefore appears that the cyclophilins and parvulins have evolved to perform conserved functions, while the FKBPs have evolved to fill ever-changing niches within the constantly evolving organisms. Many orthologous subgroups within the different PPIase families appear to have evolved from a distinct common ancestor, whereas others, such as the mitochondrial cyclophilins, appear to have evolved independently of one another. We have also identified a novel parvulin within Drosophila melanogaster that is unique to the fruit fly, indicating a recent evolutionary emergence. Interestingly, the fission yeast repertoire, which contains no unique cyclophilins and parvulins, shares no PPIases solely with the budding yeast but it does share a majority with the higher eukaryotes in this study, unlike the budding yeast. It therefore appears that, in comparison with Schizosaccharomyces pombe, Saccharomyces cerevisiae is a poor representation of the higher eukaryotes for the study of PPIases.

Differential proteomic analysis of a highly metastatic variant of human breast cancer cells using two-dimensional differential gel electrophoresis

Distant metastasis represents the major lethal cause of breast cancer. To understand the molecular mechanisms of breast cancer metastasis and identify markers with metastatic potential, we established a highly metastatic variant of parental MDA-MB-231 cells (MDA-MB-231HM). Using two-dimensional electrophoresis (2-DE), we performed a proteomic comparison of the two kinds of cells. As much as 51 protein spots were differentially expressed between the selected variant and its parental counterpart in at least 3 experiments. Ten unique proteins were identified using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS), liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS), and database searching software. Among them, nine proteins were up-regulated in MDA-MB-231HM cells, including Macrophage-capping protein (CapG), Galectin-1, Chloride intracellular channel protein 1, Endoplasmic reticulum protein ERp29 precursor, Stathmin-1 (STMN1), Isoform 1 of uridine-cytidine kinase 2(UCK2), Rho GDP-dissociation inhibitor 2 (ARHGDIB), isocitrate dehydrogenase [NADP] cytoplasmic (IDH1), and N-myc downstream regulated gene 1 (NDRG1) protein. Only transgelin-2 was down-regulated. Differential expression was confirmed for three proteins including CapG, STMN1, and transgelin-2 by Western blotting analysis. Transgelin-2 was chosen for further verification by immunohistochemistry. The results suggested that 2-DE would be an efficient way to screen the proteins responsible for specific biological function. Furthermore, the findings imply that different proteins may be involved in the metastatic process in breast carcinomas.

Overexpression of far upstream element binding proteins: a mechanism regulating proliferation and migration in liver cancer cells

Microtubule-dependent effects are partly regulated by factors that coordinate polymer dynamics such as the microtubule-destabilizing protein stathmin (oncoprotein 18). In cancer cells, increased microtubule turnover affects cell morphology and cellular processes that rely on microtubule dynamics such as mitosis and migration. However, the molecular mechanisms deregulating modifiers of microtubule activity in human hepatocarcinogenesis are poorly understood. Based on profiling data of human hepatocellular carcinoma (HCC), we identified far upstream element binding proteins (FBPs) as significantly coregulated with stathmin. Coordinated overexpression of two FBP family members (FBP-1 and FBP-2) in >70% of all analyzed human HCCs significantly correlated with poor patient survival. In vitro, FBP-1 predominantly induced tumor cell proliferation, while FBP-2 primarily supported migration in different HCC cell lines. Surprisingly, reduction of FBP-2 levels was associated with elevated FBP-1 expression, suggesting a regulatory interplay of FBP family members that functionally discriminate between cell division and mobility. Expression of FBP-1 correlated with stathmin expression in HCC tissues and inhibition of FBP-1 but not of FBP-2 drastically reduced stathmin at the transcript and protein levels. In contrast, further overexpression of FBP-1 did not affect stathmin bioavailability. Accordingly, analyzing nuclear and cytoplasmic areas of HCC cells revealed that reduced FBP-1 levels affected cell morphology and were associated with a less malignant phenotype.

CONCLUSION

The coordinated activation of FBP-1 and FBP-2 represents a novel and frequent pro-tumorigenic mechanism promoting proliferation (tumor growth) and motility (dissemination) of human liver cancer cells. FBPs promote tumor-relevant functions by at least partly employing the microtubule-destabilizing factor stathmin and represent a new potential target structure for HCC treatment.

The expanding universe of p53 targets

The p53 tumour suppressor is modified through mutation or changes in expression in most cancers, leading to the altered regulation of hundreds of genes that are directly influenced by this sequence-specific transcription factor. Central to the p53 master regulatory network are the target response element (RE) sequences. The extent of p53 transactivation and transcriptional repression is influenced by many factors, including p53 levels, cofactors and the specific RE sequences, all of which contribute to the role that p53 has in the aetiology of cancer. This Review describes the identification and functionality of REs and highlights the inclusion of non-canonical REs that expand the universe of genes and regulation mechanisms in the p53 tumour suppressor network.

Hedgehog signaling regulates proliferation of prostate cancer cells via stathmin1

Hedgehog (Hh) signaling is an essential pathway in embryonic development of prostate. Hh also plays roles in the proliferation of progenitor cells and cancer cells of adult prostate. However, how Hh signaling contributes to carcinogenesis of prostate is poorly understood. Stathmin1 is a microtubule-regulating protein that plays an important role in the assembly and disassembly of the mitotic spindle. Stathmin1 is expressed in normal developing mouse prostate and in prostate cancer. The expression pattern of stathmin1 is similar to that of Shh in prostate development and cancer, suggesting a connection between these two proteins. In this study, we examined the relationship between stathmin1 and Hh signaling. Here, we show that stathmin1 expression is regulated by Hh signaling in prostate cancer cells. Cyclopamine, a specific inhibitor of Hh signaling, reduced the expression of stathmin1 in prostate cancer cells. However, the Shh peptide induced stathmin1 expression. Overexpression of Gli1 further confirmed the relationship. Co-expression of stathmin1 and Patched 1, a receptor for Hh signaling was observed in prostate cancer tissues. Cyclopamine and stathmin1 siRNA both decreased proliferation of prostate cancer cells but did not produce an additive effect, suggesting a common pathway. These results suggest that Hh signaling regulates proliferation of prostate cancer cells by controlling stathmin1 expression.

A cohort study of STMN1 expression in colorectal cancer: body mass index and prognosis

OBJECTIVES

STMN1 (stathmin or oncoprotein-18) destabilizes microtubules and reorganizes cytoskeleton, and functions in cell cycle progression and cell migration. STMN1 activity is influenced by p53, p27, and the PI3K/AKT pathway. However, its prognostic significance in colon cancer is uncertain.

METHODS

Utilizing 546 colorectal cancers (stage I-IV) from two independent prospective cohort studies (the Nurses' Health Study and Health Professionals Follow-up Study), STMN1 expression was detected in 297 (54%) tumors by immunohistochemistry. Cox proportional hazard models computed hazard ratios (HRs) of mortality, adjusted for clinical and tumoral features, including microsatellite instability (MSI), CpG island methylation phenotype (CIMP), LINE-1 hypomethylation, KRAS, BRAF, PIK3CA, p53, p21, p27, cyclin D1, beta-catenin, fatty acid synthase, FASN, and COX-2.

RESULTS

Five-year colorectal cancer-specific survival was 78% in STMN1-positive patients and 76% in STMN1-negative patients (log-rank P=0.30). STMN1-positivity was not significantly associated with cancer-specific survival in univariate analysis with HR of 0.82 (95% confidence interval (CI), 0.59-1.14), which became significant in multivariate analysis (adjusted HR=0.60; 95% CI, 0.41-0.87; P=0.0078). Notably, the prognostic effect of obesity (body mass index, BMI> or =30 kg/m2) significantly differed by STMN1 (P(interaction)=0.005). Obesity was associated with high cancer-specific mortality among STMN1-positive patients (adjusted HR=2.36; 95% CI, 1.18-4.69), whereas obesity was not associated with high mortality among STMN1-negative patients (adjusted HR=0.51; 95% CI, 0.24-1.07).

CONCLUSIONS

STMN1 overexpression in colorectal cancer is independently associated with improved survival. The adverse prognostic effect of obesity was limited to patients with STMN1-positive tumors. Our findings suggest the presence of a tumor (STMN1)-host (BMI) interaction that potentially determines clinical outcome.

Hedgehog signaling regulates the survival of gastric cancer cells by regulating the expression of Bcl-2

Gastric cancer is the second most common cause of cancer deaths worldwide. The underlying molecular mechanisms of its carcinogenesis are relatively poorly characterized. Hedgehog (Hh) signaling, which is critical for development of various organs including the gastrointestinal tract, has been associated with gastric cancer. The present study was undertaken to reveal the underlying mechanism by which Hh signaling controls gastric cancer cell proliferation. Treatment of gastric cancer cells with cyclopamine, a specific inhibitor of Hh signaling pathway, reduced proliferation and induced apoptosis of gastric cancer cells. Cyclopamine treatment induced cytochrome c release from mitochondria and cleavage of caspase 9. Moreover, Bcl-2 expression was significantly reduced by cyclopamine treatment. These results suggest that Hh signaling regulates the survival of gastric cancer cells by regulating the expression of Bcl-2.