Proteasomal degradation of human peptidyl prolyl isomerase pin1-pointing phospho Bcl2 toward dephosphorylation

Pin1-catalyzed conformational regulation after phosphorylation: A distinct checkpoint in cell signaling and drug discovery

Protein phosphorylation is one of the most common mechanisms regulating cellular signaling pathways, and many kinases and phosphatases are proven drug targets. Upon phosphorylation, protein functions can be further regulated by the distinct isomerase Pin1 through cis-trans isomerization. Numerous protein targets and many important roles have now been elucidated for Pin1. However, no tools are available to detect or target cis and trans conformation events in cells. The development of Pin1 inhibitors and stereo- and phospho-specific antibodies has revealed that cis and trans conformations have distinct and often opposing cellular functions. Aberrant conformational changes due to the dysregulation of Pin1 can drive pathogenesis but can be effectively targeted in age-related diseases, including cancers and neurodegenerative disorders. Here, we review advances in understanding the roles of Pin1 signaling in health and disease and highlight conformational regulation as a distinct signal transduction checkpoint in disease development and treatment.

Pin1-Catalyzed Conformation Changes Regulate Protein Ubiquitination and Degradation

The unique prolyl isomerase Pin1 binds to and catalyzes cis-trans conformational changes of specific Ser/Thr-Pro motifs after phosphorylation, thereby playing a pivotal role in regulating the structure and function of its protein substrates. In particular, Pin1 activity regulates the affinity of a substrate for E3 ubiquitin ligases, thereby modulating the turnover of a subset of proteins and coordinating their activities after phosphorylation in both physiological and disease states. In this review, we highlight recent advancements in Pin1-regulated ubiquitination in the context of cancer and neurodegenerative disease. Specifically, Pin1 promotes cancer progression by increasing the stabilities of numerous oncoproteins and decreasing the stabilities of many tumor suppressors. Meanwhile, Pin1 plays a critical role in different neurodegenerative disorders via the regulation of protein turnover. Finally, we propose a novel therapeutic approach wherein the ubiquitin-proteasome system can be leveraged for therapy by targeting pathogenic intracellular targets for TRIM21-dependent degradation using stereospecific antibodies.

BCL-XL regulates the timing of mitotic apoptosis independently of BCL2 and MCL1 compensation

Mitotic catastrophe induced by prolonged mitotic arrest is a major anticancer strategy. Although antiapoptotic BCL2-like proteins, including BCL-XL, are known to regulate apoptosis during mitotic arrest, adaptive changes in their expression can complicate loss-of-function studies. Our studies revealed compensatory alterations in the expression of BCL2 and MCL1 when BCL-XL is either downregulated or overexpressed. To circumvent their reciprocal regulation, we utilized a degron-mediated system to acutely silence BCL-XL just before mitosis. Our results show that in epithelial cell lines including HeLa and RPE1, BCL-XL and BCL2 acted collaboratively to suppress apoptosis during both unperturbed cell cycle and mitotic arrest. By tagging BCL-XL and BCL2 with a common epitope, we estimated that BCL-XL was less abundant than BCL2 in the cell. Nonetheless, BCL-XL played a more prominent antiapoptotic function than BCL2 during interphase and mitotic arrest. Loss of BCL-XL led to mitotic cell death primarily through a BAX-dependent process. Furthermore, silencing of BCL-XL led to the stabilization of MCL1, which played a significant role in buffering apoptosis during mitotic arrest. Nevertheless, even in a MCL1-deficient background, depletion of BCL-XL accelerated mitotic apoptosis. These findings underscore the pivotal involvement of BCL-XL in controlling timely apoptosis during mitotic arrest, despite adaptive changes in the expression of other BCL2-like proteins.

Spastin Promotes the Migration and Invasion Capability of T98G Glioblastoma Cells by Interacting with Pin1 through Its Microtubule-Binding Domain

Microtubule-severing protein Spastin has been shown to co-localize with actin in migratory glioblastoma cells and is linked to glioblastomas' migration and invasion capacity. However, the effectiveness of Spastin in glioblastoma migration and the molecular mechanism underpinning the orientation of Spastin towards actin filaments remain unknown. Here, we demonstrated that Spastin plays an active role in glioblastoma migration by showing a reduced migratory potential of T98G glioblastoma cells using real-time cell analysis (RTCA) in Spastin-depleted cells. Pull-down assays revealed that a cis-trans isomerase Pin1 interacts with Spastin through binding to the phosphorylated Pin1 recognition motifs in the microtubule-binding domain (MBD), and immunocytochemistry analysis showed that interaction with Pin1 directs Spastin to actin filaments in extended cell regions. Consequently, by utilizing RTCA, we proved that the migration and invasion capacity of T98G glioblastoma cells significantly increased with the overexpression of Spastin, of which the Pin1 recognition motifs in MBD are constitutively phosphorylated, while the overexpression of phospho-mutant form did not have a significant effect on migration and invasion of T98G glioblastoma cells. These findings demonstrate that Pin1 is a novel interaction partner of Spastin, and their interaction drives Spastin to actin filaments, allowing Spastin to contribute to the glioblastomas' migration and invasion abilities.

Phosphorylation and Stabilization of PIN1 by JNK Promote Intrahepatic Cholangiocarcinoma Growth

BACKGROUND AND AIMS

Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive type of liver cancer in urgent need of treatment options. Aberrant activation of the c-Jun N-terminal kinase (JNK) pathway is a key feature in ICC and an attractive candidate target for its treatment. However, the mechanisms by which constitutive JNK activation promotes ICC growth, and therefore the key downstream effectors of this pathway, remain unknown for their applicability as therapeutic targets. Our aim was to obtain a better mechanistic understanding of the role of JNK signaling in ICC that could open up therapeutic opportunities.

APPROACH AND RESULTS

Using loss-of-function and gain-of-function studies in vitro and in vivo, we show that activation of the JNK pathway promotes ICC cell proliferation by affecting the protein stability of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1), a key driver of tumorigenesis. PIN1 is highly expressed in ICC primary tumors, and its expression positively correlates with active JNK. Mechanistically, the JNK kinases directly bind to and phosphorylate PIN1 at Ser115, and this phosphorylation prevents PIN1 mono-ubiquitination at Lys117 and its proteasomal degradation. Moreover, pharmacological inhibition of PIN1 through all-trans retinoic acid, a Food and Drug Administration-approved drug, impairs the growth of both cultured and xenografted ICC cells.

CONCLUSIONS

Our findings implicate the JNK-PIN1 regulatory axis as a functionally important determinant for ICC growth, and provide a rationale for therapeutic targeting of JNK activation through PIN1 inhibition.

A multi-scale systems pharmacology approach uncovers the anti-cancer molecular mechanism of Ixabepilone

It has been realized that FDA approved drugs may have more molecular targets than is commonly thought. Thus, to find the exact drug-target interactions (DTIs) is of great significance for exploring the new molecular mechanism of drugs. Here, we developed a multi-scale system pharmacology (MSSP) method for the large-scale prediction of DTIs. We used MSSP to integrate drug-related and target-related data from multiple levels, the network structural data formed by known drug-target relationships for predicting likely unknown DTIs. Prediction results revealed that Ixabepilone, an epothilone B analog for treating breast cancer patients, may target Bcl-2, an oncogene that contributes to tumor progression and therapy resistance by inhibiting apoptosis. Furthermore, we demonstrated that Ixabepilone could bind with Bcl-2 and decrease its protein expression in breast cancer cells. The down-regulation of Bcl-2 by Ixabepilone is resulted from promoting its degradation by affecting p-Bcl-2. We further found that Ixabepilone could induce autophagy by releasing Beclin1 from Beclin1/Bcl-2 complex. Inhibition of autophagy by knockdown of Beclin1 or pharmacological inhibitor augmented apoptosis, thus enhancing the antitumor efficacy of Ixabepilone against breast cancer cells in vitro and in vivo. In addition, Ixabepilone also decreases Bcl-2 protein expression and induces cytoprotective autophagy in human hepatic carcinoma and glioma cells. In conclusion, this study not only provides a feasible and alternative way exploring new molecular mechanisms of drugs by combing computation DTI prediction, but also reveals an effective strategy to reinforce the antitumor efficacy of Ixabepilone.

Degradation of GRK2 and AKT is an early and detrimental event in myocardial ischemia/reperfusion

BACKGROUND

Identification of signaling pathways altered at early stages after cardiac ischemia/reperfusion (I/R) is crucial to develop timely therapies aimed at reducing I/R injury. The expression of G protein-coupled receptor kinase 2 (GRK2), a key signaling hub, is up-regulated in the long-term in patients and in experimental models of heart failure. However, whether GRK2 levels change at early time points following myocardial I/R and its functional impact during this period remain to be established.

METHODS

We have investigated the temporal changes of GRK2 expression and their potential relationships with the cardioprotective AKT pathway in isolated rat hearts and porcine preclinical models of I/R.

FINDINGS

Contrary to the maladaptive up-regulation of GRK2 reported at later times after myocardial infarction, successive GRK2 phosphorylation at specific sites during ischemia and early reperfusion elicits GRK2 degradation by the proteasome and calpains, respectively, thus keeping GRK2 levels low during early I/R in rat hearts. Concurrently, I/R promotes decay of the prolyl-isomerase Pin1, a positive regulator of AKT stability, and a marked loss of total AKT protein, resulting in an overall decreased activity of this pro-survival pathway. A similar pattern of concomitant down-modulation of GRK2/AKT/Pin1 protein levels in early I/R was observed in pig hearts. Calpain and proteasome inhibition prevents GRK2/Pin1/AKT degradation, restores bulk AKT pathway activity and attenuates myocardial I/R injury in isolated rat hearts.

INTERPRETATION

Preventing transient degradation of GRK2 and AKT during early I/R might improve the potential of endogenous cardioprotection mechanisms and of conditioning strategies.

The protein level and transcription activity of activating transcription factor 1 is regulated by prolyl isomerase Pin1 in nasopharyngeal carcinoma progression

The function of activating transcription factor 1 (ATF1) and the mechanism about why ATF1 was over-phosphorylated in nasopharyngeal carcinoma (NPC) progression is completely undiscovered. In this study, a series of experiments both in vitro and in vivo were used to characterize a promotive function of ATF1 in NPC tumorigenesis and identify prolyl isomerase Pin1 as a novel regulator of ATF1 at post-transcription. First, we found that overexpression of ATF1 promoted colony formation in NPC. However, the high protein level of ATF1 in NPC was not resulted from high mRNA level. Then, a direct interaction between Pin1 and ATF1 at Thr184 was demonstrated using mammalian two-hybrid assay and coimmunoprecipitation. Cycloheximide (CHX) treatment indicated Pin1 stabilized the expression of ATF1 at post-transcription level. We confirmed that Pin1 upregulated ATF1 transcriptional activity of Bcl-2 using luciferase reporter assay, quantitative RT-PCR and western blot. Furthermore, the newly identified phosphorylation of ATF1 at Thr184 was suggested to have an important role in ATF1 function of transcription and tumor promotion. Finally, high expression of Pin1 in NPC tissue was found to be positively correlated with ATF1. The ATF1 promoted NPC tumorigenesis was regulated by Pin1 both in vitro and in vivo. All these findings clearly state that Pin1 is a novel regulator of ATF1 at Thr184 and thereby enhances ATF1 transcription activity and tumorigenesis promotive function in NPC.

Overexpression of PIN1 Enhances Cancer Growth and Aggressiveness with Cyclin D1 Induction in EBV-Associated Nasopharyngeal Carcinoma

Background

Nasopharyngeal carcinoma (NPC) is a peculiar Epstein Barr virus (EBV)-associated malignancy that is prevalent in South-East Asia. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) isomerizes specific phosphorylated amino acid residues, which makes it an important regulator in cell survival and apoptosis. In this study, we investigated the contribution made by PIN1 in NPC tumorigenesis and PIN1’s potential role as a therapeutic target.

Methods

The expression of PIN1 was examined in a panel of NPC cell lines, xenografts and primary tumors. The functional roles of PIN1 in NPC cells were elucidated by the knockdown and overexpression of PIN1 in in vitro and in vivo nude mice models by siRNA and lenti-viral transfection, respectively. The antitumor effects of the PIN1 inhibitor Juglone in NPC cells were also evaluated.

Results

We revealed the consistent overexpression of PIN1 in almost all EBV-associated NPC cell lines, xenografts and primary tumors. PIN1 suppression was capable of inhibiting cyclin D1 expression and activating caspase-3 in NPC cells. It positively regulated NPC cell proliferation, colony formation and anchorage-independent growth. The inhibition of PIN1 suppressed tumor growth in vitro and in vivo.

Conclusions

This study demonstrates the oncogenic role of PIN1 in NPC tumorigenesis, and shows that its overexpression can enhance tumor cell growth via the upregulation of cyclinD1. Our findings inform the development of novel treatments targeting PIN1 for NPC patients.

Bcl-2 phosphorylation confers resistance on chronic lymphocytic leukaemia cells to the BH3 mimetics ABT-737, ABT-263 and ABT-199 by impeding direct binding

BACKGROUND AND PURPOSE

Although the ongoing clinical trials of ABT-263 and ABT-199 in chronic lymphocytic leukaemia (CLL) have indicated that BH3 mimetics hold considerable promise, understanding the mechanism of CLL resistance to BH3 mimetics remains a challenge.

EXPERIMENTAL APPROACH

The LD50 values of ABT-737, ABT-263 and ABT-199 in a number of primary CLL cells from 40 patients, were determined. The levels of Bcl-2 family proteins, including phosphorylated Bcl-2 (pBcl-2) and their interactions were measured by immunoblotting and co-immunoprecipitation. In vitro binding assays were performed by isothermal titration calorimetry and ELISA. BH3 profiling in isolated mitochondria was analysed.

KEY RESULTS

The ratio of (Mcl-1 + pBcl-2) to Bcl-2 expression provided the most significant predictive marker for the cytotoxic potential of ABT-737, ABT-263 and ABT-199 in the panel of CLL samples. Mechanistically, pBcl-2 inhibited the effects of the ABT compounds on the displacement of Bax and Bim from Bcl-2, thereby suppressing mitochondrial apoptosis. The ABT compounds exhibited 100-300-fold lower binding affinity to the glutamic acid, phosphomimetic, mutant of Bcl-2 (T69E, S70E and S87E; EEE-Bcl-2). BH3 peptides exhibited different rank orders of binding affinities to full-length WT-Bcl-2 and full-length EEE-Bcl-2.

CONCLUSIONS AND IMPLICATIONS

Our study suggested that a structural alteration in the BH3-binding groove was induced by phosphorylation of Bcl-2. Our data also provided a framework to overcome resistance of CLL cells to the ABT compounds by combining pBcl-2 kinase inhibitors with the ABT compounds.

Determinants of eosinophil survival and apoptotic cell death

Eosinophils (Eos) are potent inflammatory cells and abundantly present in the sputum and lung of patients with allergic asthma. During both transit to and residence in the lung, Eos contact prosurvival cytokines, particularly IL-3, IL-5 and GM-CSF, that attenuate cell death. Cytokine signaling modulates the expression and function of a number of intracellular pro- and anti-apoptotic molecules. Both intrinsic mitochondrial and extrinsic receptor-mediated pathways are affected. This article discusses the fundamental role of the extracellular and intracellular molecules that initiate and control survival decisions by human Eos and highlights the role of the cis-trans isomerase, Pin1 in controlling these processes.

Pin1-based diagnostic and therapeutic strategies for breast cancer

Pin1 is the only known cis-to-trans isomerase that recognizes the phosphorylated pThr/pSer-Pro motifs in many signaling molecules, playing unique roles in the pathogenesis of breast cancer. First, Pin1 is prevalently over-expressed in kinds of breast cancer cell lines and tissues, such as MDA-MB-231 cell, MCF-7 cell, Her2+, ERα+, and basal-like breast cancer subtypes. Second, Pin1 amplifies many oncogenic signaling pathways, inhibits multiple tumor suppressors, promotes the angiogenesis and metastasis of breast cancer cells, and enhances the resistance of breast cancer cells to anti-tumor medicines. Third, inhibiting Pin1 blocks most of these detrimental effects in a great number of breast cancer cell lines. These findings suggest Pin1 as a promising diagnostic biomarker as well as an efficient therapeutic target for breast cancer. It is strongly expected that a Pin1-positive subtype of breast cancers should be extremely concerned and that the therapeutic efficacy of Pin1 inhibitors on breast cancer patients should be evaluated as soon as possible. Nonetheless, Pin1-based therapeutic strategies for breast cancer still deserve some debates. Hence, we give the predictions of several important issues, such as application precondition, side effects, and personalized medication, when Pin1 inhibitors are used in the breast cancer therapy. These proposals are meaningful for the further development of Pin1-based diagnostic and therapeutic strategies in order to conquer breast cancer.

Prolyl isomerase Pin1 in cancer

Proline-directed phosphorylation is a posttranslational modification that is instrumental in regulating signaling from the plasma membrane to the nucleus, and its dysregulation contributes to cancer development. Protein interacting with never in mitosis A1 (Pin1), which is overexpressed in many types of cancer, isomerizes specific phosphorylated Ser/Thr-Pro bonds in many substrate proteins, including glycolytic enzyme, protein kinases, protein phosphatases, methyltransferase, lipid kinase, ubiquitin E3 ligase, DNA endonuclease, RNA polymerase, and transcription activators and regulators. This Pin1-mediated isomerization alters the structures and activities of these proteins, thereby regulating cell metabolism, cell mobility, cell cycle progression, cell proliferation, cell survival, apoptosis and tumor development.

Destabilization of KLF10, a tumor suppressor, relies on thr93 phosphorylation and isomerase association

KLF10 is now classified as a member of the Krüppel-like transcription factor family and acts as a tumor suppressor. Although KLF10 is originally named as TGF-β-inducible early gene-1 and mimicking the anti-proliferative effect of TGF-β in various carcinoma cells, the transcriptional upregulatory function of KLF10 has been described for a variety of cytokines and in many diseases. Through in vivo and in vitro phosphorylation assays, we identified that KLF10 is a phosphorylated protein in cells. Using yeast-two hybrid screening and site direct mutagenesis, we also identified PIN1 as a novel KLF10 associated protein. PIN1 is a peptidyl-prolyl isomerase enzyme belonging to the parvulin family, which specifically recognizes phosphorylated Ser/Thr-Pro containing substrates. Through protein-protein interaction assays, we showed that the Pro-directed Ser/Thr-Pro motif at Thr-93 in the KLF10 N-terminal region is essential for the interaction between KLF10 and PIN1. More importantly, PIN1 interacts with KLF10 in a phosphorylation-dependent manner and this interaction promotes KLF10 protein degradation in cells. Therefore, KLF10 shows shorter protein stability compared with mutant KLF10 that lacks PIN1 binding ability after cycloheximide treatments. The reversely correlated expression profile between KLF10 and PIN1 as observed in cell lines was also shown in clinic pancreatic cancer specimen. Using in vitro kinase assays and depletion assays, we were able to show that RAF-1 phosphorylates the Thr-93 of KLF10 and affects the KLF10 expression level in cells. Thus these findings as a whole indicate that RAF-1 phosphorylation and PIN1 isomerization together regulate KLF10 stability and further affect the role of KLF10 in tumor progression.

The prolyl-isomerase Pin1 activates the mitochondrial death program of p53

In response to intense stress, the tumor protein p53 (p53) tumor suppressor rapidly mounts a direct mitochondrial death program that precedes transcription-mediated apoptosis. By eliminating severely damaged cells, this pathway contributes to tumor suppression as well as to cancer cell killing induced by both genotoxic drugs and non-genotoxic p53-reactivating molecules. Here we have explored the role had in this pathway by the prolyl-isomerase Pin1 (peptidylprolyl cis/trans isomerase, NIMA-interacting 1), a crucial transducer of p53's phosphorylation into conformational changes unleashing its pro-apoptotic activity. We show that Pin1 promotes stress-induced localization of p53 to mitochondria both in vitro and in vivo. In particular, we demonstrate that upon stress-induced phosphorylation of p53 on Ser46 by homeodomain interacting protein kinase 2, Pin1 stimulates its mitochondrial trafficking signal, that is, monoubiquitination. This pathway is induced also by the p53-activating molecule RITA, and we demonstrate the strong requirement of Pin1 for the induction of mitochondrial apoptosis by this compound. These findings have significant implications for treatment of p53-expressing tumors and for prospective use of p53-activating compounds in clinics.

Prolyl isomerase Pin1 as a molecular switch to determine the fate of phosphoproteins

Pin1 is a highly conserved enzyme that only isomerizes specific phosphorylated Ser/Thr-Pro bonds in certain proteins, thereby inducing conformational changes. Such conformational changes represent a novel and tightly controlled signaling mechanism regulating a spectrum of protein activities in physiology and disease; often through phosphorylation-dependent, ubiquitin-mediated proteasomal degradation. In this review, we summarize recent advances in elucidating the role and regulation of Pin1 in controlling protein stability. We also propose a mechanism by which Pin1 functions as a molecular switch to control the fates of phosphoproteins. We finally stress the need to develop tools to visualize directly Pin1-catalyzed protein conformational changes as a way to determine their roles in the development and treatment of human diseases.

Peptidyl-prolyl cis–trans isomerase Pin1 in ageing, cancer and Alzheimer disease

Phosphorylation of proteins on serine or threonine residues preceding proline is a key signalling mechanism in diverse physiological and pathological processes. Pin1 (peptidyl-prolyl cis–trans isomerase) is the only enzyme known that can isomerise specific Ser/Thr-Pro peptide bonds after phosphorylation and regulate their conformational changes with high efficiency. These Pin1-catalysed conformational changes can have profound effects on phosphorylation signalling by regulating a spectrum of target activities. Interestingly, Pin1 deregulation is implicated in a number of diseases, notably ageing and age-related diseases, including cancer and Alzheimer disease. Pin1 is overexpressed in most human cancers; it activates numerous oncogenes or growth enhancers and also inactivates a large number of tumour suppressors or growth inhibitors. By contrast, ablation of Pin1 prevents cancer, but eventually leads to premature ageing and neurodegeneration. Consistent with its neuroprotective role, Pin1 has been shown to be inactivated in neurons of patients with Alzheimer disease. Therefore, Pin1-mediated phosphorylation-dependent prolyl isomerisation represents a unique signalling mechanism that has a pivotal role in the development of human diseases, and might offer an attractive new diagnostic and therapeutic target.

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.

PIN1, the cell cycle and cancer

PIN1 is a peptidyl-prolyl isomerase that can alter the conformation of phosphoproteins and so affect protein function and/or stability. PIN1 regulates a number of proteins important for cell-cycle progression and, based on gain- and loss-of-function studies, is presumed to operate as a molecular timer of this important process. Therefore, it seems logical that alterations in the level of PIN1 can influence hyperproliferative diseases such as cancer. However, the precise role of PIN1 in cancer remains controversial.

Overexpression of Pin1 in non-small cell lung cancer (NSCLC) and its correlation with lymph node metastases

BACKGROUND

Pin1 isomerizes the bonds of molecules important for numerous oncogenic and cell-signaling pathways, including Bcl-2, p53, c-Jun, beta-catenin, NF-kappaB, cyclin D1, c-Myc and Raf-1. This can cause a change in conformation leading to alterations in catalytic activity, protein-protein interactions, subcellular localization and protein stability. These alterations have been shown to be associated with cell transformation and cancer progression. Pin1 is overexpressed in several different human cancers. This is the first report of Pin1 overexpression in clinical samples of non-small cell lung cancer (NSCLC).

METHODS

Protein expression levels of Pin1 in tumor and normal lung specimens were analyzed for expression of Pin1, cyclin D1, p53 and MDM2 using immunohistochemistry and compared to several clinicopathological characteristics. The mRNA expression of Pin1 was also analyzed using quantitative real-time RT-PCR and compared to clinicopathological characteristics.

RESULTS

Pin1 protein was shown to be overexpressed in NSCLC tumor samples, and correlated with lymph node positive disease and tumor stage. High expression of MDM2 also correlated with lymph node positive disease and with poorly differentiated tumors. High expression of MDM2 also correlated with lymph node positive disease and with poorly differentiated tumors. High expression levels of Pin1 correlated with high levels of p53 or MDM2 protein, but did not show a correlation with cyclin D1. However, high levels of MDM2 correlated with cyclin D1 overexpression. Pin1 mRNA was expressed significantly more often in the tumors of smokers than of non-smokers. The relationship between the expression of protein and mRNA of Pin1 has obviously showed that protein expression isn't significantly associated with mRNA expression.

CONCLUSIONS

Pin1 is overexpressed in many different cancers, including NSCLC, and may possibly be used as a tumor marker or as a target for cancer therapy.

Crosstalk between extrinsic and intrinsic cell death pathways in pancreatic cancer: synergistic action of estrogen metabolite and ligands of death receptor family

2-Methoxyestradiol is a physiologic metabolite of 17beta-estradiol. This orally active compound can inhibit tumor growth or metastasis in tumor models without inducing any clinical sign of toxicity. Our previous studies indicated that 2-methoxyestradiol-mediated apoptosis involves the disappearance of intact 21-kDa Bid protein, cytochrome c release, and predominant procaspase-3 cleavage. Here, using MIA PaCa-2 cells as a model, we investigated whether this estrogen metabolite induces apoptosis by converging two major pathways: the death receptor-mediated extrinsic and the mitochondrial intrinsic pathway. Exogenous expression of dominant-negative caspase-8 or dominant-negative FADD reverts the effect of 2-methoxyestradiol-mediated cell death. In parallel with this observation, Z-IETD-FMK, a cell permeable irreversible inhibitor of caspase-8, can render significant protection against 2-methoxyestradiol-induced apoptosis. RNase protection assay and cell surface receptor analysis by flow cytometry show the up-regulation of members of death receptor family in 2-methoxyestradiol-exposed pancreatic cancer cells. Our mechanistic studies also implicate that oxidative stress precedes 2-methoxyestradiol-mediated c-Jun NH2-terminal kinase activation, leading to elevated Fas level. Because 2-methoxyestradiol is able to trigger death receptor signaling, we were interested in examining the effects of 2-methoxyestradiol and Fas ligand (FasL)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) together on pancreatic cancer cell death. Interestingly, the endogenous angiogenesis inhibitor 2-methoxyestradiol augments FasL/TRAIL-induced apoptosis in these cells. Moreover, the combination of 2-methoxyestradiol and TRAIL reduces the tumor burden in vivo in MIA PaCa-2 tumor xenograft model by caspase-3 activation.

The peptidyl-prolyl isomerase Pin1 regulates the stability of granulocyte-macrophage colony-stimulating factor mRNA in activated eosinophils

The infiltration, accumulation and degranulation of eosinophils in the lung represents a hallmark of active asthma. In vivo or in vitro eosinophil activation triggers the secretion of the antiapoptotic cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). We now identify Pin1, a cis-trans isomerase, as an essential component of the ribonucleoprotein complex responsible for GM-CSF mRNA stabilization, cytokine secretion and the survival of activated eosinophils. Pin1 regulated the association of the AU-rich element-binding proteins AUF1 and hnRNP C with GM-CSF mRNA, accelerating or slowing decay, respectively. These data indicate Pin1 is a key mediator of GM-CSF production.

Gene expression profiling of dysplastic differentiation in cervical epithelial cells harboring human papillomavirus 16

Molecular events occurring with high-risk human papillomavirus (HPV)-associated dysplastic differentiation of cervical epithelial cells are largely unknown. This study used differential display PCR to identify expression changes between nondifferentiating monolayer and differentiated organotypic (raft) cultures of W12 keratinocytes. These cells were originally derived from a clinical biopsy of HPV 16-positive dysplastic cervical epithelium and retain high-risk HPV 16 and the ability to differentiate, albeit with dysplastic morphology. Using this model system we identified 84 genes with changed expression during dysplastic differentiation. Most (70/84, approximately 80%) were down-regulated with differentiation, consistent with a restriction of expression during terminal differentiation. Twenty-two genes had no known function and 6 novel expressed sequence tags were identified among this group. Of the 62 genes with known functions, 25 belonged to transcription-, translation-, and posttranslation-related categories and 30 had functions associated with neoplastic initiation/progression, calcium signaling, epithelial differentiation, and structure remodeling. Some of the genes with altered expression identified in this model of dysplastic differentiation may be useful biomarkers for early detection of cervical neoplasia and other HPV-associated oropharyngeal and anogenital cancers.

Epigallocatechin-3-gallate induces mitochondrial membrane depolarization and caspase-dependent apoptosis in pancreatic cancer cells

Polyphenols such as epigallocatechin-3-gallate (EGCG) from green tea extract can exert a growth-suppressive effect on human pancreatic cancer cells in vitro. In pursuit of our investigations to dissect the molecular mechanism of EGCG action on pancreatic cancer, we observed that the antiproliferative action of EGCG on pancreatic carcinoma is mediated through programmed cell death or apoptosis as evident from nuclear condensation, caspase-3 activation and poly-ADP ribose polymerase (PARP) cleavage. EGCG-induced apoptosis of pancreatic cancer cells is accompanied by growth arrest at an earlier phase of the cell cycle. In addition, EGCG invokes Bax oligomerization and depolarization of mitochondrial membranes to facilitate cytochrome c release into cytosol. EGCG-induced downregulation of IAP family member X chromosome linked inhibitor of apoptosis protein (XIAP) might be helpful to facilitate cytochrome c mediated downstream caspase activation. On the other end, EGCG elicited the production of intracellular reactive oxygen species (ROS), as well as the c-Jun N-terminal kinase (JNK) activation in pancreatic carcinoma cells. Interestingly, inhibitor of JNK signaling pathway as well as antioxidant N-acetyl-L-cysteine (NAC) blocked EGCG-induced apoptosis. To summarize, our studies suggest that EGCG induces stress signals by damaging mitochondria and ROS-mediated JNK activation in MIA PaCa-2 pancreatic carcinoma cells.

Prevalent overexpression of prolyl isomerase Pin1 in human cancers

Phosphorylation of proteins on serine or threonine residues preceding proline (pSer/Thr-Pro) is a major regulatory mechanism in cell proliferation and transformation. Interestingly, the pSer/Thr-Pro motifs in proteins exist in two distinct cis and trans conformations, whose conversion rate is normally reduced on phosphorylation, but is catalyzed specifically by the prolyl isomerase Pin1. Pin1 can catalytically induce conformational changes in proteins after phosphorylation, thereby having profound effects on catalytic activity, dephosphorylation, protein-protein interactions, subcellular location, and/or turnover of certain phosphorylated proteins. Recently, it has been shown that Pin1 is overexpressed in human breast cancer cell lines and cancer tissues and plays a critical role in the transformation of mammary epithelial cells by activating multiple oncogenic pathways. Furthermore, Pin1 expression is an excellent independent prognostic marker in prostate cancer. However, little is known about Pin1 expression in other human normal and cancerous tissues. In the present study, we quantified Pin1 expression in 2041 human tumor samples and 609 normal tissue samples as well as normal and transformed human cell lines. We found that Pin1 was usually expressed at very low levels in most normal tissues and its expression was normally associated with cell proliferation, with high Pin1 levels being found only in a few cell types. However, Pin1 was strikingly overexpressed in many different human cancers. Most tumors (38 of 60 tumor types) have Pin1 overexpression in more than 10% of the cases, as compared with the corresponding normal controls, which included prostate, lung, ovary, cervical, brain tumors, and melanoma. Consistent with these findings, Pin1 expression in human cancer cell lines was also higher than that in the normal cell lines examined. These results indicate that Pin1 overexpression is a prevalent and specific event in human cancers. Given previous findings that Pin1 expression is an excellent prognostic marker in prostate cancer and that inhibition of Pin1 can suppress transformed phenotypes and inhibit tumor cell growth, these findings may have important implications for the pathogenesis, diagnosis, and treatment of human cancers.

Pinning down cell signaling, cancer and Alzheimer's disease

Protein phosphorylation on certain serine or threonine residues preceding proline (Ser/Thr-Pro) is a pivitol signaling mechanism in diverse cellular processes and its deregulation can lead to human disease. However, little is known about how these phosphorylation events actually control cell signaling. Pin1 is a highly conserved enzyme that isomerizes only the phosphorylated Ser/Thr-Pro bonds in certain proteins, thereby inducing conformational changes. Recent results indicate that such conformational changes following phosphorylation are a novel signaling mechanism pivotal in regulating many cellular functions. This mechanism also offers new insights into the pathogenesis and treatment of human disease, most notably cancer and Alzheimer's disease. Thus, Pin1 plays a key role in linking signal transduction to the pathogenesis of cancer and Alzheimer's disease - two major age-related diseases.

Restoration of silenced Peutz-Jeghers syndrome gene, LKB1, induces apoptosis in pancreatic carcinoma cells

Germ line mutations of the LKB1 tumor suppressor gene lead to Peutz-Jeghers syndrome (PJS) with a predisposition to cancer. Previous reports suggest that inactivation of this tumor-suppressor gene plays a role in the pathogenesis of gastrointestinal hamartomas as well as several cancers, including adenocarcinoma of the pancreas. Here, we have shown that LKB1 gene is silenced in the pancreatic cancer cell line AsPC-1, but can be recovered by treatment with the methylation inhibitor, 5-aza-2'-deoxycytidine (5aza2dC). Restoring the level of LKB1 through gene transfer initiated mitochondria-mediated apoptosis in AsPC-1 cells, as evidenced by the release of cytochrome c from the mitochondria. By confocal microscopy as well as biochemical fractionation, we demonstrate that LKB1 is present in the nuclear and mitochondrial compartments of pancreatic cancer cells. Our observations also indicate that although functional p53 is absent, the p53 kin, p73, is inducible by doxorubicin in AsPC-1 cells. This suggests that LKB1-induced apoptosis is p53 independent but might be p73-mediated in the pancreatic tumor cell line, AsPC-1.

Identification of a novel Bcl-xL phosphorylation site regulating the sensitivity of taxol- or 2-methoxyestradiol-induced apoptosis

Bcl-xL, a close homolog of Bcl2, is an important regulator of apoptosis and is overexpressed in human cancer. Phosphorylation of Bcl-xL can be induced by microtubule-damaging drugs such as taxol or 2-methoxyestradiol (2-ME). By site-directed mutagenesis studies, we have identified that serine 62 is the necessary site for taxol- or 2-ME-induced Bcl-xL phosphorylation in prostate cancer cells. Further studies with the inhibitor of Jun kinase (JNK) and phosphorylation null mutant of Bcl-xL reveal the augmentative role of JNK-mediated Bcl-xL phosphorylation in apoptosis of prostate cancer cells. In summary, our studies suggest that the phosphorylation of Bcl-xL by stress response kinase signaling might oppose the anti-apoptotic function of Bcl-xL to permit prostate cancer cells to die by apoptosis.

Prolyl isomerase Pin1: a catalyst for oncogenesis and a potential therapeutic target in cancer

Phosphorylation of proteins on serine or threonine residues preceding proline (Ser/Thr-Pro) is a major intracellular signaling mechanism. The phosphorylated Ser/Thr-Pro motifs in a certain subset of phosphoproteins are isomerized specifically by the peptidyl-prolyl cis-trans isomerase Pin1. This post-phosphorylation isomerization can lead to conformational changes in the substrate proteins and modulate their functions. Pin1 interacts with a number of mitotic phosphoproteins, and plays a critical role in mitotic regulation. Recent work indicates that Pin1 is overexpressed in many human cancers and plays an important role in oncogenesis. Pin1 regulates the expression of cyclin D1 by cooperating with Ras signaling and inhibiting the interaction of beta-catenin with the tumor suppressor APC and also directly stabilizing cyclin D1 protein. Furthermore, PIN1 is an E2F target gene essential for the Neu/Ras-induced transformation of mammary epithelial cells. Pin1 is also a critical regulator of the tumor suppressor p53 during DNA damage response. Given its role in cell growth control and oncogenesis, Pin1 could represent a new anti-cancer target.

2-Methoxyestradiol induces mitochondria dependent apoptotic signaling in pancreatic cancer cells

The antiproliferative action of 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite is specific for cancer cells and is mediated by the induction of programmed cell death or apoptosis. But the identity of the downstream effectors of apoptotic signaling induced by 2-ME is not known. In the present study, we explored the effect of 2-ME on apoptosis in a panel of human pancreatic cancer cell lines. We have identified two categories of pancreatic cancer cell lines, which are either sensitive to 2-ME such as MIA PaCa-2, CFPAC-1, PANC-1, or non-sensitive to 2-ME such as Hs 766T. The results presented here indicated that the cell lines responsive to 2-ME could undergo apoptosis either by G2-M arrest (PANC-1) with Bcl-x(L) phosphorylation or by the accumulation of tetraploid cells in G1-S region (MIA PaCa-2) without Bcl-2/ Bcl-x(L) phosphorylation. Furthermore, 2-ME induced apoptosis in pancreatic cancer cells is mitochondria dependent as evident by the release of cytochrome c into the cytosol. 2-ME exposed cells exhibit Bid cleavage that is accompanied by the translocation of Bax into the mitochondria. Also 2-ME could induce phosphorylation of Bcl-x(L) in G2-M arrested cells, thus indicating the involvement of various anti- and pro-apoptotic regulators in the signaling cascade. The dissection of differential response of pancreatic cancer cell lines holds promise for future therapeutic intervention.