Association of rs2233678 and rs2233679 polymorphisms in the PIN1 gene with cancer risk: a meta-analysis

To data, epidemiological studies have assessed the association between peptidyl-propyl-cis/trans isomerase 1 (PIN1) gene polymorphisms and cancer risk, including breast cancer, hepatocellular carcinoma, lung cancer, esophageal cancer, head and neck squamous cell carcinoma, and laryngeal squamous cell cancer. However, the results of these studies remain controversial. We aimed to examine the associations between two SNPs (rs2233678 and rs2233679) of PIN1 gene and cancer risk by conducting a meta-analysis of case-control studies. A total of seven publications were included in this meta-analysis for both rs2233678 and rs2233679. Overall, rs2233678 polymorphism was found to be associated with decreased cancer risk in four genetic models (C-allele vs. G-allele: odd ratio (OR) = 0.73, 95% confidence interval (CI): 0.60-0.88; CC vs. GG: OR = 0.55, 95% CI: 0.36-0.84; CC+CG vs. GG: OR = 0.72, 95% CI 0.58-0.90; CC vs. CG+GG: OR = 0.58, 95% CI 0.38-0.89). However, the rs2233679 polymorphism of PIN1 gene did not appear to have an influence on caner susceptibility. In the subgroup analysis by cancer type, we observed that the PIN1 rs2233678 polymorphism was significantly associated with decreased breast cancer risk (C-allele vs. G-allele: OR = 0.73, 95% CI: 0.60-0.89; CC+CG vs. GG: OR = 0.71, 95% CI 0.57-0.89). Further subgroup analyses showed that the PIN1 rs2233678 polymorphism was associated with decreased cancer risk among Asian people (C-allele vs. G-allele: OR = 0.63, 95% CI: 0.51-0.79; CC vs. GG: OR = 0.44, 95% CI: 0.25-0.80; CC+CG vs. GG: OR = 0.63, 95% CI 0.50-0.79; CC vs. CG+GG: OR = 0.47, 95% CI 0.26-0.86). In conclusion, PIN1 rs2233678 polymorphism might be a potential biomarker for cancer risk among Asians, especially for breast cancer. Further large and well-designed studies are needed to confirm this conclusion.

The -842G/C polymorphisms of PIN1 contributes to cancer risk: a meta-analysis of 10 case-control studies

BACKGROUND

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) plays an important role in cancer development. The relationship between PIN1 -842G/C (rs2233678) polymorphism and cancer risk was inconclusive according to published literature.

METHODOLOGY/PRINCIPAL FINDINGS

A literature search, up to February 2013, was carried out using PubMed, EMBASE and the China National Knowledge Infrastructure (CNKI) database. A total of 10 case-control studies including 4619 cases and 4661 controls contributed to the quantitative analysis. Odds ratio (OR) and 95% confidence intervals (95% CI) were used to assess the strength of association. Overall, individuals with the variant CG (OR = 0.728, 95% CI: 0.585,0.906; Pheterogeneity<0.01) and CG/CC (OR = 0.731, 95% CI: 0.602,0.888; Pheterogeneity<0.01) genotypes were associated with a significantly reduced cancer risk compared with those with wild GG genotype. Sub-group analysis revealed that the variant CG (OR = 0.635, 95% CI: 0.548,0.735; Pheterogeneity = 0.240) and CG/CC (OR = 0.645, 95% CI: 0.559,0.744, Pheterogeneity = 0.258) genotypes still showed an reduced risk of cancer in Asians; while no significant association was observed in Caucasians (CG vs.GG: OR = 0.926, 95% CI: 0.572,1.499, Pheterogeneity<0.01; CG/CC vs. GG: OR = 0.892, 95% CI: 0.589,1.353; Pheterogeneity<0.01). Furthermore, sensitivity analysis confirmed the stability of results. Begg's funnel plot and Egger's test did not reveal any publication bias.

CONCLUSIONS

This meta-analysis suggests that the PIN1 -842G/C polymorphism is associated with a significantly reduced risk of cancer, especially in Asian populations.

Proteomic analysis for testis of mice exposed to carbon ion radiation

This paper investigates the mechanism of action of heavy ion radiation (HIR) on mouse testes. The testes of male mice subjected to whole body irradiation with carbon ion beam (0.5 and 4Gy) were analyzed at 7days after irradiation. A two-dimensional gel electrophoresis approach was employed to investigate the alteration of protein expression in the testes. Spot detection and matching were performed using the PDQuest 8.0 software. A difference of more than threefold in protein quantity (normalized spot volume) is the standard for detecting differentially expressed protein spots. A total of 11 differentially expressed proteins were found. Protein identification was performed using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF-TOF). Nine specific proteins were identified by searching the protein sequence database of the National Center for Biotechnology Information. These proteins were found involved in molecular chaperones, metabolic enzymes, oxidative stress, sperm function, and spermatogenic cell proliferation. HIR decreased glutathione activity and increased malondialdehyde content in the testes. Given that Pin1 is related to the cell cycle and that proliferation is affected by spermatogenesis, we analyzed testicular histological changes and Pin1 protein expression through immunoblotting and immunofluorescence. Alterations of multiple pathways may be associated with HIR toxicity to the testes. Our findings are essential for studies on the development, biology, and pathology of mouse testes after HIR in space or radiotherapy.

[Design, synthesis and biological evaluation of novel diaryl ethers bearing a pyrimidine motif as human Pin1 inhibitors]

Pin1 (peptidyl-prolyl cis-trans isomerase NIMA-interacting 1) belongs to peptidyl-prolyl cis-trans isomerase (PPIase) and is a novel promising anticancer target. Based on the lead structure of benzophenone, a series of novel diarylether derivatives containing a pyrimidine ring were designed and synthesized. The inhibitory activities on Pin1 of compounds 5a-5d and 6a-6i were evaluated by a protease-coupled enzyme assay. Of all the evaluated compounds, 6 compounds displayed inhibitory activities. Molecular docking was performed using FlexX algorithm to explore the binding mode of the active molecules.

SENP1 deSUMOylates and regulates Pin1 protein activity and cellular function

The Pin1 prolyl isomerase regulates phosphorylation signaling by controlling protein conformation after phosphorylation, and its upregulation promotes oncogenesis via acting on numerous oncogenic molecules. SUMOylation and deSUMOylation are dynamic mechanisms regulating a spectrum of protein activities. The SUMO proteases (SENP) remove SUMO conjugate from proteins, and their expression is deregulated in cancers. However, nothing is known about the role of SUMOylation in regulating Pin1 function. Here, we show that Pin1 is SUMOylated on Lys6 in the WW domain and on Lys63 in the PPIase domain. Pin1 SUMOylation inhibits its protein activity and oncogenic function. We further identify that SENP1 binds to and deSUMOylates Pin1. Importantly, either overexpression of SENP1 or disruption of Pin1 SUMOylation promotes the ability of Pin1 to induce centrosome amplification and cell transformation. Moreover, SENP1 also increases Pin1 protein stability in cell cultures, and Pin1 levels are positively correlated with SENP1 levels in human breast cancer specimens. These results not only uncover Pin1 SUMOylation on Lys6/63 as a novel mechanism to inhibit its activity and function but also identify a critical role for SENP1-mediated deSUMOylation in promoting Pin1 function during tumorigenesis.

Pin1-FADD interactions regulate Fas-mediated apoptosis in activated eosinophils

Abnormally long-lived eosinophils (Eos) are the major inflammatory component of allergic responses in the lungs of active asthmatics. Eos recruited to the airways after allergen exposure produce and respond to IL-5 and GM-CSF, enhancing their survival. Prosurvival signaling activates Pin1, a peptidyl-prolyl cis-trans isomerase that binds to Bax and prevents its activation. How long-lived Eos, despite the continued presence of GM-CSF or IL-5, eventually undergo apoptosis to end allergic inflammation remains unclear. In this study, we show that Pin1 location, activity, and protein interactions are jointly influenced by Fas and the prosurvival cytokine IL-5. Fas signaling strongly induced the phosphorylation of FADD at Ser(194) and Pin1 at Ser(16), as well as their nuclear accumulation. Phospho-mimic Ser(194)Glu FADD mutants accelerated Eos apoptosis compared with wild-type or Ser(194)Ala mutants. Downstream of FADD phosphorylation, caspase 8, 9, and 3 cleavage, as well as Eos apoptosis induced by Fas, were reduced by constitutively active Pin1 and enhanced by Pin1 inhibition. Pin1 was activated by IL-5, whereas simultaneous IL-5 and anti-Fas treatment modestly reduced peptidyl isomerase activity but induced Pin1 to associate with FADD after its phosphorylation at Ser(194). Mechanistically, Pin1-mediated isomerization facilitated the subsequent dephosphorylation of Ser(194) FADD and maintenance of cytoplasmic location. In vivo-activated bronchoalveolar Eos obtained after allergen challenge showed elevated survival and Pin1 activity that could be reversed by anti-Fas. Therefore, our data suggest that Pin1 is a critical link between FADD-mediated cell death and IL-5-mediated prosurvival signaling.

Pin1 null mice exhibit low bone mass and attenuation of BMP signaling

Bone is constantly formed and resorbed throughout life by coordinated actions of osteoblasts and osteoclasts. However, the molecular mechanisms involved in osteoblast function remain incompletely understood. Here we show, for the first time, that the peptidyl-prolyl isomerase PIN1 controls the osteogenic activity of osteoblasts. Pin1 null mice exhibited an age-dependent decrease in bone mineral density and trabecular bone formation without alteration in cortical bone. Further analysis identified a defect in BMP signaling in Pin1 null osteoblasts but normal osteoclast function. PIN1 interacted with SMAD5 and was required for the expression by primary osteoblasts of osteoblast specific transcription factors (CBFA1 and OSX), ECM (collagen I and OCN) and the formation of bone nodules. Our results thus uncover a novel aspect of the molecular underpinning of osteoblast function and identify a new therapeutic target for bone diseases.

PtdIns5P and Pin1 in oxidative stress signaling

Oxidative signaling is important in cellular health, involved in aging and contributes to the development of several diseases such as cancer, neurodegeneration and diabetes. Correct management of reactive oxygen species (ROS) prevents oxidative stress within cells and is imperative for cellular wellbeing. A key pathway that is regulated by oxidative stress is the activation of proline-directed stress kinases (p38, JNK). Phosphorylation induced by these kinases is often translated into cellular outcome through the recruitment of the prolyl-isomerase Pin1. Pin1 binds to phosphorylated substrates using its WW-domain and can induce conformational changes in the target protein through its prolyl-isomerase activity. We show that exposure of cells to UV irradiation or hydrogen peroxide (H₂O₂), induces the synthesis of the phosphoinositide second messenger PtdIns5P in part by inducing the interaction between phosphatidylinositol-5-phosphate 4-kinase (PIP4K) enzymes that remove PtdIns5P, with Pin1. In response to H₂O₂ exposure, Murine Embryonic Fibroblasts (MEFs) derived from Pin1⁻/⁻ mice showed increased cell viability and an increased abundance of PtdIns5P compared to wild-type MEFs. Decreasing the levels of PtdIns5P in Pin1⁻/⁻ MEFs decreased both their viability in response to H₂O₂ exposure and the expression of genes required for cellular ROS management. The decrease in the expression of these genes manifested itself in the increased accumulation of cellular ROS. These data strongly argue that PtdIns5P acts as a stress-induced second messenger that can calibrate how cells manage ROS.

Unraveling a phosphorylation event in a folded protein by NMR spectroscopy: phosphorylation of the Pin1 WW domain by PKA

The Pin1 protein plays a critical role in the functional regulation of the hyperphosphorylated neuronal Tau protein in Alzheimer's disease and is by itself regulated by phosphorylation. We have used Nuclear Magnetic Resonance (NMR) spectroscopy to both identify the PKA phosphorylation site in the Pin1 WW domain and investigate the functional consequences of this phosphorylation. Detection and identification of phosphorylation on serine/threonine residues in a globular protein, while mostly occurring in solvent-exposed flexible loops, does not lead to chemical shift changes as obvious as in disordered proteins and hence does not necessarily shift the resonances outside the spectrum of the folded protein. Other complications were encountered to characterize the extent of the phosphorylation, as part of the (1)H,(15)N amide resonances around the phosphorylation site are specifically broadened in the unphosphorylated state. Despite these obstacles, NMR spectroscopy was an efficient tool to confirm phosphorylation on S16 of the WW domain and to quantify the level of phosphorylation. Based on this analytical characterization, we show that WW phosphorylation on S16 abolishes its binding capacity to a phosphorylated Tau peptide. A reduced conformational heterogeneity and flexibility of the phospho-binding loop upon S16 phosphorylation could account for part of the decreased affinity for its phosphorylated partner. Additionally, a structural model of the phospho-WW obtained by molecular dynamics simulation and energy minimization suggests that the phosphate moiety of phospho-S16 could compete with the phospho-substrate.

Role of Ess1 in growth, morphogenetic switching, and RNA polymerase II transcription in Candida albicans

Candida albicans is a fungal pathogen that causes potentially fatal infections among immune-compromised individuals. The emergence of drug resistant C. albicans strains makes it important to identify new antifungal drug targets. Among potential targets are enzymes known as peptidyl-prolyl cis/trans isomerases (PPIases) that catalyze isomerization of peptide bonds preceding proline. We are investigating a PPIase called Ess1, which is conserved in all major human pathogenic fungi. Previously, we reported that C. albicans Ess1 is essential for growth and morphogenetic switching. In the present study, we re-evaluated these findings using more rigorous genetic analyses, including the use of additional CaESS1 mutant alleles, distinct marker genes, and the engineering of suitably-matched isogenic control strains. The results confirm that CaEss1 is essential for growth in C. albicans, but show that reduction of CaESS1 gene dosage by half (δ/+) does not interfere with morphogenetic switching. However, further reduction of CaEss1 levels using a conditional allele does reduce morphogenetic switching. We also examine the role of the linker α-helix that distinguishes C. albicans Ess1 from the human Pin1 enzyme, and present results of a genome-wide transcriptome analysis. The latter analysis indicates that CaEss1 has a conserved role in regulation of RNA polymerase II function, and is required for efficient termination of small nucleolar RNAs and repression of cryptic transcription in C. albicans.

The prolyl isomerase Pin1 acts synergistically with CDK2 to regulate the basal activity of estrogen receptor α in breast cancer

In hormone receptor-positive breast cancers, most tumors in the early stages of development depend on the activity of the estrogen receptor and its ligand, estradiol. Anti-estrogens, such as tamoxifen, have been used as the first line of therapy for over three decades due to the fact that they elicit cell cycle arrest. Unfortunately, after an initial period, most cells become resistant to hormonal therapy. Peptidylprolyl isomerase 1 (Pin1), a protein overexpressed in many tumor types including breast, has been demonstrated to modulate ERalpha activity and is involved in resistance to hormonal therapy. Here we show a new mechanism through which CDK2 drives an ERalpha-Pin1 interaction under hormone- and growth factor-free conditions. The PI3K/AKT pathway is necessary to activate CDK2, which phosphorylates ERalphaSer294, and mediates the binding between Pin1 and ERalpha. Site-directed mutagenesis demonstrated that ERalphaSer294 is essential for Pin1-ERalpha interaction and modulates ERalpha phosphorylation on Ser118 and Ser167, dimerization and activity. These results open up new drug treatment opportunities for breast cancer patients who are resistant to anti-estrogen therapy.

Protective effect of nectandrin B, a potent AMPK activator on neointima formation: inhibition of Pin1 expression through AMPK activation

BACKGROUND AND PURPOSE

Neointima is considered a critical event in the development of vascular occlusive disease. Nectandrin B from nutmeg functions as a potent AMP-activated protein kinase (AMPK) activators. The present study addressed whether nectandrin B inhibits intimal hyperplasia in guide wire-injured arteries and examined its molecular mechanism.

EXPERIMENTAL APPROACH

Neointima was induced by guide wire injury in mouse femoral arteries. Cell proliferation and mechanism studies were performed in rat vascular smooth muscle cells (VSMC) culture model.

KEY RESULTS

Nectandrin B increased AMPK activity in VSMC. Nectandrin B inhibited the cell proliferation induced by PDGF and DNA synthesis. Moreover, treatment of nectandrin B suppressed neointima formation in femoral artery after guide wire injury. We have recently shown that Pin1 plays a critical role in VSMC proliferation and neointima formation. Nectandrin B potently blocked PDGF-induced Pin1 and cyclin D1 expression and nectandrin B's anti-proliferation effect was diminished in Pin1 overexpressed VSMC. PDGF-induced phosphorylation of ERK and Akt was marginally affected by nectandrin B. However, nectandrin B increased the levels of p53 and its downstream target p21 and, also reversibly decreased the expression of E2F1 and phosphorylated Rb in PDGF-treated VSMC. AMPK inhibition by dominant mutant form of adenovirus rescued nectandrin B-mediated down-regulation of Pin1 and E2F1.

CONCLUSIONS AND IMPLICATIONS

Nectandrin B inhibited VSMC proliferation and neointima formation via inhibition of E2F1-dependent Pin1 gene transcription, which is mediated through the activation of an AMPK/p53-triggered pathway.

The natively disordered loop of Bcl-2 undergoes phosphorylation-dependent conformational change and interacts with Pin1

Bcl-2 plays a central role in the regulation of apoptosis. Structural studies of Bcl-2 revealed the presence of a flexible and natively disordered loop that bridges the Bcl-2 homology motifs, BH3 and BH4. This loop is phosphorylated on multiple sites in response to a variety of external stimuli, including the microtubule-targeting drugs, paclitaxel and colchicine. Currently, the underlying molecular mechanism of Bcl-2 phosphorylation and its biological significance remain elusive. In this study, we investigated the molecular characteristics of this anti-apoptotic protein. To this end, we generated synthetic peptides derived from the Bcl-2 loop, and multiple Bcl-2 loop truncation mutants that include the phosphorylation sites. Our results demonstrate that S87 in the flexible loop of Bcl-2 is the primary phosphorylation site for JNK and ERK2, suggesting some sequence or structural specificity for the phosphorylation by these kinases. Our NMR studies and molecular dynamics simulation studies support indicate that phosphorylation of S87 induces a conformational change in the peptide. Finally, we show that the phosphorylated peptides of the Bcl-2 loop can bind Pin1, further substantiating the phosphorylation-mediated conformation change of Bcl-2.

The acidic pH-induced structural changes in Pin1 as revealed by spectral methodologies

Pin1 is closely associated with the pathogenesis of cancers and Alzheimer's disease (AD). Previously, we have shown the characteristics of the thermal denaturation of Pin1. Herein, the acid-induced denaturation of Pin1 was determined by means of fluorescence emission, synchronous fluorescence, far-UV CD, ANS fluorescence and RLS spectroscopies. The fluorescence emission spectra and the synchronous fluorescence spectra suggested the partially reversible unfolding (approximately from pH 7.0 to 4.0) and refolding (approximately from pH 4.0 to 1.0) of the structures around the chromophores in Pin1, apparently with an intermediate state at about pH 4.0-4.5. The far-UV CD spectra indicated that acidic pH (below pH 4.0) induced the structural transition from α-helix and random coils to β-sheet in Pin1. The ANS fluorescence and the RLS spectra further suggested the exposure of the hydrophobic side-chains of Pin1 and the aggregation of it especially below pH 2.3, and the aggregation possibly resulted in the formation of extra intermolecular β-sheet. The present work primarily shows that acidic pH can induce kinds of irreversible structural changes in Pin1, such as the exposure of the hydrophobic side-chains, the transition from α-helix to β-sheet and the aggregation of Pin1, and also explains why Pin1 loses most of its activity below pH 5.0. The results emphasize the important role of decreased pH in the pathogenesis of some Pin1-related diseases, and support the therapeutic approach for them by targeting acidosis and modifying the intracellular pH gradients.

ERK1/2-dependent phosphorylation and nuclear translocation of PKM2 promotes the Warburg effect

Pyruvate kinase M2 (PKM2) is upregulated in multiple cancer types and contributes to the Warburg effect by unclear mechanisms. Here we demonstrate that EGFR-activated ERK2 binds directly to PKM2 Ile 429/Leu 431 through the ERK2 docking groove and phosphorylates PKM2 at Ser 37, but does not phosphorylate PKM1. Phosphorylated PKM2 Ser 37 recruits PIN1 for cis-trans isomerization of PKM2, which promotes PKM2 binding to importin α5 and translocating to the nucleus. Nuclear PKM2 acts as a coactivator of β-catenin to induce c-Myc expression, resulting in the upregulation of GLUT1, LDHA and, in a positive feedback loop, PTB-dependent PKM2 expression. Replacement of wild-type PKM2 with a nuclear translocation-deficient mutant (S37A) blocks the EGFR-promoted Warburg effect and brain tumour development in mice. In addition, levels of PKM2 Ser 37 phosphorylation correlate with EGFR and ERK1/2 activity in human glioblastoma specimens. Our findings highlight the importance of nuclear functions of PKM2 in the Warburg effect and tumorigenesis.

The prolyl isomerase Pin1 targets stem-loop binding protein (SLBP) to dissociate the SLBP-histone mRNA complex linking histone mRNA decay with SLBP ubiquitination

Histone mRNAs are rapidly degraded at the end of S phase, and a 26-nucleotide stem-loop in the 3' untranslated region is a key determinant of histone mRNA stability. This sequence is the binding site for stem-loop binding protein (SLBP), which helps to recruit components of the RNA degradation machinery to the histone mRNA 3' end. SLBP is the only protein whose expression is cell cycle regulated during S phase and whose degradation is temporally correlated with histone mRNA degradation. Here we report that chemical inhibition of the prolyl isomerase Pin1 or downregulation of Pin1 by small interfering RNA (siRNA) increases the mRNA stability of all five core histone mRNAs and the stability of SLBP. Pin1 regulates SLBP polyubiquitination via the Ser20/Ser23 phosphodegron in the N terminus. siRNA knockdown of Pin1 results in accumulation of SLBP in the nucleus. We show that Pin1 can act along with protein phosphatase 2A (PP2A) in vitro to dephosphorylate a phosphothreonine in a conserved TPNK sequence in the SLBP RNA binding domain, thereby dissociating SLBP from the histone mRNA hairpin. Our data suggest that Pin1 and PP2A act to coordinate the degradation of SLBP by the ubiquitin proteasome system and the exosome-mediated degradation of the histone mRNA by regulating complex dissociation.

Chronic cladribine administration increases amyloid beta peptide generation and plaque burden in mice

Background

The clinical uses of 2-chloro-2′-deoxyadenosine (2-CDA) or cladribine which was initially prescribed to patients with hematological and lymphoid cancers is now extended to treat patients with multiple sclerosis (MS). Previous data has shown that 2-CDA has high affinity to the brain and readily passes through the blood brain barrier reaching CSF concentrations 25% of that found in plasma. However, whether long-term administration of 2-CDA can lead to any adverse effects in patients or animal models is not yet clearly known.

Methodology

Here we show that exposure of 2-CDA to CHO cells stably expressing wild-type APP751 increased generation and secretion of amyloid β peptide (Aβ) in to the conditioned medium. Interestingly, increased Aβ levels were noticed even at non-toxic concentrations of 2-CDA. Remarkably, chronic treatment of APdE9 mice, a model of Alzheimer's disease with 2-CDA for 60 days increased amyloid plaque burden by more than 1-fold. Increased Aβ generation appears to result from increased turnover of APP as revealed by cycloheximide-chase experiments. Additionally, surface labeling of APP with biotin and immunoprecipitation of surface labeled proteins with anti-biotin antibody also indicated increased APP at the cell surface in 2-CDA treated cells compared to controls. Increased turnover of APP by 2-CDA in turn might be a consequence of decreased protein levels of PIN 1, which is known to regulate cis-trans isomerization and phosphorylation of APP. Most importantly, like many other oncology drugs, 2-CDA administration led to significant delay in acquiring a reward-based learning task in a T maze paradigm.

Conclusions

Taken together, these data provide compelling evidence for the first time that chronic 2-CDA administration can increase amyloidogenic processing of APP leading to robustly increased plaque burden which may be responsible for the observed deficits in learning skills. Thus chronic treatment of mice with 2-CDA can have deleterious effects in vivo.

Proyl isomerase Pin1 facilitates ubiquitin-mediated degradation of cyclin-dependent kinase 10 to induce tamoxifen resistance in breast cancer cells

Endocrine therapies that inhibit estrogen receptor (ER)-α signaling are the most common and effective treatment for ER-α-positive breast cancer. However, the use of these agents is limited by the frequent development of resistance. The aim of this study was to elucidate the mechanisms by which downregulation of CDK10 expression confers resistance to tamoxifen in breast cancer. Here, we show that peptidyl-prolyl isomerase Pin1 downregulates CDK10 protein as a result of its interaction with and ubiquitination of CDK10, thereby affecting CDK10-dependent Raf-1 phosphorylation (S338). Pin1(-/-) mouse embryonic fibroblasts (MEFs) show higher CDK10 expression than Pin1(+/+) MEFs, whereas CDK10 protein was downregulated in the rescued Pin1(-/-) MEFs after reexpression of Pin1. Pin1 silencing in SKBR-3 and MCF7 cells increased the CDK10 expression. In human tamoxifen-resistant breast cancer and tamoxifen-resistant MCF7 cells, immunohistochemical staining and immunoblotting analysis shows an inverse correlation between the expression of CDK10 and the degree of tamoxifen resistance. There was also a positive correlation between the high level of P-Raf-1 (Ser338) and Pin1 in human tamoxifen-resistant breast cancer and tamoxifen-resistant MCF7 (TAMR-MCF7) cells. Importantly, 4-OH tamoxifen (4-OHT), when used in combination with overexpressed CDK10 or Raf-1 inhibitor, increased cleaved PARP and DNA fragmentation to inhibit cologenic growth of MCF7 cells and Tamoxifen-resistant MCF7 cells, respectively. On the basis of these findings, we suggest that the Pin1-mediated CDK10 ubiquitination is a major regulator of tamoxifen-resistant breast cancer cell growth and survival.

Solution structural analysis of the single-domain parvulin TbPin1

Background

Pin1-type parvulins are phosphorylation-dependent peptidyl-prolyl cis-trans isomerases. Their functions have been widely reported to be involved in a variety of cellular responses or processes, such as cell division, transcription, and apoptosis, as well as in human diseases including Alzheimer's disease and cancers. TbPin1 was identified as a novel class of Pin1-type parvulins from Trypanosoma brucei, containing a unique PPIase domain, which can catalyze the isomerization of phosphorylated Ser/Thr-Pro peptide bond.

Methodology/Principal Findings

We determined the solution structure of TbPin1 and performed ¹⁵N relaxation measurements to analyze its backbone dynamics using multi-dimensional heteronuclear NMR spectroscopy. The average RMSD values of the 20 lowest energy structures are 0.50±0.05 Å for backbone heavy atoms and 0.85±0.08 Å for all heavy atoms. TbPin1 adopts the typical catalytic tertiary structure of Pin1-type parvulins, which comprises a globular fold with a four-stranded anti-parallel β-sheet core surrounded by three α-helices and one 3₁₀-helix. The global structure of TbPin1 is relatively rigid except the active site. The 2D EXSY spectra illustrate that TbPin1 possesses a phosphorylation-dependent PPIase activity. The binding sites of TbPin1 for a phosphorylated peptide substrate {SSYFSG[p]TPLEDDSD} were determined by the chemical shift perturbation approach. Residues Ser15, Arg18, Asn19, Val21, Ser22, Val32, Gly66, Ser67, Met83, Asp105 and Gly107 are involved in substantial contact with the substrate.

Conclusions/Significance

The solution structure of TbPin1 and the binding sites of the phosphorylated peptide substrate on TbPin1 were determined. The work is helpful for further understanding the molecular basis of the substrate specificity for Pin1-type parvulin family and enzyme catalysis.

Mixed-lineage kinase 3 phosphorylates prolyl-isomerase Pin1 to regulate its nuclear translocation and cellular function

Nuclear protein peptidyl-prolyl isomerase Pin1-mediated prolyl isomerization is an essential and novel regulatory mechanism for protein phosphorylation. Therefore, tight regulation of Pin1 localization and catalytic activity is crucial for its normal nuclear functions. Pin1 is commonly dysregulated during oncogenesis and likely contributes to these pathologies; however, the mechanism(s) by which Pin1 catalytic activity and nuclear localization are increased is unknown. Here we demonstrate that mixed-lineage kinase 3 (MLK3), a MAP3K family member, phosphorylates Pin1 on a Ser138 site to increase its catalytic activity and nuclear translocation. This phosphorylation event drives the cell cycle and promotes cyclin D1 stability and centrosome amplification. Notably, Pin1 pSer138 is significantly up-regulated in breast tumors and is localized in the nucleus. These findings collectively suggest that the MLK3-Pin1 signaling cascade plays a critical role in regulating the cell cycle, centrosome numbers, and oncogenesis.

Identification of phosphorylated proteins involved in the oncogenesis of prostate cancer via Pin1-proteomic analysis

BACKGROUND

The peptidyl-prolyl isomerase Pin1 regulates a subset of phosphorylated proteins by catalyzing the cis-trans isomerization of their specific phosphorylated Ser/Thr-Pro motifs. Although Pin1 has been shown to be involved in cell transformation and the maintenance of the malignant phenotype in prostate cancer, its specific substrates during these processes have not yet been determined.

METHODS

Cancer-specific phosphorylated proteins were isolated from two human prostate cancer cell lines (PC-3, LNCaP) and the Dunning rat prostate cancer cell lines by GST-pull down analysis with recombinant GST-Pin1 protein. These proteins were then identified by the LC-MS/MS analysis using a Q-Tof micro mass spectrometer and processed for further functional analysis.

RESULTS

We newly identified five prostate cancer-specific Pin1 binding proteins (PINBPs) in this screen. Among these, TRK-fused gene (TFG) was found to be preferentially up-regulated in prostate cancer cell lines and tissues. The targeted inhibition of TFG by specific siRNA resulted in the reduced cell proliferation and the induction of premature senescence in PC3 prostate cancer cells. We further found that TFG can facilitate the cell signaling mediated by NF-kappaB and androgen receptor (AR). Tissue micro-dissection based quantitative RT-PCR analysis of prostate cancer tissues following radical prostatectomy further revealed that TFG expression is closely associated with both a higher probability and shorter period of tumor recurrence following surgery.

CONCLUSIONS

Pin1-based proteomics analysis is a useful tool for the identification of prostate cancer-specific phosphorylated proteins. TFG could be a potential diagnostic and/or prognostic marker and therapeutic target in prostate cancer.

p53 Retards cell-growth and suppresses etoposide-induced apoptosis in Pin1-deficient mouse embryonic fibroblasts

We studied the effects of Pin1, a regulatory molecule of the oncosuppressor p53, on both cell cycle arrest and apoptosis by treating primary mouse embryonic fibroblasts (MEFs) with etoposide. Etoposide induced G1 arrest in both wild-type and Pin1 null (pin1(-/-)) MEFs, and G2/M arrest and apoptotic cell death in MEFs lacking either p53 only (p53(-/-)) or both Pin1 and p53 (pin1(-/-)p53(-/-)). Both pin1(-/-) and pin1(-/-)p53(-/-) MEFs were enhanced the release of cytochrome c from the mitochondria, which might induce apoptosis. In response to etoposide treatment, apoptotic cell death was displayed in pin1(-/-)p53(-/-) MEFs but not in pin1(-/-) MEFs. These results suggest that p53 retards growth and suppresses etoposide-induced apoptosis in pin1(-/-) MEFs.

Proline isomer-specific antibodies reveal the early pathogenic tau conformation in Alzheimer's disease

cis-trans isomerization of proteins phosphorylated by proline-directed kinases is proposed to control numerous signaling molecules and is implicated in the pathogenesis of Alzheimer's and other diseases. However, there is no direct evidence for the existence of cis-trans protein isomers in vivo or for their conformation-specific function or regulation. Here we develop peptide chemistries that allow the generation of cis- and trans-specific antibodies and use them to raise antibodies specific for isomers of phosphorylated tau. cis, but not trans, p-tau appears early in the brains of humans with mild cognitive impairment, accumulates exclusively in degenerated neurons, and localizes to dystrophic neurites during Alzheimer's progression. Unlike trans p-tau, the cis isomer cannot promote microtubule assembly, is more resistant to dephosphorylation and degradation, and is more prone to aggregation. Pin1 converts cis to trans p-tau to prevent Alzheimer's tau pathology. Isomer-specific antibodies and vaccines may therefore have value for the early diagnosis and treatment of Alzheimer's disease.

Prolyl isomerase Pin1 regulates mouse embryonic fibroblast differentiation into adipose cells

BACKGROUND

A peptidyl prolyl cis/trans isomerase, Pin1, regulates insulin signal transduction. Pin1 reduces responses to insulin stimulation by binding CRTC2 (CREB-regulated transcriptional co-activator 2) and PPARγ (peroxisome prolifereator- activated receptor γ), but conversely enhances insulin signaling by binding IRS-1 (insulin receptor substrate-1), Akt kinase, and Smad3. Therefore, it is still unclear whether Pin1 inhibits or enhances adipose cell differentiation.

METHODOLOGY/PRINCIPAL FINDINGS

Pin1(-/-) and wild-type mice were fed with high fat diets and adipose tissue weight was measured. Compared to wild-type mice, Pin1(-/-) mice had lower adipose tissue weight, while the weight of other tissues was similar. Mouse embryo fibroblasts (MEFs), prepared from both groups of mice, were induced to differentiate into adipose cells by stimulation with insulin. However, the rate of differentiation of MEFs from Pin1(-/-) mice was less than that of MEFs from wild-type mice. The rate of insulin-induced MEF cell differentiation in Pin1(-/-) mice was restored by increasing expression of Pin1. We found that Pin1 binds to phosphoThr172- and phosphoSer271-Pro sites in CREB suppress the activity in COS-7 cells.

CONCLUSION AND SIGNIFICANCE

Pin1 enhanced the uptake of triglycerides and the differentiation of MEF cells into adipose cells in response to insulin stimulation. Results of this study suggest that Pin1 down-regulation could be a potential approach in obesity-related dysfunctions, such as high blood pressure, diabetes, non-alcoholic steatohepatitis.