Structure and dynamics of pin1 during catalysis by NMR

The link between internal enzyme motions and catalysis is poorly understood. Correlated motions in the microsecond-to-millisecond timescale may be critical for enzyme function. We have characterized the backbone dynamics of the peptidylprolyl isomerase (Pin1) catalytic domain in the free state and during catalysis. Pin1 is a prolyl isomerase of the parvulin family and specifically catalyzes the isomerization of phosphorylated Ser/Thr-Pro peptide bonds. Pin1 has been shown to be essential for cell-cycle progression and to interact with the neuronal tau protein inhibiting its aggregation into fibrillar tangles as found in Alzheimer's disease. (15)N relaxation dispersion measurements performed on Pin1 during catalysis reveal conformational exchange processes in the microsecond timescale. A subset of active site residues undergo kinetically similar exchange processes even in the absence of a substrate, suggesting that this area is already "primed" for catalysis. Furthermore, structural data of the turning-over enzyme were obtained through inter- and intramolecular nuclear Overhauser enhancements. This analysis together with a characterization of the substrate concentration dependence of the conformational exchange allowed the distinguishing of regions of the enzyme active site that are affected primarily by substrate binding versus substrate isomerization. Together these data suggest a model for the reaction trajectory of Pin1 catalysis.

The peptidyl-prolyl isomerase Pin1 regulates granulocyte-macrophage colony-stimulating factor mRNA stability in T lymphocytes

Cytokine production is associated with both the normal and pathologic inflammatory response to injury. Previous studies have shown that the immunosuppressants cyclosporin A or FK506, which interact with the peptidyl-propyl isomerases cyclophilin A and FK506-binding protein (FKBP12), respectively, block cytokine expression. A third member of the peptidyl-propyl isomerase family, Pin1 is expressed by immune and other cells. Pin1 has been implicated in cell cycle progression, is overexpressed in human tumors, and may rescue neurons from tau-associated degeneration. However, the role of Pin1 in the immune system remains largely unknown. In this study, we analyze the role of Pin1 in GM-CSF expression by human PBMC and CD4+ lymphocytes. We show that Pin1 isomerase activity is necessary for activation-dependent, GM-CSF mRNA stabilization, accumulation, and protein secretion, but not non-AU-rich elements containing cytokine mRNAs, including TGF-beta and IL-4. Mechanistically, Pin1 mediated the association of the AU-rich element-binding protein, AUF1, with GM-CSF mRNA, which determined the rate of decay by the exosome.

Functionally Important Residues in the Peptidyl-prolyl Isomerase Pin1 Revealed by Unigenic Evolution

Pin1 is a phosphorylation-dependent member of the parvulin family of peptidyl-prolyl isomerases exhibiting functional conservation between yeast and man. To perform an unbiased analysis of the regions of Pin1 essential for its functions, we generated libraries of randomly mutated forms of the human Pin1 cDNA and identified functional Pin1 alleles by their ability to complement the Pin1 homolog Ess1 in Saccharomyces cerevisiae. We isolated an extensive collection of functional mutant Pin1 clones harboring a total of 356 amino acid substitutions. Surprisingly, many residues previously thought to be critical in Pin1 were found to be altered in this collection of functional mutants. In fact, only 17 residues were completely conserved in these mutants and in Pin1 sequences from other eukaryotic organisms, with only two of these conserved residues located within the WW domain of Pin1. Examination of invariant residues provided new insights regarding a phosphate-binding loop that distinguishes a phosphorylation-dependent peptidyl-prolyl isomerase such as Pin1 from other parvulins. In addition, these studies led to an investigation of residues involved in catalysis including C113 that was previously implicated as the catalytic nucleophile. We demonstrate that substitution of C113 with D does not compromise Pin1 function in vivo nor does this substitution abolish catalytic activity in purified recombinant Pin1. These findings are consistent with the prospect that the function of residue 113 may not be that of a nucleophile, thus raising questions about the model of nucleophilic catalysis. Accordingly, an alternative catalytic mechanism for Pin1 is postulated.

Ablation of a peptidyl prolyl isomerase Pin1 from p53-null mice accelerated thymic hyperplasia by increasing the level of the intracellular form of Notch1

Tumor suppressor p53 is essential for checkpoint control in response to a variety of genotoxic stresses. DNA damage leads to phosphorylation on the Ser/Thr-Pro motifs of p53, which facilitates interaction with Pin1, a pSer/pThr-Pro-specific peptidyl prolyl isomerase. Pin1 is required for the timely activation of p53, resulting in apoptosis or cell cycle arrest. To investigate the physiological relationship between Pin1 and p53, we created Pin1-/-p53-/- mice. These p53-deficient mice spontaneously developed lymphomas, mainly of thymic origin, as well as generalized lymphoma infiltration into other organs, including the liver, kidneys and lungs. Ablation of Pin1, in addition to p53, accelerated the thymic hyperplasia, but the thymocytes in these Pin1-/-p53-/- mice did not infiltrate other organs. The thymocytes in 12-week-old Pin1-/-p53-/- mice were CD4(-)CD8(-) (double negative) and had significantly higher levels of the intracellular form of Notch1 (NIC) than the thymocytes of p53-/- or wild-type mice. Presenilin-1, a cleavage enzyme for NIC generation from full-length Notch1 was increased in the thymocytes of Pin1-/-p53-/- mice. Pin1 depletion also inhibited the degradation of NIC by proteasomes. These results suggest that both Pin1 and p53 control the normal proliferation and differentiation of thymocytes by regulating the NIC level.

Pin1 stabilizes Emi1 during G2 phase by preventing its association with SCF(betatrcp)

The anaphase-promoting complex (APC) early mitotic inhibitor 1 (Emi1) is required to induce S- and M-phase entries by stimulating the accumulation of cyclin A and cyclin B through APC(Cdh1/cdc20) inhibition. In this report, we show that Emi1 proteolysis can be induced by cyclin A/cdk (cdk for cyclin-dependent kinase). Paradoxically, Emi1 is stable during G2 phase, when cyclin A/cdk, Plx1 and SCF(betatrcp) (SCF for Skp1-Cul1-Fbox protein)--which play a role in its degradation--are active. Here, we identify Pin1 as a new regulator of Emi1 that induces Emi1 stabilization by preventing its association with SCF(betatrcp). We show that Pin1 binds to Emi1 and prevents its association with betatrcp in an isomerization-dependent pathway. We also show that Emi1-Pin1 binding is present in vivo in XL2 cells during G2 phase and that this association protects Emi1 from being degraded during this phase of the cell cycle. We propose that S- and M-phase entries are mediated by the accumulation of cyclin A and cyclin B through a Pin1-dependent stabilization of Emi1 during G2.

[Expression of Pin1, beta-catenin and cyclin D1 in salivary adenoid cystic carcinoma and its significance]

OBJECTIVE

To investigate the expression of Pin1, beta-catenin and cyclin D1 in salivary adenoid cystic carcinomas (SACC) and to evaluate the role of beta-catenin and Pin1 in SACC carcinogenesis.

METHODS

The expressions of Pin1, beta-catenin and cyclin D1 were examined in the specimens of 65 patients with SACC by immunohistochemistry, and Pin1 protein and mRNA expressions detected by Western blot and RT-PCR in four SACC cell lines.

RESULTS

Pin1 was overexpressed in 51 cases of ACC (78%), and 41 (63%) cases showed positive immunoreactivity for cyclin D1 protein in the nuclear fraction in tumor tissues. Fourteen (22%) cases showed positive immunoreactivity for beta-catenin protein in the nuclear/cytoplasmic fraction in tumor tissues, 6 of which exhibited quite evident expression of beta-catenin in nucleolus. The expression of membranous beta-catenin was down-regulated in most of the patients with lymph node metastasis (11/14).

CONCLUSIONS

The results suggest that Pin1 and beta-catenin signalling pathway were activated in SACC and might play a pivotal role in SACC carcinogenesis and metastasis.

PIN1 expression contributes to hepatic carcinogenesis

The phospho-Ser/Thr-Pro specific prolyl-isomerase PIN1 is over-expressed in more than 50% of hepatocellular carcinomas (HCCs). To investigate its potential oncogenicity, we over-expressed PIN1 in a non-transformed human liver cell line MIHA. This resulted in up-regulation of beta-catenin and cyclin D1, leading to anchorage-independent growth in soft agar and tumorigenicity in nude mice. To further validate the role of PIN1 in hepatocarcinogenesis, PIN was suppressed by RNA interference (siRNA) in the HCC cell line PLC/PRF/5. siRNA-PIN1 transfection of PLC/PRF/5 cells led to repression of PIN1 expression, resulting in decreased levels of beta-catenin and cyclin D1. siRNA-PIN1 transfectants showed lower cell proliferation rates, reduced colony formation, and retarded cell cycle progression, with an increase in cells residing in G0/G1. Furthermore, soft agar colony formation was depressed, and tumorigenicity in nude mice was abrogated. These findings implicate PIN1 expression as an important step in hepatic carcinogenesis.

An exonic splicing silencer represses spliceosome assembly after ATP-dependent exon recognition

Precursor messenger RNA splicing is catalyzed by the spliceosome, a macromolecular complex that assembles in a stepwise process. The spliceosome's dynamic nature suggests the potential for regulation at numerous points along the assembly pathway; however, thus far, naturally occurring regulation of splicing has only been found to influence a small subset of spliceosomal intermediates. Here we report that the exonic splicing silencer (ESS1) that represses splicing of PTPRC (encoding CD45) exon 4 does not function by the typical mechanism of inhibiting binding of U1 or U2 small nuclear ribonucleoproteins (snRNPs) to the splice sites. Instead, a U1-, U2- and ATP-dependent complex forms across exon 4 that is required for inhibiting progression to the U4-U6-U5 tri-snRNP-containing B complex. Such inhibition represents a new mechanism for splicing regulation and suggests that regulation can probably occur at many of the transitions along the spliceosome assembly pathway.

Identification and comparative analysis of sixteen fungal peptidyl-prolyl cis/trans isomerase repertoires

BACKGROUND

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins is present in all known eukaryotes, prokaryotes, and archaea, and it is comprised of three member families that share the ability to catalyze the cis/trans isomerisation of a prolyl bond. Some fungi have been used as model systems to investigate the role of PPIases within the cell, however how representative these repertoires are of other fungi or humans has not been fully investigated.

RESULTS

PPIase numbers within these fungal repertoires appears associated with genome size and orthology between repertoires was found to be low. Phylogenetic analysis showed the single-domain FKBPs to evolve prior to the multi-domain FKBPs, whereas the multi-domain cyclophilins appear to evolve throughout cyclophilin evolution. A comparison of their known functions has identified, besides a common role within protein folding, multiple roles for the cyclophilins within pre-mRNA splicing and cellular signalling, and within transcription and cell cycle regulation for the parvulins. However, no such commonality was found with the FKBPs. Twelve of the 17 human cyclophilins and both human parvulins, but only one of the 13 human FKBPs, identified orthologues within these fungi. hPar14 orthologues were restricted to the Pezizomycotina fungi, and R. oryzae is unique in the known fungi in possessing an hCyp33 orthologue and a TPR-containing FKBP. The repertoires of Cryptococcus neoformans, Aspergillus fumigatus, and Aspergillus nidulans were found to exhibit the highest orthology to the human repertoire, and Saccharomyces cerevisiae one of the lowest.

CONCLUSION

Given this data, we would hypothesize that: (i) the evolution of the fungal PPIases is driven, at least in part, by the size of the proteome, (ii) evolutionary pressures differ both between the different PPIase families and the different fungi, and (iii) whilst the cyclophilins and parvulins have evolved to perform conserved functions, the FKBPs have evolved to perform more variable roles. Also, the repertoire of Cryptococcus neoformans may represent a better model fungal system within which to study the functions of the PPIases as its genome size and genetic tractability are equal to those of Saccharomyces cerevisiae, whilst its repertoires exhibits greater orthology to that of humans. However, further experimental investigations are required to confirm this.

Phospho-dependent protein recognition motifs contained in C/EBP family of transcription factors: in silico studies

CCAAT/enhancer-binding proteins (C/EBPs) are transcriptional regulators implicated in cell proliferation, differentiation, survival, and tumorigenesis. Their biological activities require interactions with several protein partners. This report presents insights from in silico analysis aimed at identifying phosphorylation-dependent protein recognition motifs in C/EBPs. (1) All C/EBP variants contain intrinsically disordered Ser/Thr- and Pro-rich segments with potential docking sites for WW and Polo-box domains of prolyl isomerase Pin1 and Polo-like kinases (Plks), respectively. (2) Consensus phosphorylation sequences for Plks are located in a highly conserved region of transactivation domains, suggesting that Plks might modulate transcriptional activities of C/EBPs in a cell cycle-dependent manner. (3) Phosphorylation at these positions, as well as at conserved Ser in the extended basic region, would create phosphoserine-containing motifs (pSXXF/Y/I/L), which could be recognized by BRCT repeats containing proteins such as the PAX-transactivation-domain-interacting protein (PTIP), and the breast cancer-associated protein (BRCA1). Proteins containing BRCT domains serve as scaffolds, mediating protein-protein interactions and formation of functional multiprotein complexes involved in DNA repair and cell cycle control. These findings add a new perspective to studies aimed at elucidation of molecular mechanisms underlying the diverse functions of C/EBPs.

Exploring the molecular function of PIN1 by nuclear magnetic resonance

PIN1 participates in the regulation of a number of signalling pathways in the cell involving protein phosphorylation/dephosphorylation. Its role seems to be an essential control level in addition to the protein phosphorylation by proline-directed kinases. Its cellular function includes regulation of the cell cycle by interaction with phosphorylated mitotic proteins such as Cdc25 and transcription factors such as p53. PIN1 was shown to be involved in the malignant transformation of cells in breast cancer, by up regulation of cyclinD1 and is thought to be involved in the development of the AD by regulating the function of phosphorylated Tau. We propose here to discuss the molecular function of PIN1 at the atomic level based on data from the recent literature and our own results obtained by the technique of Nuclear Magnetic Resonance. PIN1 specifically interacts with pThr/pSer-Pro motifs and is constituted by two domains: a WW N-terminal domain that binds pThr/pSer-Pro epitopes and a prolyl cis/trans isomerase C-terminal catalytic domain. An exception to this organisation is found in the plant PIN1 homologous enzymes, like PIN1At from Arabidopsis thaliana, that are constituted of the sole catalytic domain. The molecular function of PIN1, binding to and isomerization of pThr/pSer-Pro bonds, are thought to lead to several functional consequences. In a first mode of action, exemplified by its competition with the CKS protein, the interaction with PIN1 prevents interaction with other regulatory proteins, like ubiquitin-ligases that lead to degradation pathways. In a second mode of action, the idea is largely accepted that the local isomerization modifies the global conformation of the protein substrate and hence its intrinsic activity, although this has never been directly demonstrated. Finally, isomerization catalysis is thought to regulate the (de)phosphorylation of specific pThr/pSer-Pro motifs, exemplified by the stimulation of the dephosphorylation of pThr231 of Tau by the PP2A phosphatase.

Pin1 levels are downregulated during ER stress in human neuroblastoma cells

Previously, we showed that pretangle neurons in Alzheimer's disease (AD) brain display unfolded protein stress in the endoplasmic reticulum (ER). Others showed that the peptidylprolyl isomerase Pin1 protects against tangle formation by facilitating tau dephosphorylation, corroborating with the lower expression of Pin1 observed in tangle-bearing neurons. In this study, we investigated Pin1 expression under ER stress conditions. We show that in human, but not mouse neuroblastoma cells, Pin1 is downregulated in response to ER stress, in accordance with the presence of an ER stress response element in the mouse, but not the human Pin1 gene. This study creates a starting point to investigate whether modulation of the ER stress response may prevent or delay tau pathology in AD.

Thermodynamics of Phosphopeptide Binding to the Human Peptidyl Prolyl cis/trans Isomerase Pin1

Proteins containing phosphorylated Ser/Thr-Pro motifs play key roles in numerous regulatory processes in the cell. The peptidyl prolyl cis/trans isomerase Pin1 specifically catalyzes the conformational transition of phosphorylated Ser/Thr-Pro motifs. Here we report the direct analysis of the thermodynamic properties of the interaction of the PPIase Pin1 with its substrate-analogue inhibitor Ac-Phe-D-Thr(PO3H2)-Pip-Nal-Gln-NH2 specifically targeted to the PPIase active site based on the combination of isothermal titration calorimetry and studies on inhibition of enzymatic activity of wt Pin1 and active site variants. Determination of the thermodynamic parameters revealed an enthalpically and entropically favored interaction characterized by binding enthalpy deltaH(ITC) of -6.3 +/- 0.1 kcal mol(-1) and a TdeltaS(ITC) of 4.1 +/- 0.1 kcal mol(-1). The resulting dissociation constant KD for binding of the peptidic inhibitor with 1.8 x 10(-8) M resembles the dissociation constant of a Pin1 substrate in the transition state, suggesting a transition state analogue conformation of the bound inhibitor. The strongly decreased affinity of Pin1 for ligand at increasing ionic strength implicates that the potential of bidentate binding of a substrate protein by the PPIase and the WW domain of Pin1 may be required to deploy improved efficiency and specificity of Pin1 under conditions of physiological ionic strength.

Aberrant expression of beta-catenin, Pin1 and cylin D1 in salivary adenoid cystic carcinoma: relation to tumor proliferation and metastasis

The aims of this study were to investigate the expression levels of beta-catenin, Pin1 and cyclin D1 in salivary adenoid cystic carcinomas (SACC ) and to evaluate its clinical importance, furthermore, to elucidate whether beta-catenin expression was aberrant in SACC and whether Pin1 was involved in aberrant beta-catenin and cyclin D1 expression. The expression of Pin1, beta-catenin and cyclin D1 were examined in the specimens of 65 patients with SACC by immunohistochemistry, protein and mRNA expressions were detected by western blotting and RT-PCR in four SACC cell lines. Pin1 was overexpressed in 51 cases of SACC (78%), and high levels of Pin1 expression correlated with cyclin D1 positive expression (p = 0.02). Fourteen (22%) cases showed positive immunoreactivity for beta-catenin protein in the nuclear/cytoplasmic fraction in tumor tissues, which was defined as cytoplasm/nucleus staining, among which quite evident nuclear expression of beta-catenin was detected in six cases (9%), while cyclin D1 positive expression was detected in 41 cases of SACC (63%). Reduced membranous expression of beta-catenin was detected in the cases with metastasis (11/14). Theses results suggest that Pin1 and Wnt signalling pathway are activated in SACC and may play a pivotal role in SACC carcinogenesis and metastasis.

Cooperation between different Cdc4/Fbw7 isoforms may be associated with 2-step inactivation of SCF(Cdc4) targets

The recent description of a role for an SCF ubiquitin ligase in prolyl isomerization rather than ubiquitin ligation has led to a 2-step model for inactivation of cyclin E and, possibly, other SCF(Cdc4) targets in mammalian cells. In this proposed model, targets of SCF(Cdc4) are first subjected to prolyl isomerization, creating a signal for translocation and sequestration in the nucleolus, where they are then multiubiquitylated.

Pin1 contributes to cervical tumorigenesis by regulating cyclin D1 expression

The prolyl isomerase Pin1, which specifically catalyzes conformational changes in certain proline-directed phosphorylation sites, is thought to be a critical catalyst for multiple oncogenic pathways. However, little is known about the role of Pin1 in human cervical cancer. Our previous study showed that Pin1 was overexpressed in cervical cancer tissues as well as cell lines. In this study, whether Pin1 is involved in cervical oncogenesis by regulating cyclin D1 was explored and the potential of Pin1-targeted gene silencing in inhibiting cellular growth and tumorigenicity in cervical cancer was investigated. A Pin1-directed shRNA and a sense Pin1 plasmid were constructed, and then the effects of the shRNA and the sense plasmid on HeLa cells were evaluated. The results showed that Pin1 directly regulated cyclin D1 levels. In addition, silencing Pin1 with RNAi significantly reduced cancer cell proliferation, colony formation, and strongly enhanced the apoptosis of HeLa cells. It is suggested that Pin1 may contribute to cervical tumorigenesis by regulating cyclin D1 expression and Pin1 may serve as a promising molecular target for diagnostics and therapeutics in cervical cancer.

Ubiquitylation of cyclin E requires the sequential function of SCF complexes containing distinct hCdc4 isoforms

Cyclin E, an activator of cyclin-dependent kinase 2 (Cdk2), is targeted for proteasomal degradation by phosphorylation-dependent multiubiquitylation via the ubiquitin ligase SCF(hCdc4). SCF ubiquitin ligases are composed of a core of conserved subunits and one variable subunit (an F box protein) involved in substrate recognition. We show here that multiubiquitylation of cyclin E requires the sequential function of two distinct splice variant isoforms of the F box protein hCdc4 known as alpha and gamma. SCF(hCdc4alpha) binds a complex containing cyclin E, Cdk2, and the prolyl cis/trans isomerase Pin1 and promotes the activity of Pin1 without directly ubiquitylating cyclin E. However, due to the action of this SCF(hCdc4alpha)-Pin1 complex, cyclin E becomes an efficient ubiquitylation substrate of SCF(hCdc4gamma). Furthermore, in the context of Cdc4alpha and cyclin E, mutational data suggest that Pin1 isomerizes a noncanonical proline-proline bond, with the possibility that Cdc4alpha may serve as a cofactor for altering the specificity of Pin1.

Pin1 gene mutation is a rare event in gastric cancer

The peptidyl-prolyl isomerase Pin1 is strikingly overexpressed in human cancers and is a novel regulator of beta-catenin. To determine whether somatic mutation of the Pin1 gene is involved in the development and/or progression of gastric cancer, we searched for mutations of the Pin1 gene in 95 gastric cancer specimens. The effect of Pin1 on beta-catenin expression was further examined in wild- and mutant-type Pin1-transfected HEK 293T cells. We found only one missense mutation that led to the substitution of alanine by aspartic acid at codon 118 of the Pin1 gene. On transfection study, the mutant Pin1 showed an increased expression of beta-catenin. However, the mutation had no effect on expression of the Pin1 protein in the case with Pin1 mutation. These results suggest that Pin1 may not play a role in the development or progression of gastric cancer.

Prolyl isomerase Pin1 expression predicts prognosis in patients with esophageal squamous cell carcinoma and correlates with cyclinD1 expression

Esophageal carcinoma is one of the most lethal tumors, and identification of prognostic factors for patients with this disease is important. Propyl isomerase Pin1 is overexpressed in some human cancers and thought to be an important regulator of cyclinD1. However, the relationships between Pin1 expression and clinicopathologic features in patients with esophageal squamous cell carcinoma (SCC) have not been explored. Here, we investigated the role of Pin1 in association with cyclinD1 in esophageal SCC progression and its clinicopathological significance. The expressions of Pin1 and cyclinD1 were examined immunohistochemically in surgical specimens from 119 esophageal SCC patients. The expression levels of Pin1 and cyclinD1 in 6 esophageal SCC-derived cell lines were compared with those in an immortalized human esophageal cell line by western blotting. Pin1 overexpression was correlated with lymph node metastasis (P=0.0384), and its expression was related to cyclinD1 expression. Pin1 expression was correlated with poor prognosis in esophageal SCC patients (P=0.0044), and found to be an independent prognostic factor (P=0.0277). Pin1 was overexpressed in 5 of 6 esophageal SCC-derived cell lines compared with immortalized esophageal keratinocytes. Moreover, the Pin1 level was correlated with the cyclinD1 level in 4 of the 6 cell lines. In conclusion, Pin1 expression is correlated with cyclinD1 expression and may be a useful prognostic factor for esophageal SCC.

Targeting carcinogenesis: a role for the prolyl isomerase Pin1?

Phosphorylation of proteins on serine or threonine residues that immediately precede proline (pSer/Thr-Pro) is a central signaling mechanism in cell proliferation and transformation. Recent studies indicate that certain pSer/Thr-Pro motifs in native proteins exist in two completely distinct conformations, cis and trans, whose conversion is markedly slowed down upon phosphorylation, but specifically catalyzed by the peptidyl-prolyl cis/trans isomerase Pin1. Importantly, such Pin1-catalyzed conformational changes can have profound effects on the function of many phosphorylation signaling pathways, thereby playing an important role in various cellular processes. Moreover, increasing evidence indicates that aberrant Pin1 function plays an important role in the pathogenesis of some human diseases. Notably, Pin1 is not only overexpressed in a large number of human cancers, but also is an excellent prognostic marker in some cancers. Furthermore, Pin1 overexpression can function as a critical catalyst that amplifies multiple oncogenic signaling pathways during oncogenesis. Moreover, Pin1 overexpression causes cell transformation, centrosome amplification, genomic instability, and tumor development. In contrast, Pin1 knockout in mice prevents certain oncogenes from inducing tumors and Pin1 inhibition in cancer cells suppresses their cell proliferation, transformed phenotype and tumorigenicity in nude mice as well as increases the response to other anticancer agents. These results suggest that Pin1-mediated postphosphorylation regulation may provide a unique opportunity for disrupting oncogenic pathways, and thereby represent an appealing target for novel anticancer therapies.

Testing simplified proteins models of the hPin1 WW domain

The WW domain of the human Pin1 protein for its simple topology and large amount of experimental data is an ideal candidate to assess theoretical approaches to protein folding. The purpose of this work is to compare the reliability of the chemically based Sorenson/Head-Gordon (SHG) model and a standard native centric model in reproducing, through molecular dynamics simulations, some of the well known features of the folding transition of this small domain. Our results show that the Gō model correctly reproduces the cooperative, two-state, folding mechanism of the WW-domain, while the SHG model predicts a transition occurring in two stages: a collapse, followed by a structural rearrangement. The lack of a cooperative folding in the SHG simulations appears to be related to the nonfunnel shape of the energy landscape featuring a partitioning of the native valley in subbasins corresponding to different chain chiralities. However, the SHG approach remains more reliable in estimating the phi-values with respect to Gō-like description. This may suggest that the WW-domain folding process is stirred by energetic and topological factors as well, and it highlights the better suitability of chemically based models in simulating mutations.

Identification of human STAT5-dependent gene regulatory elements based on interspecies homology

STAT5 is a transcription factor essential for hematopoietic physiology. STAT5 functions to transduce signals from cytokines to the nucleus where it regulates gene expression. Although several important transcriptional targets of STAT5 are known, most remain unidentified. To identify novel STAT5 targets, we searched chromosomes 21 and 22 for clusters of STAT5 binding sites contained within regions of interspecies homology. We identified four such regions, including one with tandem STAT5 binding sites in the first intron of the NCAM2 gene. Unlike known STAT5 binding sites, this site is found within a very large intron and resides approximately 200 kb from the first coding exon of NCAM2. We demonstrate that this region confers STAT5-dependent transcriptional activity. We show that STAT5 binds in vivo to the NCAM2 intron in the NKL natural killer cell line and that this binding is induced by cytokines that activate STAT5. Neither STAT1 nor STAT3 bind to this region, despite sharing a consensus binding sequence with STAT5. Activation of STAT4 and STAT5 causes the accumulation of both of these STATs to the NCAM2 regulatory region. Therefore, using an informatics based approach to identify STAT5 targets, we have identified NCAM2 as both a STAT4- and STAT5-regulated gene, and we show that its expression is regulated by cytokines essential for natural killer cell survival and differentiation. This strategy may be an effective way to identify functional binding regions for transcription factors with known cognate binding sites anywhere in the genome.

Oxidative modification and down-regulation of Pin1 in Alzheimer's disease hippocampus: A redox proteomics analysis

Alzheimer disease (AD) is characterized neuropathologically by intracellular neurofibrillary tangles (NFT) and of extracellular senile plaques (SP), the central core of which is amyloid beta-peptide (Abeta) derived from amyloid precursor protein (APP), a transmembrane protein. AD brain has been reported to be under oxidative stress that may play an important role in the pathogenesis and progression of AD. The present proteomics study is focused on identification of a specific target of protein oxidation in AD hippocampus that has relevance to the role of oxidative stress in AD. Here, we report that the protein, Pin1, is significantly down-regulated and oxidized in AD hippocampus. The identity of Pin1 was confirmed immunochemically. Analysis of Pin1 activity in AD brain and separately as oxidized pure Pin1 demonstrated that oxidation of Pin1 led to loss of activity. Pin1 has been implicated in multiple aspects of cell cycle regulation and dephosphorylation of tau protein as well as in AD. The in vivo oxidative modification of Pin1 as found by proteomics in AD hippocampus in the present study suggests that oxidative modification may be related to the known loss of Pin1 isomerase activity that could be crucial in AD neurofibrillary pathology. Taken together, these results provide evidence supporting a direct link between oxidative damage to neuronal Pin1 and the pathobiology of AD.