Isolation and characterization of the Pin1/Ess1p homologue inSchizosaccharomyces pombe

Small molecules targeting Pin1 as potent anticancer drugs

Background: Pin1 is a member of the evolutionarily conserved peptidyl-prolyl isomerase (PPIase) family of proteins. Following phosphorylation, Pin1-catalyzed prolyl-isomerization induces conformational changes, which serve to regulate the function of many phosphorylated proteins that play important roles during oncogenesis. Thus, the inhibition of Pin1 provides a unique means of disrupting oncogenic pathways and therefore represents an appealing target for novel anticancer therapies.

Methods: As Pin1 is conserved between yeast and humans, we employed budding yeast to establish a high-throughput screening method for the primary screening of Pin1 inhibitors. This effort culminated in the identification of the compounds HWH8-33 and HWH8-36. Multifaceted approaches were taken to determine the inhibition profiles of these compounds against Pin1 activity in vitro and in vivo, including an isomerization assay, surface plasmon resonance (SPR) technology, virtual docking, MTT proliferation assay, western blotting, cell cycle analysis, apoptosis analysis, immunofluorescence analysis, wound healing, migration assay, and nude mouse assay.

Results:In vitro, HWH8-33 and HWH8-36 could bind to purified Pin1 and inhibited its enzyme activity; showed inhibitory effects on cancer cell proliferation; led to G2/M phase arrest, dysregulated downstream protein expression, and apoptosis; and suppressed cancer cell migration. In vivo, HWH8-33 suppressed tumor growth in the xenograft mice after oral administration for 4 weeks, with no noticeable toxicity. Together, these results show the anticancer activity of HWH8-33 and HWH8-36 against Pin1 for the first time.

Conclusion: In summary, we identified two hit compounds HWH8-33 and HWH8-36, which after further structure optimization have the potential to be developed as antitumor drugs.

The kingdom of the prolyl-isomerase Pin1: The structural and functional convergence and divergence of Pin1

More than 20 years since its discovery, our understanding of Pin1 function in various diseases continues to improve. Pin1 plays a crucial role in pathogenesis and has been implicated in metabolic disorders, cardiovascular diseases, inflammatory diseases, viral infection, cancer and neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s disease. In particular, the role of Pin1 in neurodegenerative diseases and cancer has been extensively studied. Our understanding of Pin1 in cancer also led to the development of cancer therapeutic drugs targeting Pin1, with some currently in clinical trial phases. However, identifying a Pin1-specific drug with good cancer therapeutic effect remains elusive, thus leading to the continued efforts in Pin1 research. The importance of Pin1 is highlighted by the presence of Pin1 orthologs across various species: from vertebrates to invertebrates and Kingdom Animalia to Plantae. Among these Pin1 orthologs, their sequence and structural similarity demonstrate the presence of conservation. Moreover, their similar functionality between species further highlights the conservancy of Pin1. As researchers continue to unlock the mysteries of Pin1 in various diseases, using different Pin1 models might shed light on how to better target Pin1 for disease therapeutics. This review aims to highlight the various Pin1 orthologs in numerous species and their divergent functional roles. We will examine their sequence and structural similarities and discuss their functional similarities and uniqueness to demonstrate the interconnectivity of Pin1 orthologs in multiple diseases.

p66Shc in Cardiovascular Pathology

p66Shc is a widely expressed protein that governs a variety of cardiovascular pathologies by generating, and exacerbating, pro-apoptotic ROS signals. Here, we review p66Shc’s connections to reactive oxygen species, expression, localization, and discuss p66Shc signaling and mitochondrial functions. Emphasis is placed on recent p66Shc mitochondrial function discoveries including structure/function relationships, ROS identity and regulation, mechanistic insights, and how p66Shc-cyt c interactions can influence p66Shc mitochondrial function. Based on recent findings, a new p66Shc mitochondrial function model is also put forth wherein p66Shc acts as a rheostat that can promote or antagonize apoptosis. A discussion of how the revised p66Shc model fits previous findings in p66Shc-mediated cardiovascular pathology follows.

Oncogenic Hijacking of the PIN1 Signaling Network

Cellular choices are determined by developmental and environmental stimuli through integrated signal transduction pathways. These critically depend on attainment of proper activation levels that in turn rely on post-translational modifications (PTMs) of single pathway members. Among these PTMs, post-phosphorylation prolyl-isomerization mediated by PIN1 represents a unique mechanism of spatial, temporal and quantitative control of signal transduction. Indeed PIN1 was shown to be crucial for determining activation levels of several pathways and biological outcomes downstream to a plethora of stimuli. Of note, studies performed in different model organisms and humans have shown that hormonal, nutrient, and oncogenic stimuli simultaneously affect both PIN1 activity and the pathways that depend on PIN1-mediated prolyl-isomerization, suggesting the existence of evolutionarily conserved molecular circuitries centered on this isomerase. This review focuses on molecular mechanisms and cellular processes like proliferation, metabolism, and stem cell fate, that are regulated by PIN1 in physiological conditions, discussing how these are subverted in and hijacked by cancer cells. Current status and open questions regarding the use of PIN1 as biomarker and target for cancer therapy as well as clinical development of PIN1 inhibitors are also addressed.

Structure and function of the human parvulins Pin1 and Par14/17

Parvulins belong to the family of peptidyl-prolyl cis/trans isomerases (PPIases) assisting in protein folding and in regulating the function of a broad variety of proteins in all branches of life. The human representatives Pin1 and Par14/17 are directly involved in processes influencing cellular maintenance and cell fate decisions such as cell-cycle progression, metabolic pathways and ribosome biogenesis. This review on human parvulins summarizes the current knowledge of these enzymes and intends to oppose the well-studied Pin1 to its less well-examined homolog human Par14/17 with respect to structure, catalytic and cellular function.

Multiple Roles of WNT5A in Breast Cancer

Breast cancer is one of the most common malignant tumors of women. Modern combinatorial therapeutic regimens can reduce patient tumor burdens to undetectable levels, yet in many cases these tumors will relapse. Understanding of breast cancer biology, developing more potent therapeutic approaches, and overcoming resistance are of great importance. WNT5A is a non-canonical signaling member of the WNT family. Its role in breast cancer still remains unclear. Most of the evidence shows that WNT5A is a suppressor in breast cancer and loss of its expression is associated with poor prognosis, while some evidence suggests the tumorigenicity of WNT5A. WNT signaling molecules are potent targets for treatment of cancer. Therefore, understanding the role of WNT5A in breast cancer may provide new ideas and methods for breast cancer treatment. We review the evidence concerning WNT5A and breast cancer involving the signaling pathways and the molecular-targeted therapy of WNT5A. Our results show that the role WNT5A plays depends on the availability of key receptors and intercellular interactions among different cell types.

PP2A as a master regulator of the cell cycle

Protein phosphatase 2A (PP2A) plays a critical multi-faceted role in the regulation of the cell cycle. It is known to dephosphorylate over 300 substrates involved in the cell cycle, regulating almost all major pathways and cell cycle checkpoints. PP2A is involved in such diverse processes by the formation of structurally distinct families of holoenzymes, which are regulated spatially and temporally by specific regulators. Here, we review the involvement of PP2A in the regulation of three cell signaling pathways: wnt, mTOR and MAP kinase, as well as the G1→S transition, DNA synthesis and mitotic initiation. These processes are all crucial for proper cell survival and proliferation and are often deregulated in cancer and other diseases.

Prolyl isomerases in gene transcription

BACKGROUND

Peptidyl-prolyl isomerases (PPIases) are enzymes that assist in the folding of newly-synthesized proteins and regulate the stability, localization, and activity of mature proteins. They do so by catalyzing reversible (cis-trans) rotation about the peptide bond that precedes proline, inducing conformational changes in target proteins.

SCOPE OF REVIEW

This review will discuss how PPIases regulate gene transcription by controlling the activity of (1) DNA-binding transcription regulatory proteins, (2) RNA polymerase II, and (3) chromatin and histone modifying enzymes.

MAJOR CONCLUSIONS

Members of each family of PPIase (cyclophilins, FKBPs, and parvulins) regulate gene transcription at multiple levels. In all but a few cases, the exact mechanisms remain elusive. Structure studies, development of specific inhibitors, and new methodologies for studying cis/trans isomerization in vivo represent some of the challenges in this new frontier that merges two important fields.

GENERAL SIGNIFICANCE

Prolyl isomerases have been found to play key regulatory roles in all phases of the transcription process. Moreover, PPIases control upstream signaling pathways that regulate gene-specific transcription during development, hormone response and environmental stress. Although transcription is often rate-limiting in the production of enzymes and structural proteins, post-transcriptional modifications are also critical, and PPIases play key roles here as well (see other reviews in this issue). This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

The Ess1 prolyl isomerase: traffic cop of the RNA polymerase II transcription cycle

Ess1 is a prolyl isomerase that regulates the structure and function of eukaryotic RNA polymerase II. Ess1 works by catalyzing the cis/trans conversion of pSer5-Pro6 bonds, and to a lesser extent pSer2-Pro3 bonds, within the carboxy-terminal domain (CTD) of Rpb1, the largest subunit of RNA pol II. Ess1 is conserved in organisms ranging from yeast to humans. In budding yeast, Ess1 is essential for growth and is required for efficient transcription initiation and termination, RNA processing, and suppression of cryptic transcription. In mammals, Ess1 (called Pin1) functions in a variety of pathways, including transcription, but it is not essential. Recent work has shown that Ess1 coordinates the binding and release of CTD-binding proteins that function as co-factors in the RNA pol II complex. In this way, Ess1 plays an integral role in writing (and reading) the so-called CTD code to promote production of mature RNA pol II transcripts including non-coding RNAs and mRNAs.

Trypanosomatid pin1-type peptidyl-prolyl isomerase is cytosolic and not essential for cell proliferation

Pin1-type peptidyl-prolyl cis/trans isomerases (PPIases) isomerise the peptide bond of specific phosphorylated (Ser/Thr)-Pro residues, regulating various cellular events. Previously, we reported a Pin1-type PPIase in Trypanosoma cruzi, but little is known about its function and subcellular localization. Immunofluorescence analysis revealed that in contrast with Pin1-like proteins from diverse organisms, TcPin1 mainly localized in the cytoplasm and was excluded from the nuclei. In addition, RNAi-mediated downregulation of TbPin1 in Trypanosoma brucei did not abolish cell proliferation. Using yeast two-hybrid assay, we identified a MORN domain-containing protein as putative Pin1-binding partners. These data suggest that Pin1-mediated signaling mechanism plays a different role in protozoan parasites.

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.

Pin1At encoding a peptidyl-prolyl cis/trans isomerase regulates flowering time in Arabidopsis

Floral transition in plants is regulated by an integrated network of flowering genetic pathways. We show that an Arabidopsis PIN1-type parvulin 1, Pin1At, controls floral transition by accelerating cis/trans isomerization of the phosphorylated Ser/Thr-Pro motifs in two MADS-domain transcription factors, SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and AGAMOUS-LIKE 24 (AGL24). Pin1At regulates flowering, which is genetically mediated by AGL24 and SOC1. Pin1At interacts with the phosphorylated AGL24 and SOC1 in vitro and with AGL24 and SOC1 in vivo and accelerates the cis/trans conformational change of phosphorylated Ser/Thr-Pro motifs of AGL24 and SOC1. We further demonstrate that these Ser/Thr-Pro motifs are important for Pin1At function in promoting flowering through AGL24 and SOC1 and that the interaction between Pin1At and AGL24 mediates the AGL24 stability in the nucleus. Taken together, we propose that phosphorylation-dependent prolyl cis/trans isomerization of key transcription factors is an important flowering regulatory mechanism.

Protein phosphatase 2A regulatory subunits and cancer

The serine/threonine protein phosphatase (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of a number of major signaling pathways whose deregulation can contribute to cancer. The specificity and activity of PP2A are highly regulated through the interaction of a family of regulatory B subunits with the substrates. Accumulating evidence indicates that PP2A acts as a tumor suppressor. In this review we summarize the known effects of specific PP2A holoenzymes and their roles in cancer relevant pathways. In particular we highlight PP2A function in the regulation of MAPK and Wnt signaling.

The prolyl isomerase PIN1: a pivotal new twist in phosphorylation signalling and disease

Protein phosphorylation regulates many cellular processes by causing changes in protein conformation. The prolyl isomerase PIN1 has been identified as a regulator of phosphorylation signalling that catalyses the conversion of specific phosphorylated motifs between the two completely distinct conformations in a subset of proteins. PIN1 regulates diverse cellular processes, including growth-signal responses, cell-cycle progression, cellular stress responses, neuronal function and immune responses. In line with the diverse physiological roles of PIN1, it has also been linked to several diseases that include cancer, Alzheimer's disease and asthma, and thus it might represent a novel therapeutic target.

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.

Rct1, a nuclear RNA recognition motif-containing cyclophilin, regulates phosphorylation of the RNA polymerase II C-terminal domain

Phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (RNAP II) is a dynamic process that regulates transcription and coordinates it with pre-mRNA processing. We show here that Rct1, a nuclear multidomain cyclophilin from Schizosaccharomyces pombe, is encoded by an essential gene that interacts with the CTD and regulates its phosphorylation in vivo. Downregulation of Rct1 levels results in increased phosphorylation of the CTD at both Ser2 and Ser5 and in a commensurate decrease in RNAP II transcription. In contrast, overexpression of Rct1 decreases phosphorylation on both sites. The close association of Rct1 with transcriptionally active chromatin suggests a role in regulation of RNAP II transcriptional activity. These data, together with the pleiotropic phenotype upon Rct1 deregulation, suggest that this multidomain cyclophilin is an important player in maintaining the correct phosphorylation code of the CTD and thereby regulating CTD function.

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.

CK2 interacting proteins: emerging paradigms for CK2 regulation?

Protein kinase CK2 represents a small family of highly conserved protein kinases involved in a complex series of cellular events. Furthermore, CK2 has been localised to many discrete cellular sites and has an extensive and diverse array of substrates and interaction partners in cells. Despite considerable investigation, the precise mechanism(s) of regulation of CK2 in cells remains poorly understood. In consideration of the prospect that cells contain many distinct sub-populations of CK2 that are distinguished on the basis of localisation and/or interactions with other cellular components, one possibility is that there may be differential regulation of specific sub-populations of CK2. With this in mind, some of the individual sub-populations of CK2 may be regulated through particular protein-protein interactions that may play a role in recruiting CK2 into the vicinity of its substrates and/or modulating its ability to phosphorylate specific cellular targets. In this respect, here we examine two CK2-interacting proteins, namely Pin1 and CKIP-1 that have been shown to participate in the modulation of CK2 specificity or the subcellular localisation of CK2, respectively. One aspect of this work has been focused on the prospect that Pin1 interacts with CK2 in response to UV stimulation in a manner analogous to the phosphorylation-dependent interactions of CK2 that occur following the mitotic phosphorylation of CK2. A second aspect of this work involves an examination of the structural basis for interactions between CK2 and CKIP-1 with emphasis on a putative HIKE domain in CK2.

The Ess1 prolyl isomerase is dispensable for growth but required for virulence in Cryptococcus neoformans

Cryptococcus neoformans is an important human fungal pathogen that also serves as a model for studies of fungal pathogenesis. C. neoformans contains several genes encoding peptidyl-prolyl cis/trans isomerases (PPIases), enzymes that catalyse changes in the folding and conformation of target proteins. Three distinct classes of PPIases have been identified: cyclophilins, FK506-binding proteins (FKBPs) and parvulins. This paper reports the cloning and characterization of ESS1, which is believed to be the first (and probably only) parvulin-class PPIase in C. neoformans. It is shown that ESS1 from C. neoformans is structurally and functionally homologous to ESS1 from Saccharomyces cerevisiae, which encodes an essential PPIase that interacts with RNA polymerase II and plays a role in transcription. In C. neoformans, ESS1 was found to be dispensable for growth, haploid fruiting and capsule formation. However, ESS1 was required for virulence in a murine model of cryptococcosis. Loss of virulence might have been due to the defects in melanin and urease production observed in ess1 mutants, or to defects in transcription of as-yet-unidentified virulence genes. The fact that Ess1 is not essential in C. neoformans suggests that, in this organism, some of its functions might be subsumed by other prolyl isomerases, in particular, cyclophilins Cpa1 or Cpa2. This is supported by the finding that ess1 mutants were hypersensitive to cyclosporin A. C. neoformans might therefore be a useful organism in which to investigate crosstalk among different families of prolyl isomerases.

Vanishingly low levels of Ess1 prolyl-isomerase activity are sufficient for growth in Saccharomyces cerevisiae

Ess1 is an essential peptidylprolyl-cis/trans-isomerase in the yeast Saccharomyces cerevisiae. Ess1 and its human homolog, Pin1, bind to phospho-Ser-Pro sites within proteins, including the carboxyl-terminal domain (CTD) of Rpb1, the largest subunit of RNA polymerase II (pol II). Ess1 and Pin1 are thought to control mRNA synthesis by catalyzing conformational changes in Rpb1 that affect interaction of cofactors with the pol II transcription complex. Here we have characterized wild-type and mutant Ess1 proteins in vitro and in vivo. We found that Ess1 preferentially binds and isomerizes CTD heptad-repeat (YSPTSPS) peptides that are phosphorylated on Ser5. Binding by the mutant proteins in vitro was essentially normal, and the proteins were largely stable in vivo. However, their catalytic activities were reduced >1,000-fold. These data along with results of in vivo titration experiments indicate that Ess1 isomerase activity is required for growth, but only at vanishingly low levels. We found that although wild-type cells contain about approximately 200,000 molecules of Ess1, a level of fewer than 400 molecules per cell is sufficient for growth. In contrast, higher levels of Ess1 were required for growth in the presence of certain metabolic inhibitors, suggesting that Ess1 is important for tolerance to environmental challenge.

PINA Is Essential for Growth and Positively Influences NIMA Function in Aspergillus nidulans

The phospho-Ser/Thr-directed prolyl-isomerase Pin1 was originally identified in vertebrate systems as a negative regulator of NIMA, a Ser/Thr protein kinase that regulates the G(2)/M transition in Aspergillus nidulans. Here we explore the physiological roles of the Pin1 orthologue, PINA, in A. nidulans and evaluate the relevance of the interaction of PINA with NIMA in this fungus. We find pinA to be an essential gene in A. nidulans. In addition, when PINA levels are reduced 50-fold the cells grow at a reduced rate. Upon germination under conditions that repress PINA expression, the cells are delayed in the interphase activation of NIMX(cdc2), whereas they traverse the other phases of the cell cycle at a similar rate to controls. These results indicate that a marked reduction of PINA results in a lengthening of G(1). Additionally, PINA repression increases the rate at which the cells enter mitosis following release from a hydroxyurea arrest without altering the sensitivity of the fungus to agents that activate the replication or DNA damage checkpoints. In contrast to predictions based on Pin1, the physical interaction between PINA and NIMA is primarily dependent upon the prolylisomerase domain of PINA and the C-terminal 303 amino acids of NIMA. Finally, reduction of PINA levels exacerbates the nimA5 temperature-sensitive mutant, whereas overexpression of PINA decreases the severity of this mutation, results that are consistent with a positive genetic interaction between PINA and NIMA. Thus, although PINA is essential and positively regulates NIMA function, A. nidulans is most sensitive to a reduction in PINA concentration in G(1) rather than in G(2)/M.

Regulation of peptide bond cis/trans isomerization by enzyme catalysis and its implication in physiological processes

In some cases, the slow rotational movement underlying peptide bond cis/trans isomerizations is found to control the biological activity of proteins. Peptide bond cis/trans isomerases as cyclophilins, Fk506-binding proteins, parvulins, and bacterial hsp70 generally assist in the interconversion of the polypeptide substrate cis/trans isomers, and rate acceleration is the dominating mechanism of action in cells. We present evidence disputing the hypothesis that some of the molecular properties of these proteins play an auxiliary role in enzyme function.

TheESS1Prolyl Isomerase and Its SuppressorBYE1Interact With RNA Pol II to Inhibit Transcription Elongation inSaccharomyces cerevisiae

Transcription by RNA polymerase II (pol II) requires the ordered binding of distinct protein complexes to catalyze initiation, elongation, termination, and coupled mRNA processing events. One or more proteins from each complex are known to bind pol II via the carboxy-terminal domain (CTD) of the largest subunit, Rpb1. How binding is coordinated is not known, but it might involve conformational changes in the CTD induced by the Ess1 peptidyl-prolyl cis/trans isomerase. Here, we examined the role of ESS1 in transcription by studying one of its multicopy suppressors, BYE1. We found that Bye1 is a negative regulator of transcription elongation. This led to the finding that Ess1 also inhibits elongation; Ess1 opposes elongation factors Dst1 and Spt4/5, and overexpression of ESS1 makes cells more sensitive to the elongation inhibitor 6-AU. In reporter gene assays, ess1 mutations reduce the ability of elongation-arrest sites to stall polymerase. We also show that Ess1 acts positively in transcription termination, independent of its role in elongation. We propose that Ess1-induced conformational changes attenuate pol II elongation and help coordinate the ordered assembly of protein complexes on the CTD. In this way, Ess1 might regulate the transition between multiple steps of transcription.

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.

Pin1 and Par14 peptidyl prolyl isomerase inhibitors block cell proliferation

Disruption of the parvulin family peptidyl prolyl isomerase (PPIase) Pin1 gene delays reentry into the cell cycle when quiescent primary mouse embryo fibroblasts are stimulated with serum. Since Pin1 regulates cell cycle progression, a Pin1 inhibitor would be expected to block cell proliferation. To identify such inhibitors, we screened a chemical compound library for molecules that inhibited human Pin1 PPIase activity in vitro. We found a set of compounds that inhibited Pin1 PPIase activity in vitro with low microM IC50s and inhibited the growth of several cancer lines. Among the inhibitors, PiB, diethyl-1,3,6,8-tetrahydro-1,3,6,8-tetraoxobenzo[lmn] phenanthroline-2,7-diacetate ethyl 1,3,6,8-tetrahydro-1,3,6,8-tetraoxo-benzo[lmn] phenanthroline-(2H,7H)-diacetate, had the least nonspecific toxicity. These results suggest that Pin1 inhibitors could be used as a novel type of anticancer drug that acts by blocking cell cycle progression.

Peptidyl-prolyl isomerases: a new twist to transcription

Peptidyl-prolyl isomerases (PPIs) catalyse the cis-trans isomerisation of peptide bonds N-terminal to proline residues in polypeptide chains. They have roles in the folding of newly synthesised proteins and in the function of the immune system. In addition, members of the parvulin-like family of PPIs have been implicated in cell cycle control. Their activity is directed by the prior phosphorylation of target proteins in both yeast and mammalian cells. More recent data have illustrated that they may also influence other nuclear events. This review examines PPI activity in the context of eukaryotic transcriptional regulation. The findings are consistent with a two-step model of conformational control, in which the outcome depends on the transcription factor involved.

Pinning down proline-directed phosphorylation signaling

The reversible phosphorylation of proteins on serine or threonine residues preceding proline (Ser/Thr-Pro) is a major cellular signaling mechanism. Although it is proposed that phosphorylation regulates the function of proteins by inducing a conformational change, there are few clues about the actual conformational changes and their importance. Recent identification of the novel prolyl isomerase Pin1 that specifically isomerizes only the phosphorylated Ser/Thr-Pro bonds in certain proteins led us to propose a new signaling mechanism, whereby prolyl isomerization catalytically induces conformational changes in proteins following phosphorylation to regulate protein function. Emerging data indicate that such conformational changes have profound effects on catalytic activity, dephosphorylation, protein-protein interactions, subcellular location and/or turnover. Furthermore, this post-phosphorylation mechanism might play an important role in cell growth control and diseases such as cancer and Alzheimer's.

Current awareness on yeast

In order to keep subscribers up-to-date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly-published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (3 weeks journals - search completed 5th. Dec. 2001)