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

The peptidyl-prolyl isomerase Pin1 controls GM-CSF-induced priming of NADPH oxidase in human neutrophils and priming at inflammatory sites

The production of superoxide anions and other reactive oxygen species (ROS) by neutrophils is necessary for host defense against microbes. However, excessive ROS production can induce cell damage that participates in the inflammatory response. Superoxide anions are produced by the phagocyte NADPH oxidase, a multicomponent enzyme system consisting of two transmembrane proteins (gp91phox/NOX2 and p22phox) and four soluble cytosolic proteins (p40phox, p47phox, p67phox and the small G proteins Rac1/2). Stimulation of neutrophils by various agonists, such as the bacterial peptide formyl-Met-Leu-Phe (fMLF), induces NADPH oxidase activation and superoxide production, a process that is enhanced by the pro-inflammatory cytokines such as GM-CSF. The pathways involved in this GM-CSF-induced up-regulation or priming are not fully understood. Here we show that GM-CSF induces the activation of the prolyl cis/trans isomerase Pin1 in human neutrophils. Juglone and PiB, two selective Pin1 inhibitors, were able to block GM-CSF-induced priming of ROS production by human neutrophils. Interestingly, GM-CSF induced Pin1 binding to phosphorylated p47phox at Ser345. Neutrophils isolated from synovial fluid of patients with rheumatoid arthritis are known to be primed. Here we show that Pin1 activity was also increased in these neutrophils and that Pin1 inhibitors effectively inhibited ROS hyperproduction by the same cells. These results suggest that the prolyl cis/trans isomerase Pin1 may control GM-CSF-induced priming of ROS production by neutrophils and priming of neutrophils in synovial fluid of rheumatoid arthritis patients. Pharmacological targeting of Pin1 may be a valuable approach to the treatment of inflammation.

Long-term normalization of calcineurin activity in model mice rescues Pin1 and attenuates Alzheimer's phenotypes without blocking peripheral T cell IL-2 response

BACKGROUND

Current treatments for Alzheimer's disease (AD) have largely failed to yield significant therapeutic benefits. Novel approaches are desperately needed to help address this immense public health issue. Data suggests that early intervention at the first stages of mild cognitive impairment may have a greater chance for success. The calcineurin (CN)-Pin1 signaling cascade can be selectively targeted with tacrolimus (FK506), a highly specific, FDA-approved CN inhibitor used safely for > 20 years in solid organ transplant recipients. AD prevalence was significantly reduced in solid organ recipients treated with FK506.

METHODS

Time release pellets were used to deliver constant FK506 dosage to APP/PS1 mice without deleterious manipulation or handling. Immunofluorescence, histology, molecular biology, and behavior were used to evaluate changes in AD pathology.

RESULTS

FK506 can be safely and consistently delivered into juvenile APP/PS1 mice via time-release pellets to levels roughly seen in transplant patients, leading to the normalization of CN activity and reduction or elimination of AD pathologies including synapse loss, neuroinflammation, and cognitive impairment. Pin1 activity and function were rescued despite the continuing presence of high levels of transgenic Aβ42. Indicators of neuroinflammation including Iba1 positivity and IL-6 production were also reduced to normal levels. Peripheral blood mononuclear cells (PBMC) obtained during treatment or splenocytes isolated at euthanasia activated normally after mitogens.

CONCLUSIONS

Low-dose, constant FK506 can normalize CNS CN and Pin1 activity, suppress neuroinflammation, and attenuate AD-associated pathology without blocking peripheral IL-2 responses making repurposed FK506 a viable option for early, therapeutic intervention in AD.

Function and regulation of cis P-tau in the pathogenesis and treatment of conventional and nonconventional tauopathies

Conventional tauopathies are a group of disease characterized by tau inclusions in the brains, including Alzheimer's disease (AD), Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and certain types of frontotemporal dementia (FTD), among which AD is the most prevalent. Extensive post-translational modifications, especially hyperphosphorylation, and abnormal aggregation of tau protein underlie tauopathy. Cis-trans isomerization of protein plays an important role in protein folding, function, and degradation, which is regulated by peptidyl-proline isomerases (PPIases). Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), the only PPIase found to isomerize Pro following phosphorylated Ser or Thr residues, alters phosphorylated tau protein conformation at pT231-P motif. The cis P-tau but not trans P-tau serves as an early driver of multiple neurodegenerative disease, encompassing AD, traumatic brain injury (TBI), chronic traumatic encephalopathy (CTE), and vascular contributions to cognitive impairment and dementia (VCID). Cis but not trans P-tau is resistant to protein dephosphorylation and degradation, and also prone to protein aggregation. Cis P-tau loses its ability to stabilize microtubule, causing and spreading tauopathy mainly in axons, a pathological process called cistauosis. The conformation-specific monoclonal antibody that targets only the cis P-tau serves as a very early diagnosis method and a potential treatment of not only conventional tauopathies but also nonconventional tauopathies such as VCID, with clinical trials ongoing. Notably, cis P-tau antibody is the only clinical-stage Alzheimer's therapeutic that has shown the efficacy in animal models of not only AD but also TBI and stroke, which are very early stages of dementia. Here we review the identification and pathological consequences of cis pt231-tau, the role of its regulator Pin1, as well as the clinical implication of cis pt231-tau conformation-specific antibody in conventional and nonconventional tauopathies.

Dual targeting of mTOR/IL-17A and autophagy by fisetin alleviates psoriasis-like skin inflammation

Psoriasis is a chronic autoimmune inflammatory skin disorder characterized by epidermal hyperplasia and aberrant immune response. In addition to aberrant cytokine production, psoriasis is associated with activation of the Akt/mTOR pathway. mTOR/S6K1 regulates T-lymphocyte activation and migration, keratinocytes proliferation and is upregulated in psoriatic lesions. Several drugs that target Th1/Th17 cytokines or their receptors have been approved for treating psoriasis in humans with variable results necessitating improved therapies. Fisetin, a natural dietary polyphenol with anti-oxidant and anti-proliferative properties, covalently binds mTOR/S6K1. The effects of fisetin on psoriasis and its underlying mechanisms have not been clearly defined. Here, we evaluated the immunomodulatory effects of fisetin on Th1/Th17-cytokine-activated adult human epidermal keratinocytes (HEKa) and anti-CD3/CD28-stimulated inflammatory CD4+ T cells and compared these activities with those of rapamycin (an mTOR inhibitor). Transcriptomic analysis of HEKa revealed 12,713 differentially expressed genes (DEGs) in the fisetin-treated group compared to 7,374 DEGs in the rapamycin-treated group, both individually compared to a cytokine treated group. Gene ontology analysis revealed enriched functional groups related to PI3K/Akt/mTOR signaling pathways, psoriasis, and epidermal development. Using in silico molecular modeling, we observed a high binding affinity of fisetin to IL-17A. In vitro, fisetin significantly inhibited mTOR activity, increased the expression of autophagy markers LC3A/B and Atg5 in HEKa cells and suppressed the secretion of IL-17A by activated CD4+ T lymphocytes or T lymphocytes co-cultured with HEKa. Topical administration of fisetin in an imiquimod (IMQ)-induced mouse psoriasis model exhibited a better effect than rapamycin in reducing psoriasis-like inflammation and Akt/mTOR phosphorylation and promoting keratinocyte differentiation and autophagy in mice skin lesions. Fisetin also significantly inhibited T-lymphocytes and F4/80+ macrophage infiltration into skin. We conclude that fisetin potently inhibits IL-17A and the Akt/mTOR pathway and promotes keratinocyte differentiation and autophagy to alleviate IMQ-induced psoriasis-like disease in mice. Altogether, our findings suggest fisetin as a potential treatment for psoriasis and possibly other inflammatory skin diseases.

Molecular biological mechanism of action in cancer therapies: Juglone and its derivatives, the future of development

Juglone (5 - hydroxy - 1, 4 - naphthalene diketone) is a kind of natural naphthoquinone, present in the roots, leaves, nut-hulls, bark and wood of walnut trees. Recent studies have found that Juglone has special significance in the treatment of cancer, which plays a significant role in the resistance of cancer cell proliferation, induction of cancer cell apoptosis, induction of autophagy, anti-angiogenesis and inhibition of cancer cell migration and invasion, etc. Additionally, its derivatives also play a tumor suppressive effect. In conclusion, Juglone and its derivatives have been identified as effective anticancer drugs. This paper reviews action mechanisms of Juglone and its derivatives in cancer treatment.

Molecular Mechanisms of Parathyroid Disorders in Chronic Kidney Disease

Secondary hyperparathyroidism (SHP) is a common complication of chronic kidney disease (CKD) that induces morbidity and mortality in patients. How CKD stimulates the parathyroid to increase parathyroid hormone (PTH) secretion, gene expression and cell proliferation remains an open question. In experimental SHP, the increased PTH gene expression is post-transcriptional and mediated by PTH mRNA–protein interactions that promote PTH mRNA stability. These interactions are orchestrated by the isomerase Pin1. Pin1 participates in conformational change-based regulation of target proteins, including mRNA-binding proteins. In SHP, Pin1 isomerase activity is decreased, and thus, the Pin1 target and PTH mRNA destabilizing protein KSRP fails to bind PTH mRNA, increasing PTH mRNA stability and levels. An additional level of post-transcriptional regulation is mediated by microRNA (miRNA). Mice with parathyroid-specific knockout of Dicer, which facilitates the final step in miRNA maturation, lack parathyroid miRNAs but have normal PTH and calcium levels. Surprisingly, these mice fail to increase serum PTH in response to hypocalcemia or uremia, indicating a role for miRNAs in parathyroid stimulation. SHP often leads to parathyroid hyperplasia. Reduced expressions of parathyroid regulating receptors, activation of transforming growth factor α-epidermal growth factor receptor, cyclooxygenase 2-prostaglandin E2 and mTOR signaling all contribute to the enhanced parathyroid cell proliferation. Inhibition of mTOR by rapamycin prevents and corrects the increased parathyroid cell proliferation of SHP. This review summarizes the current knowledge on the mechanisms that stimulate the parathyroid cell at multiple levels in SHP.

Pin1 as Molecular Switch in Vascular Endothelium: Notes on Its Putative Role in Age-Associated Vascular Diseases

By controlling the change of the backbones of several cellular substrates, the peptidyl-prolyl cis-trans isomerase Pin1 acts as key fine-tuner and amplifier of multiple signaling pathways, thereby inducing several biological consequences, both in physiological and pathological conditions. Data from the literature indicate a prominent role of Pin1 in the regulating of vascular homeostasis. In this review, we will critically dissect Pin1’s role as conformational switch regulating the homeostasis of vascular endothelium, by specifically modulating nitric oxide (NO) bioavailability. In this regard, Pin1 has been reported to directly control NO production by interacting with bovine endothelial nitric oxide synthase (eNOS) at Ser¹¹⁶-Pro¹¹⁷ (human equivalent is Ser¹¹⁴-Pro¹¹⁵) in a phosphorylation-dependent manner, regulating its catalytic activity, as well as by regulating other intracellular players, such as VEGF and TGF-β, thereby impinging upon NO release. Furthermore, since Pin1 has been found to act as a critical driver of vascular cell proliferation, apoptosis, and inflammation, with implication in many vascular diseases (e.g., diabetes, atherosclerosis, hypertension, and cardiac hypertrophy), evidence indicating that Pin1 may serve a pivotal role in vascular endothelium will be discussed. Understanding the role of Pin1 in vascular homeostasis is crucial in terms of finding a new possible therapeutic player and target in vascular pathologies, including those affecting the elderly (such as small and large vessel diseases and vascular dementia) or those promoting the full expression of neurodegenerative dementing diseases.

Pathological Role of Pin1 in the Development of DSS-Induced Colitis

Inflammatory bowel diseases (IBDs) are serious disorders of which the etiologies are not, as yet, fully understood. In this study, Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) protein was shown to be dramatically upregulated in the colons of dextran sodium sulfate (DSS)-induced ulcerative colitis model mice. Interestingly, Pin1 knockout (KO) mice exhibited significant attenuation of DSS-induced colitis compared to wild-type (WT) mice, based on various parameters, including body weight, colon length, microscopic observation of the intestinal mucosa, inflammatory cytokine expression, and cleaved caspase-3. In addition, a role of Pin1 in inflammation was suggested because the percentage of M1-type macrophages in the colon was decreased in the Pin1 KO mice while that of M2-type macrophages was increased. Moreover, Pin1 KO mice showed downregulation of both Il17 and Il23a expression in the colon, both of which have been implicated in the development of colitis. Finally, oral administration of Pin1 inhibitor partially but significantly prevented DSS-induced colitis in mice, raising the possibility of Pin1 inhibitors serving as therapeutic agents for IBD.

Targeting Pin1 for Modulation of Cell Motility and Cancer Therapy

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) specifically binds and isomerizes the phosphorylated serine/threonine-proline (pSer/Thr-Pro) motif, which leads to changes in protein conformation and function. Pin1 is widely overexpressed in cancers and plays an important role in tumorigenesis. Mounting evidence has revealed that targeting Pin1 is a potential therapeutic approach for various cancers by inhibiting cell proliferation, reducing metastasis, and maintaining genome stability. In this review, we summarize the underlying mechanisms of Pin1-mediated upregulation of oncogenes and downregulation of tumor suppressors in cancer development. Furthermore, we also discuss the multiple roles of Pin1 in cancer hallmarks and examine Pin1 as a desirable pharmaceutical target for cancer therapy. We also summarize the recent progress of Pin1-targeted small-molecule compounds for anticancer activity.

Serum peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 in combination with C-reactive protein and white blood cell as novel predictors for infants with community-acquired pneumonia

The aim of this study was to investigate the predictive value of peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) with C-reactive protein (CRP) and white blood cell (WBC) count for community-acquired pneumonia (CAP) in infants. A total of 84 hospitalized infants with CAP and 69 healthy infants were included in this study. The clinical manifestations and laboratory assay results of infants were recorded. Serum Pin1 level was estimated by enzyme-linked immunosorbent assay. The median serum Pin1 concentration in infants with CAP was significantly higher than that in controls (1.44 vs. 0.21 ng/mL, P < 0.0001). Receiver operating characteristic (ROC) curve analysis showed that the area under the ROC curve (AUC) of the combination Pin1, CRP and WBC (Pin1 + CRP + WBC, 0.943) was higher than Pin1, CRP, WBC alone or the combination of Pin1 and CRP ( P < 0.05). The sensitivity of Pin1 + CRP + WBC (94.0%) was higher than that of Pin1, CRP, WBC alone, or any two combined ( P < 0.05). Pin1 + CRP + WBC also had a high negative predictive value (91.4%). Moreover, serum Pin1 alone had a high specificity (97.0%) and excellent positive predictive value (96.6%) for infants with CAP, which were higher than WBC, Pin1 and WBC in combination, CRP and WBC in combination, and Pin1 + CRP + WBC ( P < 0.05). Therefore, serum Pin 1 was highly expressed in infants with CAP and can singly or in combination with CRP and WBC represent promising novel predictors for infants with CAP.

Post-transcriptional mechanisms regulating parathyroid hormone gene expression in secondary hyperparathyroidism

Parathyroid hormone (PTH) regulates serum calcium levels and bone strength. Secondary hyperparathyroidism (SHP) is a common complication of chronic kidney disease (CKD) that correlates with morbidity and mortality. In experimental SHP, the increased PTH gene expression is due to increased PTH mRNA stability and is mediated by protein-PTH mRNA interactions. Adenosine-uridine-rich binding factor 1 (AUF1) stabilizes and K-homology splicing regulatory protein (KSRP) destabilizes PTH mRNA. The peptidyl-prolyl cis/trans isomerase Pin1 acts on target proteins, including mRNA-binding proteins. Pin1 leads to KSRP dephosphorylation, but in SHP, parathyroid Pin1 activity is decreased and phosphorylated KSRP fails to bind PTH mRNA, leading to increased PTH mRNA stability and levels. A further level of post-transcriptional regulation occurs through microRNA (miRNA). Dicer mediates the final step of miRNA maturation. Parathyroid-specific Dicer knockout mice that lack miRNAs in the parathyroid develop normally. Surprisingly, these mice fail to increase serum PTH in response to both hypocalcemia and CKD, indicating that parathyroid Dicer and miRNAs are essential for stimulation of the parathyroid. Human and rodent parathyroids share similar miRNA profiles that are altered in hyperparathyroidism. The evolutionary conservation of abundant miRNAs and their regulation in hyperparathyroidism indicate their significance in parathyroid physiology and pathophysiology. let-7 and miR-148 antagonism modifies PTH secretion in vivo and in vitro, suggesting roles for specific miRNAs in parathyroid function. This review summarizes the current knowledge on the post-transcriptional mechanisms of PTH gene expression in SHP and the central contribution of miRNAs to the high serum PTH levels of both primary hyperparathyroidism and SHP.

Pinning Down the Transcription: A Role for Peptidyl-Prolyl cis-trans Isomerase Pin1 in Gene Expression

Pin1 is a peptidyl-prolyl cis-trans isomerase that specifically binds to a phosphorylated serine or threonine residue preceding a proline (pSer/Thr-Pro) motif and catalyzes the cis-trans isomerization of proline imidic peptide bond, resulting in conformational change of its substrates. Pin1 regulates many biological processes and is also involved in the development of human diseases, like cancer and neurological diseases. Many Pin1 substrates are transcription factors and transcription regulators, including RNA polymerase II (RNAPII) and factors associated with transcription initiation, elongation, termination and post-transcription mRNA decay. By changing the stability, subcellular localization, protein-protein or protein-DNA/RNA interactions of these transcription related proteins, Pin1 modulates the transcription of many genes related to cell proliferation, differentiation, apoptosis and immune response. Here, we will discuss how Pin regulates the properties of these transcription relevant factors for effective gene expression and how Pin1-mediated transcription contributes to the diverse pathophysiological functions of Pin1.

Fisetin, a 3,7,3',4'-Tetrahydroxyflavone Inhibits the PI3K/Akt/mTOR and MAPK Pathways and Ameliorates Psoriasis Pathology in 2D and 3D Organotypic Human Inflammatory Skin Models

Psoriasis is a chronic immune-mediated skin disease that involves the interaction of immune and skin cells, and is characterized by cytokine-driven epidermal hyperplasia, deviant differentiation, inflammation, and angiogenesis. Because the available treatments for psoriasis have significant limitations, dietary products are potential natural sources of therapeutic molecules, which can repair the molecular defects associated with psoriasis and could possibly be developed for its management. Fisetin (3,7,3',4'-tetrahydroxyflavone), a phytochemical naturally found in pigmented fruits and vegetables, has demonstrated proapoptotic and antioxidant effects in several malignancies. This study utilized biochemical, cellular, pharmacological, and tissue engineering tools to characterize the effects of fisetin on normal human epidermal keratinocytes (NHEKs), peripheral blood mononuclear cells (PBMC), and CD4+ T lymphocytes in 2D and 3D psoriasis-like disease models. Fisetin treatment of NHEKs dose- and time-dependently induced differentiation and inhibited interleukin-22-induced proliferation, as well as activation of the PI3K/Akt/mTOR pathway. Fisetin treatment of TNF-α stimulated NHEKs also significantly inhibited the activation of p38 and JNK, but had enhanced effect on ERK1/2 (MAPK). In addition, fisetin treatment significantly decreased the secretion of Th1/Th-17 pro-inflammatory cytokines, particularly IFN-γ and IL-17A by 12-O-tetradecanolylphorbol 13-acetate (TPA)-stimulated NHEKs and anti-CD3/CD28-activated human PBMCs. Furthermore, we established the in vivo relevance of fisetin functions, using a 3D full-thickness human skin model of psoriasis (FTRHSP) that closely mimics in vivo human psoriatic skin lesions. Herein, fisetin significantly ameliorated psoriasis-like disease features, and decreased the production of IL-17 by CD4+ T lymphocytes co-cultured with FTRHSP. Collectively, our data identify the prodifferentiative, antiproliferative, and anti-inflammatory effects of fisetin, via modulation of the PI3K-Akt-mTOR and p38/JNK pathways and the production of cytokines in 2D and 3D human skin models of psoriasis. These results suggest that fisetin has a great potential to be developed as an effective and inexpensive agent for the treatment of psoriasis and other related inflammatory skin disorders.

Juglone eliminates MDSCs accumulation and enhances antitumor immunity

Myeloid-derived suppressor cells (MDSCs) contribute to immune activity suppression and promote the tumor progression. Elimination of MDSCs is a promising cancer therapeutic strategy, and some chemotherapeutic agents have been reported to hamper tumor progression by suppressing MDSCs. Juglone has been showed to exert a direct cytotoxic effect on tumor cells. However, the effect of juglone on MDSCs and anti-tumor immune statue has remained unexplored. In our study, we observed that juglone suppressed tumor growth and metastasis markedly, and the tumor growth suppression in immunocompetent mice was more drastic than that in immunodeficient mice. Juglone reduced the accumulation of MDSCs and increased IFN-γ production by CD8⁺ T cells. Consistently, juglone affected myeloid cells differentiation and maturation, impairing the immunosuppressive functions of MDSCs. Moreover, juglone down-regulated the level of IL-1β which was mediating accumulation of MDSCs. In addition, juglone inhibited 5FU-induced liver injury in a colorectal carcinoma-bearing mice model. Thus, our work suggests that the anti-tumor effect of juglone is mediated, at least in part, by eliminating accumulation of MDSCs.

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.

Prolyl isomerase Pin1: a promoter of cancer and a target for therapy

Pin1 is the only known peptidyl-prolyl cis–trans isomerase (PPIase) that specifically recognizes and isomerizes the phosphorylated Serine/Threonine-Proline (pSer/Thr-Pro) motif. The Pin1-mediated structural transformation posttranslationally regulates the biofunctions of multiple proteins. Pin1 is involved in many cellular processes, the aberrance of which lead to both degenerative and neoplastic diseases. Pin1 is highly expressed in the majority of cancers and its deficiency significantly suppresses cancer progression. According to the ground-breaking summaries by Hanahan D and Weinberg RA, the hallmarks of cancer comprise ten biological capabilities. Multiple researches illuminated that Pin1 contributes to these aberrant behaviors of cancer via promoting various cancer-driving pathways. This review summarized the detailed mechanisms of Pin1 in different cancer capabilities and certain Pin1-targeted small-molecule compounds that exhibit anticancer activities, expecting to facilitate anticancer therapies by targeting Pin1.

Protein Translation and Signaling in Human Eosinophils

We have recently reported that, unlike IL-5 and GM-CSF, IL-3 induces increased translation of a subset of mRNAs. In addition, we have demonstrated that Pin1 controls the activity of mRNA binding proteins, leading to enhanced mRNA stability, GM-CSF protein production and prolonged eosinophil (EOS) survival. In this review, discussion will include an overview of cap-dependent protein translation and its regulation by intracellular signaling pathways. We will address the more general process of mRNA post-transcriptional regulation, especially regarding mRNA binding proteins, which are critical effectors of protein translation. Furthermore, we will focus on (1) the roles of IL-3-driven sustained signaling on enhanced protein translation in EOS, (2) the mechanisms regulating mRNA binding proteins activity in EOS, and (3) the potential targeting of IL-3 signaling and the signaling leading to mRNA binding activity changes to identify therapeutic targets to treat EOS-associated diseases.

Human eosinophil activin A synthesis and mRNA stabilization are induced by the combination of IL-3 plus TNF

Eosinophils contribute to immune regulation and wound healing/fibrosis in various diseases including asthma. Growing appreciation for the role of activin A in such processes led us to hypothesize that eosinophils are a source of this TGF-β superfamily member. TNFα (TNF) induces activin A by other cell types and is often present at the site of allergic inflammation along with the eosinophil activating common β (βc) chain-signaling cytokines (IL-5, IL-3, GM-CSF). Previously, we established that the combination of TNF plus a βc chain-signaling cytokine synergistically induces eosinophil synthesis of the remodeling enzyme MMP-9. Therefore, eosinophils were stimulated ex vivo by these cytokines and in vivo through an allergen-induced airway inflammatory response. In contrast to IL-5+TNF or GM-CSF+TNF, the combination of IL-3+TNF synergistically induced activin A synthesis and release by human blood eosinophils. IL-3+TNF enhanced activin A mRNA stability, which required sustained signaling of pathways downstream of p38 and ERK MAP kinases. In vivo, following segmental airway allergen challenge of subjects with mild allergic asthma, activin A mRNA was upregulated in airway eosinophils compared to circulating eosinophils, and ex vivo, circulating eosinophils tended to release activin A in response to IL-3+TNF. These data provide evidence that eosinophils release activin A and that this function is enhanced when eosinophils are present in an allergen-induced inflammatory environment. Moreover, these data provide the first evidence for post-transcriptional control of activin A mRNA. We propose that, an environment rich in IL-3+TNF will lead to eosinophil–derived activin A, which plays an important role in regulating inflammation and/or fibrosis.

T-cells require post-transcriptional regulation for accurate immune responses

Cytotoxic T-cells are crucial to protect us from intracellular pathogens and malignant cells. When T-cells become activated, they rapidly secrete cytokines, chemokines and cytotoxic granules that are critical to clear infected cells. However, when not properly regulated, these toxic effector molecules become one of the key mediators of autoimmune diseases. Therefore, a tight and multi-layered regulation of gene expression and protein production is required to ensure a protective yet balanced immune response. In this review, we describe how post-transcriptional events modulate the production of effector molecules in T-cells. In particular, we will focus on the role of cis-regulatory elements within the 3′-UTR of specific mRNAs and on RNA-binding proteins (RBPs) and non-coding RNAs that control the initiation and resolution of T-cell responses.

Determinants of eosinophil survival and apoptotic cell death

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

COT phosphorylates prolyl-isomerase Pin1 to promote tumorigenesis in breast cancer

Pin1, a conserved eukaryotic Peptidyl-prolyl cis/trans isomerase, has profound effects on numerous key-signaling molecules, and its deregulation contributes to disease, particularly cancer. Although Pin1-mediated prolyl isomerization is an essential and novel regulatory mechanism for protein phosphorylation, little is known about the upstream signaling pathway(s) that regulates Pin1 activity. Here, we identify MAP3K-related serine-threonine kinase (the gene encoding COT/Tpl2) as a kinase responsible for phosphorylation of Pin1 Ser16. COT interacts with and phosphorylates Pin1 on Ser16. Consequently, Pin1 Ser16 phosphorylation by COT increases cyclin D1 abundance and enhances tumorigenecity of MCF7 cells. In contrast, depletion of COT in MCF7 cells leads to downregulation of Pin1 Ser16 phosphorylation, which subsequently decrease cyclin D1 levels, inhibiting tumorigenecity of MCF7 cells. In a xenograft model, treatment of TKI, a COT inhibitor, and Juglone, a Pin1 inhibitor, abrogates tumor growth. In human breast cancer patients, immunohistochemical staining shows that Pin1 pSer16 levels are positively correlated with COT levels, providing strong evidence for an essential role of the COT/Pin1 axis in conveying oncogenic signals to promote aggressiveness in human breast cancer.

Roles of Prolyl Isomerases in RNA-Mediated Gene Expression

The peptidyl-prolyl cis-trans isomerases (PPIases) that include immunophilins (cyclophilins and FKBPs) and parvulins (Pin1, Par14, Par17) participate in cell signaling, transcription, pre-mRNA processing and mRNA decay. The human genome encodes 19 cyclophilins, 18 FKBPs and three parvulins. Immunophilins are receptors for the immunosuppressive drugs cyclosporin A, FK506, and rapamycin that are used in organ transplantation. Pin1 has also been targeted in the treatment of Alzheimer’s disease, asthma, and a number of cancers. While these PPIases are characterized as molecular chaperones, they also act in a nonchaperone manner to promote protein-protein interactions using surfaces outside their active sites. The immunosuppressive drugs act by a gain-of-function mechanism by promoting protein-protein interactions in vivo. Several immunophilins have been identified as components of the spliceosome and are essential for alternative splicing. Pin1 plays roles in transcription and RNA processing by catalyzing conformational changes in the RNA Pol II C-terminal domain. Pin1 also binds several RNA binding proteins such as AUF1, KSRP, HuR, and SLBP that regulate mRNA decay by remodeling mRNP complexes. The functions of ribonucleoprotein associated PPIases are largely unknown. This review highlights PPIases that play roles in RNA-mediated gene expression, providing insight into their structures, functions and mechanisms of action in mRNP remodeling in vivo.

Regulation of AU-Rich Element RNA Binding Proteins by Phosphorylation and the Prolyl Isomerase Pin1

The accumulation of 3' untranslated region (3'-UTR), AU-rich element (ARE) containing mRNAs, are predominantly controlled at the post-transcriptional level. Regulation appears to rely on a variable and dynamic interaction between mRNA target and ARE-specific binding proteins (AUBPs). The AUBP-ARE mRNA recognition is directed by multiple intracellular signals that are predominantly targeted at the AUBPs. These include (but are unlikely limited to) methylation, acetylation, phosphorylation, ubiquitination and isomerization. These regulatory events ultimately affect ARE mRNA location, abundance, translation and stability. In this review, we describe recent advances in our understanding of phosphorylation and its impact on conformation of the AUBPs, interaction with ARE mRNAs and highlight the role of Pin1 mediated prolyl cis-trans isomerization in these biological process.

Perspective: The RNA exosome, cytokine gene regulation and links to autoimmunity

The RNA exosome is a highly conserved exoribonuclease complex that is involved in RNA processing, quality control and turnover regulation. The exosome plays pleiotropic functions by recruiting different cofactors that regulate its target specificity. Recently, the exosome has been implicated in the regulation of immune processes including cytokine production and negative regulation of innate sensing of nucleic acids. Careful regulation of such mechanisms is critical to avoid a breakdown of self-tolerance and the pathogenesis of autoimmune disorders. This perspective briefly introduces the exosome, its its normal function in RNA biology and summarizes regulatory roles of the RNA exosome in immunity. Finally we discuss how dysregulation of exosome function can lead to autoimmune disease.

Peptidylprolyl cis/trans isomerase, NIMA-interacting 1 (PIN1) regulates pulmonary effects of endotoxin and tumor necrosis factor-α in mice

Peptidylprolyl cis/trans isomerase, NIMA-interacting 1 (PIN1) modulates phospho-signaling by catalyzing rotation of the bond between a phosphorylated serine or threonine before proline in proteins. As depletion of PIN1 increased inflammatory protein expression in cultured endothelial cells treated with bacterial endotoxin (lipopolysaccharide, LPS) and interferon-γ, we hypothesized that PIN1 knockout would increase sensitivity to LPS-induced lung inflammation in mice. Mortality due to a high dose of LPS (30mg/kg) was greater in knockout than wildtype mice. Lung myeloperoxidase activity, reflecting neutrophils, was increased to a 35% higher level in PIN1 knockout mouse lung, as compared with wildtype, after treatment with a sublethal dose of 3mgLPS/kg, ip. Unexpectedly, plasma tumor necrosis factor-α (TNF) was approximately 50% less than in wildtype mice. Knockout mice, however, were more sensitive than wildtype to TNF-induced neutrophil accumulation. The neutrophil adhesion molecule, E-selectin, was also elevated in lungs of knockout mice treated with TNF, suggesting that PIN1 depletion increases endothelial sensitivity to TNF. Indeed, TNF induced more reactive oxygen species in cultured endothelial cells depleted of PIN1 with short hairpin RNA than in control cells. Collectively, the results indicate that while PIN1 normally facilitates TNF production in LPS-treated mice, it suppresses pulmonary and endothelial reactions to the cytokine. Tissue or cell-specific effects of PIN1 may affect the overall inflammatory response to LPS and other stimuli.

The prolyl isomerase pin1 regulates mRNA levels of genes with short half-lives by targeting specific RNA binding proteins

The peptidyl-prolyl isomerase Pin1 is over-expressed in several cancer tissues is a potential prognostic marker in prostate cancer, and Pin1 ablation can suppress tumorigenesis in breast and prostate cancers. Pin1 can co-operate with activated ErbB2 or Ras to enhance tumorigenesis. It does so by regulating the activity of proteins that are essential for gene expression and cell proliferation. Several targets of Pin1 such as c-Myc, the Androgen Receptor, Estrogen Receptor-alpha, Cyclin D1, Cyclin E, p53, RAF kinase and NCOA3 are deregulated in cancer. At the posttranscriptional level, emerging evidence indicates that Pin1 also regulates mRNA decay of histone mRNAs, GM-CSF, Pth, and TGFβ mRNAs by interacting with the histone mRNA specific protein SLBP, and the ARE-binding proteins AUF1 and KSRP, respectively. To understand how Pin1 may affect mRNA abundance on a genome-wide scale in mammalian cells, we used RNAi along with DNA microarrays to identify genes whose abundance is significantly altered in response to a Pin1 knockdown. Functional scoring of differentially expressed genes showed that Pin1 gene targets control cell adhesion, leukocyte migration, the phosphatidylinositol signaling system and DNA replication. Several mRNAs whose abundance was significantly altered by Pin1 knockdown contained AU-rich element (ARE) sequences in their 3' untranslated regions. We identified HuR and AUF1 as Pin1 interacting ARE-binding proteins in vivo. Pin1 was also found to stabilize all core histone mRNAs in this study, thereby validating our results from a previously published study. Statistical analysis suggests that Pin1 may target the decay of essential mRNAs that are inherently unstable and have short to medium half-lives. Thus, this study shows that an important biological role of Pin1 is to regulate mRNA abundance and stability by interacting with specific RNA-binding proteins that may play a role in cancer progression.

Prolyl isomerase Pin1 negatively regulates the stability of SUV39H1 to promote tumorigenesis in breast cancer

Pin1, a conserved eukaryotic peptidyl-prolyl cis/trans isomerase, has profound effects on numerous key-signaling molecules, and its deregulation contributes to disease, particularly cancer. Although Pin1-mediated prolyl isomerization of protein servers as a regulatory switch in signaling pathways, the significance of proline isomerase activity in chromatin modifying complex remains unclear. Here, we identify Pin1 as a key negative regulator for suppressor of variegation 3-9 homologue 1 (SUV39H1) stability, a major methyltransferase responsible for histone H3 trimethylation on Lys9 (H3K9me3). Pin1 interacts with SUV39H1 in a phosphorylation-dependent manner and promotes ubiquitination-mediated degradation of SUV39H1. Consequently, Pin1 reduces SUV39H1 abundance and suppresses SUV39H1 ability to induce H3K9me3. In contrast, depletion of Pin1 in cancer cells leads to elevated SUV39H1 expression, which subsequently increases H3K9me3, inhibiting tumorigenecity of cancer cells. In a xenograft model with 4T1 metastatic mouse breast carcinoma cells, Pin1 overexpression increases tumor growth, whereas SUV39H1 overexpression abrogates it. In human breast cancer patients, immunohistochemical staining shows that Pin1 levels are negatively correlated with SUV39H1 as well as H3K9me3 levels. Thus, Pin1-mediated reduction of SUV39H1 stability contributes to convey oncogenic signals for aggressiveness of human breast cancer, suggesting that Pin1 may be a promising drug target for anticancer therapy.

Post-transcriptional regulatory networks in immunity

Post-transcriptional mechanisms that modulate global and/or transcript-specific mRNA stability and translation contribute to the rapid and flexible control of gene expression in immune effector cells. These mechanisms rely on RNA-binding proteins (RBPs) that direct regulatory complexes (e.g. exosomes, deadenylases, decapping complexes, RNA-induced silencing complexes) to the 3'-untranslated regions of specific immune transcripts. Here, we review the surprising variety of post-transcriptional control mechanisms that contribute to gene expression in the immune system and discuss how defects in these pathways can contribute to autoimmune disease.

Signaling pathways that control mRNA turnover

Cells regulate their genomes mainly at the level of transcription and at the level of mRNA decay. While regulation at the level of transcription is clearly important, the regulation of mRNA turnover by signaling networks is essential for a rapid response to external stimuli. Signaling pathways result in posttranslational modification of RNA binding proteins by phosphorylation, ubiquitination, methylation, acetylation etc. These modifications are important for rapid remodeling of dynamic ribonucleoprotein complexes and triggering mRNA decay. Understanding how these posttranslational modifications alter gene expression is therefore a fundamental question in biology. In this review we highlight recent findings on how signaling pathways and cell cycle checkpoints involving phosphorylation, ubiquitination, and arginine methylation affect mRNA turnover.

Hsp27 and F-box protein β-TrCP promote degradation of mRNA decay factor AUF1

Activation of the mitogen-activated protein (MAP) pathway kinases p38 and MK2 induces phosphorylation of the chaperone Hsp27 and stabilization of mRNAs containing AU-rich elements (AREs) (ARE-mRNAs). Likewise, expression of phosphomimetic mutant forms of Hsp27 also stabilizes ARE-mRNAs. It appears to perform this function by promoting degradation of the ARE-mRNA decay factor AUF1 by proteasomes. In this study, we examined the molecular mechanism linking Hsp27 phosphorylation to AUF1 degradation by proteasomes. AUF1 is a target of β-TrCP, the substrate recognition subunit of the E3 ubiquitin ligase Skp1-cullin-F-box protein complex, SCF(β-TrCP). Depletion of β-TrCP stabilized AUF1. In contrast, overexpression of β-TrCP enhanced ubiquitination and degradation of AUF1 and led to stabilization of reporter mRNAs containing cytokine AREs. Enhanced AUF1 degradation required expression of phosphomimetic mutant forms of both Hsp27 and AUF1. Our results suggest that a signaling axis composed of p38 MAP kinase-MK2-Hsp27-β-TrCP may promote AUF1 degradation by proteasomes and stabilization of cytokine ARE-mRNAs.

Post-transcriptional control of gene expression by AUF1: mechanisms, physiological targets, and regulation

AUF1 is a family of four proteins generated by alternative pre-mRNA splicing that form high affinity complexes with AU-rich, mRNA-destabilizing sequences located within the 3' untranslated regions of many labile mRNAs. While AUF1 binding is most frequently associated with accelerated mRNA decay, emerging examples have demonstrated roles as a mRNA stabilizer or even translational regulator for specific transcripts. In this review, we summarize recent advances in our understanding of mRNA recognition by AUF1 and the biochemical and functional consequences of these interactions. In addition, unique properties of individual AUF1 isoforms and the roles of these proteins in modulating expression of genes associated with inflammatory, neoplastic, and cardiac diseases are discussed. Finally, we describe mechanisms that regulate AUF1 expression in cells, and current knowledge of regulatory switches that modulate the cellular levels and/or activities of AUF1 isoforms through distinct protein post-translational modifications. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Nuclear translocation of MEK1 triggers a complex T cell response through the corepressor silencing mediator of retinoid and thyroid hormone receptor

MEK1 phosphorylates ERK1/2 and regulates T cell generation, differentiation, and function. MEK1 has recently been shown to translocate to the nucleus. Its nuclear function is largely unknown. By studying human CD4 T cells, we demonstrate that a low level of MEK1 is present in the nucleus of CD4 T cells under basal conditions. T cell activation further increases the nuclear translocation of MEK1. MEK1 interacts with the nuclear receptor corepressor silencing mediator of retinoid and thyroid hormone receptor (SMRT). MEK1 reduces the nuclear level of SMRT in an activation-dependent manner. MEK1 is recruited to the promoter of c-Fos upon TCR stimulation. Conversely, SMRT is bound to the c-Fos promoter under basal conditions and is removed upon TCR stimulation. We examined the role of SMRT in regulation of T cell function. Small interfering RNA-mediated knockdown of SMRT results in a biphasic effect on cytokine production. The production of the cytokines IL-2, IL-4, IL-10, and IFN-γ increases in the early phase (8 h) and then decreases in the late phase (48 h). The late-phase decrease is associated with inhibition of T cell proliferation. The late-phase inhibition of T cell activation is, in part, mediated by IL-10 that is produced in the early phase and, in part, by β-catenin signaling. Thus, we have identified a novel nuclear function of MEK1. MEK1 triggers a complex pattern of early T cell activation, followed by a late inhibition through its interaction with SMRT. This biphasic dual effect most likely reflects a homeostatic regulation of T cell function by MEK1.

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.

Networks controlling mRNA decay in the immune system

The active control of mRNA degradation has emerged as a key regulatory mechanism required for proper gene expression in the immune system. An adenosine/uridine (AU)-rich element (ARE) is at the heart of a first regulatory system that promotes the rapid degradation of a multitude of cytokine and chemokine mRNAs. AREs serve as binding sites for a number of regulatory proteins that either destabilize or stabilize the mRNA. Several kinase pathways regulate the activity of ARE-binding proteins and thereby coordinate the expression of their target mRNAs. Small regulatory micro (mi)-RNAs represent a second system that enhances the degradation of several mRNAs encoding important components of signal transduction cascades that are activated during adaptive and innate immune responses. Specific miRNAs are important for the differentiation of T helper cells, class switch recombination in B cells, and the maturation of dendritic cells. Excitement in this area of research is fueled by the discovery of novel RNA elements and regulatory proteins that exert control over specific mRNAs, as exemplified by an endonuclease that was found to directly cleave interleukin-6 mRNA. Together, these systems make up an extensive regulatory network that controls decay rates of individual mRNAs in a precise manner and thereby orchestrates the dynamic expression of many factors essential for adaptive and innate immune responses. In this review, we provide an overview of relevant factors regulated at the level of mRNA stability, summarize RNA-binding proteins and miRNAs that control their degradation rates, and discuss signaling pathways operating within this regulatory network.

Potent synergistic effect of IL-3 and TNF on matrix metalloproteinase 9 generation by human eosinophils

TNF (designated as TNF-α under previous nomenclature) is the preeminent activator of MMP-9 generation from a variety of cells including eosinophils. We have previously established that TNF strongly synergizes with IFN-γ and IL-4 for eosinophil synthesis of Th1- and Th2-type chemokines respectively. Thus, we sought to determine if TNF-induced synthesis of MMP-9 would be enhanced by the presence of Th1, Th2, or the eosinophil-associated common beta chain (βc) cytokines. Human blood eosinophils were cultured with TNF alone or in combination with either IFN-γ, IL-4, IL-3, IL-5, or GM-CSF. Concentrations and activities of MMP-9 in eosinophil culture supernates were measured by ELISA and gelatin zymography, mRNA transcription and stabilization by quantitative real-time PCR, and signaling events by immunoblotting and intracellular flow cytometric analysis. Individually, TNF, GM-CSF, or IL-3, but not IL-4 or IFN-γ, induced relatively small (<0.2 ng/ml) but statistically significant quantities of MMP-9. Remarkable synergistic synthesis of MMP-9 (ng/ml levels) occurred in response to TNF plus IL-3, GM-CSF or IL-5, in the order of IL-3>GM-CSF>IL-5. Zymography revealed that eosinophils release MMP-9 in its pro-form. Eosinophil stimulation with the combination of IL-3 plus TNF led to increased steady-state levels of MMP-9 mRNA, prolonged mRNA stabilization, and enhanced activation of ERK1/2 phosphorylation. Inhibition of NF-κB, MEK kinase, or p38 MAP kinase, but not JNK signaling pathways, diminished IL-3/TNF-induced MMP-9 mRNA and protein production. Thus, the synergistic regulation of eosinophil MMP-9 by IL-3 plus TNF likely involves cooperative interaction of multiple transcription factors downstream from ERK, p38, and NF-κB activation as well as post-transcriptional regulation of MMP-9 mRNA stabilization. Our data indicate that within microenvironments rich in βc-family cytokines and TNF, eosinophils are an important source of proMMP-9 and highlight a previously unrecognized role for synergistic interaction between TNF and βc-family cytokines, particularly IL-3, for proMMP-9 synthesis.

An emerging role of RNA-binding proteins as multifunctional regulators of lymphocyte development and function

Sequence-specific RNA-binding proteins (RBP) and the regulation of RNA decay have long been recognized as important regulators of the inflammatory response. RBP influence gene expression throughout the lifespan of the mRNA by regulating splicing, polyadenylation, cellular localization, translation, and decay. Increasing evidence now indicates that these proteins, together with the RNA decay machinery that they recruit, also regulate the development and activation of lymphocytes. The activity of RBP is regulated by the same signal transduction pathways that govern lymphocyte development and differentiation in response to antigen and cytokine receptor engagement. Roles for these proteins in regulating the diverse functions of lymphocytes are becoming increasingly apparent.

Calpastatin is regulated by protein never in mitosis gene A interacting-1 (PIN1) in endothelial cells

The peptidyl-proline isomerase, protein never in mitosis gene A interacting-1 (PIN1) binds and isomerizes proteins phosphorylated on serine/threonine before a proline. It was previously found that depletion of PIN1 greatly increased induction of cyclooxygenase-2 and inducible nitric oxide synthase by lowering calpain activity in murine aortic endothelial cells (MAEC). Here we investigated the effect of PIN1 on the endogenous inhibitor of heterodimeric μ- and m-calpains, calpastatin. MAEC were transduced with small hairpin (sh) RNA to knock down PIN1 (KD) or an inactive Control shRNA. Cells were also treated with non-targeted double stranded small inhibitory RNA (siRNA) or siRNA designed to deplete calpastatin. Despite reducing calpain activity, PIN1 KD did not significantly affect the expression of μ- and m-calpains, or calpastatin, compared to Control shRNA. Instead, depletion of PIN1 increased the inhibitory activity of calpastatin. Calpastatin co-immunoprecipitated with endogenous PIN1 and was pulled down with glutathione-S-transferase (GST)-PIN1 fusion protein. Adding GST-PIN1 to KD cell extracts lacking PIN1 reduced calpastatin inhibitory activity. Substrate binding and catalytic domain mutants of PIN1 failed to do so. These results suggest that protein interaction and the proline isomerase functions of PIN1 are required for it to inhibit calpastatin. Furthermore, depletion of calpastatin raised calpain activity and reduced calpain inhibitory activity to similar levels in KD and Control MAEC, indicating that calpastatin is required for PIN1 depletion to lower calpain activity. Thus, PIN1 apparently restrains the ability of calpastatin to inhibit calpain, maintaining calpain activity in endothelial cells. PIN1 may act directly via phosphorylated serine/threonine-proline motifs in calpastatin, or indirectly via other PIN1 substrates that control calpastatin.

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

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

Nephroblastoma overexpressed (Nov) induces gremlin in ST-2 stromal cell lines by post-transcriptional mechanisms

Nephroblastoma overexpressed (Nov) inhibits osteoblastogenesis in part because it binds bone morphogenetic protein (BMP)-2. In the present study, we investigated whether Nov regulated the expression of the BMP antagonist gremlin. Overexpression of Nov increased gremlin mRNA levels in ST-2 cells, and its downregulation by RNA interference decreased gremlin mRNA. Nov did not affect Grem1 transcription, but prolonged the half-life of gremlin mRNA in ST-2 cells, demonstrating that Nov acts by post-transcriptional mechanisms. This was confirmed by demonstrating that downregulation of Nov destabilizes gremlin transcripts. To assess whether the 3'-untranslated region (UTR) of gremlin mRNA mediated the effect of Nov, the decay of a chimeric cfos gremlin 3'-UTR construct was compared to that of cfos in ST-2 cells. The presence of the gremlin 3'-UTR prolonged the half-life of cfos and was responsible for the effect of Nov. To examine the binding of the gremlin 3'-UTR to ribonucleoproteins, radiolabeled gremlin RNA fragments were incubated with cytosolic extracts from Nov overexpressing and control cells. RNA electrophoretic mobility analysis revealed that Nov enhanced the binding of cytosolic proteins to the fragments spanning the 3'-UTR of gremlin between bases 1,358-1,557 and 1,158-1,357 from the transcriptional start. Mutations of AU-rich elements in these two RNA fragments prevented the formation of RNA-protein complexes induced by Nov. Nov did not alter the binding of cytosolic extracts to sequences present in the 5'-UTR or coding region of gremlin. In conclusion, Nov stabilizes gremlin transcripts, and this effect is possibly mediated by AU-rich elements present in the 3'-UTR of gremlin.

The role of AUF1 in regulated mRNA decay

Messenger ribonucleic acid (mRNA) turnover is a major control point in gene expression. In mammals, many mRNAs encoding inflammatory cytokines, oncoproteins, and G-protein-coupled receptors are destabilized by the presence of AU-rich elements (AREs) in their 3'-untranslated regions. Association of ARE-binding proteins (AUBPs) with these mRNAs promotes rapid mRNA degradation. ARE/poly(U)-binding/degradation factor 1 (AUF1), one of the best-characterized AUBPs, binds to many ARE-mRNAs and assembles other factors necessary to recruit the mRNA degradation machinery. These factors include translation initiation factor eIF4G, chaperones hsp27 and hsp70, heat-shock cognate protein hsc70, lactate dehydrogenase, poly(A)-binding protein, and other unidentified proteins. Numerous signaling pathways alter the composition of this AUF1 complex of proteins to effect changes in ARE-mRNA degradation rates. This review briefly describes the roles of mRNA decay in gene expression in general and ARE-mediated decay (AMD) in particular, with a focus on AUF1 and the different modes of regulation that govern AUF1 involvement in AMD.

The prolyl isomerase Pin1 acts as a novel molecular switch for TNF-alpha-induced priming of the NADPH oxidase in human neutrophils

Neutrophils play a key role in host defense by releasing reactive oxygen species (ROS). However, excessive ROS production by neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase can damage bystander tissues, thereby contributing to inflammatory diseases. Tumor necrosis factor-α (TNF-α), a major mediator of inflammation, does not activate NADPH oxidase but induces a state of hyperresponsiveness to subsequent stimuli, an action known as priming. The molecular mechanisms by which TNF-α primes the NADPH oxidase are unknown. Here we show that Pin1, a unique cis-trans prolyl isomerase, is a previously unrecognized regulator of TNF-α-induced NADPH oxidase hyperactivation. We first showed that Pin1 is expressed in neutrophil cytosol and that its activity is markedly enhanced by TNF-α. Inhibition of Pin1 activity with juglone or with a specific peptide inhibitor abrogated TNF-α-induced priming of neutrophil ROS production induced by N-formyl-methionyl-leucyl-phenylalanine peptide (fMLF). TNF-α enhanced fMLF-induced Pin1 and p47phox translocation to the membranes and juglone inhibited this process. Pin1 binds to p47phox via phosphorylated Ser345, thereby inducing conformational changes that facilitate p47phox phosphorylation on other sites by protein kinase C. These findings indicate that Pin1 is critical for TNF-α-induced priming of NADPH oxidase and for excessive ROS production. Pin1 inhibition could potentially represent a novel anti-inflammatory strategy.

Minireview: the play of proteins on the parathyroid hormone messenger ribonucleic Acid regulates its expression

PTH regulates serum calcium and phosphate levels and bone strength. The parathyroid is unique in that the trigger for PTH secretion is a low extracellular calcium rather than high calcium as for other hormones. The parathyroid senses small changes in serum calcium through the seven-trans-membrane G protein-coupled calcium receptor to alter PTH secretion. PTH then acts on bone and kidney to correct serum calcium. Parathyroid cells have few secretory granules as compared with other endocrine cells, and therefore PTH production is regulated largely at the levels of PTH gene expression and parathyroid cell proliferation. The regulation of PTH gene expression by changes in calcium and phosphate and in chronic kidney failure is posttranscriptional involving the binding of trans-acting proteins to a defined cis element in the PTH mRNA 3'-untranslated region. These protein-PTH mRNA interactions are orchestrated by the peptidyl-prolyl isomerase Pin1. This review discusses the mechanisms of regulation of PTH mRNA stability determining serum PTH levels and mineral metabolism.

The Pin 1 inhibitor juglone attenuates kidney fibrogenesis via Pin 1-independent mechanisms in the unilateral ureteral occlusion model

Background

Pin 1 is a peptidyl-prolyl isomerase inhibitor related to cyclophilin A and FK506 binding protein (FKBP). Juglone (5-hydroxy-1,4-naphthoquinone) is a natural inhibitor of Pin 1 with anti-inflammatory and antifibrotic properties. We evaluated the role of Pin 1 in renal fibrogenesis by evaluating the effects of juglone on epithelial to mesenchymal transition (EMT) and fibrogenesis in the rat unilateral ureteral obstruction (UUO) model and normal rat tubular epithelial cells (NRK52E).

Results

After 2 weeks of UUO, immunoblot analyses demonstrated that juglone (0.25 and 1 mg/kg/24 h) inhibited the deposition of matrix (α-smooth muscle actin (SMA), collagen type III and vimentin) and the activation of signaling pathways involved in fibrogenesis (phospho-smad2) and stress response (phospho-heat shock protein (HSP)27). Juglone also reduced EMT (α-SMA and E-cadherin dual staining) and oxidative stress (Mn superoxide dismutase (SOD) and NAPDH oxidase 2 (Nox-2) dual staining) in the obstructed kidney. There was no difference in Pin 1 levels between treatment and control groups. Pin 1 activity was significantly decreased in obstructed kidneys regardless of treatment status. In vitro, juglone (1 μM) significantly decreased α-SMA and p-smad levels compared to vehicle.

Conclusions

Juglone attenuates fibrogenesis via Pin 1-independent mechanisms in the UUO model. The antifibrotic effects of juglone may result from the inhibition of smad2 and oxidative stress.

Novel role of Pin1 induction in type II collagen-mediated rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints and subsequent destruction of cartilage and bone. Inflammatory mediators such as PGs and proinflammatory cytokines contribute to RA progress. Pin1, a peptidyl prolyl isomerase, plays important pathophysiological roles in several diseases, including cancer and neurodegeneration. We found that both Pin1 and cyclooxygenase-2 (COX-2) were highly expressed in ankle tissues of type II collagen-induced RA mice. HTB-94 cells overexpressing Pin1 and primary cultured human chondrocytes showed increased basal expression of proinflammatory proteins (COX-2, inducible NO synthase, TNF-alpha, and IL-1beta). Site-directed mutagenesis revealed that Pin1-mediated transcriptional activation of COX-2 was coordinately regulated by NF-kappaB, CREB, and C/EBP. Gel shift, reporter gene, and Western blot analyses confirmed that NF-kappaB, CREB, and C/EBP were consistently activated in chondrocytes overexpressing Pin1. Treatment of RA mice with juglone, a chemical inhibitor of Pin1, significantly reduced RA progress and COX-2 expression in the ankle tissues. Moreover, juglone dose dependently decreased the basal COX-2 expression in primary cultured chondrocytes from RA patients. These results demonstrate that Pin1 induction during RA progress stimulates proinflammatory protein expression by activating NF-kappaB, CREB, and C/EBP, and suggest that Pin1 is a potential therapeutic target of RA.

Proteomic change of peripheral lymphocytes from scald injury and Pseudomonas aeruginosa sepsis in rabbits

BACKGROUND

Increased susceptibility to infection has been related to impairment of lymphocyte-regulated immune responses after severe burn. The aim of this study is to identify the differential expression of proteins in circulating lymphocytes from scald injury and Pseudomonas aeruginosa sepsis in rabbits to provide a basis for pathogenesis of burns and sepsis.

METHODS

Rabbits were subjected to sham burn (A), 30% scald (B), A+bacterial challenge (C) or B+bacterial challenge (D). Bacterial challenge was inflicted by an injection of 2.0x10(8) CFU P. aeruginosa (ATCC27853) in the auricular vein 22 h after the burn procedure. The animals were sacrificed 24 h later. Lymphocytes were isolated, and the differential proteins in the lymphocytes from the experimental and control animals were identified by two-dimensional electrophoresis (2-DE) coupled with matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), two of which were confirmed by Western blotting.

RESULTS

Nineteen differential protein spots were found by 2-DE and 12 spots (11 proteins) were identified. Differential expression of peroxiredoxin and annexin I was validated by Western blotting. Among the identified proteins, the expression levels of cofilin, cyclophilin A, ubiquitin, nucleoside diphosphate kinase, glutamate dehydrogenase and annexin I were down-regulated in group B, excessively down-regulated in group D, but mildly in group C, and peroxiredoxin was up-regulated in groups B and D.

CONCLUSIONS

Proteome changes in lymphocytes from P. aeruginosa sepsis in the scalded rabbits were revealed, which are related to immune suppression and the pathogenesis of sepsis after scald injury.

Protein Never in Mitosis Gene A Interacting-1 regulates calpain activity and the degradation of cyclooxygenase-2 in endothelial cells

Background

The peptidyl-proline isomerase, Protein Never in Mitosis Gene A Interacting-1 (PIN1), regulates turnover of inducible nitric oxide synthase (iNOS) in murine aortic endothelial cells (MAEC) stimulated with E. coli endotoxin (LPS) and interferon-γ (IFN). Degradation of iNOS was reduced by a calpain inhibitor, suggesting that PIN1 may affect induction of other calpain-sensitive inflammatory proteins, such as cyclooxygenase (COX)-2, in MAEC.

Methods

MAEC, transduced with lentivirus encoding an inactive control short hairpin (sh) RNA or one targeting PIN1 that reduced PIN1 by 85%, were used. Cells were treated with LPS/IFN, calpain inhibitors (carbobenzoxy-valinyl-phenylalaninal (zVF), PD150606), cycloheximide and COX inhibitors to determine the effect of PIN1 depletion on COX-2 and calpain.

Results

LPS or IFN alone did not induce COX-2. However, treatment with 10 μg LPS plus 20 ng IFN per ml induced COX-2 protein 10-fold in Control shRNA MAEC. Induction was significantly greater (47-fold) in PIN1 shRNA cells. COX-2-dependent prostaglandin E2 production increased 3-fold in KD MAEC, but did not increase in Control cells. The additional increase in COX-2 protein due to PIN1 depletion was post-transcriptional, as induction of COX-2 mRNA by LPS/IFN was the same in cells containing or lacking PIN1. Instead, the loss of COX-2 protein, after treatment with cycloheximide to block protein synthesis, was reduced in cells lacking PIN1 in comparison with Control cells, indicating that degradation of the enzyme was reduced. zVF and PD150606 each enhanced the induction of COX-2 by LPS/IFN. zVF also slowed the loss of COX-2 after treatment with cycloheximide, and COX-2 was degraded by exogenous μ-calpain in vitro. In contrast to iNOS, physical interaction between COX-2 and PIN1 was not detected, suggesting that effects of PIN1 on calpain, rather than COX-2 itself, affect COX-2 degradation. While cathepsin activity was unaltered, depletion of PIN1 reduced calpain activity by 55% in comparison with Control shRNA cells.

Conclusion

PIN1 reduced calpain activity and slowed the degradation of COX-2 in MAEC, an effect recapitulated by an inhibitor of calpain. Given the sensitivity of COX-2 and iNOS to calpain, PIN1 may normally limit induction of these and other calpain substrates by maintaining calpain activity in endothelial cells.

The peptidyl-prolyl isomerase Pin1 facilitates cytokine-induced survival of eosinophils by suppressing Bax activation

The mechanisms through which cytokine signals prevent the activation and mitochondrial targeting of the pro-apoptotic Bcl-2-associated X protein (Bax) are unclear. Here we showed, using primary human eosinophils, that in the absence of the pro-survival cytokines granulocyte macrophage-colony stimulating factor (GM-CSF) or interleukin 5, Bax spontaneously undergoes activation and initiates mitochondrial disruption. Bax inhibition reduced eosinophil apoptosis, even in the absence of cytokines. GM-CSF induced activation of Erk1/2, which phosphorylated Thr167 of Bax, which facilitated de novo interaction of Bax with the prolyl isomerase Pin1. Pin1 blockade led to Bax cleavage, mitochondrial translocation and caspase activation, irrespective of the presence of cytokines. Our findings indicate that Pin1 is a key mediator of pro-survival signaling and a regulator of Bax function.

Protein Never in Mitosis Gene A Interacting-1 (PIN1) regulates degradation of inducible nitric oxide synthase in endothelial cells

The peptidyl-proline isomerase Protein Never in Mitosis Gene A Interacting-1 (PIN1) increases the level or activity of several transcription factors that can induce the inducible nitric oxide (NO) synthase (iNOS). PIN1 can also regulate mRNA and protein turnover. Here, the effect of depletion of PIN1 on induction of iNOS by Escherichia coli endotoxin (LPS) and interferon-gamma (IFNgamma) in murine aortic endothelial cells (MAEC) was determined. Suppression of PIN1 by 85% with small hairpin RNA enhanced the induction of NO and iNOS protein by LPS-IFNgamma. There was no effect on induction of iNOS mRNA, suggesting a posttranscriptional effect. The enhanced levels of iNOS protein were functionally significant since LPS-IFNgamma was cytotoxic to MAEC lacking PIN1 but not MAEC harboring an inactive control construct, and because cytotoxicity was blocked by the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester. Consistent with posttranscriptional action, knockdown of PIN1 increased the stability of iNOS protein in cycloheximide-treated cells. Furthermore, loss of iNOS was blocked by the calpain inhibitor carbobenzoxy-valinyl-phenylalaninal but not by the selective proteasome inhibitor epoxomicin. Immunoprecipitation indicated that PIN1 can interact with iNOS. Pull down of iNOS with a wild-type glutathione-S-transferase-PIN1 fusion protein, but not with a mutant of the amino terminal phospho-(serine/threonine)-proline binding WW domain of PIN1, indicated that this domain mediates interaction. The results suggest that PIN1 associates with iNOS and can limit its induction by facilitating calpain-mediated degradation in MAEC.

A new twist to adaptor proteins contributes to regulation of lymphocyte cell signaling

Cell growth and differentiation are highly controlled processes mediated by effector molecules, which are regulated by posttranslational chemical modifications. Adaptor molecules are critical players in these mechanisms because of their ability to simultaneously interact with multiple effector molecules and orchestrate the assembly of signaling complexes downstream of activated surface receptors. One family of adaptor molecules includes the CrkII/CrkL proteins that are also involved in the regulation of lymphocyte function. Although Crk proteins are amenable to regulation by protein tyrosine kinases, recent data suggest that peptidyl-prolyl cis-trans isomerases (PPIases) can alter their conformation and hence their ability to associate with binding partners. This emerging new function of PPIases is the subject of the current review.