Prolyl isomerase Pin1 in cancer

The potential role of the prolyl isomerase Pin1 during blastocyst implantation and uterine decidualization in mice

During early pregnancy in mice, the establishment of uterine receptivity and endometrial decidualization require the extensive proliferation and differentiation of endometrial epithelial cells or stromal cells. Pin1 has been suggested to act as a molecular 'timer' of the cell cycle and is involved in the regulation of cellular proliferation and differentiation by binding many cell-cycle regulatory proteins. However, its physiological role during early pregnancy is still not fully understood. Here, we employed immunohistochemistry to determine the spatiotemporal pattern of Pin1 expression during early pregnancy. We found that Pin1 was mainly localized in subluminal stromal cells on day 4, in the decidual zone on days 5 to 8 of pregnancy and in artificial decidualization. Using a uterine stromal cell culture system, we found that progesterone, but not estrogen, induced the expression of Pin1 in a progesterone receptor-dependent manner. Inhibition of Pin1 in the uterus leads to impaired embryo implantation and decidualization in mice. Notably, a decrease in Pin1 activation affected the functional execution of several implantation- or decidualization-related factors. These findings provide new evidence for a previously unknown function of Pin1 in mediating embryo implantation and decidualization during successful pregnancy establishment and maintenance.

CRABP1-complexes in exosome secretion

BACKGROUND

Cellular retinoic acid binding protein 1 (CRABP1) mediates rapid, non-canonical activity of retinoic acid (RA) by forming signalosomes via protein-protein interactions. Two signalosomes have been identified previously: CRABP1-MAPK and CRABP1-CaMKII. Crabp1 knockout (CKO) mice exhibited altered exosome profiles, but the mechanism of CRABP1 action was unclear. This study aimed to screen for and identify novel CRABP1 signalosomes that could modulate exosome secretion by using a combinatorial approach involving biochemical, bioinformatic and molecular studies.

METHODS

Immunoprecipitation coupled with mass spectrometry (IP-MS) identified candidate CRABP1-interacting proteins which were subsequently analyzed using GO Term Enrichment, Functional Annotation Clustering; and Pathway Analysis. Gene expression analysis of CKO samples revealed altered expression of genes related to exosome biogenesis and secretion. The effect of CRABP1 on exosome secretion was then experimentally validated using CKO mice and a Crabp1 knockdown P19 cell line.

RESULTS

IP-MS identified CRABP1-interacting targets. Bioinformatic analyses revealed significant association with actin cytoskeletal dynamics, kinases, and exosome secretion. The effect of CRABP1 on exosome secretion was experimentally validated by comparing circulating exosome numbers of CKO and wild type (WT) mice, and secreted exosomes from WT and siCRABP1-P19 cells. Pathway analysis identified kinase signaling and Arp2/3 complex as the major pathways where CRABP1-signalosomes modulate exosome secretion, which was validated in the P19 system.

CONCLUSION

The combinatorial approach allowed efficient screening for and identification of novel CRABP1-signalosomes. The results uncovered a novel function of CRABP1 in modulating exosome secretion, and suggested that CRABP1 could play roles in modulating intercellular communication and signal propagation.

A novel bivalent interaction mode underlies a non-catalytic mechanism for Pin1-mediated protein kinase C regulation

Regulated hydrolysis of the phosphoinositide phosphatidylinositol(4,5)-bis-phosphate to diacylglycerol and inositol-1,4,5-P3 defines a major eukaryotic pathway for translation of extracellular cues to intracellular signaling circuits. Members of the lipid-activated protein kinase C isoenzyme family (PKCs) play central roles in this signaling circuit. One of the regulatory mechanisms employed to downregulate stimulated PKC activity is via a proteasome-dependent degradation pathway that is potentiated by peptidyl-prolyl isomerase Pin1. Here, we show that contrary to prevailing models, Pin1 does not regulate conventional PKC isoforms α and βII via a canonical cis-trans isomerization of the peptidyl-prolyl bond. Rather, Pin1 acts as a PKC binding partner that controls PKC activity via sequestration of the C-terminal tail of the kinase. The high-resolution structure of full-length Pin1 complexed to the C-terminal tail of PKCβII reveals that a novel bivalent interaction mode underlies the non-catalytic mode of Pin1 action. Specifically, Pin1 adopts a conformation in which it uses the WW and PPIase domains to engage two conserved phosphorylated PKC motifs, the turn motif and hydrophobic motif, respectively. Hydrophobic motif is a non-canonical Pin1-interacting element. The structural information combined with the results of extensive binding studies and experiments in cultured cells suggest that non-catalytic mechanisms represent unappreciated modes of Pin1-mediated regulation of AGC kinases and other key enzymes/substrates.

Chromosome-level genome provides insights into environmental adaptability and innate immunity in the common dolphin (delphinus delphis)

The common dolphin (Delphinus delphis) is widely distributed worldwide and well adapted to various habitats. Animal genomes store clues about their pasts, and can reveal the genes underlying their evolutionary success. Here, we report the first high-quality chromosome-level genome of D. delphis. The assembled genome size was 2.56 Gb with a contig N50 of 63.85 Mb. Phylogenetically, D. delphis was close to Tursiops truncatus and T. aduncus. The genome of D. delphis exhibited 428 expanded and 1,885 contracted gene families, and 120 genes were identified as positively selected. The expansion of the HSP70 gene family suggested that D. delphis has a powerful system for buffering stress, which might be associated with its broad adaptability, longevity, and detoxification capacity. The expanded IFN-α and IFN-ω gene families, as well as the positively selected genes encoding tripartite motif-containing protein 25, peptidyl-prolyl cis-trans isomerase NIMA-interacting 1, and p38 MAP kinase, were all involved in pathways for antiviral, anti-inflammatory, and antineoplastic mechanisms. The genome data also revealed dramatic fluctuations in the effective population size during the Pleistocene. Overall, the high-quality genome assembly and annotation represent significant molecular resources for ecological and evolutionary studies of Delphinus and help support their sustainable treatment and conservation.

Reciprocal antagonism of PIN1-APC/CCDH1 governs mitotic protein stability and cell cycle entry

Induced oncoproteins degradation provides an attractive anti-cancer modality. Activation of anaphase-promoting complex (APC/CCDH1) prevents cell-cycle entry by targeting crucial mitotic proteins for degradation. Phosphorylation of its co-activator CDH1 modulates the E3 ligase activity, but little is known about its regulation after phosphorylation and how to effectively harness APC/CCDH1 activity to treat cancer. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1)-catalyzed phosphorylation-dependent cis-trans prolyl isomerization drives tumor malignancy. However, the mechanisms controlling its protein turnover remain elusive. Through proteomic screens and structural characterizations, we identify a reciprocal antagonism of PIN1-APC/CCDH1 mediated by domain-oriented phosphorylation-dependent dual interactions as a fundamental mechanism governing mitotic protein stability and cell-cycle entry. Remarkably, combined PIN1 and cyclin-dependent protein kinases (CDKs) inhibition creates a positive feedback loop of PIN1 inhibition and APC/CCDH1 activation to irreversibly degrade PIN1 and other crucial mitotic proteins, which force permanent cell-cycle exit and trigger anti-tumor immunity, translating into synergistic efficacy against triple-negative breast cancer.

Recent advances of Pin1 inhibitors as potential anticancer agents

Pin1 (proline isomerase peptidyl-prolyl isomerase NIMA-interacting-1), as a member of PPIase family, catalyzes cis-trans isomerization of pThr/Ser-Pro amide bonds of its substrate proteins, further regulating cell proliferation, division, apoptosis, and transformation. Pin1 is overexpressed in various cancers and is positively correlated with tumor initiation and progression. Pin1 inhibition can effectively reduce tumor growth and cancer stem cell expansion, block metastatic spread, and restore chemosensitivity, suggesting that targeting Pin1 may be an effective strategy for cancer treatment. Considering the promising therapeutic effects of Pin1 inhibitors on cancers, we herein are intended to comprehensively summarize the reported Pin1 inhibitors, mainly highlighting their structures, biological functions and binding modes, in hope of providing a reference for the future drug discovery.

pH-sensitive niosomes for ATRA delivery: A promising approach to inhibit Pin1 in high-grade serous ovarian cancer

The peptidyl-prolyl cis/trans isomerase Pin1 positively regulates numerous cancer-driving pathways, and it is overexpressed in several malignancies, including high-grade serous ovarian cancer (HGSOC). The findings that all-trans retinoic acid (ATRA) induces Pin1 degradation strongly support that ATRA treatment might be a promising approach for HGSOC targeted therapy. Nevertheless, repurposing ATRA into the clinics for the treatment of solid tumors remains an unmet need mainly due to the insurgence of resistance and its ineffective delivery. In the present study, niosomes have been employed for improving ATRA delivery in HGSOC cell lines. Characterization of niosomes including hydrodynamic diameter, ζ-potential, morphology, entrapment efficiency and stability over time and in culture media was performed. Furthermore, pH-sensitiveness and ATRA release profile were investigated to demonstrate the capability of these vesicles to release ATRA in a stimuli-responsive manner. Obtained results documented a nanometric and monodispersed samples with negative ζ-potential. ATRA was efficiently entrapped, and a substantial release was observed in the presence of acidic pH (pH 5.5). Finally, unloaded niosomes showed good biocompatibility while ATRA-loaded niosomes significantly increased ATRA Pin1 inhibitory activity, which was consistent with cell growth inhibition. Taken together, ATRA-loaded niosomes might represent an appealing therapeutic strategy for HGSOC therapy.

KPT6566 induces apoptotic cell death and suppresses the tumorigenicity of testicular germ cell tumors

Testicular germ cell tumors (TGCTs) frequently affect adolescent and young adult males. Although TGCT is more responsive to cisplatin-based chemotherapy than other solid tumors, some patients are nonresponders, and following treatment, many patients continue to experience acute and long-term cytotoxic effects from cisplatin-based chemotherapy. Consequently, it is imperative to develop new therapeutic modalities for treatment-resistant TGCTs. Peptidyl-prolyl isomerase (Pin1) regulates the activity and stability of many cancer-associated target proteins. Prior findings suggest that Pin1 contributes to the pathogenesis of multiple human cancers. However, the specific function of Pin1 in TGCTs has not yet been elucidated. TGCT cell proliferation and viability were examined using cell cycle analysis and apoptosis assays following treatment with KPT6566, a potent, selective Pin1 inhibitor that covalently binds to the catalytic domain of Pin1. A xenograft mouse model was used to assess the effect of KPT6566 on tumor growth in vivo. KPT6566 effectively suppressed cell proliferation, colony formation, and ATP production in P19 and NCCIT cells. Further, KPT6566 induced apoptotic cell death by generating cellular reactive oxygen species and downregulating the embryonic transcription factors Oct-4 and Sox2. Finally, KPT6566 treatment significantly reduced tumor volume and mass in P19 cell xenografts. The Pin1 inhibitor KPT6566 has significant antiproliferative and antitumor effects in TGCT cells. These findings suggest that Pin1 inhibitors could be considered as a potential therapeutic approach for TGCTs.

A novel bivalent interaction mode underlies a non-catalytic mechanism for Pin1-mediated Protein Kinase C regulation

Regulated hydrolysis of the phosphoinositide phosphatidylinositol(4,5)-bis-phosphate to diacylglycerol and inositol-1,4,5-P3 defines a major eukaryotic pathway for translation of extracellular cues to intracellular signaling circuits. Members of the lipid-activated protein kinase C isoenzyme family (PKCs) play central roles in this signaling circuit. One of the regulatory mechanisms employed to downregulate stimulated PKC activity is via a proteasome-dependent degradation pathway that is potentiated by peptidyl-prolyl isomerase Pin1. Here, we show that contrary to prevailing models, Pin1 does not regulate conventional PKC isoforms α and βII via a canonical cis-trans isomerization of the peptidyl-prolyl bond. Rather, Pin1 acts as a PKC binding partner that controls PKC activity via sequestration of the C-terminal tail of the kinase. The high-resolution structure of Pin1 complexed to the C-terminal tail of PKCβII reveals that a novel bivalent interaction mode underlies the non-catalytic mode of Pin1 action. Specifically, Pin1 adopts a compact conformation in which it engages two conserved phosphorylated PKC motifs, the turn motif and hydrophobic motif, the latter being a non-canonical Pin1-interacting element. The structural information, combined with the results of extensive binding studies and in vivo experiments suggest that non-catalytic mechanisms represent unappreciated modes of Pin1-mediated regulation of AGC kinases and other key enzymes/substrates.

Novel Cellular Functions of ATR for Therapeutic Targeting: Embryogenesis to Tumorigenesis

The DNA damage response (DDR) is recognized as having an important role in cancer growth and treatment. ATR (ataxia telangiectasia mutated and Rad3-related) kinase, a major regulator of DDR, has shown significant therapeutic potential in cancer treatment. ATR inhibitors have shown anti-tumor effectiveness, not just as monotherapies but also in enhancing the effects of standard chemotherapy, radiation, and immunotherapy. The biological basis of ATR is examined in this review, as well as its functional significance in the development and therapy of cancer, and the justification for inhibiting this target as a therapeutic approach, including an assessment of the progress and status of previous decades' development of effective and selective ATR inhibitors. The current applications of these inhibitors in preclinical and clinical investigations as single medicines or in combination with chemotherapy, radiation, and immunotherapy are also fully reviewed. This review concludes with some insights into the many concerns highlighted or identified with ATR inhibitors in both the preclinical and clinical contexts, as well as potential remedies proposed.

Proline Isomerization: From the Chemistry and Biology to Therapeutic Opportunities

Proline isomerization, the process of interconversion between the cis- and trans-forms of proline, is an important and unique post-translational modification that can affect protein folding and conformations, and ultimately regulate protein functions and biological pathways. Although impactful, the importance and prevalence of proline isomerization as a regulation mechanism in biological systems have not been fully understood or recognized. Aiming to fill gaps and bring new awareness, we attempt to provide a wholistic review on proline isomerization that firstly covers what proline isomerization is and the basic chemistry behind it. In this section, we vividly show that the cause of the unique ability of proline to adopt both cis- and trans-conformations in significant abundance is rooted from the steric hindrance of these two forms being similar, which is different from that in linear residues. We then discuss how proline isomerization was discovered historically followed by an introduction to all three types of proline isomerases and how proline isomerization plays a role in various cellular responses, such as cell cycle regulation, DNA damage repair, T-cell activation, and ion channel gating. We then explore various human diseases that have been linked to the dysregulation of proline isomerization. Finally, we wrap up with the current stage of various inhibitors developed to target proline isomerases as a strategy for therapeutic development.

Non-POU Domain-Containing Octomer-Binding (NONO) protein expression and stability promotes the tumorigenicity and activation of Akt/MAPK/β-catenin pathways in human breast cancer cells

Breast cancer is one of the most common cancers with a high mortality rate, underscoring the need to identify new therapeutic targets. Here we report that non-POU domain-containing octamer-binding (NONO) protein is overexpressed in breast cancer and validated the interaction of the WW domain of PIN1 with c-terminal threonine-proline (thr-pro) motifs of NONO. The interaction of NONO with PIN1 increases the stability of NONO by inhibiting its proteasomal degradation, and this identifies PIN1 as a positive regulator of NONO in promoting breast tumor development. Functionally, silencing of NONO inhibits the growth, survival, migration, invasion, epithelial to mesenchymal transition (EMT), and stemness of breast cancer cells in vitro. A human metastatic breast cancer cell xenograft was established in transparent zebrafish (Danio rerio) embryos to study the metastatic inability of NONO-silenced breast cancer cells in vivo. Mechanistically, NONO depletion promotes the expression of the PDL1 cell-surface protein in breast cancer cells. The identification of novel interactions of NONO with c-Jun and β-catenin proteins and activation of the Akt/MAPK/β-catenin signaling suggests that NONO is a novel regulator of Akt/MAPK/β-catenin signaling pathways. Taken together, our results indicated an essential role of NONO in the tumorigenicity of breast cancer and could be a potential target for anti-cancerous drugs. Video Abstract.

Peptidyl-prolyl cis/trans isomerase Pin1 interacts with hepatitis B virus core particle, but not with HBc protein, to promote HBV replication

Here, we demonstrate that the peptidyl-prolyl cis/trans isomerase Pin1 interacts noncovalently with the hepatitis B virus (HBV) core particle through phosphorylated serine/threonine-proline (pS/TP) motifs in the carboxyl-terminal domain (CTD) but not with particle-defective, dimer-positive mutants of HBc. This suggests that neither dimers nor monomers of HBc are Pin1-binding partners. The ¹⁶²TP, ¹⁶⁴SP, and ¹⁷²SP motifs within the HBc CTD are important for the Pin1/core particle interaction. Although Pin1 dissociated from core particle upon heat treatment, it was detected as an opened-up core particle, demonstrating that Pin1 binds both to the outside and the inside of the core particle. Although the amino-terminal domain S/TP motifs of HBc are not involved in the interaction, ⁴⁹SP contributes to core particle stability, and ¹²⁸TP might be involved in core particle assembly, as shown by the decreased core particle level of S49A mutant through repeated freeze and thaw and low-level assembly of the T128A mutant, respectively. Overexpression of Pin1 increased core particle stability through their interactions, HBV DNA synthesis, and virion secretion without concomitant increases in HBV RNA levels, indicating that Pin1 may be involved in core particle assembly and maturation, thereby promoting the later stages of the HBV life cycle. By contrast, parvulin inhibitors and PIN1 knockdown reduced HBV replication. Since more Pin1 proteins bound to immature core particles than to mature core particles, the interaction appears to depend on the stage of virus replication. Taken together, the data suggest that physical association between Pin1 and phosphorylated core particles may induce structural alterations through isomerization by Pin1, induce dephosphorylation by unidentified host phosphatases, and promote completion of virus life cycle.

Arsenic in medicine: past, present and future

Arsenicals are one of the oldest treatments for a variety of human disorders. Although infamous for its toxicity, arsenic is paradoxically a therapeutic agent that has been used since ancient times for the treatment of multiple diseases. The use of most arsenic-based drugs was abandoned with the discovery of antibiotics in the 1940s, but a few remained in use such as those for the treatment of trypanosomiasis. In the 1970s, arsenic trioxide, the active ingredient in a traditional Chinese medicine, was shown to produce dramatic remission of acute promyelocytic leukemia similar to the effect of all-trans retinoic acid. Since then, there has been a renewed interest in the clinical use of arsenicals. Here the ancient and modern medicinal uses of inorganic and organic arsenicals are reviewed. Included are antimicrobial, antiviral, antiparasitic and anticancer applications. In the face of increasing antibiotic resistance and the emergence of deadly pathogens such as the severe acute respiratory syndrome coronavirus 2, we propose revisiting arsenicals with proven efficacy to combat emerging pathogens. Current advances in science and technology can be employed to design newer arsenical drugs with high therapeutic index. These novel arsenicals can be used in combination with existing drugs or serve as valuable alternatives in the fight against cancer and emerging pathogens. The discovery of the pentavalent arsenic-containing antibiotic arsinothricin, which is effective against multidrug-resistant pathogens, illustrates the future potential of this new class of organoarsenical antibiotics.

Pin1 and Alzheimer's disease

Alzheimer's disease (AD) is an immense and growing public health crisis. Despite over 100 years of investigation, the etiology remains elusive and therapy ineffective. Despite current gaps in knowledge, recent studies have identified dysfunction or loss-of-function of Pin1, a unique cis-trans peptidyl prolyl isomerase, as an important step in AD pathogenesis. Here I review the functionality of Pin1 and its role in neurodegeneration.

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 Peptidyl-Prolyl cis-trans isomerase, Pin1, associates with Protein Kinase C θ via a critical Phospho-Thr-Pro motif in the V3 regulatory domain

Protein kinase C-θ (PKCθ) is a member of the novel PKC subfamily known for its selective and predominant expression in T lymphocytes where it regulates essential functions required for T cell activation and proliferation. Our previous studies provided a mechanistic explanation for the recruitment of PKCθ to the center of the immunological synapse (IS) by demonstrating that a proline-rich (PR) motif within the V3 region in the regulatory domain of PKCθ is necessary and sufficient for PKCθ IS localization and function. Herein, we highlight the importance of Thr335-Pro residue in the PR motif, the phosphorylation of which is key in the activation of PKCθ and its subsequent IS localization. We demonstrate that the phospho-Thr335-Pro motif serves as a putative binding site for the peptidyl-prolyl cis-trans isomerase (PPIase), Pin1, an enzyme that specifically recognizes peptide bonds at phospho-Ser/Thr-Pro motifs. Binding assays revealed that mutagenesis of PKCθ-Thr335-to-Ala abolished the ability of PKCθ to interact with Pin1, while Thr335 replacement by a Glu phosphomimetic, restored PKCθ binding to Pin1, suggesting that Pin1-PKCθ association is contingent upon the phosphorylation of the PKCθ-Thr335-Pro motif. Similarly, the Pin1 mutant, R17A, failed to associate with PKCθ, suggesting that the integrity of the Pin1 N-terminal WW domain is a requisite for Pin1-PKCθ interaction. In silico docking studies underpinned the role of critical residues in the Pin1-WW domain and the PKCθ phospho-Thr335-Pro motif, to form a stable interaction between Pin1 and PKCθ. Furthermore, TCR crosslinking in human Jurkat T cells and C57BL/6J mouse-derived splenic T cells promoted a rapid and transient formation of Pin1-PKCθ complexes, which followed a T cell activation-dependent temporal kinetic, suggesting a role for Pin1 in PKCθ-dependent early activation events in TCR-triggered T cells. PPIases that belong to other subfamilies, i.e., cyclophilin A or FK506-binding protein, failed to associate with PKCθ, indicating the specificity of the Pin1-PKCθ association. Fluorescent cell staining and imaging analyses demonstrated that TCR/CD3 triggering promotes the colocalization of PKCθ and Pin1 at the cell membrane. Furthermore, interaction of influenza hemagglutinin peptide (HA307-319)-specific T cells with antigen-fed antigen presenting cells (APCs) led to colocalization of PKCθ and Pin1 at the center of the IS. Together, we point to an uncovered function for the Thr335-Pro motif within the PKCθ-V3 regulatory domain to serve as a priming site for its activation upon phosphorylation and highlight its tenability to serve as a regulatory site for the Pin1 cis-trans isomerase.

The metabolic crosstalk between PIN1 and the tumour microenvironment

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) is a member of a family of peptidyl-prolyl isomerases that specifically recognizes and binds phosphoproteins, catalyzing the rapid cis-trans isomerization of phosphorylated serine/threonine-proline motifs, which leads to changes in the structures and activities of the targeted proteins. Through this complex mechanism, PIN1 regulates many hallmarks of cancer including cell autonomous metabolism and the crosstalk with the cellular microenvironment. Many studies showed that PIN1 is largely overexpressed in cancer turning on a set of oncogenes and abrogating the function of tumor suppressor genes. Among these targets, recent evidence demonstrated that PIN1 is involved in lipid and glucose metabolism and accordingly, in the Warburg effect, a characteristic of tumor cells. As an orchestra master, PIN1 finely tunes the signaling pathways allowing cancer cells to adapt and take advantage from a poorly organized tumor microenvironment. In this review, we highlight the trilogy among PIN1, the tumor microenvironment and the metabolic program rewiring.

Mechanical Regulation of Redox Balance via the Induction of the PIN1/NRF2/ARE Axis in Pancreatic Cancer

Pancreatic cancer is one of the most lethal malignancies. Desmoplastic stroma and metabolic reprogramming are two hallmarks of pancreatic cancer that support its malignant biological behaviors. However, the underlying mechanism by which the stroma maintain the redox balance remains unclear in pancreatic ductal adenocarcinoma (PDAC). Here, we demonstrated that the physical properties of the stroma could regulate the expression of PIN1 in pancreatic cancer cells. Moreover, we found that hard matrix-cultured pancreatic cancer cells induced the upregulation of PIN1 expression. Since PIN1 maintained redox balance via synergistic activation of NRF2 transcription, PIN1 promoted the expression of NRF2 to induce the expression of intracellular antioxidant response element (ARE)-driven genes. Consequently, the antioxidant stress ability of PDAC was increased, and the intracellular level of reactive oxygen species (ROS) was decreased. Thus, PIN1 is expected to be an important target for the treatment of PDAC, especially PDAC with an exuberant desmoplastic stroma.

PPIases Par14/Par17 Affect HBV Replication in Multiple Ways

Human parvulin 14 (Par14) and parvulin 17 (Par17) are peptidyl-prolyl cis/trans isomerases that upregulate hepatitis B virus (HBV) replication by binding to the conserved ¹³³Arg-Pro¹³⁴ (RP) motif of HBc and core particles, and ¹⁹RP²⁰-²⁸RP²⁹ motifs of HBx. In the absence of HBx, Par14/Par17 have no effect on HBV replication. Interaction with Par14/Par17 enhances the stability of HBx, core particles, and HBc. Par14/Par17 binds outside and inside core particles and is involved in HBc dimer-dimer interaction to facilitate core particle assembly. Although HBc RP motif is important for HBV replication, R133 residue is solely important for its interaction with Par14/Par17. Interaction of Par14 and Par17 with HBx involves two substrate-binding residues, Glu46/Asp74 (E46/D74) and E71/D99, respectively, and promotes HBx translocation to the nucleus and mitochondria. In the presence of HBx, Par14/Par17 are efficiently recruited to cccDNA and promote transcriptional activation via specific DNA-binding residues Ser19/44 (S19/44). S19 and E46/D74 of Par14, and S44 and E71/D99 of Par17, are also involved in the recruitment of HBc onto cccDNA. Par14/Par17 upregulate HBV replication via various effects that are mediated in part through the HBx-Par14/Par17-cccDNA complex and triple HBc, Par14/Par17, and cccDNA interactions in the nucleus, as well as via core particle-Par14/Par17 interactions in the cytoplasm.

Reciprocal inhibition of PIN1 and APC/CCDH1 controls timely G1/S transition and creates therapeutic vulnerability

Cyclin-dependent kinases (CDKs) mediated phosphorylation inactivates the anaphase-promoting complex (APC/CCDH1), an E3 ubiquitin ligase that contains the co-activator CDH1, to promote G1/S transition. PIN1 is a phosphorylation-directed proline isomerase and a master cancer signaling regulator. However, little are known about APC/CCDH1 regulation after phosphorylation and about PIN1 ubiquitin ligases. Here we uncover a domain-oriented reciprocal inhibition that controls the timely G1/S transition: The non-phosphorylated APC/CCDH1 E3 ligase targets PIN1 for degradation in G1 phase, restraining G1/S transition; APC/CCDH1 itself, after phosphorylation by CDKs, is inactivated by PIN1-catalyzed isomerization, promoting G1/S transition. In cancer, PIN1 overexpression and APC/CCDH1 inactivation reinforce each other to promote uncontrolled proliferation and tumorigenesis. Importantly, combined PIN1- and CDK4/6-inhibition reactivates APC/CCDH1 resulting in PIN1 degradation and an insurmountable G1 arrest that translates into synergistic anti-tumor activity against triple-negative breast cancer in vivo. Reciprocal inhibition of PIN1 and APC/CCDH1 is a novel mechanism to control timely G1/S transition that can be harnessed for synergistic anti-cancer therapy.

Mechanism and function of miR-140 in human cancers: A review and in silico study

MicroRNA-140 (miR-140) acts as a tumor suppressor and plays a vital role in cell biological functions such as cell proliferation, apoptosis, and DNA repair. The expression of this miRNA has been shown to be considerably decreased in cancer tissues and cell lines compared with normal adjacent tissues. Consequently, aberrant expression of some miR-140 target genes can lead to the initiation and progression of various human cancers, such as breast cancer, gastrointestinal cancers, lung cancer, and prostate cancer. The dysregulation of the miR-140 network also affects cell proliferation, invasion, metastasis, and apoptosis of cancer cells by affecting various signaling pathways. Besides, up-regulation of miR-140 could enhance the efficacy of chemotherapeutic agents in different cancer. We aimed to cover most aspects of miR-140 function in cancer development and address its importance in different stages of cancer progression.

Targeting prolyl isomerase Pin1 as a promising strategy to overcome resistance to cancer therapies

The development of tumor therapeutic resistance is one of the important reasons for the failure of antitumor therapy. Starting with multiple targets and multiple signaling pathways is helpful in understanding the mechanism of tumor resistance. The overexpression of prolyl isomerase Pin1 is highly correlated with the malignancy of cancer, since Pin1 controls many oncogenes and tumor suppressors, as well as a variety of cancer-driving signaling pathways. Strikingly, numerous studies have shown that Pin1 is directly involved in therapeutic resistance. In this review, we mainly summarize the functions and mechanisms of Pin1 in therapeutic resistance of multifarious cancers, such as breast, liver, and pancreatic carcinomas. Furtherly, from the perspective of Pin1-driven cancer signaling pathways including Raf/MEK/ERK, PI3K/Akt, Wnt/β-catenin, NF-κB, as well as Pin1 inhibitors containing juglone, epigallocatechin-3-gallate (EGCG), all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), it is better to demonstrate the important potential role and mechanism of Pin1 in resistance and sensitization to cancer therapies. It will provide new therapeutic approaches for clinical reversal and prevention of tumor resistance by employing synergistic administration of Pin1 inhibitors and chemotherapeutics, implementing combination therapy of Pin1-related cancer signaling pathway inhibitors and Pin1 inhibitors, and exploiting novel Pin1-specific inhibitors.

Critical Role of Aquaporins in Cancer: Focus on Hematological Malignancies

Simple Summary

Aquaporins are proteins able to regulate the transfer of water and other small substances such as ions, glycerol, urea, and hydrogen peroxide across cellular membranes. AQPs provide for a huge variety of physiological phenomena; their alteration provokes several types of pathologies including cancer and hematological malignancies. Our review presents data revealing the possibility of employing aquaporins as biomarkers in patients with hematological malignancies and evaluates the possibility that interfering with the expression of aquaporins could represent an effective treatment for hematological malignancies.

Abstract

Aquaporins are transmembrane molecules regulating the transfer of water and other compounds such as ions, glycerol, urea, and hydrogen peroxide. Their alteration has been reported in several conditions such as cancer. Tumor progression might be enhanced by aquaporins in modifying tumor angiogenesis, cell volume adaptation, proteases activity, cell–matrix adhesions, actin cytoskeleton, epithelial–mesenchymal transitions, and acting on several signaling pathways facilitating cancer progression. Close connections have also been identified between the aquaporins and hematological malignancies. However, it is difficult to identify a unique action exerted by aquaporins in different hemopathies, and each aquaporin has specific effects that vary according to the class of aquaporin examined and to the different neoplastic cells. However, the expression of aquaporins is altered in cell cultures and in patients with acute and chronic myeloid leukemia, in lymphoproliferative diseases and in multiple myeloma, and the different expression of aquaporins seems to be able to influence the efficacy of treatment and could have a prognostic significance, as greater expression of aquaporins is correlated to improved overall survival in leukemia patients. Finally, we assessed the possibility that modifying the aquaporin expression using aquaporin-targeting regulators, specific monoclonal antibodies, and even aquaporin gene transfer could represent an effective therapy of hematological malignancies.

Inhibition of the PIN1-NRF2/GPX4 axis imparts sensitivity to cisplatin in cervical cancer cells

The incidence of cervical cancer (CC) ranks the fourth in female malignant tumors globally. Chemoresistance is one of the main causes of treatment failure in advanced recurrent CC. Prolyl isomerase 1 (PIN1) is overexpressed in a variety of tumors, and is closely associated with the malignant potential of tumor cells, such as transformation, proliferation, invasion and metastasis. In the present study, we demonstrate that cell death induced by suppression of PIN1 could be inhibited by ferrostatin-1 (Fer-1) and ferroptosis biomarkers including lactate dehydrogenase (LDH) release, lipid peroxidation and malondialdehyde (MDA) are upregulated by downregulating PIN1. We then discover that abrogation of PIN1 greatly decreases the level of glutathione peroxidase 4 (GPX4) and the level of PIN1 is positively correlated with the level of GPX4. Furthermore, the knockdown of PIN1 promotes ferroptosis induced by RSL3. The mechanism involves PIN1 silencing which downregulates GPX4 by decreasing the level of nuclear factor E2-related factor 2 (NRF2). Furthermore, overexpression of NRF2 inhibits RSL3-mediated ferroptosis of CC cells when PIN1 is silenced. In addition, our results indicate that cisplatin (DDP) induces ferroptosis, which is restrained by overexpression of PIN1. The PIN1 inhibitor, KPT-6566, promotes the cytotoxic effect of DDP. The present study reveals that PIN1 affects ferroptosis and sensitivity to DDP in CC cells via the NRF2/GPX4 axis, thereby identifying PIN1 as a potential therapeutic target for CC.

Pancreatic tumor eradication via selective Pin1 inhibition in cancer-associated fibroblasts and T lymphocytes engagement

Cancer associated fibroblasts (CAFs) support tumors via multiple mechanisms, including maintaining the immunosuppressive tumor microenvironment and limiting infiltration of immune cells. The prolyl isomerase Pin1, whose overexpression in CAFs has not been fully profiled yet, plays critical roles in tumor initiation and progression. To decipher effects of selective Pin1 inhibition in CAFs on pancreatic cancer, here we formulate a DNA-barcoded micellular system (DMS) encapsulating the Pin1 inhibitor AG17724. DMS functionalized with CAF-targeting anti-FAP-α antibodies (antiCAFs-DMS) can selectively inhibit Pin1 in CAFs, leading to efficacious but transient tumor growth inhibition. We further integrate DNA aptamers (AptT), which can engage CD8+ T lymphocytes, to obtain a bispecific antiCAFs-DMS-AptT system. AntiCAFs-DMS-AptT inhibits tumor growth in subcutaneous and orthotopic pancreatic cancer models.

Pharmacological inhibition of the prolyl isomerase PIN1, highly expressed in cancer cells and cancer associated fibroblasts (CAF), has been proposed for cancer therapy. Here the authors report the design of a DNA-barcoded micellular system functionalized with antibodies targeting CAFs and a T cell recruiting aptamer to deliver the PIN1 inhibitor AG17724, showing antitumor response in preclinical models of pancreatic cancer.

Cinobufacini Injection Inhibits the Proliferation of Triple-Negative Breast Cancer Through the Pin1-TAZ Signaling Pathway

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer (BC), which is characterized by the total absence of human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), and estrogen receptor (ER) expression. Cinobufacini injection (CI) is the aqueous extract from the dry skin of Bufo gargarizans, which is broadly used for the treatment of malignant tumors. However, the potential mechanism of CI against TNBC has not been fully revealed. In this study, we found that CI inhibited the proliferation of MDA-MB-231 and 4T1 cells in a time- and dose-dependent manner. RNA-seq data showed that downregulated and upregulated genes were mainly enriched in biological processes related to tumor cell proliferation, including cell cycle arrest and regulation of apoptosis signaling pathways. Indeed, after CI treatment, the protein level of CDK1 and Bcl-2/Bax decreased, indicating that CI induced the cell cycle of MDA-MB-231 arrest in the G2/M phase and increased the rate of apoptosis. Meanwhile, CI significantly inhibited the growth of tumor in vivo, and RNA-seq data showed that the TAZ signaling pathway played a vital role after CI treatment. Both immunohistochemistry and Western blot analysis confirmed the downregulation of Pin1 and TAZ, caused by CI treatment. Furthermore, the bioinformatics analysis indicated that Pin1 and TAZ were indeed elevated in TNBC patients, with poor staging, classification, and patient survival rate. In conclusion, CI effectively inhibited the proliferation of TNBC in vitro and in vivo and induced their apoptosis and cycle arrest through the Pin1–TAZ pathway.

Proteomics Study of Mesenchymal Stem Cell-Like Cells Obtained from Tumor Microenvironment of Patients with Malignant and Benign Salivary Gland Tumors

Objective

Salivary gland tumors (SGTs) show some aggressive and peculiar clinicopathological behaviors that might be related to the components of the tumor microenvironment, especially mesenchymal stem cells (MSCs)-associated proteins. However, the role of MSCs-related proteins in SGTs tumorigenesis is poorly understood. This study aimed to isolate and characterize MSCs from malignant and benign tumor tissues and to identify differentially expressed proteins between these two types of MSCs.

Materials and Methods

In this experimental study, MSC-like cells derived from benign (pleomorphic adenoma, n=5) and malignant (mucoepidermoid carcinoma, n=5) tumor tissues were verified by fluorochrome antibodies and flow cytometric analysis. Differentially expressed proteins were identified using two-dimensional polyacrylamide gel electrophoresis (2DE) and Mass spectrometry.

Results

Results showed that isolated cells strongly expressed characteristic MSCs markers such as CD44, CD73, CD90, CD105, and CD166, but they did not express or weakly expressed CD14, CD34, CD45 markers. Furthermore, the expression of CD24 and CD133 was absent or near absent in both isolated cells. Results also discovered overexpression of Annexin A4 (Anxa4), elongation factor 1-delta (EF1-D), FK506 binding protein 9 (FKBP9), cytosolic platelet-activating factor acetylhydrolase type IB subunit beta (PAFAH1B), type II transglutaminase (TG2), and s-formylglutathione hydrolase (FGH) in MSCs isolated from the malignant tissues. Additionally, heat shock protein 70 (Hsp70), as well as keratin, type II cytoskeletal 7 (CK-7), were found to be overexpressed in MSCs derived from the benign ones.

Conclusion

Malignant and benign SGTs probably exhibit a distinct pattern of tissue proteins that are most likely related to the metabolic pathway. However, further studies in a large number of patients are required to determine the applicability of identified proteins as new targets for cancer therapy.

Juglone and KPT6566 Suppress the Tumorigenic Potential of CD44+CD133+ Tumor-Initiating Caco-2 Cells In Vitro and In Vivo

Pin1, a cis/trans isomerase of peptidyl-prolyl peptide bonds, plays a crucial role in the pathogenesis of many human cancers. Although chemical inhibitors of Pin1 show potent antitumor therapeutic properties against various cancers, their effect on colorectal cancer, especially colorectal tumor-initiating cells, remains unknown. Here, we investigated the effect of Juglone and KPT6566 on Caco-2 cells and tumor-initiating Caco-2 cells. Juglone and KPT6566 inhibited cell growth and colony formation, and induced apoptosis of Caco-2 cells. We also found that Juglone and KPT6566 downregulated expression of G1-phase-specific cyclins and cyclin-dependent kinases in a time-dependent manner, consistent with suppression of Caco-2 cell proliferation and colony formation. Although tumor-initiating cells are thought to be responsible for resistance to traditional chemotherapeutic drugs, our experiments demonstrate that Juglone or KPT6566 kill both tumor-initiating and non-tumor-initiating Caco-2 cells with equal or similar efficacy. Finally, when CD44⁺CD133⁺ tumor-initiating Caco-2 cells were injected into NSG mice, Juglone or KPT6566 led to a meaningful reduction in tumor volume and mass compared with tumors isolated from mice that received control treatment. Overall, these results indicate that chemical Pin1 inhibitors may be a valuable therapeutic option against colorectal tumor-initiating cancer cells.

Clinical significance of FBXW7 loss of function in human cancers

FBXW7 (F-Box and WD Repeat Domain Containing 7) (also referred to as FBW7 or hCDC4) is a component of the Skp1-Cdc53 / Cullin-F-box-protein complex (SCF/β-TrCP). As a member of the F-box protein family, FBXW7 serves a role in phosphorylation-dependent ubiquitination and proteasome degradation of oncoproteins that play critical role(s) in oncogenesis. FBXW7 affects many regulatory functions involved in cell survival, cell proliferation, tumor invasion, DNA damage repair, genomic instability and telomere biology. This thorough review of current literature details how FBXW7 expression and functions are regulated through multiple mechanisms and how that ultimately drives tumorigenesis in a wide array of cell types. The clinical significance of FBXW7 is highlighted by the fact that FBXW7 is frequently inactivated in human lung, colon, and hematopoietic cancers. The loss of FBXW7 can serve as an independent prognostic marker and is significantly correlated with the resistance of tumor cells to chemotherapeutic agents and poorer disease outcomes. Recent evidence shows that genetic mutation of FBXW7 differentially affects the degradation of specific cellular targets resulting in a distinct and specific pattern of activation/inactivation of cell signaling pathways. The clinical significance of FBXW7 mutations in the context of tumor development, progression, and resistance to therapies as well as opportunities for targeted therapies is discussed.

Regulation of gene expression by glycolytic and gluconeogenic enzymes

Gene transcription and cell metabolism are two fundamental biological processes that mutually regulate each other. Upregulated or altered expression of glucose metabolic genes in glycolysis and gluconeogenesis is a major driving force of enhanced aerobic glycolysis in tumor cells. Importantly, glycolytic and gluconeogenic enzymes in tumor cells acquire moonlighting functions and directly regulate gene expression by modulating chromatin or transcriptional complexes. The mutual regulation between cellular metabolism and gene expression in a feedback mechanism constitutes a unique feature of tumor cells and provides specific molecular and functional targets for cancer treatment.

Depletion of mitochondrial methionine adenosyltransferase α1 triggers mitochondrial dysfunction in alcohol-associated liver disease

MATα1 catalyzes the synthesis of S-adenosylmethionine, the principal biological methyl donor. Lower MATα1 activity and mitochondrial dysfunction occur in alcohol-associated liver disease. Besides cytosol and nucleus, MATα1 also targets the mitochondria of hepatocytes to regulate their function. Here, we show that mitochondrial MATα1 is selectively depleted in alcohol-associated liver disease through a mechanism that involves the isomerase PIN1 and the kinase CK2. Alcohol activates CK2, which phosphorylates MATα1 at Ser114 facilitating interaction with PIN1, thereby inhibiting its mitochondrial localization. Blocking PIN1-MATα1 interaction increased mitochondrial MATα1 levels and protected against alcohol-induced mitochondrial dysfunction and fat accumulation. Normally, MATα1 interacts with mitochondrial proteins involved in TCA cycle, oxidative phosphorylation, and fatty acid β-oxidation. Preserving mitochondrial MATα1 content correlates with higher methylation and expression of mitochondrial proteins. Our study demonstrates a role of CK2 and PIN1 in reducing mitochondrial MATα1 content leading to mitochondrial dysfunction in alcohol-associated liver disease.

Targeting peptidyl-prolyl isomerase 1 in experimental pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by pro-proliferative and anti-apoptotic phenotype in vascular cells, leading to pulmonary vascular remodelling and right heart failure. Peptidylprolyl cis/trans isomerase, NIMA interacting 1 (Pin1), a highly conserved enzyme, which binds to and catalyses the isomerisation of specific phosphorylated Ser/Thr-Pro motifs, acting as a molecular switch in multiple coordinated cellular processes. We hypothesised that Pin1 plays a substantial role in PAH and its inhibition with a natural organic compound, Juglone, would reverse experimental pulmonary hypertension (PH).

We demonstrated that the expression of Pin1 was markedly elevated in experimental PH (i.e. hypoxia induced mouse and Sugen/hypoxia induced rat models) and pulmonary arterial smooth muscle cells (PASMCs) of patients with clinical PAH. In vitro Pin1 inhibition by either Juglone treatment or siRNA knock-down resulted in an induction of apoptosis and decrease in proliferation of human pulmonary vascular cells. Stimulation with growth factors induced Pin1 expression, while its inhibition reduced the activity of numerous PAH-related transcription factors, such as hypoxia-inducible factor alpha (HIF) and signal transducer and activator of transcription (STAT). Juglone administration lowered pulmonary vascular resistance, enhanced RV function, improved pulmonary vascular and cardiac remodelling in the Sugen/hypoxia rat model of PAH and the chronic hypoxia-induced PH model in mice.

Our study demonstrates that targeting of Pin1 with small molecule inhibitor, Juglone, might be an attractive future therapeutic strategy for PAH and right heart disease secondary to PAH.

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 directly binds and stabilizes Nrf2 in breast cancer

Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) has been frequently overexpressed in many types of malignancy, suggesting its oncogenic function. It recognizes phosphorylated serine or threonine (pSer/Thr) of a target protein and isomerizes the adjacent proline (Pro) residue, thereby altering folding, subcellular localization, stability, and function of target proteins. The oncogenic transcription factor, Nrf2 harbors the pSer/Thr-Pro motif. This prompted us to investigate whether Pin1 could bind to Nrf2 and influence its stability and function in the context of implications for breast cancer development and progression. The correlation between Pin1 and Nrf2 in the triple-negative breast cancer cells was validated by RNASeq analysis as well as immunofluorescence staining. Interaction between Pin1 and Nrf2 was assessed by co-immunoprecipitation and an in situ proximity ligation assay. We found that mRNA and protein levels of Pin1 were highly increased in the tumor tissues of triple-negative breast cancer patients and the human breast cancer cell line. Genetic or pharmacologic inhibition of Pin1 enhanced the ubiquitination and degradation of Nrf2. In contrast, the overexpression of Pin1 resulted in the accumulation of Nrf2 in the nucleus, without affecting its transcription. Notably, the phosphorylation of Nrf2 at serine 215, 408, and 577 is essential for its interaction with Pin1. We also identified phosphorylated Ser104 and Thr277 residues in Keap1, a negative regulator of Nrf2, for Pin1 binding. Pin1 plays a role in breast cancer progression through stabilization and constitutive activation of Nrf2 by competing with Keap1 for Nrf2 binding.

New PIN1 inhibitors identified through a pharmacophore-driven, hierarchical consensus docking strategy

PIN1 is considered as a therapeutic target for a wide variety of tumours. However, most of known inhibitors are devoid of cellular activity despite their good enzyme inhibitory profile. Hence, the lack of effective compounds for the clinic makes the identification of novel PIN1 inhibitors a hot topic in the medicinal chemistry field. In this work, we reported a virtual screening study for the identification of new promising PIN1 inhibitors. A receptor-based procedure was applied to screen different chemical databases of commercial compounds. Based on the whole workflow, two compounds were selected and biologically evaluated. Both ligands, compounds VS1 and VS2, showed a good enzyme inhibitory activity and VS2 also demonstrated a promising antitumoral activity in ovarian cancer cells. These results confirmed the reliability of our in silico protocol and provided a structurally novel ligand as a valuable starting point for the development of new PIN1 inhibitors.

Pathologic role of peptidyl-prolyl isomerase Pin1 in pulmonary artery remodeling

Peptidyl-prolyl isomerase Pin1 is crucial for cell proliferation, but its role in pulmonary artery remodeling (PAR) is unclear. In the present study, we aimed to evaluate the expression and contribution of Pin1 in PAR. Treatment with Pin1 inhibitor Juglone or Pin1-specific siRNAs ameliorated the expression of Pin1 and proliferating cell nuclear antigen (PCNA) in human pulmonary artery smooth muscle cells (PASMCs) in vitro, and Juglone treatment arrested the cell cycle at the G1 phase. Treatment with transforming growth factor β1 (TGF-β1) also enhanced Pin1 expression and PASMC proliferation. Immunohistochemical staining revealed that Pin1 and PCNA expression levels were increased and positively correlated with each other in PAR samples from humans and monocrotaline-treated Sprague-Dawley rats; these proteins were mainly localized in arteries undergoing remodeling, as well as inflammatory cells, and hyperplastic bronchial epithelial cells. Intraperitoneal injection of Juglone also led to morphologic and hemodynamic changes in PAR rats. Additionally, PAR rats displayed higher serum and lung TGF-β1 levels compared with controls, while administration of Juglone to PAR rats suppressed serum and lung TGF-β1 levels. The findings in this study suggest that TGF-β1 and Pin1 constitute a positive feedback loop, which plays an important role in the pathophysiology of PAR.

Detecting ligand-protein interactions inside cells using reactive peptide tags and split luciferase

We report a method for detecting ligand-protein interactions occurring within cells using short peptide reactive tags appended to ligands and proteins, along with a split NanoLuc luciferase. This method can be applied to estimate the binding affinities of ligand-protein interactions and to detect the interactions of proteins with unstable synthetic ligands inside the cells.

Prolyl isomerase Pin1 plays an essential role in SARS-CoV-2 proliferation, indicating its possibility as a novel therapeutic target

Novel coronavirus disease 2019 (COVID-19) has emerged as a global pandemic with far-reaching societal impact. Here we demonstrate that Pin1 is a key cellular molecule necessary for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) propagation. In this study, siRNA-mediated silencing of Pin1 expression markedly suppressed the proliferation of SARS-CoV-2 in VeroE6/TMPRSS2 cells. In addition, several recently generated Pin1 inhibitors showed strong inhibitory effects on SARS-CoV-2 proliferation, measured by both viral mRNA and protein synthesis, and alleviated the cytopathic effect (CPE) on VeroE6/TMPRSS2 cells. One compound, termed H-77, was found to block SARS-CoV-2 proliferation at an EC₅₀ below 5 μM regardless of whether it was added to the culture medium prior to or after SARS-CoV-2 infection. The inhibition of viral N protein mRNA synthesis by H-77 implies that the molecular mechanism underlying SARS-CoV-2 inhibition is likely to be associated with viral gene transcription or earlier steps. Another Pin1 inhibitor, all-trans retinoic acid (ATRA)—a commercially available drug used to treat acute promyelocytic leukemia (APL) and which both activates the retinoic acid receptor and inhibits the activity of Pin1—similarly reduced the proliferation of SARS-CoV-2. Taken together, the results indicate that Pin1 inhibitors could serve as potential therapeutic agents for COVID-19.

Spectroscopic and computational studies on the binding interaction between gallic acid and Pin1

Gallic acid (GA) is a natural ingredient in functional foods, which has various health-promoting and antitumour effects. Peptidyl-prolyl cis/trans isomerase Pin1 plays an important role in preventing the development of some malignant tumours. However, whether there was an interaction between Pin1 and GA remains unknown. In this work, the binding information of GA and Pin1 was investigated systematically using multiple spectral and computational methods. GA bound to Pin1 directly with moderate binding affinity in the order of 10⁴  mol/L, therefore decreasing the activity of Pin1. Also, the binding process of GA to Pin1 was driven through weak van der Waals forces, hydrogen bonds, and electrostatic forces. In addition, the important residues Lys63, Arg68, and Arg69 played a significant role in maintaining the binding stability between Pin1 and GA. Interestingly, GA reduced the activity of Pin1 by affecting its conformational characteristics. Our present work showed that GA binds to Pin1 and inhibits its activity, affecting its structural and functional properties, which may contribute to the therapy of Pin1-related diseases.

Targeting Pin1 renders pancreatic cancer eradicable by synergizing with immunochemotherapy

Pancreatic ductal adenocarcinoma (PDAC) is characterized by notorious resistance to current therapies attributed to inherent tumor heterogeneity and highly desmoplastic and immunosuppressive tumor microenvironment (TME). Unique proline isomerase Pin1 regulates multiple cancer pathways, but its role in the TME and cancer immunotherapy is unknown. Here, we find that Pin1 is overexpressed both in cancer cells and cancer-associated fibroblasts (CAFs) and correlates with poor survival in PDAC patients. Targeting Pin1 using clinically available drugs induces complete elimination or sustained remissions of aggressive PDAC by synergizing with anti-PD-1 and gemcitabine in diverse model systems. Mechanistically, Pin1 drives the desmoplastic and immunosuppressive TME by acting on CAFs and induces lysosomal degradation of the PD-1 ligand PD-L1 and the gemcitabine transporter ENT1 in cancer cells, besides activating multiple cancer pathways. Thus, Pin1 inhibition simultaneously blocks multiple cancer pathways, disrupts the desmoplastic and immunosuppressive TME, and upregulates PD-L1 and ENT1, rendering PDAC eradicable by immunochemotherapy.

Roles of XBP1s in Transcriptional Regulation of Target Genes

The spliced form of X-box binding protein 1 (XBP1s) is an active transcription factor that plays a vital role in the unfolded protein response (UPR). Under endoplasmic reticulum (ER) stress, unspliced Xbp1 mRNA is cleaved by the activated stress sensor IRE1α and converted to the mature form encoding spliced XBP1 (XBP1s). Translated XBP1s migrates to the nucleus and regulates the transcriptional programs of UPR target genes encoding ER molecular chaperones, folding enzymes, and ER-associated protein degradation (ERAD) components to decrease ER stress. Moreover, studies have shown that XBP1s regulates the transcription of diverse genes that are involved in lipid and glucose metabolism and immune responses. Therefore, XBP1s has been considered an important therapeutic target in studying various diseases, including cancer, diabetes, and autoimmune and inflammatory diseases. XBP1s is involved in several unique mechanisms to regulate the transcription of different target genes by interacting with other proteins to modulate their activity. Although recent studies discovered numerous target genes of XBP1s via genome-wide analyses, how XBP1s regulates their transcription remains unclear. This review discusses the roles of XBP1s in target genes transcriptional regulation. More in-depth knowledge of XBP1s target genes and transcriptional regulatory mechanisms in the future will help develop new therapeutic targets for each disease.

A short review on cross-link between pyruvate kinase (PKM2) and Glioblastoma Multiforme

Pyruvate kinase (PK) catalyzes the last irreversible reaction of glycolysis pathway, generating pyruvate and ATP, from Phosphoenol Pyruvate (PEP) and ADP precursors. In mammals, four different tissue-specific isoforms (M1, M2, L and R) of PK exist, which are translated from two genes (PKL and PKR). PKM2 is the highly expressed isoform of PK in cancers, which regulates the aerobic glycolysis via reprogramming cancer cell's metabolic pathways to provide an anabolic advantage to the tumor cells. In addition to the established role of PKM2 in aerobic glycolysis of multiple cancer types, various recent findings have highlighted the non-metabolic functions of PKM2 in brain tumor development. Nuclear PKM2 acts as a co-activator and directly regulates gene transcription. PKM2 dependent transactivation of various oncogenic genes is instrumental in the progression and aggressiveness of Glioblastoma Multiforme (GBM). Also, PKM2 acts as a protein kinase in histone modification which regulates gene expression and tumorigenesis. Ongoing research has explored novel regulatory mechanisms of PKM2 and its association in GBM progression. This review enlists and summarizes the metabolic and non-metabolic roles of PKM2 at the cellular level, and its regulatory function highlights the importance of the nuclear functions of PKM2 in GBM progression, and an emerging role of PKM2 as novel cancer therapeutics.

Path Ensembles for Pin1-Catalyzed Cis-Trans Isomerization of a Substrate Calculated by Weighted Ensemble Simulations

Pin1 enzyme protein recognizes specifically phosphorylated serine/threonine (pSer/pThr) and catalyzes the slow interconversion of the peptidyl-prolyl bond between cis and trans forms. Structural dynamics between the cis and trans forms are essential to reveal the underlying molecular mechanism of the catalysis. In this study, we apply the weighted ensemble (WE) simulation method to obtain comprehensive path ensembles for the Pin1-catalyzed isomerization process. Associated rate constants for both cis-to-trans and trans-to-cis isomerization are calculated to be submicroseconds time scales, which are in good agreement with the calculated free energy landscape where the cis form is slightly less favorable. The committor-like analysis indicates the shift of the transition state toward trans form (at the isomerization angle ω ∼ 110°) compared to the intrinsic position for the isolated substrate (ω ∼ 90°). The calculated structural ensemble clarifies a role of both the dual-histidine motif, His59/His157, and the basic residues, Lys63/Arg68/Arg69, to anchor both sides of the peptidyl-prolyl bond, the aromatic ring in Pro, and the phosphate in pSer, respectively. The rotation of the torsion angle is found to be facilitated by relaying the hydrogen-bond partner of the main-chain oxygen in pSer from Cys113 in the cis form to Arg68 in the trans form, through Ser154 at the transition state, which is really the cause of the shift in the transition state. The role of Ser154 as a driving force of the isomerization is confirmed by additional WE and free energy calculations for S154A mutant where the isomerization takes place slightly slower and the free energy barrier increases through the mutation. The present study shows the usefulness of the WE simulation for substantial path samplings between the reactant and product states, unraveling the molecular mechanism of the enzyme catalysis.

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.

Inhibitory effect of miR-140-5p on doxorubicin resistance of hepatocellular carcinoma

To investigate the role of microRNA (miR)-140-5p in doxorubicin (DOX) sensitivity in hepatocellular carcinoma, miR-140-5p and peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) expression was first evaluated in hepatocellular carcinoma tissues using starBase. Next, in vitro experiments were performed. Cell line expression of miR-140-5p and PIN1 expression was detected by reverse transcription polymerase chain reaction. Cell viability and proliferation were determined by the Cell Counting Kit-8 and EdU assays. The relationship between miR-140-5p and PIN1 was evaluated by TargetScan and a luciferase reporter system. Western blotting was used to detect the expression of PIN1. It was observed that miR-140-5p was downregulated in hepatocellular carcinoma tissues and cell lines compared with normal samples in HCC or normal liver cells. Gain-of-function experiments revealed that miR-140-5p mimics were able to enhance DOX sensitivity of hepatocellular carcinoma cells. Further studies revealed that PIN1 was a target gene of miR-140-5p. Suppression of PIN1 led to higher DOX sensitivity in hepatocellular carcinoma cells. Finally, when comparing a PIN1-siRNA alone group and a PIN1-siRNA plus miR-140-5p inhibitor group, there was no significant difference in cell viability. Furthermore, miR-140-5p mimics did not reduce the sensitivity of PIN1mut plasmid to DOX in HUH7 and SNU449 cells. The present study demonstrated that miR-140-5p could enhance DOX sensitivity in hepatocellular carcinoma cells by targeting PIN1.

PIN1 facilitates ubiquitin-mediated degradation of serine/threonine kinase 3 and promotes melanoma development via TAZ activation

The Hippo signaling pathway controls cellular processes including growth, homeostasis, and apoptosis. The kinase STK3 acts upstream in this pathway to activate LATS1/2 kinase, which phosphorylates and inactivates the transcriptional coactivators YAP/TAZ. The dysregulation of Hippo signaling leads to human diseases including cancer; however, the molecular mechanisms underlying its dysregulation in melanoma are unknown. We aimed to determine the role of the PIN1 in Hippo signaling dysregulation and melanoma tumorigenesis. We report that PIN1 interacts with STK3 and induces ubiquitination-dependent proteasomal degradation of STK3. Furthermore, PIN1 plays a critical role in the nuclear translocation of TAZ, which forms a complex with TEAD to increase CTGF expression. PIN1 ablation blocks TAZ/TEAD complex formation and decreases CTGF expression. PIN1-mediated STK3 degradation is associated with enhanced cell growth, induction of cell transformation, and increased tumorigenicity. In clinical context, PIN1 and STK3 levels are inversely correlated in patient melanoma tissues. These findings indicate that PIN1-mediated STK3 destabilization contributes to the dysregulation of Hippo signaling, leading to oncogenic signaling and melanoma tumorigenesis. Our data suggest that inhibition of the PIN1-STK3 axis could be a novel treatment strategy for malignant melanoma.

Impact of PIN1 Inhibition on Tumor Progression and Chemotherapy Sensitivity in Colorectal Cancer

BACKGROUND

Deregulated PIN1 is associated with cancer development and progression. Herein, for the first time, we evaluate the roles that PIN1 in tumorigenic characteristics of colorectal cancer (CRC) cells.

METHODS

In this study, PIN1 expression was knocked down in SW-48 cells by synthetic small interfering RNA (siRNA). After confirming the knockdown of PIN1, cell viability, colony formation, apoptosis, autophagy, cancer stem cell (CSC)-related genes, CSC-related signaling pathways, cell migration, and 5-FU chemosensitivity were evaluated in vitro.

RESULTS

Transfection of PIN1 siRNA into SW-48 cells inhibited cancer cell proliferation, migration, and increased apoptosis and autophagy. Transfected SW-48 cells had lower properties of CSCs through the inhibition of β-catenin and Notch1 gene expression. Moreover, inhibition of PIN1 enhanced the inhibitory effect of 5-FU on SW-48 cell proliferation.

CONCLUSION

Our results indicated that targeting of PIN1 serves as a promising therapeutic solution for the suppression of tumor progression processes in CRC.

The fission yeast Pin1 peptidyl-prolyl isomerase promotes dissociation of Sty1 MAPK from RNA polymerase II and recruits Ssu72 phosphatase to facilitate oxidative stress induced transcription

Pin1 is a peptidyl-prolyl isomerase that regulates the structure and function of eukaryotic RNA polymerase II (Pol II) through interaction with the C-terminal domain (CTD) of Rpb1, the largest subunit of Pol II. We demonstrated that this function is important for cellular response to oxidative stress in the fission yeast Schizosaccharomyces pombe. In response to oxidative stress, the Atf1 transcription factor targets Sty1, the mitogen-activated protein kinase (MAPK), to specific stress-responsive promoters. Anchored Sty1 recruits Pol II through direct association with Rpb1-CTD and phosphorylates the reiterated heptad sequence at Serine 5. Pin1 binds phosphorylated CTD to promote dissociation of Sty1 from it, and directly recruits Ssu72 phosphatase to facilitate dephosphorylation of CTD for transcription elongation. In the absence of Pin1, the association of Sty1-Atf1 with Rpb1 persists on stress-responsive promoters failed to generate transcripts of the corresponding genes effectively. The identified characteristic features of the fission yeast Pin1 are conserved in humans. We demonstrated that elevated Pin1 level in cancer cells might help to sustain survival under oxidative stress generated from their altered metabolic pathways. Together, these results suggest a conserved function of Pin1 in cellular response to oxidative stress among eukaryotic cells that might have clinical implication.