Pin1 inhibition exerts potent activity against acute myeloid leukemia through blocking multiple cancer-driving pathways

TCP1 promotes the progression of malignant tumours by stabilizing c-Myc through the AKT/GSK-3β and ERK signalling pathways

The chaperonin tailless complex polypeptide 1 (TCP1) is a key subunit of chaperonin containing TCP1 (CCT) that regulates the folding and stability of proteins during cancer progression. Here, the prognostic significance of TCP1 was explored mainly in patients with hepatocellular carcinoma (HCC) and pancreatic ductal adenocarcinoma (PDAC). We showed that TCP1 expression was significantly greater in clinically malignant tumour tissues than in normal tissues and that high TCP1 expression was associated with poor prognosis. TCP1 suppression not only decreased the proliferation and invasion of cancer cells in vitro but also inhibited tumour growth and metastasis in vivo. The underlying mechanisms were determined by ubiquitination assays and Co-IP (Co-Immunoprecipitation) experiments, and it was found that TCP1 regulated the stability of c-Myc through the RAC-alpha serine/threonine-protein kinase (AKT) /Glycogen synthase kinase 3β (GSK-3β) and extracellular regulated protein kinases (ERK) signalling pathways. Moreover, TCP1 knock-in (TCP1-KI) dramatically promoted the occurrence of diethylnitrosamine (DEN) -induced primary HCC in mice. Our results highlight the critical role of TCP1 in HCC and PDAC and reveal a novel mechanism to suppress HCC and PDAC by targeting c-Myc via the TCP1-induced promotion of the AKT/GSK-3β and ERK signalling pathways. TCP1 is able to modulate the stability of target proteins by multiple pathways, thus promoting the progression of HCC and PDAC. Our study identifies TCP1 as a prognostic novel marker and therapeutic target of HCC and PDAC.

Comparison of radiobiological effects induced by radiolabeled antibodies in human cancer cells and fungal cells

PURPOSE

Acute myeloid leukemia (AML) is a deadly form of leukemia, and its treatment often leaves patients immunocompromised, making them vulnerable to fungal infections. Radioimmunotherapy (RIT) is explored for both AML and fungal infections. This study compares the radiobiological effects of alpha emitter Actinium-225 (225Ac) and beta emitter Lutetium-177 (177Lu)-labeled antibodies on AML and Cryptococcus neoformans cells.

MATERIALS AND METHODS

AML OCI-AML3 and C. neoformans Cap-67 cells were treated with anti-(1-3)-beta-glucan antibody 400-2 and anti-CD33 antibody HuM-195, conjugated to DOTA and radiolabeled with 225Ac or 177Lu. Clonogenic survival, γH2A/X staining, and micronuclei assays were conducted. Antibody internalization was assessed by flow cytometry.

RESULTS

Both 225Ac- and 177Lu-enabled RIT resulted in decreased clonogenic survival in Cap-67 and OCI-AML3 cells, with Cap-67 recovering more rapidly. DNA double-strand breaks and micronuclei formation revealed DNA damage, with fewer micronuclei in OCI-AML3 cells due to radiation destruction. HuM-195 antibody internalized into OCI-AML3 cells, whereas 400-2 did not internalize into Cap-67 cells.

CONCLUSIONS

While both cell lines showed similar responses to 225Ac- and 177Lu-enabled RIT, variations were observed based on cellular structure, doubling times and DNA repair mechanisms. This study offers insights for future in vivo research on fungal infections in cancer setting.

Overexpression of Pin1 regulated by TOP2A, which subsequently stabilizes Pyk2 to promote bortezomib resistance in multiple myeloma

Multiple myeloma (MM), a hematological malignancy of plasma cells, has remained largely incurable owing to drug resistance and disease relapse, which requires novel therapeutic targets and treatment approaches. Peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (Pin1) acts as an oncoprotein linked to the development of various tumors. However, the functional consequence of Pin1 overexpression in modulating MM biology has not been established. In the present study, we show that Pin1 expression is highly variable in myeloma cell lines and primary MMs and that high Pin1 expression is associated with poor survival of MM patients. Next, TOP2A is identified to be a Pin1 promoter-binding protein and CK2 activates TOP2A to promote the expression level of Pin1. Additionally, we demonstrate that Pin1 positively modulates the stability and function of Pyk2 to enhance bortezomib resistance in MM. Pin1 recognizes three phosphorylated Ser/Thr-Pro motifs in Pyk2 via its WW domain and increases the cellular levels of Pyk2 in an isomerase activity-dependent manner by inhibiting the ubiquitination and proteasomal degradation of Pyk2. Moreover, Pin1 inhibition combined with Pyk2 inhibition decreases myeloma burden both in vitro and in vivo. Altogether, our findings reveal the tumor-promoting role of Pin1 in MM and provide evidence that targeting Pin1 could be a therapeutic strategy for MM.

Non-canonical Function of Prolyl Hydroxylase Domain 2 in Breast Cancer Cell Growth and Progression: Role of Peptidyl-prolyl Cis-trans Isomerase NIMA-interacting 1

Prolyl hydroxylase domain 2 (PHD2) is the primary oxygen sensing enzyme involved in hydroxylation of hypoxia-inducible factor (HIF). Under normoxic conditions, PHD2 hydroxylates specific proline residues in HIF-1α and HIF-2α, promoting their ubiquitination and subsequent proteasomal degradation. Although PHD2 activity decreases in hypoxia, notable residual activity persists, but its function in these conditions remains unclear. Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) targets proteins with phosphorylated serine/threonine-proline (pSer/Thr-Pro) motifs. As PHD2 contains several pSer/Thr-Pro motifs, it may be a potential substrate of Pin1. In the present study, we found Pin1 and PHD2 interactions in human breast cancer MDA-MB-231 cells. The breast cancer tissue array revealed higher levels of PHD2 and Pin1 in tumors compared to adjacent normal tissues. Through liquid chromatography-tandem mass spectrometry spectrometry, three phosphorylation sites (S125, T168, and S174) on PHD2 were identified, with serine 125 as the main site for Pin1 binding. As a new Pin1 binding partner, oncogenic PHD2 could be a potential therapeutic target for breast cancer treatment.

PIN1 promotes the metastasis of cholangiocarcinoma cells by RACK1-mediated phosphorylation of ANXA2

BACKGROUND

Cholangiocarcinoma (CCA), a primary hepatobiliary malignancy, is characterized by a poor prognosis and a lack of effective treatments. Therefore, the need to explore novel therapeutic approaches is urgent. While the role of Peptidylprolyl Cis/Trans Isomerase, NIMA-Interacting 1 (PIN1) has been extensively studied in various tumor types, its involvement in CCA remains poorly understood.

METHODS

In this study, we employed tissue microarray (TMA), reverse transcription-polymerase chain reaction (RT-PCR), and The Cancer Genome Atlas (TCGA) database to assess the expression of PIN1. Through in vitro and in vivo functional experiments, we investigated the impact of PIN1 on the adhesion and metastasis of CCA. Additionally, we explored downstream molecular pathways using RNA-seq, western blotting, co-immunoprecipitation, immunofluorescence, and mass spectrometry techniques.

RESULTS

Our findings revealed a negative correlation between PIN1 overexpression and prognosis in CCA tissues. Furthermore, high PIN1 expression promoted CCA cell proliferation and migration. Mechanistically, PIN1 functioned as an oncogene by regulating ANXA2 phosphorylation, thereby promoting CCA adhesion. Notably, the interaction between PIN1 and ANXA2 was facilitated by RACK1. Importantly, pharmacological inhibition of PIN1 using the FDA-approved drug all-trans retinoic acid (ATRA) effectively suppressed the metastatic potential of CCA cells in a nude mouse lung metastasis model.

CONCLUSION

Overall, our study emphasizes the critical role of the PIN1/RACK1/ANXA2 complex in CCA growth and functionality, highlighting the potential of targeting PIN1 as a promising therapeutic strategy for CCA.

Pin1-catalyzed conformational regulation after phosphorylation: A distinct checkpoint in cell signaling and drug discovery

Protein phosphorylation is one of the most common mechanisms regulating cellular signaling pathways, and many kinases and phosphatases are proven drug targets. Upon phosphorylation, protein functions can be further regulated by the distinct isomerase Pin1 through cis-trans isomerization. Numerous protein targets and many important roles have now been elucidated for Pin1. However, no tools are available to detect or target cis and trans conformation events in cells. The development of Pin1 inhibitors and stereo- and phospho-specific antibodies has revealed that cis and trans conformations have distinct and often opposing cellular functions. Aberrant conformational changes due to the dysregulation of Pin1 can drive pathogenesis but can be effectively targeted in age-related diseases, including cancers and neurodegenerative disorders. Here, we review advances in understanding the roles of Pin1 signaling in health and disease and highlight conformational regulation as a distinct signal transduction checkpoint in disease development and treatment.

Pin1 Exacerbates Non-Alcoholic Fatty Liver Disease by Enhancing Its Activity through Binding to ACC1

Non-alcoholic fatty liver disease (NAFLD) is a clinicopathological syndrome characterized by diffuse hepatocellular steatosis due to fatty deposits in hepatocytes, excluding alcohol and other known liver injury factors. However, there are no specific drugs for the clinical treatment of NAFLD. Therefore, research on the pathogenesis of NAFLD at the cellular and molecular levels is a promising approach to finding therapeutic targets and developing targeted drugs for NAFLD. Pin1 is highly expressed during adipogenesis and contributes to adipose differentiation, but its specific mechanism of action in NAFLD is unclear. In this study, we investigated the role of Pin1 in promoting the development of NAFLD and its potential mechanisms in vitro and in vivo. First, Pin1 was verified in the NAFLD model in vitro using MCD diet-fed mice by Western Blot, RT-qPCR and immunohistochemistry (IHC) assays. In the in vitro study, we used the oleic acid (OA) stimulation-induced lipid accumulation model and examined the lipid accumulation in each group of cells by oil red O staining as well as BODIPY staining. The results showed that knockdown of Pin1 inhibited lipid accumulation in hepatocytes in an in vitro lipid accumulation model and improved lipid indices and liver injury levels. Moreover, in vivo, WT and Pin1-KO mice were fed a methionine-choline deficient (MCD) diet for 4 weeks to induce the NAFLD model. The effects of Pin1 on lipid accumulation, hepatic fibrosis, and oxidative stress were evaluated by biochemical analysis, glucose and insulin tolerance tests, histological analysis, IHC, RT-qPCR and Western blot assays. The results indicate that Pin1 knockdown significantly alleviated hepatic steatosis, fibrosis and inflammation in MCD-induced NAFLD mice, improved glucose tolerance and alleviated insulin resistance in mice. Further studies showed that the AMPK/ACC1 signalling pathway might take part in the process by which Pin1 regulates NAFLD, as evidenced by the inhibition of the AMPK/ACC1 pathway. In addition, immunofluorescence (IF), coimmunoprecipitation (Co-IP) and GST pull-down experiments also showed that Pin1 interacts directly with ACC1 and inhibits ACC1 phosphorylation levels. Our study suggests that Pin1 promotes NAFLD progression by inhibiting the activation of the AMPK/ACC1 signalling pathway, and it is possible that this effect is achieved by Pin1 interacting with ACC1 and inhibiting the phosphorylation of ACC1.

Pin1 Downregulation Is Involved in Excess Retinoic Acid-Induced Failure of Neural Tube Closure

Neural tube defects (NTDs), which are caused by impaired embryonic neural tube closure, are one of the most serious and common birth defects. Peptidyl-prolyl cis/trans isomerase 1 (Pin1) is a prolyl isomerase that uniquely regulates cell signaling by manipulating protein conformation following phosphorylation, although its involvement in neuronal development remains unknown. In this study, we explored the involvement of Pin1 in NTDs and its potential mechanisms both in vitro and in vivo. The levels of Pin1 expression were reduced in NTD models induced by all-trans retinoic acid (Atra). Pin1 plays a significant role in regulating the apoptosis, proliferation, differentiation, and migration of neurons. Moreover, Pin1 knockdown significantly was found to exacerbate oxidative stress (OS) and endoplasmic reticulum stress (ERs) in neuronal cells. Further studies showed that the Notch1-Nrf2 signaling pathway may participate in Pin1 regulation of NTDs, as evidenced by the inhibition and overexpression of the Notch1-Nrf2 pathway. In addition, immunofluorescence (IF), co-immunoprecipitation (Co-IP), and GST pull-down experiments also showed that Pin1 interacts directly with Notch1 and Nrf2. Thus, our study suggested that the knocking down of Pin1 promotes NTD progression by inhibiting the activation of the Notch1-Nrf2 signaling pathway, and it is possible that this effect is achieved by disrupting the interaction of Pin1 with Notch1 and Nrf2, affecting their proteostasis. Our research identified that the regulation of Pin1 by retinoic acid (RA) and its involvement in the development of NTDs through the Notch1-Nrf2 axis could enhance our comprehension of the mechanism behind RA-induced brain abnormalities.

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.

A machine learning model identifies M3-like subtype in AML based on PML/RARα targets

The typical genomic feature of acute myeloid leukemia (AML) M3 subtype is the fusion event of PML/RARα, and ATRA/ATO-based combination therapy is current standard treatment regimen for M3 subtype. Here, a machine-learning model based on expressions of PML/RARα targets was developed to identify M3 patients by analyzing 1228 AML patients. Our model exhibited high accuracy. To enable more non-M3 AML patients to potentially benefit from ATRA/ATO therapy, M3-like patients were further identified. We found that M3-like patients had strong GMP features, including the expression patterns of M3 subtype marker genes, the proportion of myeloid progenitor cells, and deconvolution of AML constituent cell populations. M3-like patients exhibited distinct genomic features, low immune activity and better clinical survival. The initiative identification of patients similar to M3 subtype may help to identify more patients that would benefit from ATO/ATRA treatment and deepen our understanding of the molecular mechanism of AML pathogenesis.

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.

A study of deregulated MMR pathways and anticancer potential of curcuma derivatives using computational approach

Plant derived products have steadily gained momentum in treatment of cancer over the past decades. Curcuma and its derivatives, in particular, have diverse medicinal properties including anticancer potential with proven safety as supported by numerous in vivo and in vitro studies. A defective Mis-Match Repair (MMR) is implicated in solid tumors but its role in haematologic malignancies is not keenly studied and the current literature suggests that it is limited. Nonetheless, there are multiple pathways interjecting the mismatch repair proteins in haematologic cancers that may have a direct or indirect implication in progression of the disease. Here, through computational analysis, we target proteins that are involved in rewiring of multiple signaling cascades via altered expression in cancer using various curcuma derivatives (Curcuma longa L. and Curcuma caesia Roxb.) which in turn, profoundly controls MMR protein function. These biomolecules were screened to identify their efficacy on selected targets (in blood-related cancers); aberrations of which adversely impacted mismatch repair machinery. The study revealed that of the 536 compounds screened, six of them may have the potential to regulate the expression of identified targets and thus revive the MMR function preventing genomic instability. These results reveal that there may be potential plant derived biomolecules that may have anticancer properties against the tumors driven by deregulated MMR-pathways.

Retinoids in hematology: a timely revival?

The retinoic acid receptors (RARA, RARB, and RARG) are ligand-regulated nuclear receptors that act as transcriptional switches. These master genes drew significant interest in the 1990s because of their key roles in embryogenesis and involvement in a rare malignancy, acute promyelocytic leukemia (APL), in which the RARA (and very rarely, RARG or RARB) genes are rearranged, underscoring the central role of deregulated retinoid signaling in leukemogenesis. Several recent provocative observations have revived interest in the roles of retinoids in non-APL acute myeloid leukemia (AML), as well as in normal hematopoietic differentiation. We review the role of retinoids in hematopoiesis, as well as in the treatment of non-APL AMLs. From this perspective, broader uses of retinoids in the management of hematopoietic tumors are discussed.

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.

Roles of peptidyl-prolyl isomerase Pin1 in disease pathogenesis

Pin1 belongs to the peptidyl-prolyl cis-trans isomerases (PPIases) superfamily and catalyzes the cis-trans conversion of proline in target substrates to modulate diverse cellular functions including cell cycle progression, cell motility, and apoptosis. Dysregulation of Pin1 has wide-ranging influences on the fate of cells; therefore, it is closely related to the occurrence and development of various diseases. This review summarizes the current knowledge of Pin1 in disease pathogenesis.

The Molecular 'Myc-anisms' Behind Myc-Driven Tumorigenesis and the Relevant Myc-Directed Therapeutics

MYC, a well-studied proto-oncogene that is overexpressed in >20% of tumors across all cancers, is classically known as “undruggable” due to its crucial roles in cell processes and its lack of a drug binding pocket. Four decades of research and creativity led to the discovery of a myriad of indirect (and now some direct!) therapeutic strategies targeting Myc. This review explores the various mechanisms in which Myc promotes cancer and highlights five key therapeutic approaches to disrupt Myc, including transcription, Myc-Max dimerization, protein stability, cell cycle regulation, and metabolism, in order to develop more specific Myc-directed therapies.

Development of Pin1 Inhibitors and their Potential as Therapeutic Agents

The prolyl isomerase Pin1 is a unique enzyme, which isomerizes the cis-trans conformation between pSer/pThr and proline and thereby regulates the function, stability and/or subcellular distribution of its target proteins. Such regulations by Pin1 are involved in numerous physiological functions as well as the pathogenic mechanisms underlying various diseases. Notably, Pin1 deficiency or inactivation is a potential cause of Alzheimer's disease, since Pin1 induces the degradation of Tau. In contrast, Pin1 overexpression is highly correlated with the degree of malignancy of cancers, as Pin1 controls a number of oncogenes and tumor suppressors. Accordingly, Pin1 inhibitors as anti-cancer drugs have been developed. Interestingly, recent intensive studies have demonstrated Pin1 to be responsible for the onset or development of nonalcoholic steatosis, obesity, atherosclerosis, lung fibrosis, heart failure and so on, all of which have been experimentally induced in Pin1 deficient mice. In this review, we discuss the possible applications of Pin1 inhibitors to a variety of diseases including malignant tumors and also introduce the recent advances in Pin1 inhibitor research, which have been reported.

Adaptive T cell immunotherapy in cancer

Impaired tumor-specific effector T cells contribute to tumor progression and unfavorable clinical outcomes. As a compensatory T cell-dependent cancer immunoediting strategy, adoptive T cell therapy (ACT) has achieved encouraging therapeutic results, and this strategy is now on the center stage of cancer treatment and research. ACT involves the ex vivo stimulation and expansion of tumor-infiltrating lymphocytes (TILs) with inherent tumor reactivity or T cells that have been genetically modified to express the cognate chimeric antigen receptor or T cell receptor (CAR/TCR), followed by the passive transfer of these cells into a lymphodepleted host. Primed T cells must provide highly efficient and long-lasting immune defense against transformed cells during ACT. Anin-depth understanding of the basic mechanisms of these living drugs can help us improve upon current strategies and design better next-generation T cell-based immunotherapies. From this perspective, we provide an overview of current developments in different ACT strategies, with a focus on frontier clinical trials that offer a proof of principle. Meanwhile, insights into the determinants of ACT are discussed, which will lead to more rational, potent and widespread applications in the future.

Phosphorylation-Dependent Pin1 Isomerization of ATR: Its Role in Regulating ATR's Anti-apoptotic Function at Mitochondria, and the Implications in Cancer

Peptidyl-prolyl isomerization is an important post-translational modification of protein because proline is the only amino acid that can stably exist as cis and trans, while other amino acids are in the trans conformation in protein backbones. This makes prolyl isomerization a unique mechanism for cells to control many cellular processes. Isomerization is a rate-limiting process that requires a peptidyl-prolyl cis/trans isomerase (PPIase) to overcome the energy barrier between cis and trans isomeric forms. Pin1, a key PPIase in the cell, recognizes a phosphorylated Ser/Thr-Pro motif to catalyze peptidyl-prolyl isomerization in proteins. The significance of the phosphorylation-dependent Pin1 activity was recently highlighted for isomerization of ATR (ataxia telangiectasia- and Rad3-related). ATR, a PIKK protein kinase, plays a crucial role in DNA damage responses (DDR) by phosphorylating hundreds of proteins. ATR can form cis or trans isomers in the cytoplasm depending on Pin1 which isomerizes cis-ATR to trans-ATR. Trans-ATR functions primarily in the nucleus. The cis-ATR, containing an exposed BH3 domain, is anti-apoptotic at mitochondria by binding to tBid, preventing activation of pro-apoptotic Bax. Given the roles of apoptosis in many human diseases, particularly cancer, we propose that cytoplasmic cis-ATR enables cells to evade apoptosis, thus addicting cancer cells to cis-ATR formation for survival. But in normal DDR, a predominance of trans-ATR in the nucleus coordinates with a minimal level of cytoplasmic cis-ATR to promote DNA repair while preventing cell death; however, cells can die when DNA repair fails. Therefore, a delicate balance/equilibrium of the levels of cis- and trans-ATR is required to ensure the cellular homeostasis. In this review, we make a case that this anti-apoptotic role of cis-ATR supports oncogenesis, while Pin1 that drives the formation of trans-ATR suppresses tumor growth. We offer a potential, novel target that can be specifically targeted in cancer cells, without killing normal cells, to significantly reduce the adverse effects usually seen in cancer treatment. We also raise important issues regarding the roles of phosphorylation-dependent Pin1 isomerization of ATR in diseases and propose areas of future studies that would shed more understanding on this important cellular mechanism.

Prognostic value of peptidyl-prolyl cis-trans isomerase 1 (PIN1) in human malignant tumors

BACKGROUND

PIN1, a peptidyl-prolyl cis-trans isomerase, specifically can regulate phosphorylation of proteins on serine/threonine residues that precede proline and has critical roles in cell proliferation and transformation. Many studies have revealed that overexpression of PIN1 is involved in the malignant biological behavior of various cancers, but to date, no meta-analyses have evaluated PIN1 clinical and prognostic value in patients with malignant tumors.

METHODS

We retrieved related articles from PubMed, Web of Science and Scopus databases up to April 20, 2019. Pooled odds ratios (ORs) and hazard ratios (HRs) with 95% CIs were used to estimate the correlation of PIN1 expression with clinicopathological characteristics and survival outcomes. The methodology was according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Cochrane Collaboration guidelines.

RESULTS

A total of 20 studies containing 2574 patients with various tumors were included in this analysis. Pooled results showed that PIN1 overexpression was significantly associated with the advanced clinical stages of cancer (OR = 1.37, 95% CI 1.06-1.78), positive lymph node metastasis (OR = 1.65, 95% CI 1.15-2.37) and poor prognosis (HR = 2.40, 95% CI 1.55-3.74), although no correlation with poor differentiation was found.

CONCLUSIONS

These results suggest that high expression of PIN1 can be considered as a risk factor for progression and invasion of malignant tumors and thus may serve as a promising therapeutic target and prognostic biomarker for human solid tumors.

Prolyl isomerase Pin1 in metabolic reprogramming of cancer cells

Pin1 is one member of a group consisting of three prolyl isomerases. Pin1 interacts with the motif containing phospho-Ser/Thr-Pro of substrates and enhances cis-trans isomerization of peptide bonds, thereby controlling the functions of these substrates. Importantly, the Pin1 expression level is highly upregulated in most cancer cells and correlates with malignant properties, and thereby with poor outcomes. In addition, Pin1 was revealed to promote the functions of multiple oncogenes and to abrogate tumor suppressors. Accordingly, Pin1 is well recognized as a master regulator of malignant processes. Recent studies have shown that Pin1 also binds to a variety of metabolic regulators, such as AMP-activated protein kinase, acetyl CoA carboxylase and pyruvate kinase2, indicating Pin1 to have major impacts on lipid and glucose metabolism in cancer cells. In this review, we focus on the roles of Pin1 in metabolic reprogramming, such as "Warburg effects", of cancer cells. Our aim is to introduce these important roles of Pin1, as well as to present evidence supporting the possibility of Pin1 inhibition as a novel anti-cancer strategy.

Targeting PIN1 exerts potent antitumor activity in pancreatic ductal carcinoma via inhibiting tumor metastasis

The human prolyl isomerase PIN1, best known for its association with carcinogenesis, has recently been indicated in the disease of pancreatic ductal adenocarcinoma (PDAC). However, the functions of PIN1 and the feasibility of targeting PIN1 in PDAC remain elusive. For this purpose, we examined the expression of PIN1 in cancer, related paracarcinoma and metastatic cancer tissues by immunohistochemistry and analyzed the associations with the pathogenesis of PDAC in 173 patients. The functional roles of PIN1 in PDAC were explored in vitro and in vivo using both genetic and chemical PIN1 inhibition. We showed that PIN1 was upregulated in pancreatic cancer and metastatic tissues. High PIN1 expression is significantly association with poor clinicopathological features and shorter overall survival and disease‐free survival. Further stratified analysis showed that PIN1 phenotypes refined prognostication in PDAC. Inhibition of PIN1 expression with RNA interference or with all trans retinoic acid decreased not only the growth but also the migration and invasion of PDAC cells through regulating the key molecules of multiple cancer‐driving pathways, simultaneously resulting in cell cycle arrest and mesenchymal‐epithelial transition in vitro. Furthermore, genetic and chemical PIN1 ablation showed dramatic inhibition of the tumorigenesis and metastatic spread and then reduced the tumor burden in vivo. We provided further evidence for the use of PIN1 as a promising therapeutic target in PDAC. Genetic and chemical PIN1 ablation exerted potent antitumor effects through blocking multiple cancer‐driving pathways in PDAC. More potent and specific PIN1 targeted inhibitors could be exploited to treat this aggressive cancer.

Pin1 inhibition potently suppresses gastric cancer growth and blocks PI3K/AKT and Wnt/β-catenin oncogenic pathways

Gastric cancer is the second leading cause of cancer-related mortality and the fourth most common cancer globally. High intratumor heterogeneity of advanced gastric cancer poses great challenges to targeted therapy due to simultaneous activation of many redundant cancer-driving pathways. A central common signaling mechanism in cancer is proline-directed phosphorylation, which is further regulated by the unique proline isomerase Pin1. Pin1 inhibition exerts anticancer activity by blocking multiple cancer-driving pathways in some cancers, but its role in gastric cancer is not fully understood. Here we detected Pin1 protein expression in 1065 gastric cancer patients and paired normal tissues using immunohistochemistry and Western blot, and then examined the effects of Pin1 overexpression, and genetic and chemical Pin1 inhibition using Pin1 short hairpin RNA or small molecule inhibitor all-trans retinoic acid (ATRA) on tumorigenesis of human gastric cancer in vitro and in vivo, followed by biochemical analyses to elucidate Pin1 regulated oncogenic pathways. We found that Pin1 was significantly overexpressed in primary and metastasized tumors, with Pin1 overexpression being correlated with advanced stage and poor prognosis. Furthermore, whereas Pin1 overexpression promoted the transformed phenotype in immortalized and nontransformed human gastric cells, either genetic or chemical Pin1 inhibition in multiple human gastric cancer cells potently suppressed cell growth, G1/S transition and colony formation in vitro, as well as tumor growth in xenograft tumor models in vivo, which were further supported by downregulation of multiple key oncoproteins in PI3K/AKT and Wnt/β-catenin signaling pathways. These results not only provide the first evidence for a critical role of Pin1 in the tumorigenesis of gastric cancer but also suggest that targeting Pin1 using ATRA or other inhibitors offers an effective new therapeutic approach for treating advanced gastric cancer.

Downregulation of CD73 associates with T cell exhaustion in AML patients

Background

Successful treatment for acute myeloid leukemia (AML) remains challenging. Inhibiting immune checkpoint to enhance anti-tumor response is an attractive strategy for effective leukemia therapeutics. CD73 is a recently recognized immune checkpoint mediator that is highly expressed on tumor cells and stromal cells in tumor microenvironment. The ectonucleotidase activity of CD73 catalyzes AMP to adenosine, which subsequently inhibits anti-tumor immune responses. In this study, we aim to explore the effect of CD73 in AML.

Methods

Peripheral blood samples collected from patients with newly diagnosed AML (n = 27) were used in this study. CD73 expression on each immune cell component was examined by flow cytometry. Phenotypic study of CD73-expressing T cells and analysis of the correlation between CD73 and other immune checkpoints were performed using flow cytometry-based assays. Functional status of CD73⁺ vs. CD73⁻ T cells was assessed in an in vitro cytokine release assay upon CD3/CD28 antibody stimulation.

Results

In contrast to the long recognized immune suppressive effect of CD73-adenosine signaling in tumor tissue, we made a striking observation that in AML, CD73 expression on CD8 T cells associates with an increased immune response. CD73⁺ CD8 T cells are more functional, whereas CD73⁻ CD8 T cells exhibit features of exhaustion manifested by high expression of inhibitory receptors such as PD-1 and TIGIT, increased intracellular expression of Eomes, reduced capacity of cytokine production, and high susceptibility to apoptosis.

Conclusions

Our data highlight the potential of CD73 as a double-edged sword in anti-leukemia immunity and argue strongly for the combinational treatment by adding immune checkpoint inhibitors to the CD73-targeting approaches.

Pin1 inhibition reverses the acquired resistance of human hepatocellular carcinoma cells to Regorafenib via the Gli1/Snail/E-cadherin pathway

Hepatocellular carcinoma (HCC) is the second leading cancer death because of its high metastasis and drug resistance. Regorafenib was newly approved by FDA for HCC treatment, but its resistance is not understood. The unique isomerase Pin1 is critical for HCC development, but its role in metastasis and drug resistance is unknown. Here we generated Regorafenib-resistant HCC cells and found that they exhibited enhanced tumor invasion and metastasis in vitro and in vivo, and elevated Pin1 levels. Furthermore, Pin1 was highly overexpressed and closely related to the EMT in human HCC tissues. Depletion or overexpression of Pin1 correspondingly inhibited or promoted HCC cell migration and invasion, with altered expression of EMT-related molecules, E-cadherin and Snail. Significantly, Pin1 interacted with Gli1, a regulator of the EMT, and silencing Gli1 partly blocked Pin1-induced EMT in HCC cells. Moreover, genetic or chemical Pin1 inhibition reversed Regorafenib resistance of HCC with reducing EMT, migration, invasion and metastasis in vitro and in vivo. These results reveal a novel molecular mechanism underlying Regorafenib resistance in HCC, and also provide first evidence that Pin1 inhibitors offer an attractive strategy for treating Regorafenib-resistant HCC.

Arsenic targets Pin1 and cooperates with retinoic acid to inhibit cancer-driving pathways and tumor-initiating cells

Arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) combination safely cures fatal acute promyelocytic leukemia, but their mechanisms of action and efficacy are not fully understood. ATRA inhibits leukemia, breast, and liver cancer by targeting isomerase Pin1, a master regulator of oncogenic signaling networks. Here we show that ATO targets Pin1 and cooperates with ATRA to exert potent anticancer activity. ATO inhibits and degrades Pin1, and suppresses its oncogenic function by noncovalent binding to Pin1's active site. ATRA increases cellular ATO uptake through upregulating aquaporin-9. ATO and ATRA, at clinically safe doses, cooperatively ablate Pin1 to block numerous cancer-driving pathways and inhibit the growth of triple-negative breast cancer cells and tumor-initiating cells in cell and animal models including patient-derived orthotopic xenografts, like Pin1 knockout, which is substantiated by comprehensive protein and microRNA analyses. Thus, synergistic targeting of Pin1 by ATO and ATRA offers an attractive approach to combating breast and other cancers.