Structural insights into the molecular mechanism of phytoplasma immunodominant membrane protein.

Immunodominant membrane protein (IMP) is a prevalent membrane protein in phytoplasma and has been confirmed to be an F-actin-binding protein. However, the intricate molecular mechanisms that govern the function of IMP require further elucidation. In this study, the X-ray crystallographic structure of IMP was determined and insights into its interaction with plant actin are provided. A comparative analysis with other proteins demonstrates that IMP shares structural homology with talin rod domain-containing protein 1 (TLNRD1), which also functions as an F-actin-binding protein. Subsequent molecular-docking studies of IMP and F-actin reveal that they possess complementary surfaces, suggesting a stable interaction. The low potential energy and high confidence score of the IMP-F-actin binding model indicate stable binding. Additionally, by employing immunoprecipitation and mass spectrometry, it was discovered that IMP serves as an interaction partner for the phytoplasmal effector causing phyllody 1 (PHYL1). It was then shown that both IMP and PHYL1 are highly expressed in the S2 stage of peanut witches' broom phytoplasma-infected Catharanthus roseus. The association between IMP and PHYL1 is substantiated through in vivo immunoprecipitation, an in vitro cross-linking assay and molecular-docking analysis. Collectively, these findings expand the current understanding of IMP interactions and enhance the comprehension of the interaction of IMP with plant F-actin. They also unveil a novel interaction pathway that may influence phytoplasma pathogenicity and host plant responses related to PHYL1. This discovery could pave the way for the development of new strategies to overcome phytoplasma-related plant diseases.

A bacterial binary toxin system that kills both insects and aquatic crustaceans: Photorhabdus insect-related toxins A and B.

Photorhabdus insect-related toxins A and B (PirA and PirB) were first recognized as insecticidal toxins from Photorhabdus luminescens. However, subsequent studies showed that their homologs from Vibrio parahaemolyticus also play critical roles in the pathogenesis of acute hepatopancreatic necrosis disease (AHPND) in shrimps. Based on the structural features of the PirA/PirB toxins, it was suggested that they might function in the same way as a Bacillus thuringiensis Cry pore-forming toxin. However, unlike Cry toxins, studies on the PirA/PirB toxins are still scarce, and their cytotoxic mechanism remains to be clarified. In this review, based on our studies of V. parahaemolyticus PirAvp/PirBvp, we summarize the current understanding of the gene locations, expression control, activation, and cytotoxic mechanism of this type of toxin. Given the important role these toxins play in aquatic disease and their potential use in pest control applications, we also suggest further topics for research. We hope the information presented here will be helpful for future PirA/PirB studies.

Expression of the AHPND Toxins PirAvp and PirBvp Is Regulated by Components of the Vibrio parahaemolyticus Quorum Sensing (QS) System.

Acute hepatopancreatic necrosis disease (AHPND) in shrimp is caused by Vibrio strains that harbor a pVA1-like plasmid containing the pirA and pirB genes. It is also known that the production of the PirA and PirB proteins, which are the key factors that drive the observed symptoms of AHPND, can be influenced by environmental conditions and that this leads to changes in the virulence of the bacteria. However, to our knowledge, the mechanisms involved in regulating the expression of the pirA/pirB genes have not previously been investigated. In this study, we show that in the AHPND-causing Vibrio parahaemolyticus 3HP strain, the pirAvp and pirBvp genes are highly expressed in the early log phase of the growth curve. Subsequently, the expression of the PirAvp and PirBvp proteins continues throughout the log phase. When we compared mutant strains with a deletion or substitution in two of the quorum sensing (QS) master regulators, luxO and/or opaR (luxOD47E, ΔopaR, ΔluxO, and ΔopaRΔluxO), our results suggested that expression of the pirAvp and pirBvp genes was related to the QS system, with luxO acting as a negative regulator of pirAvp and pirBvp without any mediation by opaRvp. In the promoter region of the pirAvp/pirBvp operon, we also identified a putative consensus binding site for the QS transcriptional regulator AphB. Real-time PCR further showed that aphBvp was negatively controlled by LuxOvp, and that its expression paralleled the expression patterns of pirAvp and pirBvp. An electrophoretic mobility shift assay (EMSA) showed that AphBvp could bind to this predicted region, even though another QS transcriptional regulator, AphAvp, could not. Taken together, these findings suggest that the QS system may regulate pirAvp/pirBvp expression through AphBvp.

A Review of the Functional Annotations of Important Genes in the AHPND-Causing pVA1 Plasmid.

Acute hepatopancreatic necrosis disease (AHPND) is a lethal shrimp disease. The pathogenic agent of this disease is a special Vibrio parahaemolyticus strain that contains a pVA1 plasmid. The protein products of two toxin genes in pVA1, pirAvp and pirBvp, targeted the shrimp's hepatopancreatic cells and were identified as the major virulence factors. However, in addition to pirAvp and pirBvp, pVA1 also contains about ~90 other open-reading frames (ORFs), which may encode functional proteins. NCBI BLASTp annotations of the functional roles of 40 pVA1 genes reveal transposases, conjugation factors, and antirestriction proteins that are involved in horizontal gene transfer, plasmid transmission, and maintenance, as well as components of type II and III secretion systems that may facilitate the toxic effects of pVA1-containing Vibrio spp. There is also evidence of a post-segregational killing (PSK) system that would ensure that only pVA1 plasmid-containing bacteria could survive after segregation. Here, in this review, we assess the functional importance of these pVA1 genes and consider those which might be worthy of further study.

Structural insight into the differential interactions between the DNA mimic protein SAUGI and two gamma herpesvirus uracil-DNA glycosylases.

Uracil-DNA glycosylases (UDGs) are conserved DNA-repair enzymes that can be found in many species, including herpesviruses. Since they play crucial roles for efficient viral DNA replication in herpesviruses, they have been considered as potential antiviral targets. In our previous work, Staphylococcus aureus SAUGI was identified as a DNA mimic protein that targets UDGs from S. aureus, human, Herpes simplex virus (HSV) and Epstein-Barr virus (EBV). Interestingly, SAUGI has the strongest inhibitory effects with EBVUDG. Here, we determined complex structures of SAUGI with EBVUDG and another γ-herpesvirus UDG from Kaposi's sarcoma-associated herpesvirus (KSHVUDG), which SAUGI fails to effectively inhibit. Structural analysis of the SAUGI/EBVUDG complex suggests that the additional interaction between SAUGI and the leucine loop may explain why SAUGI shows the highest binding capacity with EBVUDG. In contrast, SAUGI appears to make only partial contacts with the key components responsible for the compression and stabilization of the DNA backbone in the leucine loop extension of KSHVUDG. The findings in this study provide a molecular explanation for the differential inhibitory effects and binding strengths that SAUGI has on these two UDGs, and the structural basis of the differences should be helpful in developing inhibitors that would interfere with viral DNA replication.

A shrimp glycosylase protein, PmENGase, interacts with WSSV envelope protein VP41B and is involved in WSSV pathogenesis.

Viral glycoproteins are expressed by many viruses, and during infection they usually play very important roles, such as receptor attachment or membrane fusion. The mature virion of the white spot syndrome virus (WSSV) is unusual in that it contains no glycosylated proteins, and there are currently no reports of any glycosylation mechanisms in the pathogenesis of this virus. In this study, we cloned a glycosylase, mannosyl-glycoprotein endo-ß-N-acetylglucosaminidase (ENGase, EC 3.2.1.96), from Penaeus monodon and found that it was significantly up-regulated in WSSV-infected shrimp. A yeast two-hybrid assay showed that PmENGase interacted with both structural and non-structural proteins, and GST-pull down and co-immunoprecipitation (Co-IP) assays confirmed its interaction with the envelope protein VP41B. In the WSSV challenge tests, the cumulative mortality and viral copy number were significantly decreased in the PmEngase-silenced shrimp, from which we conclude that shrimp glycosylase interacts with WSSV in a way that benefits the virus. Lastly, we speculate that the deglycosylation activity of PmENGase might account for the absence of glycosylated proteins in the WSSV virion.

Structural insights into the interaction between phytoplasmal effector causing phyllody 1 and MADS transcription factors.

Phytoplasmas are bacterial plant pathogens which can induce severe symptoms including dwarfism, phyllody and virescence in an infected plant. Because phytoplasmas infect many important crops such as peanut and papaya they have caused serious agricultural losses. The phytoplasmal effector causing phyllody 1 (PHYL1) is an important phytoplasmal pathogenic factor which affects the biological function of MADS transcription factors by interacting with their K (keratin-like) domain, thus resulting in abnormal plant developments such as phyllody. Until now, lack of information on the structure of PHYL1 has prevented a detailed understanding of the binding mechanism between PHYL1 and the MADS transcription factors. Here, we present the crystal structure of PHYL1 from peanut witches'-broom phytoplasma (PHYL1PnWB ). This protein was found to fold into a unique α-helical hairpin with exposed hydrophobic residues on its surface that may play an important role in its biological function. Using proteomics approaches, we propose a binding mode of PHYL1PnWB with the K domain of the MADS transcription factor SEPALLATA3 (SEP3_K) and identify the residues of PHYL1PnWB that are important for this interaction. Furthermore, using surface plasmon resonance we measure the binding strength of PHYL1PnWB proteins to SEP3_K. Lastly, based on confocal images, we found that α-helix 2 of PHYL1PnWB plays an important role in PHYL1-mediated degradation of SEP3. Taken together, these results provide a structural understanding of the specific binding mechanism between PHYL1PnWB and SEP3_K.

Structural Insights to the Heterotetrameric Interaction between the Vibrio parahaemolyticus PirAvp and PirBvp Toxins and Activation of the Cry-Like Pore-Forming Domain.

Acute hepatopancreatic necrosis disease (AHPND) is a newly emergent penaeid shrimp disease which can cause 70-100% mortality in Penaeus vannamei and Penaeus monodon, and has resulted in enormous economic losses since its appearance. AHPND is caused by the specific strains of Vibrio parahaemolyticus that harbor the pVA1 plasmid and express PirAvp and PirBvp toxins. These two toxins have been reported to form a binary complex. When both are present, they lead to the death of shrimp epithelial cells in the hepatopancreas and cause the typical histological symptoms of AHPND. However, the binding mode of PirAvp and PirBvp has not yet been determined. Here, we used isothermal titration calorimetry (ITC) to measure the binding affinity of PirAvp and PirBvp. Since the dissociation constant (Kd = 7.33 ± 1.20 µM) was considered too low to form a sufficiently stable complex for X-ray crystallographic analysis, we used alternative methods to investigate PirAvp-PirBvp interaction, first by using gel filtration to evaluate the molecular weight of the PirAvp/PirBvp complex, and then by using cross-linking and hydrogen-deuterium exchange (HDX) mass spectrometry to further understand the interaction interface between PirAvp and PirBvp. Based on these results, we propose a heterotetrameric interaction model of this binary toxin complex. This model provides insight of how conformational changes might activate the PirBvp N-terminal pore-forming domain and should be helpful for devising effective anti-AHPND strategies in the future.

Structural Insights into the Cytotoxic Mechanism of Vibrio parahaemolyticus PirAvp and PirBvp Toxins.

In aquaculture, shrimp farming is a popular field. The benefits of shrimp farming include a relatively short grow-out time, high sale price, and good cost recovery. However, outbreaks of serious diseases inflict serious losses, and acute hepatopancreatic necrosis disease (AHPND) is an emerging challenge to this industry. In South American white shrimp (Penaeus vannamei) and grass shrimp (Penaeus monodon), this disease has a 70-100% mortality. The pathogenic agent of AHPND is a specific strain of Vibrio parahaemolyticus which contains PirAvp and PirBvp toxins encoded in the pVA1 plasmid. PirAvp and PirBvp have been shown to cause the typical histological symptoms of AHPND in infected shrimps, and in this review, we will focus on our structural understanding of these toxins. By analyzing their structures, a possible cytotoxic mechanism, as well as strategies for anti-AHPND drug design, is proposed.

The monomeric form of Neisseria DNA mimic protein DMP19 prevents DNA from binding to the histone-like HU protein.

DNA mimicry is a direct and effective strategy by which the mimic competes with DNA for the DNA binding sites on other proteins. Until now, only about a dozen proteins have been shown to function via this strategy, including the DNA mimic protein DMP19 from Neisseria meningitides. We have shown previously that DMP19 dimer prevents the operator DNA from binding to the transcription factor NHTF. Here, we provide new evidence that DMP19 monomer can also interact with the Neisseria nucleoid-associated protein HU. Using BS3 crosslinking, gel filtration and isothermal titration calorimetry assays, we found that DMP19 uses its monomeric form to interact with the Neisseria HU dimer. Crosslinking conjugated mass spectrometry was used to investigate the binding mode of DMP19 monomer and HU dimer. Finally, an electrophoretic mobility shift assay (EMSA) confirmed that the DNA binding affinity of HU is affected by DMP19. These results showed that DMP19 is bifunctional in the gene regulation of Neisseria through its variable oligomeric forms.

TR2 and TR4 Orphan Nuclear Receptors: An Overview.

Testicular nuclear receptors 2 and 4 (TR2, TR4), also known as NR2C1 and NR2C2, belong to the nuclear receptor superfamily and were first cloned in 1989 and 1994, respectively. Although classified as orphan receptors, several natural molecules, their metabolites, and synthetic compounds including polyunsaturated fatty acids (PUFAs), PUFA metabolites 13-hydroxyoctadecadienoic acid, 15-hydroxyeicosatetraenoic acid, and the antidiabetic drug thiazolidinediones can transactivate TR4. Importantly, many of these ligands/activators can also transactivate peroxisome proliferator-activated receptor gamma (PPARγ), also known as NR1C3 nuclear receptor. Both TR4 and PPARγ can bind to similar hormone response elements (HREs) located in the promoter of their common downstream target genes. However, these two nuclear receptors, even with shared ligands/activators and shared binding ability for similar HREs, have some distinct functions in many diseases they influence. In cancer, PPARγ inhibits thyroid, lung, colon, and prostate cancers but enhances bladder cancer. In contrast, TR4 inhibits liver and prostate cancer initiation but enhances pituitary corticotroph, liver, and prostate cancer progression. In type 2 diabetes, PPARγ increases insulin sensitivity but TR4 decreases insulin sensitivity. In cardiovascular disease, PPARγ inhibits atherosclerosis but TR4 enhances atherosclerosis through increasing foam cell formation. In bone physiology, PPARγ inhibits bone formation but TR4 increases bone formation. Together, the contrasting impact of TR4 and PPARγ on different diseases may raise a critical issue about drug used to target any one of these nuclear receptors.

Natural killer cells suppress enzalutamide resistance and cell invasion in the castration resistant prostate cancer via targeting the androgen receptor splicing variant 7 (ARv7).

Despite the success of androgen-deprivation therapy (ADT) with the newly developed anti-androgen enzalutamide (Enz, also known as MDV3100) to suppress castration resistant prostate cancer (CRPC) in extending patient survival by an extra 4.8 months, eventually patients die with the development of Enz resistance that may involve the induction of the androgen receptor (AR) splicing variant ARv7. Here we identify an unrecognized role of Natural Killer (NK) cells in the prostate tumor microenvironment that can be better recruited to the CRPC cells to suppress ARv7 expression resulting in suppressing the Enz resistant CRPC cell growth and invasion. Mechanism dissection revealed that CRPC cells, compared to normal prostate epithelial cells, could recruit more NK cells that might then lead to alterations of the microRNA-34 and microRNA-449 to suppress both ARv7 expression and ARv7-induced EZH2 expression to suppress CRPC cell invasion. Together, these results identify a new potential therapy using recruited NK cells to better suppress the Enz resistance and cell invasion in CRPC at the later enzalutamide resistant stage.

New therapy with ASC-J9® to suppress the prostatitis via altering the cytokine CCL2 signals.

Prostatitis is a common disease contributing to 8% of all urologist visits. Yet the etiology and effective treatment remain to be further elucidated. Using a non-obese diabetes mouse model that can be induced by autoimmune response for the spontaneous development of prostatitis, we found that injection of the ASC-J9® at 75 mg/Kg body weight/48 hours led to significantly suppressed prostatitis that was accompanied with reduction of lymphocyte infiltration with reduced CD4+ T cells in prostate. In vitro studies with a co-culture system also confirmed that ASC-J9® treatment could suppress the CD4+ T cell migration to prostate stromal cells. Mechanisms dissection indicated that ASC-J9® can suppress CD4+ T cell migration via decreasing the cytokine CCL2 in vitro and in vivo, and restoring CCL2 could interrupt the ASC-J9® suppressed CD4+ T cell migration. Together, results from in vivo and in vitro studies suggest that ASC-J9® can suppress prostatitis by altering the autoimmune response induced by CD4+ T cell recruitment, and using ASC-J9® may help us to develop a potential new therapy to battle the prostatitis with little side effects.

The opportunistic marine pathogen Vibrio parahaemolyticus becomes virulent by acquiring a plasmid that expresses a deadly toxin.

Acute hepatopancreatic necrosis disease (AHPND) is a severe, newly emergent penaeid shrimp disease caused by Vibrio parahaemolyticus that has already led to tremendous losses in the cultured shrimp industry. Until now, its disease-causing mechanism has remained unclear. Here we show that an AHPND-causing strain of V. parahaemolyticus contains a 70-kbp plasmid (pVA1) with a postsegregational killing system, and that the ability to cause disease is abolished by the natural absence or experimental deletion of the plasmid-encoded homologs of the Photorhabdus insect-related (Pir) toxins PirA and PirB. We determined the crystal structure of the V. parahaemolyticus PirA and PirB (PirA(vp) and PirB(vp)) proteins and found that the overall structural topology of PirA(vp)/PirB(vp) is very similar to that of the Bacillus Cry insecticidal toxin-like proteins, despite the low sequence identity (<10%). This structural similarity suggests that the putative PirAB(vp) heterodimer might emulate the functional domains of the Cry protein, and in particular its pore-forming activity. The gene organization of pVA1 further suggested that pirAB(vp) may be lost or acquired by horizontal gene transfer via transposition or homologous recombination.

TR4 Nuclear Receptor Different Roles in Prostate Cancer Progression.

Nuclear receptors are important to maintain the tissue homeostasis. Each receptor is tightly controlled and under a very complicated balance. In this review, we summarize the current findings regarding the nuclear receptor TR4 and its role in prostate cancer (PCa) progression. In general, TR4 can inhibit the PCa carcinogenesis. However, when PPARγ is knocked out, activation of TR4 can have an opposite effect to promote the PCa carcinogenesis. Clinical data also indicates that higher TR4 expression is found in PCa tissues with high Gleason scores compared to those tissues with low Gleason scores. In vitro and in vivo studies show that TR4 can promote PCa progression. Mechanism dissection indicates that TR4 inhibits PCa carcinogenesis through regulating the tumor suppressor ATM to reduce DNA damages. On the other hand, in the absence of PPARγ, TR4 tends to increase the stem cell population and epithelial-mesenchymal transition (EMT) via regulating CCL2, Oct4, EZH2, and miRNA-373-3p expression that results in increased PCa carcinogenesis. In opposition to PCa initiation, TR4 can increase PCa metastasis via modulating the CCL2 signals. Finally, targeting TR4 enhances the chemotherapy and radiation therapy sensitivity in PCa. Together, these data suggest TR4 is a key player to control PCa progression, and targeting TR4 with small molecules may provide us a new and better therapy to suppress PCa progression.

The Differential Effects of Anti-Diabetic Thiazolidinedione on Prostate Cancer Progression Are Linked to the TR4 Nuclear Receptor Expression Status.

The insulin sensitizers, thiazolidinediones (TZDs), have been used as anti-diabetic drugs since the discovery of their ability to alter insulin resistance through transactivation of peroxisome proliferator-activated receptors (PPARs). However, their side effects in hepatitis, cardiovascular diseases, and bladder cancer resulted in some selling restrictions in the USA and Europe. Here, we found that the potential impact of TZDs on the prostate cancer (PCa) progression might be linked to the TR4 nuclear receptor expression. Clinical surveys found that 9% of PCa patients had one allele TR4 deletion in their tumors. TZD increased cell growth and invasion in PCa cells when TR4 was knocked down. In contrast, TZD decreased PCa progression in PCa cells with wild type TR4. Mechanism dissection found that the Harvey Rat Sarcoma (HRAS) oncogene increased on TZD treatment of the TR4 knocked-down CWR22Rv1 and C4-2 cells, and interruption with HRAS inhibitor resulted in reversal of TZD-induced PCa progression. Together, these results suggest that TZD treatment may promote PCa progression depending on the TR4 expression status that may be clinically relevant since extra caution may be needed for those diabetic PCa patients receiving TZD treatment who have one allele TR4 deletion.

TR4 nuclear receptor enhances prostate cancer initiation via altering the stem cell population and EMT signals in the PPARG-deleted prostate cells.

A recent report indicated that the TR4 nuclear receptor might suppress the prostate cancer (PCa) initiation via modulating the DNA damage/repair system. Knocking-out peroxisome proliferator-activated receptor gamma (PPARG), a nuclear receptor that shares similar ligands/activators with TR4, promoted PCa initiation. Here we found 9% of PCa patients have one allele of PPARG deletion. Results from in vitro cell lines and in vivo mouse model indicated that during PCa initiation TR4 roles might switch from suppressor to enhancer in prostate cells when PPARG was deleted or suppressed (by antagonist GW9662). Mechanism dissection found targeting TR4 in the absence of PPARG might alter the stem cell population and epithelial-mesenchymal transition (EMT) signals. Together, these results suggest that whether TR4 can enhance or suppress PCa initiation may depend on the availability of PPARG and future potential therapy via targeting PPARG to battle PPARG-related diseases may need to consider the potential side effects of TR4 switched roles during the PCa initiation.

White spot syndrome virus protein kinase 1 defeats the host cell's iron-withholding defense mechanism by interacting with host ferritin.

UNLABELLED: Iron is an essential nutrient for nearly all living organisms, including both hosts and invaders. Proteins such as ferritin regulate the iron levels in a cell, and in the event of a pathogenic invasion, the host can use an iron-withholding mechanism to restrict the availability of this essential nutrient to the invading pathogens. However, pathogens use various strategies to overcome this host defense. In this study, we demonstrated that white spot syndrome virus (WSSV) protein kinase 1 (PK1) interacted with shrimp ferritin in the yeast two-hybrid system. A pulldown assay and 27-MHz quartz crystal microbalance (QCM) analysis confirmed the interaction between PK1 and both ferritin and apoferritin. PK1 did not promote the release of iron ions from ferritin, but it prevented apoferritin from binding ferrous ions. When PK1 was overexpressed in Sf9 cells, the cellular labile iron pool (LIP) levels were elevated significantly. Immunoprecipitation and atomic absorption spectrophotometry (AAS) further showed that the number of iron ions bound by ferritin decreased significantly at 24 h post-WSSV infection. Taken together, these results suggest that PK1 prevents apoferritin from iron loading, and thus stabilizes the cellular LIP levels, and that WSSV uses this novel mechanism to counteract the host cell's iron-withholding defense mechanism. IMPORTANCE: We show here that white spot syndrome virus (WSSV) ensures the availability of iron by using a previously unreported mechanism to defeat the host cell's iron-withholding defense mechanism. This defense is often implemented by ferritin, which can bind up to 4,500 iron atoms and acts to sequester free iron within the cell. WSSV's novel counterstrategy is mediated by a direct protein-protein interaction between viral protein kinase 1 (PK1) and host ferritin. PK1 interacts with both ferritin and apoferritin, suppresses apoferritin's ability to sequester free iron ions, and maintains the intracellular labile iron pool (LIP), and thus the availability of free iron is increased within cells.

TR4 nuclear receptor promotes prostate cancer metastasis via upregulation of CCL2/CCR2 signaling.

Testicular nuclear receptor 4 (TR4) plays protective roles against oxidative stress and DNA damage and might contribute to aging. Our recent clinical tumor tissue staining results showed higher expression of TR4 in prostate cancer (PCa) patients with high Gleason scores compared to the tissues with the low Gleason scores. In vitro migration/invasion assays after manipulation of the TR4 expression in PCa cells showed that TR4 promoted PCa cells migration/invasion. Mechanism dissection found that the CCL2/CCR2 signal plays the key role in the mediation of TR4-promoted PCa cells migration/invasion. Chromatin immunoprecipitation and Luciferase assays further confirmed TR4 modulation of CCL2 at the transcriptional level and addition of the CCR2 antagonist led to interruption of the TR4-enhanced PCa cells migration/invasion. Finally, the orthotopic xenografted mice studies using the luciferase expressing CWR22Rv1 cells found that TR4 enhanced PCa metastasis and this increased metastasis was reversed when the CCR2 antagonist was injected into the mice. Together, these in vitro and in vivo results revealed a positive role of TR4 in PCa metastasis and demonstrated CCL2/CCR2 signaling as an important mediator in exerting TR4 action. This finding suggests that TR4 may represent a biomarker related to PCa metastasis and targeting the TR4-CCL2/CCR2 axis may become a new therapeutic approach to battle PCa metastasis.

Minireview: Pathophysiological roles of the TR4 nuclear receptor: lessons learned from mice lacking TR4.

Testicular nuclear receptor 4 (TR4), also known as NR2C2, belongs to the nuclear receptor superfamily and shares high homology with the testicular nuclear receptor 2. The natural ligands of TR4 remained unclear until the recent discoveries of several energy/lipid sensors including the polyunsaturated fatty acid metabolites, 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatetraenoic acid, and their synthetic ligands, thiazolidinediones, used for treatment of diabetes. TR4 is widely expressed throughout the body and particularly concentrated in the testis, prostate, cerebellum, and hippocampus. It has been shown to play important roles in cerebellar development, forebrain myelination, folliculogenesis, gluconeogenesis, lipogenesis, muscle development, bone development, and prostate cancer progression. Here we provide a comprehensive summary of TR4 signaling including its upstream ligands/activators/suppressors, transcriptional coactivators/repressors, downstream targets, and their in vivo functions with potential impacts on TR4-related diseases. Importantly, TR4 shares similar ligands/activators with another key nuclear receptor, peroxisome proliferator-activated receptor γ, which raised several interesting questions about how these 2 nuclear receptors may collaborate with or counteract each other's function in their related diseases. Clear dissection of such molecular mechanisms and their differential roles in various diseases may help researchers to design new potential drugs with better efficacy and fewer side effects to battle TR4 and peroxisome proliferator-activated receptor γ involved diseases.