Fragile X-related Protein Research Articles

An in-depth review of the function of RNA-binding protein FXR1 in neurodevelopment.

FMR1 autosomal homolog 1 (FXR1) is an RNA-binding protein that belongs to the Fragile X-related protein (FXR) family. FXR1 is critical for development, as its loss of function is intolerant in humans and results in neonatal death in mice. Although FXR1 is expressed widely including the brain, functional studies on FXR1 have been mostly performed in cancer cells. Limited studies have demonstrated the importance of FXR1 in the brain. In this review, we will focus on the roles of FXR1 in brain development and pathogenesis of brain disorders. We will summarize the current knowledge in FXR1 in the context of neural biology, including structural features, isoform diversity and nomenclature, expression patterns, post-translational modifications, regulatory mechanisms, and molecular functions. Overall, FXR1 emerges as an important regulator of RNA metabolism in the brain, with strong implications in neurodevelopmental and psychiatric disorders.

The FXR1 network acts as a signaling scaffold for actomyosin remodeling

It is currently not known whether mRNAs fulfill structural roles in the cytoplasm. Here, we report the fragile X-related protein 1 (FXR1) network, an mRNA-protein (mRNP) network present throughout the cytoplasm, formed by FXR1-mediated packaging of exceptionally long mRNAs. These mRNAs serve as an underlying condensate scaffold and concentrate FXR1 molecules. The FXR1 network contains multiple protein binding sites and functions as a signaling scaffold for interacting proteins. We show that it is necessary for RhoA signaling-induced actomyosin reorganization to provide spatial proximity between kinases and their substrates. Point mutations in FXR1, found in its homolog FMR1, where they cause fragile X syndrome, disrupt the network. FXR1 network disruption prevents actomyosin remodeling-an essential and ubiquitous process for the regulation of cell shape, migration, and synaptic function. Our findings uncover a structural role for cytoplasmic mRNA and show how the FXR1 RNA-binding protein as part of the FXR1 network acts as an organizer of signaling reactions.

UBAP2L ensures homeostasis of nuclear pore complexes at the intact nuclear envelope.

Assembly of macromolecular complexes at correct cellular sites is crucial for cell function. Nuclear pore complexes (NPCs) are large cylindrical assemblies with eightfold rotational symmetry, built through hierarchical binding of nucleoporins (Nups) forming distinct subcomplexes. Here, we uncover a role of ubiquitin-associated protein 2-like (UBAP2L) in the assembly and stability of properly organized and functional NPCs at the intact nuclear envelope (NE) in human cells. UBAP2L localizes to the nuclear pores and facilitates the formation of the Y-complex, an essential scaffold component of the NPC, and its localization to the NE. UBAP2L promotes the interaction of the Y-complex with POM121 and Nup153, the critical upstream factors in a well-defined sequential order of Nups assembly onto NE during interphase. Timely localization of the cytoplasmic Nup transport factor fragile X-related protein 1 (FXR1) to the NE and its interaction with the Y-complex are likewise dependent on UBAP2L. Thus, this NPC biogenesis mechanism integrates the cytoplasmic and the nuclear NPC assembly signals and ensures efficient nuclear transport, adaptation to nutrient stress, and cellular proliferative capacity, highlighting the importance of NPC homeostasis at the intact NE.

Wild-type IDH1 maintains NSCLC stemness and chemoresistance through activation of the serine biosynthetic pathway

Tumor-initiating cells (TICs) reprogram their metabolic features to meet their bioenergetic, biosynthetic, and redox demands. Our previous study established a role for wild-type isocitrate dehydrogenase 1 (IDH1 WT ) as a potential diagnostic and prognostic biomarker for non–small cell lung cancer (NSCLC), but how IDH1 WT modulates NSCLC progression remains elusive. Here, we report that IDH1 WT activates serine biosynthesis by enhancing the expression of phosphoglycerate dehydrogenase (PHGDH) and phosphoserine aminotransferase 1 (PSAT1), the first and second enzymes of de novo serine synthetic pathway. Augmented serine synthesis leads to GSH/ROS imbalance and supports pyrimidine biosynthesis, maintaining tumor initiation capacity and enhancing gemcitabine chemoresistance. Mechanistically, we identify that IDH1 WT interacts with and stabilizes PHGDH and fragile X–related protein-1 (FXR1) by impeding their association with the E3 ubiquitin ligase parkin by coimmunoprecipitation assay and proximity ligation assay. Subsequently, stabilized FXR1 supports PSAT1 mRNA stability and translation, as determined by actinomycin D chase experiment and in vitro translation assay. Disrupting IDH1 WT -PHGDH and IDH1 WT -FXR1 interactions synergistically reduces NSCLC stemness and sensitizes NSCLC cells to gemcitabine and serine/glycine–depleted diet therapy in lung cancer xenograft models. Collectively, our findings offer insights into the role of IDH1 WT in serine metabolism, highlighting IDH1 WT as a potential therapeutic target for eradicating TICs and overcoming gemcitabine chemoresistance in NSCLC.

Comprehensive bioinformatics analysis of FXR1 across pan-cancer: Unraveling its diagnostic, prognostic, and immunological significance.

Fragile X-related protein 1 (FXR1) is an RNA-binding protein that belongs to the fragile X-related (FXR) family. Studies have shown that FXR1 plays an important role in cancer cell proliferation, invasion and migration and is differentially expressed in cancers. This study aimed to gain a comprehensive and systematic understanding of the analysis of FXR1's role in cancers. This would lead to a better understanding of how it contributes to the development and progression of various malignancies. this study conducted through The Cancer Genome Atlas (TCGA), GTEx, cBioPortal, TISIDB, GEPIA2 and HPA databases to investigated FXR1's role in cancers. For data analysis, various software platforms and web platforms were used, such as R, Cytoscape, hiplot plateform. A significant difference in FXR1 expression was observed across molecular and immune subtypes and across types of cancer. FXR1 expression correlates with disease-specific survival (DSS), and overall survival (OS) in several cancer pathways, further in progression-free interval (PFI) in most cancers. Additionally, FXR1 showed a correlation with genetic markers of immunomodulators in different cancer types. Our study provides insights into the role of FXR1 in promoting, inhibiting, and treating diverse cancers. FXR1 has the potential to serve as a diagnostic and prognostic biomarker for cancer, with therapeutic value in immune-based, targeted, or cytotoxic treatments. Further clinical validation and exploration of FXR1 in cancer treatment is necessary.

FXR1 knockdown inhibits the malignant behavior of colorectal cancer by suppressing epithelial-tomesenchymal transition

Purpose: To determine the role of Fragile X-related protein-1 (FXR1) in colon cancer progression and its relationship to patients’ survival.Methods: A total of 164 colorectal cancer (CRC) patients, admitted to the Affiliated Hospital of Jiangnan University, Wuxi, Jiangsu, China between 2006 and 2008, were included in this study. Immunohistochemistry was used to semi-quantitatively analyze the intensity and extent of immunological staining of diaminobenzidine-stained paraffin blocks of CRC samples. The study also retrieved COAD mRNA and patients’ clinical data from TCGA and cultured human colon cancer cell lines (SW480, SW620, HCT8, HCT116, and Caco2) in RPMI 1640 medium to assess the propensity of CRC cells to proliferate, invade the tumorigenicity in BALB/c nude mice.Results: The prognosis of CRC patients was inversely linked with the expression of FXR1. Additionally, FXR1 knockdown in CRC cells reduced cellular growth, colony development and tumorigenesis. After presenting BALB/c nude mice with tumors in FXR1 knockdown, the cells displayed higher E-cadherin levels (p < 0.01) as well as decreased TGF-1 (p < 0.01) and N-cadherin levels (p < 0.001).Conclusion: Fragile X-related protein-1 is an oncogene in colon cancer and its knockdown inhibits HCT116 cells from behaving malignantly. Thus, FXR1 is a potential treatment option for CRC.

Genetic Deletion of FXR1 Reduces Intimal Hyperplasia and Induces Senescence in Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMC) play a critical role in the development and pathogenesis of intimal hyperplasia indicative of restenosis and other vascular diseases. Fragile-X related protein-1 (FXR1) is a muscle-enhanced RNA binding protein whose expression is increased in injured arteries. Previous studies suggest that FXR1 negatively regulates inflammation, but its causality in vascular disease is unknown. In the current study, RNA-sequencing of FXR1-depleted VSMC identified many transcripts with decreased abundance, most of which were associated with proliferation and cell division. mRNA abundance and stability of a number of these transcripts were decreased in FXR1-depleted hVSMC, as was proliferation (P<0.05); however, increases in beta-galactosidase (P<0.05) and γH2AX (P<0.01), indicative of senescence, were noted. Further analysis showed increased abundance of senescence-associated genes with FXR1 depletion. A novel SMC-specific conditional knockout mouse (FXR1SMC/SMC) was developed for further analysis. In a carotid artery ligation model of intimal hyperplasia, FXR1SMC/SMC mice had significantly reduced neointima formation (P<0.001) after ligation, as well as increases in senescence drivers p16, p21, and p53 compared with several controls. These results suggest that in addition to destabilization of inflammatory transcripts, FXR1 stabilized cell cycle-related genes in VSMC, and absence of FXR1 led to induction of a senescent phenotype, supporting the hypothesis that FXR1 may mediate vascular disease by regulating stability of proliferative mRNA in VSMC.

Roles of the cumulus-oocyte transzonal network and the Fragile X protein family in oocyte competence.

RNA granules travel through the cumulus cell network of transzonal projections which is associated with oocyte developmental competence, and RNA packaging involves RNA-binding proteins of the Fragile X protein family. The determinants of oocyte developmental competence have puzzled scientists for decades. It is known that follicular conditions can nurture the production of a high-quality oocyte, but the underlying mechanisms remain unknown. Somatic cumulus cells most proximal to the oocyte are known to have cellular extensions that reach across the zona pellucida and contact with the oocyte plasma membrane. Herein, it was found that transzonal projections (TZPs) network quality is associated with developmental competence. Knowing that ribonucleoparticles are abundant within TZPs, the distribution of RNA-binding proteins was studied. The Fragile X-related proteins (FXR1P and FXR2P) and two partnering protein families, namely cytoplasmic FMRP-interacting protein and nuclear FMRP-interacting protein, exhibited distinctive patterns consistent with roles in regulating mRNA packaging, transport, and translation. The expression of green fluorescent protein (GFP)-FMRP fusion protein in cumulus cells showed active granule formation and their transport and transfer through filipodia connecting with neighboring cells. Near the projections' ends was found the cytoskeletal anchoring protein Filamin A and active protein synthesis sites. This study highlights key proteins involved in delivering mRNA to the oocyte. Thus, cumulus cells appear to indeed support the development of high-quality oocytes via the transzonal network.

CircSETD3 mediates acquired resistance to gefitinib in non-small lung cancer cells by FXR1/ECT2 pathway.

Gefitinib is the first-line treatment for non-small cell lung cancer (NSCLC) harboring EGFR sensitive mutation. However, acquired resistance significantly limits its therapeutic efficacy. CircSETD3 has been reported to promote gefitinib resistance in NSCLC cells, however, its underlying mechanisms have not been fully clarified. The expression of circSETD3 were detected in NSCLC patients who received gefitinib as first-line treatment, including 20 gefitinib-sensitive patients and 20 acquired gefitinib-resistant patients. Cell viability were examined by CCK8 assay. The mRNA and protein levels were detected by qRT-PCR and western blot. Using RNA pull-down assay followed by mass spectrometry to identified proteins that interact with circSETD3. The interaction between circSETD3 and fragile X-related protein-1 (FXR1) were further validated by RNA immunoprecipitation (RIP) and pull-down analysis. Fuorescence in situ hybridization (FISH) and immunofluorescence (IF) assays was used for the identification of sub-location of circSETD3 and FXR1 in cells. The effect of circSETD3 overexpression and knockdown on NSCLC tumor growth to gefitinib sensitivity was detected using the mouse xenograft model. CircSETD3 was significantly upregulated in gefitinib-resistant NSCLC cells, and decreased the gefitinib sensitivity in vitro and in vivo. Mechanically, circSETD3 facilitated FXR1 binding to its downstream mRNA target, epithelial cell-transforming sequence 2 (ECT2), promoting ECT2 mRNA decay, which further inhibited cellular apoptosis. CircSETD3/FXR1/ECT2 axis plays a critical role in the acquired resistance to gefitinib in NSCLC. Our results highlight the potential of circSETD3 as a biomarker and therapeutic target for NSCLC patients with acquired gefitinib resistance.

Abstract P126: FXR1 Regulates Vascular Smooth Muscle Cell Cytoskeletal Dynamics By Multiple Mechanisms

Introduction: Hypertension is a major risk factor for cardiovascular disease and stroke. Optimally treated hypertensive patients have a 50% greater cardiovascular risk than untreated normotensive subjects, presenting a need for additional targets. Vascular smooth muscle cells (VSMC) play a critical role in vascular contractility and regulation of blood pressure. Fragile X-related protein (FXR1) is a muscle-enhanced RNA binding protein. In addition to containing mRNA binding domains, FXR1 has an agenet-like domain for protein-protein interactions and four WH2 motif domains to mediate actin dynamics. The structure of FXR1 supports its role in post-transcriptional regulation and though largely ignored, cytoskeletal dynamics via potential protein-protein interactions. This study will test the hypothesis that FXR1 regulates vascular contractility by RNA stability and protein interactions. Results: RNA immuno-precipitation sequencing (RIPseq) analysis in human VSMC identified that FXR1 binds to mRNA that participate in VSMC contractility and cytoskeletal reorganization, and FXR1 depletion decreases mRNA abundance and stability of these transcripts. Mass-spectrometry and co-immunoprecipitation identified that FXR1 interacts with members of the WAVE complex, a five-subunit protein complex involved in the formation of the actin cytoskeleton, including CYFIP1 (Cytoplasmic FMR1-interacting protein 1) and Actin Related Protein 2/3 complex (ARP2). The WAVE complex is activated by an ARP2-mediated interaction with Rac1, promoting actin remodeling and cytoskeletal reorganization in a GTP-dependent manner. FXR1 depletion decreases small GTPases RAC1 and CDC42 activation in VSMC. Additionally, FXR1 depletion decreases VSMC lamellipodia formation, adhesion, migration and collagen gel contraction. Novel, VSMC-specific FXR1 conditional knock out mice show decreased diastolic (P &lt; 0.05) blood pressure at baseline compared to controls. Conclusion: These data are the first to suggest that FXR1 regulates mRNA stability of contractile proteins and interacts with members of the WAVE complex. Deletion of FXR1 abrogates VSMC cytoskeletal reorganization, resulting in a hypotensive phenotype in VSMC-specific conditional knockout mice.

Fragile X-Related Protein 1 Regulates Nucleoporin Localization in a Cell Cycle-Dependent Manner.

Nuclear pore complexes (NPCs) are embedded in the nuclear envelope (NE) where they ensure the transport of macromolecules between the nucleus and the cytoplasm. NPCs are built from nucleoporins (Nups) through a sequential assembly order taking place at two different stages during the cell cycle of mammalian cells: at the end of mitosis and during interphase. In addition, fragile X–related proteins (FXRPs) can interact with several cytoplasmic Nups and facilitate their localization to the NE during interphase likely through a microtubule-dependent mechanism. In the absence of FXRPs or microtubule-based transport, Nups aberrantly localize to the cytoplasm forming the so-called cytoplasmic nucleoporin granules (CNGs), compromising NPCs’ function on protein export. However, it remains unknown if Nup synthesis or degradation mechanisms are linked to the FXRP–Nup pathway and if and how the action of FXRPs on Nups is coordinated with the cell cycle progression. Here, we show that Nup localization defects observed in the absence of FXR1 are independent of active protein translation. CNGs are cleared in an autophagy- and proteasome-independent manner, and their presence is restricted to the early G1 phase of the cell cycle. Our results thus suggest that a pool of cytoplasmic Nups exists that contributes to the NPC assembly specifically during early G1 to ensure NPC homeostasis at a short transition from mitosis to the onset of interphase.

Abstract 13129: FXR1 Regulates Blood Pressure by Altering Vascular Contractility

Introduction: Hypertension is a major risk factor for heart disease and stroke. Despite current medication, half a million deaths in the United States include hypertension as a primary contributing cause, presenting a need for additional targets. Vascular smooth muscle cells (VSMCs) play a central role in vascular contractility and the regulation of blood pressure (BP). Fragile X-related protein (FXR1) is a muscle-enhanced RNA binding protein. Knock down of FXR1 increases inflammatory mRNA stability, and overexpression of FXR1 decreases inflammatory mRNA stability in VSMC. FXR1 knock out mice have a muscle-specific phenotype. While little is known concerning FXR1 protein binding partners and its role in vascular disease, its muscle-enhanced expression suggests a specialized role in VSMC. The specific aim of this study is to test the hypothesis that FXR1 regulates vascular contractility by regulation of RNA stability and protein-protein interactions. Results: To characterize an in vivo role of FXR1 in vascular disease, we generated a novel, VSMC-specific FXR1 conditional knock out mouse (FXR1 VSMC/VSMC ). Preliminary data indicates that these mice are hypotensive as they show decreased systolic (P &lt; 0.001) and diastolic (P &lt; 0.01) BP, and increased resting heart rate (P &lt; 0.05) at baseline compared to controls. To identify mRNA binding targets, gene ontology of RNA immuno-precipitation sequencing analysis (RIPseq) in human VSMCs identified that FXR1 preferentially binds to mRNA that participate in VSMC contractility and regulation of BP. Although considered an RNA stability protein, mass-spectrometry identified that FXR1 interacts with proteins related to VSMC contractile processes such as cell migration, adhesion and stress fiber formation. At a functional level, siRNA knock down of FXR1 decreased VSMC migration and collagen gel contraction corroborating in vivo observations. Conclusion: These data show that deletion of FXR1 decrease BP and VSMC contractile processes. They are the first to suggest FXR1 regulates BP and vascular contractility potentially by two mechanisms: mRNA stability and functional activity by protein-protein interactions. The findings support FXR1 activity may represent a target for therapeutic invention to regulate BP.

LncRNA TUG1 facilitates the development of endometrial cancer via interaction with FXR1

Purpose: To investigate the potential influence of long non-coding RNA (lncRNA) TUG1 on the development of endometrial cancer (EC).Methods: A total of 24 paired EC species and paracancerous species were collected, and the differential expressions of TUG1 in them were determined. The regulatory effects of TUG1 on proliferative and migratory potential in Ishikawa and HEC-1A cells were assessed using cell counting kit-8 (CCK-8) and Transwell assay, respectively. Potential protein binding TUG1 was predicted by bioinformatics analysis and subsequently verified using RIP (RNA-Binding Protein Immunoprecipitation) assay. Rescue experiments were conducted to uncover the mechanism of TUG1 in regulating the development of EC.Results: TUG1 was highly expressed in EC species and cell lines. Higher levels of TUG1 was observed in EC patients with metastases than those without metastatic cancer (p &lt; 0.05). Overexpression of TUG1 markedly facilitated proliferative and migratory potential in EC cells. Taurine-upregulated gene 1 (TUG1) directly bound Fragile X-related protein 1 (FXR1) and positively regulated its level (p &lt; 0.05). Through interaction with FXR1, TUG1 stimulated the malignant development of EC.Conclusion: LncRNA TUG1 is upregulated in EC species, which facilitates proliferative and migratory potentials in EC cells by interacting with FXR1.

RNA-binding protein FXR1 drives cMYC translation by recruiting eIF4F complex to the translation start site.

SUMMARYFragile X-related protein-1 (FXR1) gene is highly amplified in patients with ovarian cancer, and this amplification is associated with increased expression of both FXR1 mRNA and protein. FXR1 expression directly associates with the survival and proliferation of cancer cells. Surface sensing of translation (SUnSET) assay demonstrates that FXR1 enhances the overall translation in cancer cells. Reverse-phase protein array (RPPA) reveals that cMYC is the key target of FXR1. Mechanistically, FXR1 binds to the AU-rich elements (ARE) present within the 3′ untranslated region (3′UTR) of cMYC and stabilizes its expression. In addition, the RGG domain in FXR1 interacts with eIF4A1 and eIF4E proteins. These two interactions of FXR1 result in the circularization of cMYC mRNA and facilitate the recruitment of eukaryotic translation initiation factors to the translation start site. In brief, we uncover a mechanism by which FXR1 promotes cMYC levels in cancer cells.

Fragile X-Related Protein 1 (FXR1) Promotes Trophoblast Migration at Early Pregnancy via Downregulation of GDF-15 Expression

Fragile X-related protein 1 (FXR1) is an RNA-binding protein that can regulate specific mRNA decay in cells. Our previous study showed that FXR1 expression was significantly decreased in trophoblasts from patients with unexplained recurrent spontaneous abortion (RSA); however, the role of FXR1 in trophoblast function during early placenta development has not been fully elucidated. In this study, we found that knockdown of FXR1 using siRNA effectively inhibited the migration of HTR-8 cells and extravillous trophoblast (EVT) outgrowth in an ex vivo extravillous explant culture model. Furthermore, through analysis of a panel of cytokines, we found that the GDF-15 protein was upregulated after knockdown of FXR1 in HTR-8/SVneo cells. This was further confirmed by western blotting and immunofluorescence in HTR-8/SVneo cells and an extravillous explant. Our data also showed that FXR1 expression was downregulated and GDF-15 was upregulated in chorionic villous tissues from RSA patients compared with those from healthy controls (HCs). Further, immunohistochemistry showed a strong expression of GDF-15 in chorionic villous tissue in the RSA group, which was mainly distributed in villous trophoblasts (CTBs) and syncytiotrophoblasts (STBs). Moreover, knockdown of GDF-15 enhanced the migration of HTR-8 cells, while overexpression of GDF-15 using plasmid or treatment with recombinant human GDF-15 protein inhibited trophoblast migration. Importantly, RNA-binding protein immunoprecipitation showed that FXR1 directly bound to the 3′-UTR of GDF-15 mRNA to promote GDF-15 mRNA decay. Together, our data provide new insight into the function of FXR1 in human placenta via regulation of GDF-15 expression in trophoblasts and suggest a possible pathological process involved in RSA.

A serum microRNA sequence reveals fragile X protein pathology in amyotrophic lateral sclerosis.

Knowledge about converging disease mechanisms in the heterogeneous syndrome amyotrophic lateral sclerosis (ALS) is rare, but may lead to therapies effective in most ALS cases. Previously, we identified serum microRNAs downregulated in familial ALS, the majority of sporadic ALS patients, but also in presymptomatic mutation carriers. A 5-nucleotide sequence motif (GDCGG; D = G, A or U) was strongly enriched in these ALS-related microRNAs. We hypothesized that deregulation of protein(s) binding predominantly to this consensus motif was responsible for the ALS-linked microRNA fingerprint. Using microRNA pull-down assays combined with mass spectrometry followed by extensive biochemical validation, all members of the fragile X protein family, FMR1, FXR1 and FXR2, were identified to directly and predominantly interact with GDCGG microRNAs through their structurally disordered RGG/RG domains. Preferential association of this protein family with ALS-related microRNAs was confirmed by in vitro binding studies on a transcriptome-wide scale. Immunohistochemistry of lumbar spinal cord revealed aberrant expression level and aggregation of FXR1 and FXR2 in C9orf72- and FUS-linked familial ALS, but also patients with sporadic ALS. Further analysis of ALS autopsies and induced pluripotent stem cell-derived motor neurons with FUS mutations showed co-aggregation of FXR1 with FUS. Hence, our translational approach was able to take advantage of blood microRNAs to reveal CNS pathology, and suggests an involvement of the fragile X-related proteins in familial and sporadic ALS already at a presymptomatic stage. The findings may uncover disease mechanisms relevant to many patients with ALS. They furthermore underscore the systemic, extra-CNS aspect of ALS.

Absence of RNA-binding protein FXR2P prevents prolonged phase of kainate-induced seizures

Status epilepticus (SE) is a condition in which seizures are not self-terminating and thereby pose a serious threat to the patient's life. The molecular mechanisms underlying SE are likely heterogeneous and not well understood. Here, we reveal a role for the RNA-binding protein Fragile X-Related Protein 2 (FXR2P) in SE. Fxr2 KO mice display reduced sensitivity specifically to kainic acid-induced SE. Immunoprecipitation of FXR2P coupled to next-generation sequencing of associated mRNAs shows that FXR2P targets are enriched in genes that encode glutamatergic post-synaptic components. Of note, the FXR2P target transcriptome has a significant overlap with epilepsy and SE risk genes. In addition, Fxr2 KO mice fail to show sustained ERK1/2 phosphorylation induced by KA and present reduced burst activity in the hippocampus. Taken together, our findings show that the absence of FXR2P decreases the expression of glutamatergic proteins, and this decrease might prevent self-sustained seizures.

Spatial control of nucleoporin condensation by fragile X‐related proteins

Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve‐like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X‐related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule‐dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule‐containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation.

MiR-132 Regulates PTSD-like Behaviors in Rats Following Single-Prolonged Stress Through Fragile X-Related Protein 1.

Fragile X-related protein 1 (FXR1) is a member of the fragile X family of RNA-binding proteins, which regulates a number of neurological and neuropsychiatric disorders such as fragile X syndrome, and is expected as a novel therapeutic target for some psychiatric diseases. However, it is unknown how FXR1 changes and functions in post-traumatic stress disorder (PTSD), a common mental disorder related to trauma and stressor. In this study, we characterized the expression pattern of FXR1 in the pathophysiological process of PTSD and further investigated the possible mechanism underlying these changes by finding an upstream regulator, namely miRNA-132 (miR-132). Furthermore, we verified whether miR-132 silence had an effect on the PTSD-like behaviors of single prolonged stress (SPS) rats through open field test, forced swimming test, and water maze test. At last, we examined the expression levels of PSD95 and synapsin I in the hippocampus, which was one of the key brain regions associated with PTSD. We showed that the levels of FXR1 and fragile X mental retardation protein (FMRP), an autosomal homolog of FXR1, were decreased in the hippocampus of PTSD rats, but the levels of PSD95 and synapsin I were increased, which could be reversed by downregulation of miR-132. The results revealed that miR-132 could modulate PTSD-like behaviors in rats following SPS through regulating FXR1 and FMRP.

Fragile X-related protein 1 (FXR1) regulates cyclooxygenase-2 (COX-2) expression at the maternal-fetal interface.

Cyclooxygenase-2 (COX-2) is regulated post-transcriptionally by the AU-rich element (ARE) in the 3'-untranslated region (UTR) of its mRNA. However, the mechanism of COX-2 induction in infertility has not been thoroughly elucidated to date. The aim of this study was to examine the association between COX-2 and fragile X-related protein 1 (FXR1) in trophoblasts. Using quantitative reverse transcription polymerase chain reaction, our results showed that FXR1 mRNA expression levels were significantly decreased in trophoblasts from recurrent miscarriage patients compared with healthy controls; conversely, COX-2 mRNA expression levels were increased in patient samples. We also observed that FXR1 was highly expressed in human placental villi during early pregnancy. Furthermore, we used western blotting and immunofluorescence to analyse the expression levels of FXR1 and COX-2 in HTR-8 cells that were treated with tumour necrosis factor α; we observed that the expression of COX-2 was clearly increased in HTR-8 cells treated with FXR1 small interfering RNA, whereas the expression of COX-2 was effectively decreased in HTR-8 cells with FXR1 overexpressed via a plasmid. Importantly, bioinformatics analysis identified FXR1 binding sites in the 3'-UTR region of COX-2 and firefly luciferase reporter assay analysis verified that FXR1 binds directly to the 3'-UTR region of COX-2. ELISA assays showed that overexpression of FXR1 enhanced vascular endothelial growth factor-A and interleukin-8 expression in HTR-8 cells, whereas conversely, knockdown of FXR1 effectively repressed these effects. In conclusion, the results of this study indicate that FXR1 is a novel COX-2 regulatory factor.