Generation of a Rat Monoclonal Antibody for Human PAICS, a de novo Purine Biosynthetic Enzyme.

Phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS) is a de novo purine biosynthetic enzyme. It has been found to be overexpressed in various types of cancer and is related to cell proliferation, invasion, the epithelial-mesenchymal transition, and efficient tumor growth. In this study, we describe a rat monoclonal antibody (mAb) 6A10, which was generated as an antigen of human PAICS. This mAb was generated to interact with the N-terminal region of human PAICS and was found to recognize endogenous PAICS enzymes in several cancer cells. Our results also indicated that it can recognize monkey and dog PAICS, which possess the same amino acid sequence in the antigenic region as human PAICS, but it does not recognize rat and mouse PAICS. Furthermore, our data indicated that this mAb is suitable for immunoprecipitation and immunoblotting use for several cancer cell lines. We, therefore, anticipate that mAb 6A10 will be useful for functional analyses of human PAICS in several cancers and for diagnosis of malignant transformation.

Development of a high-affinity anti-bovine PD-1 rabbit-bovine chimeric antibody using an efficient selection and large production system.

Immune checkpoint molecules PD-1/PD-L1 cause T-cell exhaustion and contribute to disease progression in chronic infections of cattle. We established monoclonal antibodies (mAbs) that specifically inhibit the binding of bovine PD-1/PD-L1; however, conventional anti-PD-1 mAbs are not suitable as therapeutic agents because of their low binding affinity to antigen. In addition, their sensitivity for the detection of bovine PD-1 is low and their use for immunostaining PD-1 is limited. To address these issues, we established two anti-bovine PD-1 rabbit mAbs (1F10F1 and 4F5F2) and its chimeric form using bovine IgG1 (Boch1D10F1), which exhibit high binding affinity. One of the rabbit mAb 1D10F1 binds more strongly to bovine PD-1 compared with a conventional anti-PD-1 mAb (5D2) and exhibits marked inhibitory activity on the PD-1/PD-L1 interaction. In addition, PD-1 expression in bovine T cells could be detected with higher sensitivity by flow cytometry using 1D10F1. Furthermore, we established higher-producing cells of Boch1D10F1 and succeeded in the mass production of Boch1D10F1. Boch1D10F1 exhibited a similar binding affinity to bovine PD-1 and the inhibitory activity on PD-1/PD-L1 binding compared with 1D10F1. The immune activation by Boch1D10F1 was also confirmed by the enhancement of IFN-γ production. Finally, Boch1D10F1 was administered to bovine leukemia virus-infected cows to determine its antiviral effect. In conclusion, the high-affinity anti-PD-1 antibody developed in this study represents a powerful tool for detecting and inhibiting bovine PD-1 and is a candidate for PD-1-targeted immunotherapy in cattle.

Generation of Rat Monoclonal Antibody for Human Nucleolin.

Nucleolin (NCL) is a multifunctional phosphoprotein that is mainly localized in the nucleolus, but it is also found in the nucleoplasm, cytoplasm, and cell membrane. The principal functions of NCL involve DNA and RNA metabolism, gene transcription and translation, ribosome biogenesis, and mRNA stability. It was also reported that the localization of human NCL (hNCL) is related to tumor malignancy. Therefore, analyzing the cellular dynamics of NCL could be useful. In this article, we describe rat monoclonal antibody (mAb) 6F9A6 that was generated against a hNCL peptide. This mAb recognizes endogenous human, monkey, dog, and mouse NCL and was shown to be useful in immunofluorescence staining, immunoprecipitation, and immunoblotting experiments in several cancer cell lines. We anticipate that the mAb 6F9A6 will be useful for functional analyses of hNCL in cancer cells.

Effective SARS-CoV-2 replication of monolayers of intestinal epithelial cells differentiated from human induced pluripotent stem cells.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes severe acute respiratory symptoms in humans. Controlling the coronavirus disease pandemic is a worldwide priority. The number of SARS-CoV-2 studies has dramatically increased, and the requirement for analytical tools is higher than ever. Here, we propose monolayered-intestinal epithelial cells (IECs) derived from human induced pluripotent stem cells (iPSCs) instead of three-dimensional cultured intestinal organoids as a suitable tool to study SARS-CoV-2 infection. Differentiated IEC monolayers express high levels of angiotensin-converting enzyme 2 and transmembrane protease serine 2 (TMPRSS2), host factors essential for SARS-CoV-2 infection. SARS-CoV-2 efficiently grows in IEC monolayers. Using this propagation system, we confirm that TMPRSS2 inhibition blocked SARS-CoV-2 infection in IECs. Hence, our iPSC-derived IEC monolayers are suitable for SARS-CoV-2 research under physiologically relevant conditions.

Generation of Rat Monoclonal Antibodies Against Human Epidermal Growth Factor Receptor 2.

Human epidermal growth factor receptor 2 (HER2) is a transmembrane tyrosine kinase receptor without any known ligands and a member of the epidermal growth factor receptor (EGFR) family. It is a proto-oncogenic protein that, through signaling cascades, promotes cell proliferation and inhibits apoptosis in cancer cells through homo- and heterodimerization with other EGFR family receptors. Since several cancers, including breast cancer, overexpress HER2, it is a target of tumor therapy. Both trastuzumab and pertuzumab are recombinant humanized monoclonal antibodies (mAbs) used in clinical trials that target the extracellular domain (ECD) of HER2. Therefore, it is important to generate antibodies against various ECDs of HER2. In this study, we describe rat mAbs, which were generated against the ECD of human HER2. The human breast cancer cell line SK-BR-3 was subjected to immunofluorescence staining as it expresses HER2, and mAbs can detect both intact and endogenous HER2 within the cell line.

Septin-microtubule association via a motif unique to isoform 1 of septin 9 tunes stress fibers.

Septins, a family of GTP-binding proteins that assemble into higher order structures, interface with the membrane, actin filaments and microtubules, and are thus important regulators of cytoarchitecture. Septin 9 (SEPT9), which is frequently overexpressed in tumors and mutated in hereditary neuralgic amyotrophy (HNA), mediates the binding of septins to microtubules, but the molecular determinants of this interaction remained uncertain. We demonstrate that a short microtubule-associated protein (MAP)-like motif unique to SEPT9 isoform 1 (SEPT9_i1) drives septin octamer-microtubule interaction in cells and in vitro reconstitutions. Septin-microtubule association requires polymerizable septin octamers harboring SEPT9_i1. Although outside of the MAP-like motif, HNA mutations abrogate this association, identifying a putative regulatory domain. Removal of this domain from SEPT9_i1 sequesters septins on microtubules, promotes microtubule stability and alters actomyosin fiber distribution and tension. Thus, we identify key molecular determinants and potential regulatory roles of septin-microtubule interaction, paving the way to deciphering the mechanisms underlying septin-associated pathologies. This article has an associated First Person interview with the first author of the paper.

Gαq modulates the energy metabolism of osteoclasts.

Introduction: The bacterial protein toxin Pasteurella multocida toxin (PMT) mediates RANKL-independent osteoclast differentiation. Although these osteoclasts are smaller, their resorptive activity is high which helps in efficient destruction of nasal turbinate bones of pigs. Methods: The proteome of bone marrow-derived macrophages differentiated into osteoclasts with either RANKL or PMT was analysed. The results were verified by characterizing the metabolic activity using Seahorse analysis, a protein translation assay, immunoblots, real-time PCR as well as flow cytometry-based monitoring of mitochondrial activity and ROS production. A Gαq overexpression system using ER-Hoxb8 cells was used to identify Gαq-mediated metabolic effects on osteoclast differentiation and function. Results: PMT induces the upregulation of metabolic pathways, which included strong glycolytic activity, increased expression of GLUT1 and upregulation of the mTOR pathway. As OxPhos components were expressed more efficiently, cells also displayed increased mitochondrial respiration. The heterotrimeric G protein Gαq plays a central role in this hypermetabolic cell activation as it triggers mitochondrial relocalisation of pSerSTAT3 and an increase in OPA1 expression. This seems to be caused by a direct interaction between STAT3 and OPA1 resulting in enhanced mitochondrial respiration. Overexpression of Gαq mimicked the hypermetabolic phenotype observed for PMT-induced osteoclasts and resulted in higher glycolytic and mitochondrial activity as well as increased bone resorptive activity. In addition, rheumatoid arthritis (RA) patients showed an increase in GNAQ expression, especially in the synovial fluid. Discussion: Our study suggests that Gαq plays a key role in PMT-induced osteoclastogenesis. Enhanced expression of GNAQ at the site of inflammation in RA patients indicates its pathophysiological relevance in the context of inflammatory bone disorders.

Canopy Homolog 2 as a Novel Molecular Target in Hepatocarcinogenesis.

In the present study, the role of a novel protein involved in neurite development and endoplasmic reticulum (ER) stress, canopy homolog 2 (CNPY2), was investigated in mouse and human hepatocarcinogenesis. Firstly, a sensitive quantitative and qualitative detection of protein expression using QSTAR Elite LC-Ms/Ms was performed for the analysis of lysates of microdissected hepatocellular altered foci (AF), adenomas (HCAs), carcinomas (HCCs) and peri-tumoral livers from C57Bl/6J mice treated with diethylnitrosamine (DEN) and then maintained for 27 or 38 weeks on basal diet. Significant overexpression of 18.5 kDa CNPY2 processed form was demonstrated in AF, HCAs and HCCs, while low expression was observed in the livers of DEN-treated and control mice. Furthermore, CNPY2 elevation in AF and tumors was coordinated with accumulation of numerous cytoskeletal proteins, including cytokeratins 8 and 18, actin, non-muscle myosin and septin 9 and those involved in ER and mitochondrial stresses such as calreticulin, prohibitins 1 and 2 and YME1-like-1. Knockdown of CNPY2 in Huh7 and HepG2 human liver cancer cells resulted in significant suppression of cell survival and invasive potential, inhibition of cyclin D1, induction of p21Waf1/Cip1 and suppression of the apoptosis inhibitor Bcl2. In contrast, transfection of a mouse CNPY2 (mCNPY2-Ds-Red) vector plasmid in Huh7 and HepG2 cancer cells, with subsequent accumulation of CNPY2 in the ER, resulted in significant increase in cancer cells survival. Clinicopathological analysis in 90 HCV-positive HCC patients, revealed significant association of CNPY2 overexpression with poor overall (p = 0.041) survival. Furthermore, CNPY2 increase was associated with vessel invasion (p = 0.038), poor histological differentiation (p = 0.035) and advanced clinical stage (p = 0.016). In conclusion, CNPY2 is a promising molecular target elevated early in hepatocarcinogenesis and prognostic marker for human HCV-associated HCC. CNPY2 is involved in the processes of ER stress, cell cycle progression, proliferation, survival and invasion of liver tumor cells.

Generation of the Rat Monoclonal Antibody Against the Extracellular Domain of Human CD63 by DNA Immunization.

Human cluster of differentiation 63 (hCD63) is one of the tetraspanin receptors that is abundant on the surface of exosomes. Exosomes are involved in cell-to-cell communication, including from cancer cells to normal cells. It is very important to detect exosomes as a marker for the diagnosis of various diseases. In this study, we report the generation and characterization of a monoclonal antibody (mAb) against the extracellular domain of hCD63 using DNA immunization. This mAb, clone 1C8-2B11, exhibits high performance for use in immunofluorescence and flow cytometry, and it has 10-fold higher affinity than the control antibody that is commercially available. mAb 1C8-2B11 has great potential to be a tool for research and clinical diagnosis.

Detection of Rhizopus-specific antigen in human and murine serum and bronchoalveolar lavage.

Mucormycosis is a deep-seated fungal infection that mainly develops in patients with severe immunodeficiencies such as those with malignant hematological diseases. Despite poor prognosis, there is no reliable and minimally invasive diagnostic method-such as serodiagnosis-for making a clinical decision regarding the condition. As early diagnosis and early treatment improve the prognosis of mucormycosis, the development of a sensitive early diagnostic method is important. We had previously identified a Rhizopus-specific antigen (RSA) by signal sequence trapping and retrovirus-mediated expression (SST-REX), and evaluated its utility as a diagnostic antigen by constructing a sandwich enzyme-linked immunosorbent assay (ELISA) system to detect serum RSA levels in inoculated mice. In this study, we used the RSA-specific rabbit monoclonal antibodies generated by novel hybridoma technology to improve the sensitivity of the ELISA system. We observed an increase in serum and bronchoalveolar lavage fluid (BALF) levels of RSA in mouse model 1 day after inoculation, suggesting that this newly developed monoclonal antibody-based ELISA system may be useful for the diagnosis of mucormycosis in the early stages of infection. In addition, we measured RSA levels in human serum and BALF, and found that serum RSA level was higher in mucormycosis patients (15.1 ng/ml) than that in invasive pulmonary aspergillosis patients (0.53 ng/ml) and the negative control (0.49 ng/ml). Our results suggest that RSA may be a powerful tool for the diagnosis of pulmonary mucormycosis, and its differentiation from other deep-seated mycoses such as aspergillosis.

A straightforward approach to antibodies recognising cancer specific glycopeptidic neoepitopes.

Aberrantly truncated immature O-glycosylation in proteins occurs in essentially all types of epithelial cancer cells, which was demonstrated to be a common feature of most adenocarcinomas and strongly associated with cancer proliferation and metastasis. Although extensive efforts have been made toward the development of anticancer antibodies targeting MUC1, one of the most studied mucins having cancer-relevant immature O-glycans, no anti-MUC1 antibody recognises carbohydrates and the proximal MUC1 peptide region, concurrently. Here we present a general strategy that allows for the creation of antibodies interacting specifically with glycopeptidic neoepitopes by using homogeneous synthetic MUC1 glycopeptides designed for the streamlined process of immunization, antibody screening, three-dimensional structure analysis, epitope mapping and biochemical analysis. The X-ray crystal structure of the anti-MUC1 monoclonal antibody SN-101 complexed with the antigenic glycopeptide provides for the first time evidence that SN-101 recognises specifically the essential epitope by forming multiple hydrogen bonds both with the proximal peptide and GalNAc linked to the threonine residue, concurrently. Remarkably, the structure of the MUC1 glycopeptide in complex with SN-101 is identical to its solution NMR structure, an extended conformation induced by site-specific glycosylation. We demonstrate that this method accelerates dramatically the development of a new class of designated antibodies targeting a variety of "dynamic neoepitopes" elaborated by disease-specific O-glycosylation in the immunodominant mucin domains and mucin-like sequences found in intrinsically disordered regions of many proteins.

Correction: A straightforward approach to antibodies recognising cancer specific glycopeptidic neoepitopes.

[This corrects the article DOI: 10.1039/D0SC00317D.].

Chromatin-bound CRM1 recruits SET-Nup214 and NPM1c onto HOX clusters causing aberrant HOX expression in leukemia cells.

We previously demonstrated that CRM1, a major nuclear export factor, accumulates at Hox cluster regions to recruit nucleoporin-fusion protein Nup98HoxA9, resulting in robust activation of Hox genes (Oka et al., 2016). However, whether this phenomenon is general to other leukemogenic proteins remains unknown. Here, we show that two other leukemogenic proteins, nucleoporin-fusion SET-Nup214 and the NPM1 mutant, NPM1c, which contains a nuclear export signal (NES) at its C-terminus and is one of the most frequent mutations in acute myeloid leukemia, are recruited to the HOX cluster region via chromatin-bound CRM1, leading to HOX gene activation in human leukemia cells. Furthermore, we demonstrate that this mechanism is highly sensitive to a CRM1 inhibitor in leukemia cell line. Together, these findings indicate that CRM1 acts as a key molecule that connects leukemogenic proteins to aberrant HOX gene regulation either via nucleoporin-CRM1 interaction (for SET-Nup214) or NES-CRM1 interaction (for NPM1c).

Crumbs3 is a critical factor that regulates invasion and metastasis of colon adenocarcinoma via the specific interaction with FGFR1.

Epithelial cell polarity regulator Crumbs3 (Crb3), a mammalian homolog within the Drosophila Crb gene family, was initially identified as an essential embryonic development factor. It is recently implicated in tumor suppression, though its specific functions are controversial. We here demonstrate that Crb3 strongly promotes tumor invasion and metastasis of human colon adenocarcinoma cells. Crb3 centrality to tumor migration was supported by strong expression at invasive front and metastatic foci of colonic adenocarcinoma of the patient tissues. Accordingly, two different Crb3-knockout (KO) lines, Crb3-KO (Crb3 -/-) DLD-1 and Crb3-KO WiDr from human colonic adenocarcinomas, were generated by the CRISPR-Cas9 system. Crb3-KO DLD-1 cells exhibited loss of cellular mobility in vitro and dramatic suppression of liver metastases in vivo in contrast to the wild type of DLD-1. Unlike DLD-1, Crb3-KO WiDr mobility and metastasis were unaffected, which were similar to wild-type WiDr. Proteome analysis of Crb3-coimmunopreciptated proteins identified different respective fibroblast growth factor receptor (FGFR) isotypes specifically bound to Crb3 isoform a through their intracellular domain. In DLD-1, Crb3 showed membranous localization of FGFR1 leading to its functional activation, whereas Crb3 bound to cytoplasmic FGFR4 in WiDr without FGFR1 expression, leading to cellular growth. Correlative expression between Crb3 and FGFR1 was consistently detected in primary and metastatic colorectal cancer patient tissues. Taking these together, Crb3 critically accelerates cell migration, namely invasion and metastasis of human colon cancers, through specific interaction to FGFR1 on colon cancer cells.

EB1-binding-myomegalin protein complex promotes centrosomal microtubules functions.

Control of microtubule dynamics underlies several fundamental processes such as cell polarity, cell division, and cell motility. To gain insights into the mechanisms that control microtubule dynamics during cell motility, we investigated the interactome of the microtubule plus-end-binding protein end-binding 1 (EB1). Via molecular mapping and cross-linking mass spectrometry we identified and characterized a large complex associating a specific isoform of myomegalin termed "SMYLE" (for short myomegalin-like EB1 binding protein), the PKA scaffolding protein AKAP9, and the pericentrosomal protein CDK5RAP2. SMYLE was associated through an evolutionarily conserved N-terminal domain with AKAP9, which in turn was anchored at the centrosome via CDK5RAP2. SMYLE connected the pericentrosomal complex to the microtubule-nucleating complex (γ-TuRC) via Galectin-3-binding protein. SMYLE associated with nascent centrosomal microtubules to promote microtubule assembly and acetylation. Disruption of SMYLE interaction with EB1 or AKAP9 prevented microtubule nucleation and their stabilization at the leading edge of migrating cells. In addition, SMYLE depletion led to defective astral microtubules and abnormal orientation of the mitotic spindle and triggered G1 cell-cycle arrest, which might be due to defective centrosome integrity. As a consequence, SMYLE loss of function had a profound impact on tumor cell motility and proliferation, suggesting that SMYLE might be an important player in tumor progression.

A statistical image analysis framework for pore-free islands derived from heterogeneity distribution of nuclear pore complexes.

Nuclear pore complexes (NPCs) maintain cellular homeostasis by mediating nucleocytoplasmic transport. Although cyclin-dependent kinases (CDKs) regulate NPC assembly in interphase, the location of NPC assembly on the nuclear envelope is not clear. CDKs also regulate the disappearance of pore-free islands, which are nuclear envelope subdomains; this subdomain gradually disappears with increase in homogeneity of the NPC in response to CDK activity. However, a causal relationship between pore-free islands and NPC assembly remains unclear. Here, we elucidated mechanisms underlying NPC assembly from a new perspective by focusing on pore-free islands. We proposed a novel framework for image-based analysis to automatically determine the detailed 'landscape' of pore-free islands from a large quantity of images, leading to the identification of NPC intermediates that appear in pore-free islands with increased frequency in response to CDK activity. Comparison of the spatial distribution between simulated and the observed NPC intermediates within pore-free islands showed that their distribution was spatially biased. These results suggested that the disappearance of pore-free islands is highly related to de novo NPC assembly and indicated the existence of specific regulatory mechanisms for the spatial arrangement of NPC assembly on nuclear envelopes.

Application of Monoclonal Antibodies Against Mouse Dermokine.

Dermokine is one of the most highly expressed proteins in differentiating keratinocytes. Mouse dermokine has been reported to be encoded by 22 exons, and its expression leads to three transcripts, ß, γ, and α, which are transcribed from two different transcriptional start sites. The α isoform represents the carboxyl-terminal domain of the ß isoform, whereas the γ isoform lacks this domain. To reveal the distributions and expression levels of each isoform in mice, we generated rat monoclonal antibodies against dermokine-ß/γ and dermokine-ß/α. In immunofluorescence studies, the expression levels of dermokine in the cytosol of the cultured mouse keratinocytes were significantly elevated by high levels of extracellular calcium. In Western blot analyses, the expression levels of dermokine-ß and dermokine-α were increased in the presence of high calcium. Finally, we developed a monoclonal antibody-based sensitive sandwich enzyme-linked immunosorbent assay (ELISA) and showed that the secreted dermokine-ß into the culture medium from mouse keratinocytes was significantly increased in a manner dependent on the extracellular calcium concentration. These dermokine-specific antibodies have allowed us to gain new insights into the role of each dermokine isoform in cutaneous homeostasis.

ARHGEF10 directs the localization of Rab8 to Rab6-positive executive vesicles.

The function of ARHGEF10, a known guanine nucleotide exchange factor (GEF) for RhoA with proposed roles in various diseases, is poorly understood. To understand the precise function of this protein, we raised a monoclonal antibody against ARHGEF10 and determined its localization in HeLa cells. ARHGEF10 was found to localize to vesicles containing Rab6 (of which there are three isoforms, Rab6a, Rab6b and Rab6c), Rab8 (of which there are two isoforms, Rab8a and Rab8b), and/or the secretion marker neuropeptide Y (NPY)-Venus in a Rab6-dependent manner. These vesicles were known to originate from the Golgi and contain secreted or membrane proteins. Ectopic expression of an N-terminal-truncated ARHGEF10 mutant led to the generation of large vesicle-like structures containing both Rab6 and Rab8. Additionally, small interfering (si)RNA-mediated knockdown of ARHGEF10 impaired the localization of Rab8 to these exocytotic vesicles. Furthermore, the invasiveness of MDA-MB231 cells was markedly decreased by knockdown of ARHGEF10, as well as of Rab8. From these results, we propose that ARHGEF10 acts in exocytosis and tumor invasion in a Rab8-dependent manner.

Generation of Rat Monoclonal Antibodies Against Human Pancreatic Ductal Adenocarcinoma Cells.

Pancreatic ductal adenocarcinoma is an aggressive tumor with a poor prognosis. Biomarkers that can detect the tumor in its early stages when it may be amenable to curative resection might improve prognosis. To discover novel markers expressed in primary pancreatic cancer, we generated a panel of monoclonal antibodies against pancreatic ductal adenocarcinoma cell line BxPC3 using a rat medial iliac lymph node method. The antigen recognized by 1B5A5 was expressed on the cell surface and secreted into the conditioned medium of BxPC3 cells, and characterized as glycoproteins with molecular mass between 60 and 90 kDa. A wide range of molecular weights of 1B5A5 antigen in several pancreatic cancer cell lines were observed. Immunohistochemistry using a human multiple organ tumor tissue array showed an enhanced expression of 1B5A5 antigen in pancreas, lung, stomach, breast, urinary bladder, colon, and cervix uteri cancers. Immunoprecipitation followed by proteomic analyses identified CEACAM6 as a 1B5A5 antigen. In addition, western blot analysis results indicated that the 1B5A5 epitope is located within an amino-terminal domain of CEACAM6. These results raised the possibility that our approach could lead to discovery of novel biomarkers for the early stage of cancers in a relatively short period of time.

Chromatin-prebound Crm1 recruits Nup98-HoxA9 fusion to induce aberrant expression of Hox cluster genes.

The nucleoporin Nup98 is frequently rearranged to form leukemogenic Nup98-fusion proteins with various partners. However, their function remains largely elusive. Here, we show that Nup98-HoxA9, a fusion between Nup98 and the homeobox transcription factor HoxA9, forms nuclear aggregates that frequently associate with facultative heterochromatin. We demonstrate that stable expression of Nup98-HoxA9 in mouse embryonic stem cells selectively induces the expression of Hox cluster genes. Genome-wide binding site analysis revealed that Nup98-HoxA9 is preferentially targeted and accumulated at Hox cluster regions where the export factor Crm1 is originally prebound. In addition, leptomycin B, an inhibitor of Crm1, disassembled nuclear Nup98-HoxA9 dots, resulting in the loss of chromatin binding of Nup98-HoxA9 and Nup98-HoxA9-mediated activation of Hox genes. Collectively, our results indicate that highly selective targeting of Nup98-fusion proteins to Hox cluster regions via prebound Crm1 induces the formation of higher order chromatin structures that causes aberrant Hox gene regulation.