ArfGAP1 acts as a GTPase-activating protein for human ADP-ribosylation factor-like 1 protein.

ADP-ribosylation factors (Arfs) and Arf-like (Arl) GTPases are key regulators of intracellular vesicle trafficking and Golgi structure. Both Arf and Arl proteins cycle between active GTP-bound and inactive GDP-bound forms, where guanine nucleotide exchange factors (GEFs) regulate the exchange of GDP for GTP, whereas GTPase-activating proteins (GAPs) promote the hydrolysis of bound GTP. Human Arl1 is located at the trans-Golgi network (TGN) and regulates the function and structure of the Golgi complex. However, neither GEFs nor GAPs for human Arl1 have been identified. Here, we report that ArfGAP1, an Arf1 GAP, can promote GTP hydrolysis of Arl1. We show that ArfGAP1 directly interacts with GTP-bound Arl1 and exhibits GAP activity toward Arl1 in vitro. Exogenous expression of ArfGAP1, but not ArfGAP2 and ArfGAP3, causes dissociation of endogenous Arl1 from the TGN. In addition, GAP activity-deficient ArfGAP1 fails to regulate the Golgi localization of Arl1. Using an activity pull-down assay, we demonstrated that ArfGAP1 regulates the levels of Arl1-GTP in cells expressing ArfGAP1-myc or with ArfGAP1 knockdown. Finally, we observed that, similar to expression of putative active Arl1 (Arl1QL), ArfGAP1 knockdown impairs endosome-to-TGN retrograde transport of the Shiga toxin B-subunit. Thus, our findings support the idea that ArfGAP1 acts as an Arl1 GAP to regulate the function of Arl1 in vesicle trafficking at the TGN.

Golgi tethering factor golgin-97 suppresses breast cancer cell invasiveness by modulating NF-κB activity.

BACKGROUND: Golgin-97 is a tethering factor in the trans-Golgi network (TGN) and is crucial for vesicular trafficking and maintaining cell polarity. However, the significance of golgin-97 in human diseases such as cancer remains unclear. METHODS: We searched for a potential role of golgin-97 in cancers using Kaplan-Meier Plotter ( http://kmplot.com ) and Oncomine ( www.oncomine.org ) datasets. Specific functions of golgin-97 in migration and invasion were examined in golgin-97-knockdown and golgin-97-overexpressing cells. cDNA microarray, pathway analysis and qPCR were used to identify gene profiles regulated by golgin-97. The role of golgin-97 in NF-κB signaling pathway was examined by using subcellular fractionation, luciferase reporter assay, western blot analysis and immunofluorescence assay (IFA). RESULTS: We found that low expression of golgin-97 correlated with poor overall survival of cancer patients and was associated with invasiveness in breast cancer cells. Golgin-97 knockdown promoted cell migration and invasion, whereas re-expression of golgin-97 restored the above phenotypes in breast cancer cells. Microarray and pathway analyses revealed that golgin-97 knockdown induced the expression of several invasion-promoting genes that were transcriptionally regulated by NF-κB p65. Mechanistically, golgin-97 knockdown significantly reduced IκBα protein levels and activated NF-κB, whereas neither IκBα levels nor NF-κB activity was changed in TGN46- or GCC185-knockdown cells. Conversely, golgin-97 overexpression suppressed NF-κB activity and restored the levels of IκBα in golgin-97-knockdown cells. Interestingly, the results of Golgi-disturbing agent treatment revealed that the loss of Golgi integrity was not involved in the NF-κB activation induced by golgin-97 knockdown. Moreover, both TGN-bound and cytosolic golgin-97 inhibited NF-κB activation, indicating that golgin-97 functions as an NF-κB suppressor regardless of its subcellular localization. CONCLUSION: Our results collectively demonstrate a novel and suppressive role of golgin-97 in cancer invasiveness. We also provide a new avenue for exploring the relationship between the TGN, golgin-97 and NF-κB signaling in tumor progression.

ASC contributes to metastasis of oral cavity squamous cell carcinoma.

ASC (Apoptosis-associated Speck-like protein containing a CARD) acts as a platform protein in the inflammasome cascade of some cancer types. However, its potential involvement in OSCC (oral cavity squamous cell carcinoma) has not yet been determined. Here, we investigated the potential role of ASC in OSCC. RT-qPCR analysis of 20 paired tumor and adjacent normal tissue samples revealed that the mRNA levels of ASC, along with IL-1ß, CASP1, and NLRP3 in ASC-associated NLRP3 inflammasome were significantly elevated in OSCC tissues. Immunohistochemical staining of these four proteins in 111 clinical specimens revealed that high-level expression of ASC was significantly associated with tumor stage, node stage (p=0.001), overall stage (p<0.001), extracapsular spread (p<0.001), perineural invasion (p=0.004) and tumor depth (p<0.001). Kaplan-Meier survival analysis further revealed that high-level ASC expression was correlated with poorer overall survival (p=0.001), disease-specific survival (p<0.001) and disease-free survival (p<0.001). Studies using OSCC cell lines indicated that high-level ASC expression enhanced cell migration and invasion, and experiments using an orthotropic nude mouse model confirmed that ASC overexpression induced metastasis of OSCC cells. This is the first report to show that ASC contributes to OSCC metastasis, and that high-level ASC expression is a marker for poor prognosis in OSCC patients.

Investigation of Overrun-Processed Porous Hyaluronic Acid Carriers in Corneal Endothelial Tissue Engineering.

Hyaluronic acid (HA) is a linear polysaccharide naturally found in the eye and therefore is one of the most promising biomaterials for corneal endothelial regenerative medicine. This study reports, for the first time, the development of overrun-processed porous HA hydrogels for corneal endothelial cell (CEC) sheet transplantation and tissue engineering applications. The hydrogel carriers were characterized to examine their structures and functions. Evaluations of carbodiimide cross-linked air-dried and freeze-dried HA samples were conducted simultaneously for comparison. The results indicated that during the fabrication of freeze-dried HA discs, a technique of introducing gas bubbles in the aqueous biopolymer solutions can be used to enlarge pore structure and prevent dense surface skin formation. Among all the groups studied, the overrun-processed porous HA carriers show the greatest biological stability, the highest freezable water content and glucose permeability, and the minimized adverse effects on ionic pump function of rabbit CECs. After transfer and attachment of bioengineered CEC sheets to the overrun-processed HA hydrogel carriers, the therapeutic efficacy of cell/biopolymer constructs was tested using a rabbit model with corneal endothelial dysfunction. Clinical observations including slit-lamp biomicroscopy, specular microscopy, and corneal thickness measurements showed that the construct implants can regenerate corneal endothelium and restore corneal transparency at 4 weeks postoperatively. Our findings suggest that cell sheet transplantation using overrun-processed porous HA hydrogels offers a new way to reconstruct the posterior corneal surface and improve endothelial tissue function.

Effect of matrix nanostructure on the functionality of carbodiimide cross-linked amniotic membranes as limbal epithelial cell scaffolds.

Carbodiimide cross-linked amniotic membrane (AM) can potentially serve as an artificial corneal epithelial stem cell niche in ocular surface wound healing. For the first time, this study was performed to investigate the relationship between nanostructure and functionality of carbodiimide cross-linked AM tissues as limbal epithelial cell (LEC) scaffold biomaterials. The triple-helical molecular conformation of AM collagen was checked after chemical treatment for varying cross-linking durations (1-4 h). Our data indicated that the unraveling of the helical structure into a more random globular state is accompanied by an increase in the cross-linking index of AM samples. The cross-linker-mediated alterations in tissue ultrastructure and substrate nanotopography of these proteinaceous matrices were confirmed by transmission electron and atomic force microscopy studies. With increasing treatment time, the chemically cross-linked AM possessed larger nanofiber diameter and exhibited rougher texture. Marked increases in the water content, light transmittance, and resistance to enzymatic degradation were found, probably due to collagen fibril aggregation in biological tissues. All the test AM materials were not toxic to the human corneal epithelial cell cultures and retained anti-inflammatory activity, indicating the tolerability and safety of carbodiimide (i.e., a zero-length cross-linker). In addition, the enhanced LEC growth and increased p63 and ABCG2 gene expressions were significantly noted on the AM samples with greater cross-linking degree. In summary, the findings reported in this paper suggest that a specific limbal epithelial stem cell-biomaterial interaction may occur in response to biophysical cue such as nanostructure of carbodiimide cross-linked AM matrix.

A gender-specific association of CNV at 6p21.3 with NPC susceptibility.

Copy number variations (CNVs), a major source of human genetic polymorphism, have been suggested to have an important role in genetic susceptibility to common diseases such as cancer, immune diseases and neurological disorders. Nasopharyngeal carcinoma (NPC) is a multifactorial tumor closely associated with genetic background and with a male preponderance over female (3:1). Previous genome-wide association studies have identified single-nucleotide polymorphisms (SNPs) that are associated with NPC susceptibility. Here, we sought to explore the possible association of CNVs with NPC predisposition. Utilizing genome-wide SNP-based arrays and five CNV-prediction algorithms, we identified eight regions with CNV that were significantly overrepresented in NPC patients compared with healthy controls. These CNVs included six deletions (on chromosomes 3, 6, 7, 8 and 19), and two duplications (on chromosomes 7 and 12). Among them, the CNV located at chromosome 6p21.3, with single-copy deletion of the MICA and HCP5 genes, showed the highest association with NPC. Interestingly, it was more specifically associated with an increased NPC risk among males. This gender-specific association was replicated in an independent case-control sample using a self-established deletion-specific polymerase chain reaction strategy. To the best of our knowledge, this is the first study to explore the role of constitutional CNVs in NPC, using a genome-wide platform. Moreover, we identified eight novel candidate regions with CNV that merit future investigation, and our results suggest that similar to neuroblastoma and prostate cancer, genetic structural variations might contribute to NPC predisposition.

A novel role of RASSF9 in maintaining epidermal homeostasis.

The physiological role of RASSF9, a member of the Ras-association domain family (RASSF), is currently unclear. Here, we report a mouse line in which an Epstein-Barr virus Latent Membrane Protein 1 (LMP1) transgene insertion has created a 7.2-kb chromosomal deletion, which abolished RASSF9 gene expression. The RASSF9-null mice exhibited interesting phenotypes that resembled human ageing, including growth retardation, short lifespan, less subcutaneous adipose layer and alopecia. In the wild-type mice, RASSF9 is predominantly expressed in the epidermal keratinocytes of skin, as determined by quantitative reverse-transcription PCR, immunofluorescence and in situ hybridization. In contrast, RASSF9-/- mice presented a dramatic change in epithelial organization of skin with increased proliferation and aberrant differentiation as detected by bromodeoxyuridine incorporation assays and immunofluorescence analyses. Furthermore, characteristic functions of RASSF9-/- versus wild type (WT) mouse primary keratinocytes showed significant proliferation linked to a reduction of p21Cip1 expression under growth or early differentiation conditions. Additionally, in RASSF9-/- keratinocytes there was a drastic down-modulation of terminal differentiation markers, which could be rescued by infection with a recombinant adenovirus, Adv/HA-RASSF9. Our results indicate a novel and significant role of RASSF9 in epidermal homeostasis.

Carbodiimide cross-linked amniotic membranes for cultivation of limbal epithelial cells.

In ophthalmic tissue engineering, amniotic membrane (AM) is one of the most prevalent natural matrices used for limbal epithelial cell (LEC) cultivation and transplantation. However, the application of AM as a scaffold is limited by its low biomechanical strength and rapid biodegradation. The present study reports the development of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linked AM as an LEC carrier. The collagenous tissue materials were modified with varying cross-linker concentrations (0-0.25 mmol EDC/mg AM) and were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), ninhydrin assays, electron microscopy, light transmission measurements, mechanical and in vitro degradation tests, as well as diffusion permeability and cell culture studies. Our results showed that chemical cross-linking approaches saturation at concentrations of 0.05 mmol EDC/mg AM. The formation of cross-links (i.e., amide bonds) in the samples treated with 0.05 mmol EDC/mg AM may cause significant aggregation of tropocollagen molecules and collagen microfibrils without affecting cell morphology of biological tissues. With the optimum concentration of 0.05 mmol EDC/mg AM, chemical cross-linker could significantly enhance the mechanical and thermal stability, optical transparency, and resistance to collagenase digestion. Continuous permeation of albumin through the cross-linked AM would be helpful to cell growth over the matrix surface. In addition, the EDC cross-linked samples were able to support LEC proliferation and preserve epithelial progenitor cells in vitro and in vivo. It is concluded that the AM cross-linked with 0.05 mmol EDC/mg AM may be a potential biomaterial for regenerative medicine.

Ocular biocompatibility of carbodiimide cross-linked hyaluronic acid hydrogels for cell sheet delivery carriers.

Due to its innocuous nature, hyaluronic acid (HA) is one of the most commonly used biopolymers for ophthalmic applications. We recently developed a cell sheet delivery system using carbodiimide cross-linked HA carriers. Chemical cross-linking provides an improvement in stability of polymer gels, but probably causes toxic side-effects. The aim of this study was to investigate the ocular biocompatibility of HA hydrogels cross-linked by 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC). HA discs without cross-linking and glutaraldehyde (GTA) cross-linked HA samples were used for comparison. The disc implants were inserted in the anterior chamber of rabbit eyes for 24 weeks and characterized by slit-lamp biomicroscopy, histology and scanning electron microscopy. The ophthalmic parameters obtained from biomicroscopic examinations were also scored to provide a quantitative grading system. Results of this study showed that the HA discs cross-linked with EDC had better ocular biocompatibility than those with GTA. The continued residence of GTA cross-linked HA implants in the intraocular cavity elicited severe tissue responses and significant foreign body reactions, whereas no adverse inflammatory reaction was observed after contact with non-cross-linked HA or EDC cross-linked HA samples. It is concluded that the cross-linking agent type gives influence on ocular biocompatibility of cell carriers and the EDC-HA hydrogel is an ideal candidate for use as an implantable material in cell sheet delivery applications.

The zebrafish homeobox gene irxl1 is required for brain and pharyngeal arch morphogenesis.

Iroquois homeobox-like 1 (irxl1) is a novel member of the TALE superfamily of homeobox genes that is most closely related to the Iroquois class. We have identified the zebrafish irxl1 gene and characterized its structure. The protein contains a homeodomain that shares 100% sequence identity with other vertebrate orthologs. During embryogenesis, irxl1 is expressed from 18 hours postfertilization onward and prominent expression is detected in the pharyngeal arches. Knockdown of irxl1 by morpholinos results in malformed brain and arch structures, which can be partially rescued by cRNA injection. The heads of the morphants become small and flat, and extensions along the anterior-posterior/dorso-ventral axes are reduced without affecting regional specification. Loss of irxl1 function also causes deficit in neural crest cells which consequently results in partial loss of craniofacial muscles and severe deformation of arch cartilages. These observations suggest that irxl1 may regulate factors involved in brain and pharyngeal arch development.

Low Bloom strength gelatin as a carrier for potential use in retinal sheet encapsulation and transplantation.

Retinal transplantation aims to restore vision for patients suffering from retinitis pigmentosa and age-related macular degeneration. Because the retinal sheets are fragile in nature, it is difficult to maintain graft integrity during surgical manipulation and after transplantation. In the present work, we report the feasibility of applying sandwich-like gelatin membranes as encapsulating carriers for retinal sheet transplantation applications. The relationship between the Bloom index of gelatin and the functionality of carrier membranes was studied by determinations of mechanical property, dissolution degree, melting point, cytocompatibility, biocompatibility, and transplant transfer and encapsulation efficiency. Irrespective of their Bloom strength, the gelatin membranes had a thickness sufficient to provide mechanical support for retinal sheets and would be beneficial to overcome the fragility of transplants during intraocular delivery. It was found that the lower the Bloom value of gelatin, the lower melting point of membranes. This allowed for easy fabrication of a stable sandwich-like encapsulating structure at 37 degrees C. The gelatins with lower Bloom strengths could possibly be dissolved to an extent required for the establishment of close contact between the retinal grafts and defective tissues. In addition, the carrier membranes made from the gelatins with low Bloom values showed a relatively higher cytocompatibility and biocompatibility as well as a higher transfer and encapsulation efficiency as compared to those with high Bloom values. It is concluded that the effect of Bloom index of gelatin plays a significant role in the membrane functionality and the gelatins with low Bloom values have substantial potential to be further developed as effective encapsulating carriers for the intraocular delivery of retinal sheets.