Regulation of E-cadherin and TGF-β3 expression by CD24 in cultured oral epithelial cells

IFIT2 Depletion Promotes Cancer Stem Cell-like Phenotypes in Oral Cancer

(1) Background: Cancer stem cells (CSCs) are a small cell population associated with chemoresistance, metastasis and increased mortality rate in oral cancer. Interferon-induced proteins with tetratricopeptide repeats 2 (IFIT2) depletion results in epithelial to mesenchymal transition, invasion, metastasis, and chemoresistance in oral cancer. To date, no study has demonstrated the effect of IFIT2 depletion on the CSC-like phenotype in oral cancer cells. (2) Methods: Q-PCR, sphere formation, Hoechst 33,342 dye exclusion, immunofluorescence staining, and flow cytometry assays were performed to evaluate the expression of the CSC markers in IFIT2-depleted cells. A tumorigenicity assay was adopted to assess the tumor formation ability. Immunohistochemical staining was used to examine the protein levels of IFIT2 and CD24 in oral cancer patients. (3) Results: The cultured IFIT2 knockdown cells exhibited an overexpression of ABCG2 and CD44 and a downregulation of CD24 and gave rise to CSC-like phenotypes. Clinically, there was a positive correlation between IFIT2 and CD24 in the patients. IFIT2high/CD24high/CD44low expression profiles predicted a better prognosis in HNC, including oral cancer. The TNF-α blockade abolished the IFIT2 depletion-induced sphere formation, indicating that TNF-α may be involved in the CSC-like phenotypes in oral cancer. (4) Conclusions: The present study demonstrates that IFIT2 depletion promotes CSC-like phenotypes in oral cancer.

An early report: a modified porphyrin-linked metronidazole targeting intracellular Porphyromonas gingivalis in cultured oral epithelial cells

Porphyromonas gingivalis (P. gingivalis) has a strong association with the pathogenesis of periodontal disease. Recurrence of periodontal disease following therapy is attributed to numerous factors, and of growing interest is the potential problem of intracellular bacteria that are able to persist and multiply within the host cell, thereby facilitating relapse of infection. The effect of antibiotic therapy in controlling P. gingivalis is questionable. Accordingly, while metronidazole is very effective against anaerobic extracellular P. gingivalis by disrupting the DNA of anaerobic microbial cells, this antibiotic does not effectively penetrate into mammalian cells to inhibit intracellular bacteria. Therefore in the present study, a modified porphyrin-linked metronidazole adducts, developed in our laboratory, was used to kill intracellular P. gingivalis. A series of experiments were performed, including cytotoxicity assays and cellular uptake of adducts by flow cytometry coupled with live cell imaging analysis, P. gingivalis invasion and elimination assays, and the analysis of colocalization of P. gingivalis and porphyrin-linked metronidazole by confocal laser scanning microscopy. Findings indicated that P. gingivalis and porphyrin-linked metronidazole were colocalized in the cytoplasm, and this compound was able to kill P. gingivalis intracellular with a sufficient culture time. This is a novel antimicrobial approach in the elimination of P. gingivalis from the oral cavity.

Impaired bone healing at tooth extraction sites in CD24-deficient mice: A pilot study

AIM

To use a micro-computed tomography (micro-CT) to quantify bone healing at maxillary first molar extraction sites, and test the hypothesis that bone healing is impaired in CD24-knockout mice as compared with wild-type C57BL/6J mice.

MATERIALS AND METHODS

Under ketamine-xylazine general anaesthesia, mice had either extraction of the right maxillary first molar tooth or sham operation. Mice were sacrificed 1 (n = 12/group), 2 (n = 6/group) or 4 (n = 6/group) weeks postoperatively. The right maxillae was disected. Micro-CT was used to quantify differences in bone microstructural features at extrction sites, between CD24-knockout mice and wild-type mice.

RESULTS

CD24-Knockout mice displayed impaired bone healing at extraction sites that was manifested as decreased trabecular bone density, and decreased number and thickness of trabeculae.

CONCLUSIONS

This pilot study suggests that CD24 plays an important role in extraction socket bone healing and may be used as a novel biomarker of bone quality and potential therapeutic target to improve bone healing and density following alveolar bone injury.

Analysis of differential expression of tight junction proteins in cultured oral epithelial cells altered by Porphyromonas gingivalis, Porphyromonas gingivalis lipopolysaccharide, and extracellular adenosine triphosphate

Tight junctions (TJs) are the most apical intercellular junctions of epithelial cells formed by occludin, claudins, junctional adhesion molecules (JAMs), and zonula occludens (ZO). Tight junction proteins can sense the presence of bacteria and regulate the transcription of target genes that encode effectors and regulators of the immune response. The aim of this study was to determine the impact of TJ proteins in response to Porphyromonas gingivalis (P. gingivalis), P. gingivalis lipopolysaccharide (P. gingivalis LPS), and extracellular adenosine triphosphate (ATP) in the oral epithelial cell culture model. Quantified real time-polymerase chain reaction (RT-PCR), immunoblots, and immunostaining were performed to assess the gene and protein expression in TJs. It was found that P. gingivalis infection led to transient upregulation of the genes encoding occludin, claudin-1, and claudin-4 but not JAM-A, claudin-15, or ZO-1, while P. gingivalis LPS increased claudin-1, claudin-15, and ZO-1 and decreased occludin, JAM-A, and claudin-4. Tight junction proteins showed significant upregulation in the above two groups when cells were pretreated with ATP for 3 h. The findings indicated that P. gingivalis induced the host defence responses at an early stage. P. gingivalis LPS exerted a more powerful stimulatory effect on the disruption of the epithelial barrier than P. gingivalis. ATP stimulation enhanced the reaction of TJ proteins to P. gingivalis invasion and LPS destruction of the epithelium.

Inhibition of Notch signaling pathway using γ-secretase inhibitor delivered by a low dose of Triton-X100 in cultured oral cancer cells

How to effectively delivering therapeutic agents, including γ-secretase inhibitors (GSIs), into live cells, remains a significant challenge. This study assessed the effect of Notch signaling inhibition by examining levels of the Notch1 intracellular domain (N1ICD) in cultured oral cancer cells analyzed with random stitched images (2D) and 3D visualizations using confocal microscopy and quantitative gene analysis. Substantially, we have developed a novel method to assist the delivery of γ-secretase inhibitor, DAPT, into live cells in the presence of an effective minimum concentration of Triton-X100 (0.001%) without damaging cell activity and membrane integrity assessed with cell proliferation assays. The images obtained in this study showed that DAPT alone could not block the γ-secretase inhibitor despite inhibiting cell growth. Further analysis of quantitative gene expressions of Notch signaling canonical pathway to verify the effectiveness of the novel method for delivering inhibitor into live cells, displayed deregulation of Notch1, Delta-like ligand 1 (DLL1) and hairy and enhancer of split 1 (Hes1). Our data suggest that Notch1/Hes1 signaling pathway is deactivated using DAPT with a low dose of Triton-X100 in this cancer cells. And the finding also suggests that Notch1 could be engaged by DLL1 to promote differentiation in oral cancer cells. Using this approach, we demonstrate that Triton-X100 is a promising and effective permeabilization agent to deliver γ-secretase inhibitor DAPT into live oral epithelial cells. This strategy has the potential to implicate in the treatment of cancer diseases.

Three/four-dimensional (3D/4D) microscopic imaging and processing in clinical dental research

BACKGROUND

Confocal laser scanning microscope (CLSM) has been widely employed in our laboratory for structural and functional analysis of clinical dental specimens and live cell imaging of cultured oral epithelial cells.

METHODS

In this vitro study, a Fluoview 1000 (Olympus) confocal system was utilised to study thick sections of carious lesions (40-100 μm) and periodontal disease tissue samples (20-40 μm) by 2D Z stacking imaging and 3-dimentional (3D) reconstruction. Four-dimensional (4D) imaging when including time or position points was used for live cells to assess penetration/localisation/co-localization of oral pathogen proteins and therapeutic drugs.

RESULTS

Three-dimensional (3D) reconstruction revealed latent features of carious hard tissues (strongly expressed amelogenin proteins in dentin tubules), and soft tissues (increased glial markers GFAP and S100B in pulp components). We also found the oral microbial specific pathogens, Porphyromonas gingivalis to be widely localised inside the periodontal pocket epithelial tissues as detected by 3D reconstruction from a series of 2D sections from periodontal disease tissue samples. 4D live cell imaging showed the diffusion patterns of fluorescent molecules in response to a bacterial virulence factor, the pathogen (gingipain haemagglutinin) domain that attacked epithelial integrity. This technology also showed uptake of a novel porphyrin-linked metronidazole antibiotic into epithelial cells to kill intracellular oral pathogen, P. gingivalis.

CONCLUSIONS

Three/four-dimensional (3D/4D) imaging and processing in confocal microscopy is of great interest and benefit to clinical dental researchers.

The activation of pyrin domain-containing-3 inflammasome depends on lipopolysaccharide from Porphyromonas gingivalis and extracellular adenosine triphosphate in cultured oral epithelial cells

Background

Gingival epithelial cells are the major population of the gingival tissue, acting as the front-line defense against microbial intrusion and regulating the homeostasis of the periodontal tissue in health and disease via NLR family pyrin domain-containing-3 (NLRP3) inflammasome, which recognizes pathogen- and danger-associated molecular patterns (PAMPs and DAMPs). The aim of this study was to determine whether the activation of NLRP3 inflammasome depends on infection with the periodontal pathogen Porphyromonas gingivalis (P. gingivalis), or stimulation with P. gingivalis lipopolysaccharide (LPS), and/or extracellular adenosine triphosphate (ATP).

Methods

An oral epithelial cell line was treated with P. gingivalis, P. gingivalis LPS and ATP. The gene and protein expression of NLRP3 inflammasome components were quantified by real time RT-PCR and immunoblots. Production of IL-1β and IL-18 was measured by ELISA.

Results

There was no increase in NLRP3 inflammasome gene expression after P. gingivalis infection unless pre-stimulated by ATP. Obvious increases of NLRP3 inflammasome gene expression was observed after P. gingivalis LPS stimulation, even pre-stimulated by ATP at 2 h.

Conclusions

The findings indicate that the activation of NLRP3 inflammasome does not rely on P. gingivalis infection, unless stimulated by P. gingivalis LPS and/or extracellular ATP, suggesting diverse signaling pathways are involved in the host immune response.

CD24 activates the NLRP3 inflammasome through c-Src kinase activity in a model of the lining epithelium of inflamed periodontal tissues

Chronic periodontitis is characterized by perturbation of the epithelial attachment to the tooth with subsequent migration of the lining epithelium and formation of a cleft or pocket. This non-keratinized lining epithelium provides initial responses to bacterial products by signalling through receptors of innate immunity to activate inflammasome pathways. These comprise an intracellular network of regulatory and effector molecules leading to synthesis and activation of pro-inflammatory cytokines. Conversely, CD24 is characteristically strongly expressed by the pocket epithelium and is reported to function as an important negative regulator for danger signals, protecting tissues from excessive leukocyte activity. The objective of the study was to determine the impact of ligation of CD24 on expression of inflammasome components. An epithelial mimic of pocket epithelium was used to evaluate activation of the NLRP3 inflammasome pathway. Surprisingly, antibody ligation of CD24 enhanced expression of NLRP3 together with co-activators ASC and caspase-1 resulting in burst release of activated interleukin (IL)-18. Potent product inhibition was detected with IL-18 suppressing expression of NLRP3, ASC, and caspase-1. Scant distribution of these products within pocket epithelium compared with healthy gingival attachment provided indication of potential cycling of NLRP3 inflammasome expression. As subjects with mild chronic periodontitis have increased titres of serum antibodies auto-reactive with CD24 compared with those of subjects with severe periodontitis, a molecular mechanism for regulated expression of the NLRP3 inflammasome mediated by c-Src kinase activity, is proposed. This pathway could be regionally disrupted by products of pathogenic bacteria with profound downregulation in the dysbiosis associated with severe disease.

Expansion of breast cancer stem cells with fibrous scaffolds

Cancer stem cells (CSCs) are hypothesized as tumor-initiating cells within tumors and main contributors of tumor growth, metastasis and recurrence. Mammary cancer cells, MCF-7 cells, were cultured on 3D polycaprolactone (PCL) fibrous scaffolds, showing an increased proportion of CSCs. The expression of stem cell markers, including OCT3/4 and SOX2, and breast CSC-specific markers, SOX4 and CD49f, was significantly upregulated, and the mammosphere-forming capability in cells cultured on PCL fibrous scaffolds increased. The fibrous scaffolds also induced the elongation of MCF-7 cells and extended cell proliferation. The increase of CSC properties after being cultured on fibrous scaffolds was further confirmed with two luminal-type mammary cell lines, T47D and SK-BR-3, and a basal-type cell line, MDA-MB-231, by ALDEFLUOR assay and mammosphere formation assay. Moreover, we observed the upregulation of epithelial to mesenchymal transition and increased invasive capability in cells cultured on PCL fibrous scaffolds. These data suggest that the increase of CSC proportion in a 3D culture system may account for the enhanced malignancy. Therefore, our PCL fibrous scaffolds can potentially be used for CSCs enrichment and anti-cancer drug screening.

Curcumin Suppresses Metastasis via Sp-1, FAK Inhibition, and E-Cadherin Upregulation in Colorectal Cancer

Colorectal cancer (CRC) is a serious public health problem that results due to changes of diet and various environmental stress factors in the world. Curcumin is a traditional medicine used for treatment of a wide variety of tumors. However, antimetastasis mechanism of curcumin on CRC has not yet been completely investigated. Here, we explored the underlying molecular mechanisms of curcumin on metastasis of CRC cells in vitro and in vivo. Curcumin significantly inhibits cell migration, invasion, and colony formation in vitro and reduces tumor growth and liver metastasis in vivo. We found that curcumin suppresses Sp-1 transcriptional activity and Sp-1 regulated genes including ADEM10, calmodulin, EPHB2, HDAC4, and SEPP1 in CRC cells. Curcumin inhibits focal adhesion kinase (FAK) phosphorylation and enhances the expressions of several extracellular matrix components which play a critical role in invasion and metastasis. Curcumin reduces CD24 expression in a dose-dependent manner in CRC cells. Moreover, E-cadherin expression is upregulated by curcumin and serves as an inhibitor of EMT. These results suggest that curcumin executes its antimetastasis function through downregulation of Sp-1, FAK, and CD24 and by promoting E-cadherin expression in CRC cells.

Expression patterns of tight junction components induced by CD24 in an oral epithelial cell-culture model correlated to affected periodontal tissues

BACKGROUND AND OBJECTIVE

Previously we demonstrated uniformly strong expression of CD24 in the epithelial attachment to the tooth and in the migrating epithelium of the periodontitis lesion. Titers of serum antibodies autoreactive with CD24 peptide correlated with reduced severity of periodontal disease. Ligation of CD24 expressed by oral epithelial cells induced formation of tight junctions that limited paracellular diffusion. In this study, we aimed to reveal that the lack of uniform expression of tight junction components in the pocket epithelium of periodontitis lesions is likely to contribute to increased paracellular permeability to bacterial products. This is proposed as a potential driver of the immunopathology of periodontitis.

MATERIAL AND METHODS

An epithelial culture model with close correspondence for expression patterns for tight junction components in periodontal epithelia was used. Immunohistochemical staining and confocal laser scanning microscopy were used to analyse patterns of expression of gingival epithelial tight junction components.

RESULTS

The minimally inflamed gingival attachment was characterized by uniformly strong staining at cell contacts for the tight junction components zona occludens-1, zona occludens-2, occludin, junction adhesion molecule-A, claudin-4 and claudin-15. In contrast, the pocket epithelium of the periodontal lesion showed scattered, uneven staining for these components. This pattern correlated closely with that of unstimulated oral epithelial cells in culture. Following ligation of CD24 expressed by these cells, the pattern of tight junction component expression of the minimally inflamed gingival attachment developed rapidly.

CONCLUSION

There was evidence for non-uniform and focal expression only of tight junction components in the pocket epithelium. In the cell-culture model, ligation of CD24 induced a tight junction expression profile equivalent to that observed for the minimally inflamed gingival attachment. Ligation of CD24 expressed by gingival epithelial cells by lectin-like receptors of commensal oral streptococci could mediate the phenotype of health, whereas pathogenic organisms associated with periodontal disease might not signal effectively through CD24.

More than markers: biological significance of cancer stem cell-defining molecules

Small populations within an increasing array of solid tumors, labeled cancer stem cells (CSC) or tumor-initiating cells (TIC), have the ability to differentiate, self-renew, and replicate the original tumor in vivo. To date, these cells have been distinguished from the bulk-tumor population by the expression pattern of cell-surface proteins (e.g., CD24, CD44, CD133) and cellular activities, such as the efflux of Hoechst dye or aldehyde dehydrogenase activity. Recent data have shown that these markers are inducible by exposure to anticancer agents; this finding highlights not only the potential fluidity of the CSC compartment, but also the functionality of these markers. The involvement of CD44 in invasion, adhesion, and metastasis, or the role of CD24 in modulation of src, FAK, and GLI1 are examples of these relevant roles. Instead of looking solely at the marker expression in these populations, we hope to clarify the biologically significant roles these markers and activities play in tumor progression, metastases, and as possible targets for therapy.

Immortalization of normal human gingival keratinocytes and cytological and cytogenetic characterization of the cells

Most in vitro studies of oral carcinogenesis in human cells are carried out with oral keratinocytes immortalized by human papillomavirus type 16 DNA. However, because various etiological factors for oral cancer are known, it is important to establish new human keratinocyte cell lines useful for studying the mechanism of oral carcinogenesis. Normal human gingival keratinocytes in secondary cultures grown in serum-free medium were either transfected with origin (-) SV40 DNA or sequentially transfected with origin (-) SV40 DNA and human c-fos. The transfected cells were continually passaged and analyzed for cytological and cytogenetic characterizations. Four immortal cell lines were grown for over 1100 days in culture and maintained a vigorous growth for over 250 population doublings. They expressed SV40 T antigen, cytokeratins 8 and 18, and E-cadherin, and overexpressed the c-Fos protein. The immortal cell lines had telomerase activity but lacked transformed phenotypes on soft agar or in nude mice. Each cell line had nonrandom chromosomal abnormalities and minisatellite alterations. One of the immortal cell lines, NDUSD-1, retained the capability to deposit calcium, which was also demonstrated in normal human gingival keratinocytes by alizarin red staining, indicating the possibility that NDUSD-1 cells may retain some natural characteristics of normal gingival keratinocytes. Because the oral ectoderm plays an important role in tooth development, these immortal cell lines may be useful in various experimental models for investigations of oral biology and oral carcinogenesis.

CD24 regulated gene expression and distribution of tight junction proteins is associated with altered barrier function in oral epithelial monolayers

Background

Control of intercellular penetration of microbial products is critical for the barrier function of oral epithelia. We demonstrated that CD24 is selectively and strongly expressed in the cells of the epithelial attachment to the tooth and the epithelial lining of the diseased periodontal pocket and studies in vitro showed that CD24 regulated expression of the epithelial intercellular adhesion protein E-cadherin.

Results

In the present study, the barrier function of oral epithelial cell monolayers to low molecular weight dextran was assayed as a model for the normal physiological function of the epithelial attachment to limit ingress of microbial products from oral microbial biofilms. Paracellular transfer of low molecular weight dextran across monolayers of oral epithelial cells was specifically decreased following incubation with anti-CD24 peptide antibody whereas passage of dextran across the monolayer was increased following silencing of mRNA for CD24. Changes in barrier function were related to the selective regulation of the genes encoding zonula occludens-1, zonula occludens-2 and occludin, proteins implicated in tight junctions. More particularly, enhanced barrier function was related to relocation of these proteins to the cell periphery, compatible with tight junctions.

Conclusion

CD24 has the constitutive function of maintaining expression of selected genes encoding tight junction components associated with a marginal barrier function of epithelial monolayers. Activation by binding of an external ligand to CD24 enhances this expression but is also effective in re-deployment of tight junction proteins that is aligned with enhanced intercellular barrier function. These results establish the potential of CD24 to act as a potent regulator of the intercellular barrier function of epithelia in response to local microbial ecology.

siRNA, miRNA, and shRNA: in vivo Applications

RNA interference (RNAi), an accurate and potent gene-silencing method, was first experimentally documented in 1998 in Caenorhabditis elegans by Fire et al., who subsequently were awarded the 2006 Nobel Prize in Physiology/Medicine. Subsequent RNAi studies have demonstrated the clinical potential of synthetic small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs) in dental diseases, eye diseases, cancer, metabolic diseases, neurodegenerative disorders, and other illnesses. siRNAs are generally from 21 to 25 base-pairs (bp) in length and have sequence-homology-driven gene-knockdown capability. RNAi offers researchers an effortless tool for investigating biological systems by selectively silencing genes. Key technical aspects—such as optimization of selectivity, stability, in vivo delivery, efficacy, and safety—need to be investigated before RNAi can become a successful therapeutic strategy. Nevertheless, this area shows a huge potential for the pharmaceutical industry around the globe. Interestingly, recent studies have shown that the small RNA molecules, either indigenously produced as microRNAs (miRNAs) or exogenously administered synthetic dsRNAs, could effectively activate a particular gene in a sequence-specific manner instead of silencing it. This novel, but still uncharacterized, phenomenon has been termed ‘RNA activation’ (RNAa). In this review, we analyze these research findings and discussed the in vivo applications of siRNAs, miRNAs, and shRNAs.