Probing the role of the actin cytoskeleton during regulated exocytosis by intravital microscopy.

The actin cytoskeleton plays a fundamental role in controlling several steps during regulated exocytosis. Here, we describe a combination of procedures that are aimed at studying the dynamics and the mechanism of the actin cytoskeleton in the salivary glands of live rodents, a model for exocrine secretion. Our approach relies on intravital microscopy, an imaging technique that enables imaging biological events in live animals at a subcellular resolution, and it is complemented by the use of pharmacological agents and indirect immunofluorescence in the salivary tissue.

Gravity loading induces adenosine triphosphate release and phosphorylation of extracellular signal-regulated kinases in human periodontal ligament cells.

AIM: The periodontal ligament (PDL) receives mechanical stress (MS) from dental occlusion or orthodontic tooth movement. Mechanical stress is thought to be a trigger for remodeling of the PDL and alveolar bone, although its signaling mechanism is still unclear. So we investigated the effect of MS on adenosine triphosphate (ATP) release and extracellular signal-regulated kinases (ERK) phosphorylation in PDL cells. METHODS: Mechanical stress was applied to human PDL cells as centrifugation-mediated gravity loading. Apyrase, Ca(2+)-free medium and purinergic receptor agonists and antagonists were utilized to analyze the contribution of purinergic receptors to ERK phosphorylation. RESULTS: Gravity loading and ATP increased ERK phosphorylation by 5 and 2.5 times, respectively. Gravity loading induced ATP release from PDL cells by tenfold. Apyrase and suramin diminished ERK phosphorylation induced by both gravity loading and ATP. Under Ca(2+)-free conditions the phosphorylation by gravity loading was partially decreased, whereas ATP-induced phosphorylation was unaffected. Receptors P2Y4 and P2Y6 were prominently expressed in the PDL cells. CONCLUSION: Gravity loading induced ATP release and ERK phosphorylation in PDL fibroblasts, and ATP signaling via P2Y receptors was partially involved in this phosphorylation, which in turn would enhance gene expression for the remodeling of PDL tissue during orthodontic tooth movement.

VAMP4 is required to maintain the ribbon structure of the Golgi apparatus.

The Golgi apparatus forms a twisted ribbon-like network in the juxtanuclear region of vertebrate cells. Vesicle-associated membrane protein 4 (VAMP4), a v-SNARE protein expressed exclusively in the vertebrate trans-Golgi network (TGN), plays a role in retrograde trafficking from the early endosome to the TGN, although its precise function within the Golgi apparatus remains unclear. To determine whether VAMP4 plays a functional role in maintaining the structure of the Golgi apparatus, we depleted VAMP4 gene expression using RNA interference technology. Depletion of VAMP4 from HeLa cells led to fragmentation of the Golgi ribbon. These fragments were not uniformly distributed throughout the cytoplasm, but remained in the juxtanuclear area. Electron microscopy and immunohistochemistry showed that in the absence of VAMP4, the length of the Golgi stack was shortened, but Golgi stacking was normal. Anterograde trafficking was not impaired in VAMP4-depleted cells, which contained intact microtubule arrays. Depletion of the cognate SNARE partners of VAMP4, syntaxin 6, syntaxin 16, and Vti1a also disrupted the Golgi ribbon structure. Our findings suggested that the maintenance of Golgi ribbon structure requires normal retrograde trafficking from the early endosome to the TGN, which is likely to be mediated by the formation of VAMP4-containing SNARE complexes.

Isoproterenol stimulates transient SNAP23-VAMP2 interaction in rat parotid glands.

The exocytosis of salivary proteins is mainly regulated by cAMP, although soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), which mediate cAMP-dependent exocytic membrane fusion, have remained unidentified. Here we examined the effect of isoproterenol (ISO) and cytochalasin D (CyD) on the level of SNARE complexes in rat parotid glands. When SNARE complexes were immunoprecipitated by anti-SNAP23, the coprecipitation of VAMP2 was significantly increased in response to ISO and/or CyD, although the coprecipitation of VAMP8 or syntaxin 4 was scarcely augmented. These results suggest that the SNAP23-VAMP2 interaction plays a key role in cAMP-mediated exocytosis from parotid glands.

SNARE proteins are not excessive for the formation of post-Golgi SNARE complexes in HeLa cells.

To evaluate the role of SNARE proteins in the constitutive exocytosis, we knocked down syntaxin 3, 4, 5, 6, 7, and VAMP3, 5, 7, 8 with their siRNAs, and determined the cell-to-medium ratio of CLuc, a secreted luciferase of Cypridina noctiluca. Although the protein level of SNAREs in HeLa cells was markedly reduced by the siRNA treatment, the cell/medium ratio was scarcely increased by any siRNAs except for syntaxin 5. The accumulation of GFP-tagged human growth hormone was also visible only by the knockdown of syntaxin 5. To examine whether the residual amount of SNAREs are sufficient for maintaining normal constitutive exocytosis, we estimated the effect of siRNAs on the level of post-Golgi SNARE complexes containing syntaxin 4, SNAP23, and VAMP3 or VAMP8. The amount of SNARE complexes was robustly decreased by siRNAs and was well correlated with the residual amount of SNAREs in the lysates, suggesting that SNAREs are unnecessarily excessive for the formation of post-Golgi SNARE complexes in HeLa cells.

Expression of functional Stim1-mKO1 in rat submandibular acinar cells by retrograde ductal injection of an adenoviral vector.

OBJECTIVE: Adenoviruses are used for gene transfer to salivary glands cells in vivo. We constructed an adenovirus vector that expressed a fusion protein of human Stim1 and the fluorescent protein mKO1 (Ad-Stim1-mKO1), and used it to investigate the molecular dynamics and functions of exogenously expressed proteins in living salivary acinar cells. DESIGN: Ad-Stim1-mKO1 was transferred to rat submandibular glands by retrograde ductal injection. Expression and distribution of Stim1-mKO1 were examined by confocal microscopy. In addition, the effects of Stim1-mKO1 on store-operated Ca(2+) entries were examined in fura-2-loaded cells. RESULTS: The expression of Stim1-mKO1 was detected in approximately 40% of rat submandibular acini, whereas the expression in HSY-EA1 cells was ∼80%. Confocal microscopy revealed Stim1-mKO1 fluorescence along the endoplasmic reticulum-like network in the cytoplasm of both HSY-EA1 and dispersed acinar cells. The depletion of intracellular Ca(2+) stores with thapsigargin (ThG), a sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA) inhibitor, led to the translocation of Stim1-mKO1 to the peripheral region in these cells. In addition, expression of Stim1-mKO1 enhanced store-operated Ca(2+) entry in these cells. CONCLUSIONS: We succeeded in expressing Stim1-mKO1 fluorescent protein in the salivary glands of live animals by retrograde ductal injection of an adenoviral vector. This method allowed us to investigate the functions and molecular dynamics of these expressed molecules in living salivary acinar cells.

A polymerase chain reaction-based method for constructing a linear vector with site-specific DNA methylation.

DNA methylation is an important epigenetic modification that leads to a wide variety of biological functions, including transcription, growth and development, and diseases associated with altered gene expression such as cancers. However, tools to insert site-specific methylation into DNA for analyzing epigenetic functions are limited. Here we describe a novel polymerase chain reaction (PCR)-based approach to provide site-specific DNA methylation at any site, including CpG or CpNpG islands. This method is simple and versatile, and it consists of four steps to construct the DNA methylation vector: (I) design and synthesis of methylated primers, (II) PCR amplification, (III) isolation of single-stranded DNA, and (IV) annealing and ligation of isolated single-stranded DNAs. First we produced and validated a linear green fluorescence protein (GFP) vector by this method. Next we applied this method to introduce methyl groups into the promoter of the cyclooxygenase-2 (COX-2) gene and found that site-specific DNA methylation at the CRE element significantly altered COX-2 gene expression. These results demonstrate that this PCR-based approach is useful for the analysis of biological functions that depend on DNA methylation.

Nicotine induces upregulated expression of beta defensin-2 via the p38MAPK pathway in the HaCaT human keratinocyte cell line.

Human beta-defensins (hBDs), a group of antimicrobial peptides, are involved in the protective barrier of the oral epithelium. Nicotine induces periodontal and oral epithelial diseases. The purpose of the present study was to investigate the effect of nicotine on the expression pattern of hBD-2 in keratinocytes. HaCaT cells, a keratinocyte cell line, were incubated with 8, 15, 30, or 80 µM nicotine for 24 h. Expression of hBD-2 was observed by RT-PCR, qRTPCR, and ELISA assay. The cells were treated with inhibitors for intracellular pathways (p38MAP kinase, NF-κB, JNK, MAPK-ERK) and with nicotinic acetylcholine receptor (nAChR) inhibitors in a series of experiments. Data were analyzed using Student's t test. qRT-PCR revealed that the expression level of hBD-2 mRNA was significantly higher at 30 and 80 µM nicotine than the control without nicotine (P < 0.05). The 80 µM cell extraction contained significantly higher hBD-2 peptide levels than the control (P < 0.05). The p38MAP kinase inhibitor abolished the upregulated expression of hBD-2 by nicotine. Both nAChR inhibitors also abolished the upregulation of hBD-2 by nicotine. The present study demonstrated that nicotine causes upregulated expression of hBD-2 via the p38MAP kinase pathway in keratinocytes.

Role of VAMP8/endobrevin in constitutive exocytotic pathway in HeLa cells.

To evaluate the role of VAMP8/endobrevin in constitutive exocytosis, we have examined the exocytotic pathways of VAMP8 and human growth hormone, both GFP-tagged, by total internal reflection fluorescence microscopy (TIRF-M). Human GH-GFP and VAMP8-GFP were similarly expressed in small round vesicles and elongated tubular vesicles in HeLa cells, and were mostly exocytosed at the peripheral area of the cells. VAMP8-GFP gave 2 types of exocytotic images: a burst type and a non-burst type. The burst type showed a sharp transient increase in the peak fluorescence intensity and a much slower decrease in the average intensity in the active windows, where exocytosis took place, as observed in the "full-fusion" type of exocytosis. The non-burst type showed a relatively long-lasting fusion to the plasma membrane with little transfer of VAMP8-GFP to the plasma membrane, as observed in the so-called "kiss-and-run" type of exocytosis. Endogenous VAMP8 and hGH-GFP were colocalized on the same vesicles at least in part. However, the constitutive exocytosis of hGH-GFP and CLuc, a secreted luciferase from Cypridina noctiluca, was normal, even when siRNAs for VAMP8 and VAMP3 robustly decreased their proteins. These results suggest that VAMP8 is not essential for constitutive exocytosis, although it can be involved in the exocytosis.

Profiling of differentially expressed genes in porcine epithelial cells derived from periodontal ligament and gingiva by DNA microarray.

OBJECTIVE: It is unknown which genes are differentially expressed in cultured epithelial cells derived from the epithelial rests of Malassez (ERM) in periodontal ligament and oral gingival epithelium (OGE). This study analysed the different gene expression of OGE and ERM cells using a DNA microarray technique. DESIGN: Epithelial cells from ERM and OGE were isolated from porcine periodontal ligament and oral gingival epithelium. Each RNA sample extracted from the cells was reverse transcribed into cDNA and labelled with either cytidine 5-dUTP (Cy5) or cytidine 3-dUTP (Cy3). These labelled cDNA probes were then mixed and simultaneously hybridised to the Pig 13K microarray plate bearing 13,295 different genes (Operon, AL). Cellular enzyme-linked immunosorbent assay (CELISA) was performed to confirm the expression at protein level. RESULTS: There were nine genes common to the triplicate microarrays in ERM cells and one in OGE cells. Four of the nine genes including tissue factor (TF), FAT cadherin (FAT) and two unknown genes were expressed at levels more than threefold higher in ERM cells than in OGE cells. The protein levels of both TF and FAT in ERM cells were significantly higher than those in OGE. CONCLUSION: TF and FAT may act as markers to distinguish ERM cells from OGE cells in vitro.

High frequency of hypermethylation of p14, p15 and p16 in oral pre-cancerous lesions associated with betel-quid chewing in Sri Lanka.

BACKGROUND: Oral squamous cell carcinoma and the most common oral pre-malignancies appear to be related to the habit of betel-quid chewing in Sri Lanka. Although hypermethylation of the tumour suppressor genes in oral cancer have been well documented, little information has been available concerning hypermethylation in oral pre-cancerous lesions. In the present study, we investigated the hypermethylation of p14, p15 and p16 in pre-cancerous lesions including epithelial dysplasia and submucous fibrosis. METHODS: All samples were obtained from patients with a betel-quid chewing habit in Sri Lanka. Sixty-four patients were clinically diagnosed with leukoplakia, and histopathologically diagnosed with mild or severe dysplasia. Ten patients were diagnosed with submucous fibrosis without epithelial dysplasia. CpG island hypermethylation was assessed by a methylation-specific PCR method. Immunohistochemical staining was performed using anti-p53 antibodies. RESULTS: A high frequency of hypermethylation of p14, p15 and p16 was detected in the pre-cancerous lesions, although no hypermethylation was found in normal epithelium. The frequency of hypermethylation was higher than that of positive staining for p53 mutation except in the case of p16 in mild dysplasia. No significant correlation was observed between p53-positive reactions and hypermethylation in any lesions. The hypermethylation was highly detectable even in p53-negative lesions, suggesting that hypermethylation of p14, p15 and p16 occur regardless of whether the lesions have p53 mutations or not. CONCLUSIONS: The present study indicates that hypermethylation may be involved in the pathogenesis of oral pre-cancerous lesions associated with betel-quid chewing in Sri Lanka.

Increased expression of beta-defensin-2 and -3 during the development of autoimmune sialoadenitis in MRL/lpr mice.

beta-Defensins (BD) are small cationic antimicrobial peptides that produced principally in the epithelial cells of a number of organs. The present study analyzed the expression patterns of BD-1, -2, and -3 during the development of sialoadenitis in MRL/lpr mice. Submandibular glands were dissected from MRL/lpr mice at 4, 8, 10, 12, 14, and 16 weeks of age. The expression of mouse (m) BD-1, -2, and -3 mRNAs was examined by RT-PCR and quantified using TaqMan real-time RT-PCR. No significant differences in the level of expression of mBD-1 were observed among mice of different ages. The level of expression of mBD-2 was significantly higher at 16 weeks than at 4 or 8 weeks. The expression level of mBD-3 was highest in 14-week-old mice and was significantly higher than in 4-week or 16-week-old animals. Immunohistochemical staining showed that BD-3 was clearly localized in the ductal cells with variable intensities. In the center of the foci of lymphatic infiltration, ductal staining was faint or often not present. The results indicate that BD-2 and -3 may be upregulated during the development of autoimmune sialoadenitis.

SNAP-23 is not essential for constitutive exocytosis in HeLa cells.

We applied the small interfering RNA (siRNA) technique and over-expression of a dominant-negative mutant to evaluate the role of SNAP-23, a non-neuronal isoform of SNAP-25, in constitutive exocytosis from HeLa cells. Although the protein level of SNAP-23 was reduced to less than 10% of the control value by siRNA directed against SNAP-23, exocytosis of SEAP (secreted alkaline phosphatase) was normal. Double knockdown of SNAP-23 and syntaxin-4 also failed to inhibit the secretion. Furthermore, over-expression of deltaC8-SNAP-23, a dominant-negative mutant of SNAP-23, did not abrogate SEAP secretion. These results suggest that SNAP-23 is not essential for constitutive exocytosis of SEAP.

Role of VAMP-2, VAMP-7, and VAMP-8 in constitutive exocytosis from HSY cells.

We evaluated the role of VAMP-2/synaptobrevin, VAMP-7/TI-VAMP, and VAMP-8/endobrevin in exocytic pathways of HSY cells, a human parotid epithelial cell line, by coexpressing these VAMP proteins tagged with green fluorescent protein (GFP) and human growth hormone (hGH) as a secretory cargo. Exocytosis of hGH was constitutive and the fluorescent signal of hGH-GFP was observed in the Golgi area and small vesicles quickly moving throughout the cytoplasm. The cytoplasmic vesicles containing hGH overlapped well with VAMP-7-GFP, but did so scarcely with VAMP-2-GFP or VAMP-8-GFP. However, when the vesicle transport from the trans-Golgi network to the plasma membrane was arrested by incubation at 20 degrees C for 2 h and then released by warming up to 37 degrees C; VAMP-2-GFP and hGH were clearly colocalized together in small cytoplasmic vesicles. Neither VAMP-7-GFP nor hGH-GFP was colocalized with LAMP-1, a marker for lysosomes and late endosomes. These results suggest that (1) VAMP-2 can be one of the v-SNAREs for constitutive exocytosis; (2) VAMP-7 is involved in the constitutive exocytosis as a slow, minor v-SNARE, but not in the lysosomal transport; and (3) VAMP-8 is unlikely to be a v-SNARE for constitutive exocytosis in HSY cells.

Expression and localization of versican during postnatal development of rat temporomandibular joint disc.

To analyze the growth-related changes in extracellular matrix components in temporomandibular joint (TMJ) discs, the expression and localization of the core protein of a large chondroitin sulphate proteoglycan, versican, in rat TMJ discs during postnatal development (2-32 weeks) were examined using Western blot analysis, real-time quantitative PCR and immunohistochemistry. Western blot analysis showed that rat TMJ discs predominantly expressed one isoform (V1) and the core protein sharply increased after birth, reached a peak at 8 weeks, and then gradually decreased up to 32 weeks. Real-time quantitative PCR with TaqMan probes indicated that mRNA expression of versican was highest at 2 weeks and gradually decreased with growth. An immunohistochemical study showed that staining for versican was weak and evenly distributed in TMJ discs at 2 weeks. Regional differences in staining for versican became prominent after 8 weeks; staining was intense in the anterior and posterior peripheral attachments, and weak in the central part of the discs. These results demonstrate that growth-related changes and regional differences exist in the expression of versican in the TMJ discs of growing rats, and these probably reflect the changes in the biomechanical environment caused by the development of orofacial functions.

Correlated expression of human beta defensin-1, -2 and -3 mRNAs in gingival tissues of young children.

OBJECTIVE: Human beta-defensins (hBDs) are a group of antimicrobial peptides, expressed by the epithelial cells of many organs including gingival epithelium. The present study examined correlation between the gene expressions of hBD-1, -2, -3 mRNAs and the inflammatory cytokines in human gingival tissues. STUDY DESIGN: The gingival tissues were obtained from surgical discards from 20 different patients (age range, 5-13 years). The expression levels of mRNAs were evaluated by quantitative RT-PCR with LightCycler. The mRNA expression levels were normalized with those of keratin 10 mRNA. The data were statistically analysed using Person's correlation coefficient. RESULTS: The expression levels of hBD-1,-2 and -3 were significantly correlated with each other and also correlated with that of TNF-alpha. CONCLUSIONS: The results indicate that the expression levels of hBDs vary from one individual to another.

Upregulated expression of human beta defensin-1 and -3 mRNA during differentiation of keratinocyte immortalized cell lines, HaCaT and PHK16-0b.

BACKGROUND: Human beta-defensins (hBDs) belong to a group of antimicrobial peptide that are expressed in the epithelial cells. OBJECTIVE: The present study investigated mRNA expression levels of the beta-defensins, hBD-1, -2 and -3, in human keratinocytes during differentiation in vitro. METHODS: Immortalized keratinocyte cell lines, HaCaT and PHK16-0b, were used in this study; in order to stimulate differentiation, the Ca(2+) concentration in the growth media was increased from 0.3 to 1.8 mM. RESULTS: Four days after the increase, the expression levels of hBD-1 and -3 were increased in both cell lines, followed by an increase in the mRNA levels of the differentiation markers, involucrin and keratin 10. No increased expression of hBD-2 was observed. CONCLUSION: The results indicate that keratinocyte differentiation may stimulate hBD-1 and -3 expression in stratified squamous epithelia.

Expression of MIP-3alpha/CCL20, a macrophage inflammatory protein in oral squamous cell carcinoma.

We have examined the expression of MIP-3alpha/CCL20 in oral squamous cell carcinoma (SCC) in vivo and in vitro. In addition, we have investigated whether the expression of MIP-3alpha/CCL20 is regulated by bacterial infection and inflammatory cytokines. In order to determine the mRNA level of MIP-3alpha, quantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed with LightCycler using the double-stranded DNA dye, SYBR Green I. Oral epithelial cells and six SCC cell lines (SCC-9, SAS, BSC-OF, HSC-4, HSC, Ca9-22) were found to express MIP-3alpha mRNA. The expression of MIP-3alpha was upregulated by infection with Actinobacillus actinomycetemcomitans and by stimulation with lipopolysaccharide and TNF-alpha. By in situ hybridization, the detectable MIP-3alpha expression in SCC was localized primarily at the epithelial pearls corresponding to the spinous layer. These results suggest that MIP-3alpha contributes to the oral immunoresponse to bacterial infection, and may be involved in the growth of SCC.

Trafficking of green fluorescent protein-tagged SNARE proteins in HSY cells.

SNARE proteins are widely accepted to be involved in the docking and fusion process of intracellular vesicle trafficking. VAMP-2, syntaxin-4, and SNAP-23 are plausible candidate SNARE proteins for non-neuronal exocytosis. Thus, we examined the localization, protein-protein interaction, and intracellular trafficking of these proteins by expressing them as green fluorescent protein (GFP)- and FLAG-tagged fusion proteins in various cells, including HSY cells, a human parotid epithelial cell line. GFP-VAMP-2 was ex-pressed strongly in the Golgi area and weakly on the plasma membrane. Although GFP-SNAP-23 seemed to be expressed universally in the cytosol, the GFP signal was clearly seen on the plasma membrane, when soluble GFP-SNAP-23 was removed by treatment with saponin. GFP-syntaxin-4 was undetectable on the plasma membrane but was strongly expressed on unidentified unusually large vesicles. GFP-syntaxin-4 without its transmembrane domain was still incompletely soluble and observed as aggregates. When syntaxin-4 and munc18c were coexpressed, syntaxin-4 was translocated at least in part to the plasma membrane. The protein-protein interaction between syntaxin-4 and VAMP-2 with their transmembrane domains was markedly inhibited on coexpression of munc18c. These results suggest that munc18c plays an important role in the trafficking of syntaxin-4 to its proper destination by preventing premature interactions with other proteins, including SNARE proteins.

Biochemical and immunohistochemical studies of the protein expression and localization of decorin and biglycan in the temporomandibular joint disc of growing rats.

To analyze the growth-related changes in extracellular matrix components, biochemical/immunohistochemical techniques were used to examine the protein expression and localization of two small leucine-rich proteoglycans, biglycan and decorin, in the temporomandibular joint discs of growing rats. Western blotting showed that the protein expression of decorin increased with age, but that of biglycan gradually decreased. An immunohistochemical study showed that staining for decorin was weak and homogeneously distributed in the discs from birth to 2 weeks. Regional differences in staining for decorin became prominent at 4, 8 and 16 weeks; decorin was more abundant in the peripheral area (the periphery of the band and the attachment) than in the central area (the intermediate zone and central area of the posterior band). In contrast, staining for biglycan was evenly distributed throughout the disc until 4 weeks, and after that became rather intense in the anterior and posterior bands. These results demonstrate that there are growth-related changes and regional differences in the expression of biglycan and decorin in the temporomandibular joint discs of growing rats, which probably reflect changes in the biomechanical environment caused by the development of orofacial functions.